Reference picture management in video coding

Abstract

To provide, for example, a method of decoding a coded video bitstream.SOLUTION: A method includes the steps of: acquiring a first reference picture list structure and a second reference picture list structure represented by a coded video bitstream; deriving a first reference picture list of the current slice and a second reference picture list of the current slice based on the first reference picture list structure and second reference picture list structure, the current slice including an intra (I) slice or a single prediction (P) slice; subsequent to the derivation of the first reference picture list and second reference picture list, acquiring at least one reconstructed block of the current slice.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] Cross-reference of related applications This patent application claims the benefit of U.S. Provisional Patent Application No. 62 / 719,360, titled "Reference Picture in Video Coding," filed on 17 August 2018 by Ye-Kui Wang et al., which is incorporated herein by reference.

[0002] This disclosure relates in general to techniques for managing reference pictures in video coding. More specifically, this disclosure describes techniques for building reference picture lists and marking reference pictures. [Background technology]

[0003] Even relatively short videos can require a considerable amount of video data to render, which can pose difficulties when data is streamed with limited bandwidth or otherwise communicated over a communication network. Therefore, video data is generally compressed before being transmitted over modern telecommunication networks. Video size can also be a concern when video is stored on a storage device, as memory resources can be limited. Video compression devices often use software and / or hardware at the source to encode the video data before transmission or storage, thereby reducing the amount of data required to represent the digital video image. The compressed data is then received at the destination by a video decompression device that decodes the video data. Given limited network resources and the growing demand for higher quality video, improved compression and decompression techniques that increase the compression ratio with little to no sacrifice of image quality are desirable. [Overview of the Initiative] [Means for solving the problem]

[0004] The first aspect relates to a method for decoding a coded video bitstream. The method comprises the steps of: obtaining a first reference picture list structure and a second reference picture list structure represented in the coded video bitstream; deriving a first reference picture list and a second reference picture list of the current slice based on the first and second reference picture list structures, wherein the current slice comprises an intra (I) slice, a single predictive (P) slice, or a double predictive (B) slice; and obtaining at least one reconstructed block of the current slice following the derivation of the first and second reference picture lists.

[0005] The method provides a technique for signaling reference picture lists in a concise and more efficient manner, thereby improving the overall coding process.

[0006] In the first implementation of the method according to the first aspect, the order of entries in the reference picture list structure is the same as the order of the corresponding reference pictures in the reference picture list.

[0007] In the second implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the order is from 0 to the indicated value.

[0008] In the third implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the value shown ranges from 0 to the value shown by sps_max_dec_pic_buffering_minus1.

[0009] In the fourth implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the reference picture list is called RefPictList[0].

[0010] In the fifth implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the reference picture list is called RefPictList[1].

[0011] In the sixth implementation of the method according to the first embodiment itself, or in any preceding implementation of the first embodiment, at least one reconstructed block is used to generate an image to be displayed on the display of an electronic device.

[0012] In the seventh implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the reference picture list comprises a list of reference pictures used for interpretation.

[0013] In the eighth implementation of the method according to the first embodiment itself, or in any preceding implementation of the first embodiment, the inter prediction is for P-slice or B-slice.

[0014] In the ninth implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the slice header includes a reference picture list sequence parameter set (SPS) flag called ref_pic_list_sps_flag[i].

[0015] In the tenth implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the slice header includes a number reference index active override flag specified by num_ref_idx_active_override_flag.

[0016] In the eleventh implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the reference picture list is called RefPictList[0] or RefPictList[1], and the order of entries in the reference picture list structure is the same as the order of the corresponding reference pictures in the reference picture list.

[0017] In the twelfth implementation of the method according to the first aspect, or in any preceding implementation of the first aspect, the current slice is an I slice or a P slice.

[0018] A second aspect relates to a decoding device comprising a receiver configured to receive a coded video bitstream, a memory coupled to the receiver for storing instructions, and a processor coupled to the memory, wherein the processor is configured to cause the processor to obtain a first reference picture list structure and a second reference picture list structure represented in the coded video bitstream, to derive a first reference picture list and a second reference picture list of the current slice based on the first and second reference picture list structures, and to execute the instructions stored in memory such that the current slice comprises an intra (I) slice, a single predictive (P) slice, or a double predictive (B) slice, and to obtain at least one reconstructed block of the current slice following the derivation of the first and second reference picture lists.

[0019] The decoding device provides techniques for signaling the reference picture list in a concise and more efficient manner. Therefore, the entire coding process is improved.

[0020] In the first implementation of the decoding device according to the second embodiment, the decoding device further includes a display configured to display an image based on at least one reconstructed block.

[0021] A third aspect relates to a coding device including a receiver configured to receive a bitstream to be decoded, a transmitter coupled to the receiver and configured to transmit the decoded image to a display, a memory coupled to at least one of the receiver or the transmitter and configured to store instructions, and a processor coupled to the memory and configured to execute the instructions stored in the memory to perform the method according to any of the foregoing aspects or embodiments.

[0022] A fourth aspect relates to a system including an encoder and a decoder communicating with the encoder. The encoder or the decoder includes any of the decoding devices or coding devices according to any of the foregoing aspects or embodiments.

[0023] The system provides techniques for simplifying and making more efficient the signaling of reference picture lists. Accordingly, the overall coding process is improved.

[0024] A fifth aspect relates to means for coding including receiving means configured to receive a picture to be encoded or a bitstream to be decoded, transmitting means coupled to the receiving means and configured to transmit the bitstream to a decoder or the decoded image to display means, storage means coupled to at least one of the receiving means or the transmitting means and configured to store instructions, and processing means coupled to the storage means and configured to execute the instructions stored in the storage means to perform the method according to any of the foregoing aspects or embodiments.

[0025] The means for coding provides techniques for simplifying and making more efficient the signaling of reference picture lists. Accordingly, the overall coding process is improved. <00ness="center">

[0026] For a more complete understanding of the present disclosure, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, in which like reference numerals represent like parts.

Brief Description of the Drawings

[0027] [Figure 1] FIG. 8 is a block diagram showing an exemplary coding system that can utilize bilateral prediction techniques. [Figure 2] FIG. 11 is a block diagram showing an exemplary video encoder that can implement bilateral prediction techniques. [Figure 3] FIG. 14 is a block diagram showing an example of a video decoder that can implement bilateral prediction techniques. [Figure 4] FIG. 17 is a schematic diagram showing a reference picture set (RPS) having a picture with entries in all subsets of the RPS. [Figure 5] FIG. 20 is an embodiment of a method for decoding a coded video bitstream. [Figure 6] FIG. 23 is a schematic diagram of a video coding device. [Figure 7] FIG. 26 is a schematic diagram of an embodiment of means for coding.

Best Mode for Carrying Out the Invention

[0028] Figure 1 is a block diagram illustrating an exemplary coding system 10 that may utilize video coding techniques as described herein. As shown in Figure 1, the coding system 10 includes a source device 12 that provides encoded video data to be later decoded by a destination device 14. Specifically, the source device 12 may provide video data to the destination device 14 via a computer-readable medium 16. The source device 12 and destination device 14 may comprise any of a wide range of devices, including desktop computers, notebook (e.g., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called "smart" phones, so-called "smart" pads, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, and the like. In some cases, the source device 12 and destination device 14 may be compatible with wireless communication.

[0029] Destination device 14 may receive encoded video data, which will be decoded via computer-readable medium 16. Computer-readable medium 16 may comprise any type of medium or device capable of moving the encoded video data from source device 12 to destination device 14. For example, computer-readable medium 16 may comprise a communication medium that enables source device 12 to transmit the encoded video data directly to destination device 14 in real time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful in facilitating communication from source device 12 to destination device 14.

[0030] In some examples, encoded data may be output to a storage device via the output interface 22. Similarly, encoded data may be accessed from the storage device via the input interface. The storage device may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray® disc, digital video disc (DVD), compact disc read-only memory (CD-ROM), flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data. In further examples, the storage device may correspond to a file server or another intermediate storage device capable of storing encoded video generated by the source device 12. The destination device 14 may access the stored video data from the storage device via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting encoded video data to the destination device 14. Exemplary file servers include web servers (e.g., for websites), file transfer protocol (FTP) servers, network-attached storage (NAS) devices, or local disk drives. The destination device 14 may access the encoded video data through any standard data connection, including an internet connection. This may include wireless channels (e.g., Wi-Fi connection), wired connections (e.g., digital subscriber line (DSL), cable modem, etc.), or a combination of both suitable for accessing encoded video data stored on a file server. Transmission of the encoded video data from the storage device may be streaming transmission, download transmission, or a combination thereof.

[0031] The techniques of this disclosure are not necessarily limited to wireless applications or configurations. These techniques may also be applied to video coding supporting a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, internet streaming video transmission such as dynamic adaptive streaming over HTTP (DASH), digital video encoded to a data storage medium, decoding of digital video stored to a data storage medium, or other applications. In some examples, the coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and / or video telephony.

[0032] In the example shown in Figure 1, the source device 12 includes a video source 18, a video encoder 20, and an output interface 22. The destination device 14 includes an input interface 28, a video decoder 30, and a display device 32. According to this disclosure, the video encoder 20 of the source device 12 and / or the video decoder 30 of the destination device 14 may be configured to apply techniques for video coding. In other examples, the source device and destination device may include other components or configurations. For example, the source device 12 may receive video data from an external video source, such as an external camera. Similarly, the destination device 14 may interface with an external display device rather than including an integrated display device.

[0033] The coding system 10 shown in Figure 1 is merely an example. The technique for video coding can be performed by any digital video coding and / or decoding device. While the technique of this disclosure is generally performed by a video coding device, it can also be performed by a video encoder / decoder, commonly referred to as a “codec.” Furthermore, the technique of this disclosure can also be performed by a video preprocessor. The video encoder and / or decoder may be a graphics processing unit (GPU) or a similar device.

[0034] The source device 12 and destination device 14 are merely examples of coding devices, such that the source device 12 generates coded video data for transmission to the destination device 14. In some examples, the source device 12 and destination device 14 may operate substantially symmetrically, such that each of the source device 12 and destination device 14 includes a video coding component and a video decoding component. Thus, the coding system 10 may support one-way or two-way video transmission between video devices 12 and 14 for, for example, video streaming, video playback, video broadcasting, or video phone calls.

[0035] The video source 18 of source device 12 may include a video capture device such as a video camera, a video archive containing previously captured video, and / or a video feed interface for receiving video from a video content provider. As a further alternative, the video source 18 may generate computer graphics-based data as source video, or generate a combination of live video, archived video, and computer-generated video.

[0036] In some cases, when the video source 18 is a video camera, the source device 12 and destination device 14 may form a so-called camera phone or video phone. However, as mentioned above, the techniques described herein may be applicable to video coding in general, and may be applicable to wireless and / or wired applications. In each case, captured, pre-captured, or computer-generated video may be encoded by the video encoder 20. The encoded video information may then be output to a computer-readable medium 16 via the output interface 22.

[0037] The computer-readable medium 16 may include temporary media such as wireless broadcast or wired network transmission, or storage media (i.e., non-temporary storage media) such as hard disks, flash drives, compact discs, digital video discs, Blu-ray® discs, or other computer-readable media. In some examples, a network server (not shown) may receive encoded video data from a source device 12 and provide the encoded video data to a destination device 14, for example, via network transmission. Similarly, a computing device in a media production facility, such as a disc stamping facility, may receive encoded video data from a source device 12 and produce discs containing the encoded video data. Thus, the computer-readable medium 16 may be understood to include one or more computer-readable media in various forms in various examples.

[0038] The input interface 28 of the destination device 14 receives information from the computer-readable medium 16. The information on the computer-readable medium 16 may include syntax information defined by the video encoder 20, which includes syntax elements that describe the characteristics and / or processing of blocks and other coded units, such as picture groups (GOPs), and which are also used by the video decoder 30. The display device 32 displays the decoded video data to the user and may comprise any of a variety of display devices, such as a cathode ray tube (CRT), liquid crystal display (LCD), plasma display, organic light-emitting diode (OLED) display, or another type of display device.

[0039] The video encoder 20 and video decoder 30 may operate in accordance with a video coding standard, such as the High Efficiency Video Coding (HEVC) standard currently under development, and may conform to the HEVC Test Model (HM). Alternatively, the video encoder 20 and video decoder 30 may operate in accordance with other proprietary or industry standards, such as the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) H.264 standard, H.265 / HEVC, or extensions of such standards, also known as Moving Picture Expert Group (MPEG)-4, Part 10, Advanced Video Coding (AVC). However, the techniques of this disclosure are not limited to any particular coding standard. Other examples of video coding standards include MPEG-2 and ITU-T H.263. Although not shown in Figure 1, in some embodiments, the video encoder 20 and video decoder 30 may be integrated with an audio encoder and decoder, respectively, and may include a suitable multiplexer-demultiplexer (MUX-DEMUX) unit or other hardware and software for handling the encoding of both audio and data in a common data stream and separate data streams. Where applicable, the MUX-DEMUX unit may conform to the ITU H.223 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

[0040] The video encoder 20 and video decoder 30 can each be implemented as any of a variety of suitable encoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic circuits, software, hardware, firmware, or any combination thereof. When the technique is partially implemented in software, the device may store instructions for the software in a suitable non-temporary computer-readable medium and execute the instructions in hardware using one or more processors to perform the technique of this disclosure. Each of the video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, and any of them may be integrated as part of a composite encoder / decoder (codec) in their respective devices. A device including the video encoder 20 and / or video decoder 30 may include an integrated circuit, a microprocessor, and / or a wireless communication device such as a mobile phone.

[0041] Figure 2 is a block diagram showing an example of a video encoder 20 capable of performing video coding techniques. The video encoder 20 can perform intracoding and intercoding of video blocks within a video slice. Intracoding relies on spatial prediction to reduce or eliminate spatial redundancy in video within a given video frame or picture. Intercoding relies on temporal prediction to reduce or eliminate temporal redundancy in video within adjacent frames or pictures in a video sequence. Intra-mode (I-mode) can refer to any of several spatial-based coding modes. Inter-modes, such as unidirectional (also known as single prediction) prediction (P-mode) or bi-prediction (also known as bi-prediction) (B-mode), can refer to any of several temporal-based coding modes.

[0042] As shown in Figure 2, the video encoder 20 receives the current video block in the video frame to be encoded. In the example in Figure 2, the video encoder 20 includes a mode selection unit 40, a reference frame memory 64, an adder 50, a transformation unit 52, a quantization unit 54, and an entropy coding unit 56. The mode selection unit 40 includes a motion compensation unit 44, a motion estimation unit 42, an intra-prediction (also known as intra-prediction) unit 46, and a segmentation unit 48. For video block reconstruction, the video encoder 20 also includes an inverse quantization unit 58, an inverse transformation unit 60, and an adder 62. A deblocking filter (not shown in Figure 2) may also be included to filter block boundaries and remove blocking artifacts from the reconstructed video. If desired, the deblocking filter typically filters the output of the adder 62. Additional filters (in-loop or after-loop) may also be used in addition to the deblocking filter. For the sake of brevity, such a filter is not shown, but if desired, the output of adder 50 can be filtered (as an in-loop filter).

[0043] During the encoding process, the video encoder 20 receives video frames or slices to be coded. A frame or slice may be divided into multiple video blocks. Motion estimation units 42 and motion compensation units 44 perform inter-predictive coding of the received video blocks relative to one or more blocks in one or more reference frames to perform temporal prediction. Alternatively, an intra-predictive unit 46 may perform intra-predictive coding of the received video blocks relative to one or more neighboring blocks in the same frame or slice as the block to be coded to perform spatial prediction. The video encoder 20 may execute multiple coding paths, for example, to select an appropriate coding mode for each block of video data.

[0044] Furthermore, the partitioning unit 48 may partition blocks of video data into sub-blocks based on an evaluation of a previous partitioning method in a previous coding pass. For example, the partitioning unit 48 may first partition a frame or slice into a maximum coding unit (LCU), and then, based on rate distortion analysis (e.g., rate distortion optimization), partition each LCU into a sub-coding unit (sub-CU). The mode selection unit 40 may further generate a quadtree data structure that shows the partitioning of LCUs into sub-CUs. The leaf nodes CU of the quadtree may include one or more prediction units (PUs) and one or more transformation units (TUs).

[0045] This disclosure uses the term “block” to refer to a CU, PU, ​​or TU in the context of HEVC, or a similar data structure in the context of other standards (for example, macroblocks and subblocks of macroblocks in H.264 / AVC). A CU includes a coding node, a PU, and a TU associated with the coding node. The size of a CU corresponds to the size of the coding node and is square in shape. The size of a CU can range from 8x8 pixels to the size of a tree block of 64x64 pixels or more. Each CU may contain one or more PUs and one or more TUs. Syntax data associated with a CU may, for example, describe the division of the CU into one or more PUs. The division mode may differ depending on whether the CU is encoded in skip mode or direct mode, intra-prediction mode, or inter-prediction mode. A PU may be divided to have a non-square shape. The syntax data associated with a CU may also describe, for example, the division of the CU into one or more TUs according to a quadtree. The TUs may be square or non-square (for example, rectangular).

[0046] The mode selection unit 40 selects a coding mode, i.e., one of intra-coding mode or inter-coding mode, based, for example, on the result of an error, and provides the resulting intra-coded or inter-coded block to the adder 50 to generate residual block data, which is then provided to the adder 62 to reconstruct the encoded block for use as a reference frame. The mode selection unit 40 also provides syntax elements such as motion vectors, intra-mode indicators, segmentation information, and other such syntax information to the entropy coding unit 56.

[0047] The motion estimation unit 42 and the motion compensation unit 44 can be highly integrated, but are shown separately for conceptual purposes. The motion estimation performed by the motion estimation unit 42 is the process of generating motion vectors that estimate the motion of a video block. The motion vectors may, for example, show the PU deviation of a video block in the current video frame or picture from a predicted block in a reference frame (or other coded unit) to a current block coded in the current frame (or other coded unit). A predicted block is a block that is found to closely match the block to be coded with respect to pixel differences, which may be determined by the absolute difference sum (SAD), square difference sum (SSD), or other difference measures. In some examples, the video encoder 20 may calculate values ​​for sub-integer pixel positions of a reference picture stored in the reference frame memory 64. For example, the video encoder 20 may interpolate values ​​for quarter-pixel positions, eighth-pixel positions, or other fractional pixel positions of the reference picture. Thus, the motion estimation unit 42 may perform motion searches for all pixel positions and fractional pixel positions and output motion vectors with fractional pixel precision.

[0048] The motion estimation unit 42 calculates motion vectors for video blocks in the intercoded slice relative to the PU by comparing the PU's position with the predicted block's position in the reference picture. The reference picture may be selected from a first reference picture list (list 0) or a second reference picture list (list 1), each of which identifies one or more reference pictures stored in the reference frame memory 64. The motion estimation unit 42 transmits the calculated motion vectors to the entropy coding unit 56 and the motion compensation unit 44.

[0049] Motion compensation performed by the motion compensation unit 44 may involve fetching or generating a predicted block based on a motion vector determined by the motion estimation unit 42. Again, in some examples, the motion estimation unit 42 and the motion compensation unit 44 may be functionally integrated. Upon receiving the motion vector of the current video block, the motion compensation unit 44 may find the predicted block pointed to by the motion vector in one of the reference picture lists. As discussed below, the adder 50 forms a residual video block by subtracting the pixel values ​​of the predicted block from the pixel values ​​of the current video block being coded, which form the pixel difference value. Generally, the motion estimation unit 42 performs motion estimation for the lumens component, and the motion compensation unit 44 uses a motion vector calculated based on the lumens component for both the chromens and lumens components. The mode selection unit 40 may also generate syntax elements associated with video blocks and video slices for use by the video decoder 30 when decoding video blocks of video slices.

[0050] As described above, the intra-prediction unit 46 may intra-predict the current block as an alternative to the inter-prediction performed by the motion estimation unit 42 and the motion compensation unit 44. Specifically, the intra-prediction unit 46 may determine which intra-prediction mode should be used to encode the current block. In some examples, the intra-prediction unit 46 may encode the current block using various intra-prediction modes, for example, between separate encoding passes, and the intra-prediction unit 46 (or, in some examples, the mode selection unit 40) may select an appropriate intra-prediction mode to use from the tested modes.

[0051] For example, the intra-prediction unit 46 may calculate rate distortion values ​​using rate distortion analysis for various intra-prediction modes under test and select the intra-prediction mode with the best rate distortion characteristics from among the tested modes. Rate distortion analysis generally determines the amount of distortion (or error) between the encoded block and the original unencoded block encoded to produce the encoded block, as well as the bit rate (i.e., the number of bits) used to produce the encoded block. The intra-prediction unit 46 may calculate a ratio from the distortion and rate for various encoded blocks to determine which intra-prediction mode exhibits the best rate distortion value for a block.

[0052] In addition, the intra-prediction unit 46 may be configured to code depth blocks of the depth map using a depth modeling mode (DMM). The mode selection unit 40 may determine, for example, using rate distortion optimization (RDO), whether an available DMM mode produces better coding results than the intra-prediction mode and other DMM modes. Data for the texture image corresponding to the depth map may be stored in the reference frame memory 64. The motion estimation unit 42 and the motion compensation unit 44 may also be configured to inter-predict depth blocks of the depth map.

[0053] After selecting an intra-prediction mode for a block (for example, one of the conventional intra-prediction mode or DMM mode), the intra-prediction unit 46 may provide the entropy coding unit 56 with information indicating the selected intra-prediction mode for the block. The entropy coding unit 56 may encode the information indicating the selected intra-prediction mode. The video encoder 20 may include in the transmitted bitstream configuration data definitions for various blocks, instructions for the most probable intra-prediction mode, intra-prediction mode index tables, and modified intra-prediction mode index tables to be used for each context.

[0054] The video encoder 20 forms a residual video block by subtracting predicted data from the mode selection unit 40 from the original video block being coded. The adder 50 represents one or more components that perform this subtraction operation.

[0055] The transformation processing unit 52 applies a transformation, such as a discrete cosine transform (DCT) or a conceptually similar transformation, to the residual block to produce a video block containing residual transformation coefficient values. The transformation processing unit 52 may perform other transformations conceptually similar to the DCT. Wavelet transforms, integer transforms, subband transforms, or other types of transformations may also be used.

[0056] The conversion processing unit 52 applies the transformation to the residual block, generating a block of residual transformation coefficients. This transformation can convert the residual information from the pixel value domain to a transformation domain, such as the frequency domain. The conversion processing unit 52 may transmit the resulting transformation coefficients to the quantization unit 54. The quantization unit 54 quantizes the transformation coefficients to further reduce the bit rate. The quantization process can reduce the bit depth associated with some or all of the coefficients. The degree of quantization can be modified by adjusting the quantization parameters. In some examples, the quantization unit 54 may then perform a scan of the matrix containing the quantized transformation coefficients. Alternatively, the entropy coding unit 56 may perform the scan.

[0057] Following quantization, the entropy coding unit 56 codes the quantized transformation coefficients. For example, the entropy coding unit 56 may perform context-adaptive variable-length coding (CALVC), context-adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval piecewise entropy (PIPE) coding, or another entropy coding technique. In the case of context-based entropy coding, the context may be based on neighboring blocks. Following entropy coding by the entropy coding unit 56, the encoded bitstream may be transmitted to another device (e.g., video decoder 30) or stored for later transmission or retrieval.

[0058] The inverse quantization unit 58 and the inverse transform unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual block in the pixel region for later use, for example, as a reference block. The motion compensation unit 44 may compute a reference block by adding the residual block to a predicted block of one of the frames in the reference frame memory 64. The motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to compute sub-integer pixel values ​​for use in motion estimation. The adder 62 adds the reconstructed residual block to the motion-compensated predicted block produced by the motion compensation unit 44 to produce a reconstructed video block for storage in the reference frame memory 64. The reconstructed video block may be used as a reference block by the motion estimation unit 42 and the motion compensation unit 44 to intercode blocks in subsequent video frames.

[0059] Figure 3 is a block diagram showing an example of a video decoder 30 capable of performing video coding techniques. In the example in Figure 3, the video decoder 30 includes an entropy decoding unit 70, a motion compensation unit 72, an intra-prediction unit 74, an inverse quantization unit 76, an inverse transform unit 78, a reference frame memory 82, and an adder 80. In some examples, the video decoder 30 performs a decoding path that is generally the reverse of the coding path described with respect to the video encoder 20 (Figure 2). The motion compensation unit 72 may generate prediction data based on motion vectors received from the entropy decoding unit 70, while the intra-prediction unit 74 may generate prediction data based on an intra-prediction mode indicator received from the entropy decoding unit 70.

[0060] During the decoding process, the video decoder 30 receives an encoded video bitstream from the video encoder 20, representing the video blocks and associated syntax elements of the encoded video slice. The entropy decoding unit 70 of the video decoder 30 entropy-decodes the bitstream to generate quantized coefficients, motion vectors or intra-predictive mode indicators, and other syntax elements. The entropy decoding unit 70 transfers the motion vectors and other syntax elements to the motion compensation unit 72. The video decoder 30 may receive syntax elements at the video slice level and / or video block level.

[0061] When a video slice is coded as an intra-coded (I) slice, the intra-prediction unit 74 may generate prediction data for the video blocks of the current video slice based on the signaled intra-prediction mode and data from previously decoded blocks of the current frame or picture. When a video frame is coded as an intercoded (e.g., B, P, or GPB) slice, the motion compensation unit 72 generates prediction blocks for the video blocks of the current video slice based on motion vectors and other syntax elements received from the entropy decoding unit 70. The prediction blocks may be generated from one of the reference pictures in one of the reference picture lists. The video decoder 30 may construct reference frame lists, namely List 0 and List 1, using a default construction technique based on the reference pictures stored in the reference frame memory 82.

[0062] The motion compensation unit 72 determines prediction information for the video blocks of the current video slice by analyzing the motion vectors and other syntax elements, and uses the prediction information to generate prediction blocks for the current video blocks being decoded. For example, the motion compensation unit 72 uses some of the received syntax elements to determine the prediction mode used to code the video blocks of the video slice (e.g., intra-prediction or inter-prediction), the inter-prediction slice type (e.g., B-slice, P-slice, or GPB-slice), construction information for one or more of the reference picture lists for the slice, the motion vector for each inter-coded video block of the slice, the inter-prediction status for each inter-coded video block of the slice, and other information for decoding the video blocks in the current video slice.

[0063] The motion compensation unit 72 may also perform interpolation based on an interpolation filter. The motion compensation unit 72 may calculate interpolated values ​​for sub-integer pixels of a reference block using an interpolation filter such as the one used by the video encoder 20 during the encoding of the video block. In this case, the motion compensation unit 72 may determine the interpolation filter to be used by the video encoder 20 from the received syntax elements and use the interpolation filter to generate a predicted block.

[0064] Data for the texture image corresponding to the depth map can be stored in the reference frame memory 82. The motion compensation unit 72 can also be configured to interpret depth blocks of the depth map.

[0065] Image and video compression has advanced rapidly, leading to various coding standards. These standards include Advanced Video Coding (AVC), also known as ITU-T H.261, ISO / IEC Motion Picture Experts Group (MPEG)-1 Part 2, ITU-T H.262 or International Organization for Standardization (ISO) / International Electrotechnical Commission (IEC) MPEG-2 Part 2, ITU-T H.263, ISO / IEC MPEG-4 Part 2, ITU-T H.264 or ISO / IEC MPEG-4 Part 10, and High Efficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part 2. AVC includes extensions such as Scalable Video Coding (SVC), Multiview Video Coding (MVC), Multiview Video Coding plus Depth (MVC+D), and 3D AVC (3D-AVC). HEVC includes extensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and 3D HEVC (3D-HEVC).

[0066] Versatile Video Coding (VVC) is a new video coding standard under development by the ITU-T and ISO / IEC joint video expert team (JVET). As of this writing, the latest working draft (WD) of VVC is included in JVET-K1001-v1. JVET document JVET-K0325-v3 includes updates to the high-level syntax of VVC.

[0067] Generally, this disclosure describes techniques based on the development of the VVC standard. However, these techniques are also applicable to other video / media codec specifications.

[0068] Video compression techniques perform spatial (intra-picture) and / or temporal (inter-picture) prediction to reduce or eliminate redundancy inherent in a video sequence. In block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be divided into video blocks, which may also be called tree blocks, coding tree blocks (CTBs), coding tree units (CTUs), coding units (CUs), and / or coding nodes. A video block in an intra-coded (I) slice of a picture is coded using spatial prediction about a reference sample in a neighboring block within the same picture. A video block in an inter-coded (P or B) slice of a picture may use spatial prediction about a reference sample in a neighboring block within the same picture, or temporal prediction about a reference sample in another reference picture. A picture may be called a frame, and a reference picture may be called a reference frame.

[0069] Spatial or temporal prediction yields a predicted block for the block to be coded. Residual data represents the pixel difference between the original block to be coded and the predicted block. Intercoded blocks are coded according to a motion vector pointing to the reference sample block forming the predicted block and residual data showing the difference between the coded block and the predicted block. Intracoded blocks are coded according to the intracoded mode and residual data. For further compression, the residual data may be transformed from the pixel domain to the transformation domain, yielding residual transformation coefficients, which can then be quantized. The quantized transformation coefficients, initially arranged in a two-dimensional array, may be scanned to produce a one-dimensional vector of transformation coefficients, and entropy coding may be applied to achieve further compression.

[0070] In video codec specifications, pictures are identified for multiple purposes, including use as reference pictures in interpretation, output of pictures from the decoded picture buffer (DPB), scaling of motion vectors, and weighted prediction. In AVC and HEVC, pictures can be identified by a picture order count (POC). In AVC and HEVC, pictures in the DPB can be marked as "used for short-term reference," "used for long-term reference," or "not used for reference." When a picture is marked as "not used for reference," it can no longer be used for prediction. When a picture is no longer needed for output, it can be removed from the DPB.

[0071] In AVC, there are two types of reference pictures: short-term and long-term. A reference picture can be marked as "not for reference" when it is no longer needed for predictive referencing. The conversion between these three statuses (short-term, long-term, and not for reference) is controlled by the decrypted reference picture marking process. There are two alternative decrypted reference picture marking mechanisms: the implicit sliding window process and the explicit memory management control operation (MMCO) process. The sliding window process marks a short-term reference picture as "not for reference" when the number of reference frames equals a given maximum number (max_num_ref_frames in the Sequence Parameter Set (SPS)). Short-term reference pictures are stored in a first-in, first-out manner so that the most recent decrypted short-term picture is held in the DPB.

[0072] An explicit MMCO process may include multiple MMCO commands. An MMCO command may mark one or more short-term or long-term reference pictures as “not for reference,” or it may mark all pictures as “not for reference,” or it may mark the current reference picture or an existing short-term reference picture as long-term and then assign a long-term picture index to that long-term reference picture.

[0073] In AVC, the process of marking reference pictures, as well as the process of outputting and deleting pictures from the DPB, is performed after the pictures have been decoded.

[0074] HEVC introduces a different technique for managing reference pictures called the Reference Picture Set (RPS). The most fundamental difference in the concept of RPS compared to AVC's MMCO / sliding window process is that for each particular slice, a complete set of reference pictures used by the current picture or any subsequent pictures is provided. Thus, the complete set of all pictures that must be retained in the DPB for use by current or future pictures is signaled. This is different from the AVC method, where only changes relative to the DPB are signaled. With the concept of RPS, information from earlier pictures in the decoding order is not needed to maintain the correct status of reference pictures in the DPB.

[0075] To leverage the advantages of RPS and enhance fault tolerance, the order of picture decoding and DPB operations in HEVC is modified compared to AVC. In AVC, picture marking and buffer operations (both outputting and deleting decoded pictures from the DPB) are generally applied after the current picture has been decoded. In HEVC, RPS is first decoded from the slice header of the current picture, and then picture marking and buffer operations are generally applied before the current picture is decoded.

[0076] Each slice header in HEVC must include parameters for signaling the RPS for the picture containing the slice. The only exception is that the RPS is not signaled for Instantaneous Decode Refresh (IDR) slices; instead, the RPS is presumed to be empty. For I slices that do not belong to an IDR picture, an RPS may be provided even if the I slice belongs to an I picture, because there may be a picture that comes after the I picture in the decoding order, and the interpretation from the picture that came before the I picture in the decoding order is used for I slices that do not belong to an I picture. The number of pictures in the RPS should not exceed the DPB size limit, as specified by the sps_max_dec_pic_buffering syntax element in the SPS.

[0077] Each picture is associated with a POC value that represents the output order. The slice header contains a fixed-length codeword, pic_order_cnt_lsb, which represents the least significant bit (LSB) of the complete POC value, also known as the POC LSB. The length of the codeword is signaled in the SPS and can be between, for example, 4 bits and 16 bits. The RPS concept uses the POC to identify the reference picture. In addition to its own POC value, each slice header directly contains, or inherits from, the coded representation of the POC value (or LSB) of each picture in the RPS.

[0078] The RPS for each picture consists of five different sets of reference pictures, also known as the five RPS subsets. RefPicSetStCurrBefore consists of all short-term reference pictures that are ahead of the current picture in both the decoding and output order and can be used in the interpretation of the current picture. RefPicSetStCurrAfter consists of all short-term reference pictures that are ahead of the current picture in the decoding order, after the current picture in the output order, and can be used in the interpretation of the current picture. RefPicSetStFoll consists of all short-term reference pictures that can be used in the interpretation of one or more pictures that are after the current picture in the decoding order, but are not used in the interpretation of the current picture. RefPicSetLtCurr consists of all long-term reference pictures that can be used in the interpretation of the current picture. RefPicSetLtFoll consists of all long-term reference pictures that can be used in the interpretation of one or more pictures that are after the current picture in the decoding order, but are not used in the interpretation of the current picture.

[0079] RPS is signaled using up to three loops that iterate through different types of reference pictures: short-term reference pictures with a lower POC value than the current picture, short-term reference pictures with a higher POC value than the current picture, and long-term reference pictures. In addition, a flag (used_by_curr_pic_X_flag) is sent for each reference picture indicating whether the reference picture is used for reference by the current picture (included in one of the lists RefPicSetStCurrBefore, RefPicSetStCurrAfter, or RefPicSetLtCurr) or not (included in one of the lists RefPicSetStFoll or RefPicSetLtFoll).

[0080] Figure 4 shows the RPS400 with the current picture B14, along with entries (e.g., pictures) from all subsets 402 of the RPS400. In the example in Figure 4, the current picture B14 contains exactly one picture from each of the five subsets 402 (also known as RPS subsets). P8 is a picture in subset 402 called RefPicSetStCurrBefore because the picture is earlier in the output order and used by B14. P12 is a picture in subset 402 called RefPicSetStCurrAfter because the picture is later in the output order and used by B14. P13 is a picture in subset 402 called RefPicSetStFoll because it is a short-term reference picture that is not used by B14 (but must be retained in the DPB because it is used by B15). P4 is a picture in subset 402 called RefPicSetLtCurr because it is a long-term reference picture used by B14. I0 is a picture in subset 402 called RefPicSetStLtFoll because it is a long-term reference picture that is not used by the current picture (but must be kept in DPB because it is used by B15).

[0081] The short-term portion of RPS400 may be directly included in the slice header. Alternatively, the slice header may contain only a syntax element representing an index that references a predetermined list of RPSs transmitted in an active SPS. The short-term portion of RPS402 may be signaled using one of two different methods: interRPS as described below and intraRPS as described here. When intraRPS is used, num_negative_pics and num_positive_pics are signaled, representing the lengths of two different lists of reference pictures. These lists each contain reference pictures with negative and positive POC differences compared to the current picture. Each element in these lists is encoded using a variable-length code that represents the difference in POC value relative to the previous element in the list minus 1.

[0082] When encoding recurring RPS in a sequence parameter set, it is possible to encode elements of one RPS (e.g., RPS400) in relation to another RPS already encoded in the sequence parameter set. This is called interRPS. Since all RPS in a sequence parameter set are in the same Network Abstraction Layer (NAL) unit, there are no fault tolerance issues associated with this method. The interRPS syntax takes advantage of the fact that the RPS of the current picture can be predicted from the RPS of previously decoded pictures. This is because all reference pictures of the current picture must be either reference pictures of previous pictures or previously decoded pictures themselves. It is only necessary to indicate which of these pictures should be reference pictures and which should be used for predicting the current picture. Thus, the syntax comprises an index pointing to an RPS to be used as a predictor, a delta_POC to be added to the predictor's delta_POC to obtain the delta POC of the current RPS, and a set of indicators to show which pictures are reference pictures and whether they are used only for predicting future pictures.

[0083] Encoders wishing to utilize long-term reference pictures must set the SPS syntax element long_term_ref_pics_present_flag to 1. Long-term reference pictures can then be signaled in the slice header by a fixed-length codeword pos_lst_lt representing the least significant bit of the complete POC value for each long-term picture. Each pos_lsb_lt is a copy of the pic_order_cnt_lsb codeword signaled for a particular long-term picture. It is also possible to signal a set of long-term pictures in the SPS as a list of POC LSB values. The POC LSBs for long-term pictures can then be signaled in the slice header as an index to this list.

[0084] The `delta_poc_msb_cycle_lt_minus1` syntax element may be additionally signaled to enable the calculation of the full POC distance of long-term reference pictures to the current picture. The codeword `delta_poc_msb_cycle_lt_minus1` is required to be signaled for each long-term reference picture that has the same POC LSB value as any other reference picture in the RPS.

[0085] For reference picture marking in HEVC, there are typically a number of pictures in the DPB before picture decoding. Some of these pictures may be available for prediction and are therefore marked as "Used for reference." Other pictures may not be available for prediction but are waiting for output and are therefore marked as "Not used for reference." Once the slice header is parsed, the picture marking process takes place before the slice data is decoded. Pictures that exist in the DPB and are marked as "Used for reference" but are not included in the RPS are marked as "Not used for reference." Pictures that do not exist in the DPB but are included in the reference picture set are ignored when used_by_curr_pic_X_flag is equal to 0. However, if used_by_curr_pic_X_flag is equal to 1 instead, this reference picture was intended to be used for prediction in the current picture but has been lost. An unintended loss of a picture is inferred, and the decoder must take appropriate action.

[0086] After the current picture is decrypted, it will be marked as "to be used for short-term reference".

[0087] Next, the construction of the reference picture list in HEVC is discussed. In HEVC, the term inter-prediction is used to indicate a prediction derived from data elements (e.g., sample values ​​or motion vectors) of reference pictures other than the currently decoded picture. Like AVC, a picture can be predicted from multiple reference pictures. The reference pictures used for inter-prediction are organized in one or more reference picture lists. The reference index identifies which of the reference pictures in the list should be used to create the prediction signal.

[0088] A single reference picture list, list 0, is used for the P slice, and two reference picture lists, list 0 and list 1, are used for the B slice. Similar to AVC, reference picture list construction in HEVC involves reference picture list initialization and reference picture list modification.

[0089] In AVC, the initialization process for list 0 differs for P slices (where the decoding order is used) and B slices (where the output order is used). In HEVC, the output order is used in both cases.

[0090] Reference picture list initialization creates default lists 0 and 1 (if the slice is a B slice) based on three RPS subsets: RefPicSetStCurrBefore, RefPicSetStCurrAfter, and RefPicSetLtCurr. Short-term pictures with earlier (later) output order are first inserted into list 0 (list 1) in ascending order of POC distance to the current picture, then short-term pictures with later (earlier) output order are inserted into list 0 (list 1) in ascending order of POC distance to the current picture, and finally, long-term pictures are inserted at the end. Regarding RPS, for list 0, entries in RefPicSetStCurrBefore are inserted into the initial list, followed by entries in RefPicSetStCurrAfter. Then, if available, entries in RefPicSetLtCurr are appended.

[0091] In HEVC, if the number of entries in the list is less than the number of target active reference pictures (signaled in the picture parameter set or slice header), the above process is repeated (reference pictures already added to the reference picture list are added again). If the number of entries is greater than the number of targets, the list is truncated.

[0092] After the referenced picture list is initialized, the referenced picture list can be modified based on referenced picture list modification commands so that the referenced pictures for the current picture can be arranged in any order, including cases where a particular referenced picture may appear at more than one position in the list. When the flag indicating the presence of list modification is set to 1, a fixed number of commands (equal to the target number of entries in the referenced picture list) are signaled, with each command inserting one entry into the referenced picture list. The referenced picture is identified in the command by its index to the list of referenced pictures for the current picture, derived from the RPS signaling. This differs from referenced picture list modification in H.264 / AVC, where pictures are identified by either a picture number (derived from the frame_num syntax element) or a long-term referenced picture index, and fewer commands may be required, for example, to swap the first two entries in the initial list, or to insert one entry at the beginning of the initial list and shift the other entry.

[0093] The reference picture list is allowed to contain any reference picture with a TemporalId greater than the current picture. An HEVC bitstream can consist of several temporal sublayers. Each NAL unit belongs to a specific sublayer, indicated by its TemporalId (equal to temporal_id_plus1-1).

[0094] Reference picture management is directly based on the reference picture list. The JCT-VC document JCTVC-G643 includes a method for directly using three reference picture lists—reference picture list 0, reference picture list 1, and idle reference picture list—for managing reference pictures in the DPB, thereby eliminating the need for signaling and decoding processes that include either 1) sliding window and MMCO processes, as well as reference picture list initialization and modification processes in AVC, or 2) reference picture sets, as well as reference picture list initialization and modification processes in HEVC.

[0095] Several problems can exist with methods for managing reference pictures. The AVC method involves sliding windows, MMCO processes, and reference picture list initialization and modification processes, which are complex. Furthermore, the loss of a picture can lead to a loss of DPB status regarding which pictures should have been in the DPB for the purpose of further interpredictive referencing. The HEVC method does not have the problem of DPB status loss. However, the HEVC method involves complex reference picture set signaling and derivation processes, as well as reference picture list initialization and modification processes, which are also complex. The JCTVC-G643 method for directly using three reference picture lists—reference picture list 0, reference picture list 1, and idle reference picture list—for managing reference pictures in a DPB involves a third reference picture list, i.e., the idle reference picture list; bipartite coding of POC differences as a "short-term" portion and a "long-term" portion coded with ue(v); TemporalId-based POC granularity for POC difference coding; the use of bipartite coding of POC differences to determine whether a marking is "used for short-term references" or "used for long-term references"; reference picture list subset descriptions that allow specifying a reference picture list by deleting a reference picture from the end of some earlier reference picture list description; a reference picture list copy mode enabled by the syntax element ref_pic_list_copy_flag; and a reference picture list description process. Each of the preceding aspects unnecessarily complicates the method. Furthermore, the decoding process for reference picture lists in JCTVC-G643 is also complex. Signaling long-term reference pictures may require signaling POC cycles in slice headers, which is inefficient.

[0096] To address the problems listed above, the following solutions are disclosed herein, each of which may be applied individually or some of which may be applied in combination: 1) Reference picture marking is directly based on two reference picture lists, namely reference picture list 0 and reference picture list 1. 1a) Information for the derivation of the two reference picture lists is signaled based on syntax elements and syntax structures in the SPS, PPS, and / or slice header. 1b) Each of the two reference picture lists for a picture is explicitly signaled in the reference picture list structure. 1b.i) One or more reference picture list structures may be signaled in the SPS, each of which may be referenced by an index from the slice header. 1b.ii) Each of reference picture lists 0 and 1 may be directly signaled in the slice header. 2) Information for deriving two reference picture lists is signaled for all types of slices, namely B (biprediction), P (singleprediction), and I (intra) slices. The term slice refers to a collection of coding tree units, such as slices in HEVC or modern VVC WD, and may also refer to any other collection of coding tree units, such as tiles in HEVC. 3) Two reference picture lists are generated for all types of slices, namely B slices, P slices, and I slices. 4) The two reference picture lists are constructed directly without using the reference picture list initialization process and the reference picture list modification process. 5) In each of the two reference picture lists, the reference pictures that can be used for interprediction of the current picture can only be referenced by the first a certain number of entries in the list. These entries are called active entries in the list, and the other entries are called inactive entries in the list. Both the total number of entries in the list and the number of active entries can be derived.6) A picture referenced by an inactive entry in the reference picture list may not be referenced by another entry in the reference picture list, or by an entry in any other reference picture list. 7) Long-term reference pictures are identified by only a certain number of POC LSBs, which may be greater than the number of POC LSBs signaled in the slice header for the derivation of the POC value, and this number is shown in the SPS. 8) The reference picture list structure is signaled only in the slice header, and both short-term and long-term reference pictures are identified by their POC LSBs, which may be represented by a different number of bits than the number of bits used to represent the POC LSBs signaled in the slice header for the derivation of the POC value, and the number of bits used to represent the POC LSB for identifying a short-term reference picture may be different from the number of bits used to represent the POC LSB for identifying a long-term reference picture. 9) The reference picture list structure is signaled only in the slice header, there is no distinction between short-term and long-term reference pictures, all reference pictures are simply named reference pictures, reference pictures are identified by their POC LSB, and their POC LSB may be represented by a different number of bits than the number of bits used to represent the POC LSB that is signaled in the slice header for the derivation of the POC value.

[0097] A first embodiment of the present disclosure is provided. This description is for the latest VVC WD. In this embodiment, two sets of reference picture list structures, one for each of reference picture list 0 and reference picture list 1, are signaled in the SPS.

[0098] Some definitions of terms used herein are given. Intra-Random Access Point (IRAP) picture: A coded picture in which each video coding layer (VCL) NAL unit has a nal_unit_type equal to IRAP_NUT. Non-IRAP picture: A coded picture in which each VCL NAL unit has a nal_unit_type equal to NON_IRAP_NUT. Reference picture list: A list of reference pictures used for interpretation of P or B slices. Two reference picture lists, reference picture list 0 and reference picture list 1, are generated for each slice of non-IRAP picture. The set of unique pictures referenced by all entries in the two reference picture lists associated with a picture consists of all reference pictures that can be used for interpretation of the associated picture, or any picture that follows the associated picture in the decoding order. To decode the slice data of a P slice, only reference picture list 0 is used for interpretation. To decode the slice data of a B slice, both reference picture lists are used for interpretation. To decode the slice data of an I-slice, the reference picture list is not used for interpretation. Long-term reference picture (LTRP): A picture marked as "used for long-term reference". Short-term reference picture (STRP): A picture marked as "used for short-term reference".

[0099] The terms “used for short-term reference,” “used for long-term reference,” and “not used for reference” are defined in Section 8.3.3, “Decoding Process for Reference Picture Marking,” of VVC, Section 8.3.2, “Decoding Process for Reference Picture Sets,” of HEVC, and Section 7.4.3.3, “Decoded Reference Picture Marking Semantics,” of AVC. In this specification, these terms have the same meaning.

[0100] The relevant syntax and semantics for the first embodiment are given below.

[0101] NAL Unit Header Syntax

[0102] [Table 1]

[0103] Sequence parameter set Raw Byte Sequence Payload (RBSP) syntax

[0104] [Table 2]

[0105] Picture parameter set RBSP syntax

[0106] [Table 3]

[0107] Slice header syntax

[0108] [Table 4]

[0109] Reference picture list structure syntax

[0110] [Table 5]

[0111] NAL Unit Header Semantics

[0112] `forbidden_zero_bit` is assumed to be equal to 0. `nal_unit_type` specifies the type of RBSP data structure included in the NAL unit.

[0113] Table 6

[0114] The value obtained by subtracting 1 from nuh_temporal_id_plus1 specifies the time identifier for the NAL unit. The value of nuh_temporal_id_plus1 must not be equal to 0. The variable TemporalId is specified as TemporalId=nuh_temporal_id_plus1-1. When nal_unit_type is equal to IRAP_NUT, the coded slice belongs to an IRAP picture, and TemporalId is equal to 0. The value of TemporalId is the same for all VCL NAL units of an access unit. The value of TemporalId for a coded picture or access unit is the value of TemporalId for the VCL NAL unit of the coded picture or access unit. The value of TemporalId for non-VCL NAL units is constrained as follows: When nal_unit_type is equal to SPS_NUT, TemporalId is equal to 0, and the TemporalId of an access unit containing a NAL unit is equal to 0. Instead, if nal_unit_type is equal to EOS_NUT or EOB_NUT, TemporalId shall be equal to 0. Otherwise, TemporalId shall be greater than or equal to the TemporalId of the access unit containing the NAL unit. When the NAL unit is a non-VCL NAL unit, the value of TemporalId shall be equal to the minimum TemporalId value of all access units to which the non-VCL NAL unit applies. When nal_unit_type is equal to PPS_NUT, TemporalId may be greater than or equal to the TemporalId of the access unit containing it, because all Picture Parameter Sets (PPS) may be included at the beginning of the bitstream, and the first coded picture shall have a TemporalId equal to 0.When nal_unit_type is equal to PREFIX_SEI_NUT or SUFFIX_SEI_NUT, the TemporalId may be greater than or equal to the TemporalId of the containing access unit, because an SEI NAL unit may contain information applicable to a subset of the bitstream that contains access units with a TemporalId value greater than the TemporalId of the access unit containing the SEI NAL unit. nuh_reserved_zero_7bits shall be equal to "0000000". Other values ​​for nuh_reserved_zero_7bits may be specified in the future by ITU-T|ISO / IEC. The decoder shall ignore (i.e., remove and discard from the bitstream) any NAL unit with a nuh_reserved_zero_7bits value that is not equal to "0000000".

[0115] Sequence parameter set RBSP semantics

[0116] log2_max_pic_order_cnt_lsb_minus4 specifies the value of the variable MaxPicOrderCntLsb, which is used in the decryption process for picture order counting, as MaxPicOrderCntLsb=2(log2_max_pic_order_cnt_lsb_minus4+4). The value of log2_max_pic_order_cnt_lsb_minus4 should be in the range of 0 to 12, including both ends. sps_max_dec_pic_buffering_minus1 plus 1 specifies the maximum required size of the decrypted picture buffer for CVS, in units of picture storage buffers. The value of sps_max_dec_pic_buffering_minus1 should be in the range of 0 to MaxDpbSize-1, including both ends, where MaxDpbSize is as specified elsewhere. long_term_ref_pics_flag equal to 0 specifies that LTRP is not used for interpretation of any coded pictures in CVS. A long_term_ref_pics_flag equal to 1 specifies that LTRP may be used for interpretation of one or more coded pictures in CVS. additional_lt_poc_lsb specifies the value of the variable MaxLtPicOrderCntLsb used in the decoding process for the reference picture list, as MaxLtPicOrderCntLsb=2(log2_max_pic_order_cnt_lsb_minus4+4+additional_lt_poc_lsb). The value of additional_lt_poc_lsb should be in the range of 0 to 32-log2_max_pic_order_cnt_lsb_minus4-4, including both ends. If it does not exist, the value of additional_lt_poc_lsb is presumed to be equal to 0. num_ref_pic_lists_in_sps[i] specifies the number of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures in SPS where listIdx is equal to i.The value of num_ref_pic_lists_in_sps[i] is assumed to be in the range of 0 to 64, including both ends. For each value of listIdx (equal to 0 or 1), the decoder should allocate memory for a total of num_ref_pic_lists_in_sps[i] ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures, because there may be one ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure that is directly signaled in the slice header of the current picture.

[0117] Picture parameter set RBSP semantics

[0118] The value of num_ref_idx_default_active_minus1[i] plus 1 specifies the inferred value of the variable NumRefIdxActive[0] for P or B slices where num_ref_idx_active_override_flag is equal to 0 when i is equal to 0, and specifies the inferred value of NumRefIdxActive[1] for B slices where num_ref_idx_active_override_flag is equal to 0 when i is equal to 1. The value of num_ref_idx_default_active_minus1[i] is assumed to be in the range of 0 to 14, including both endpoints.

[0119] Slice header semantics

[0120] If present, the values ​​of the slice header syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb, respectively, shall be the same for all slice headers of the coded picture. slice_type specifies the coding type of the slice according to Table 7-3.

[0121] [Table 7]

[0122] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type is assumed to be equal to 2. slice_pic_order_cnt_lsb specifies the picture order count modulo MaxPicOrderCntLsb for the current picture. The length of the slice_pic_order_cnt_lsb syntax element is log2_max_pic_order_cnt_lsb_minus4+4 bits. The value of slice_pic_order_cnt_lsb is assumed to be in the range of 0 to MaxPicOrderCntLsb-1, including both ends. If slice_pic_order_cnt_lsb does not exist, it is assumed to be equal to 0. A ref_pic_list_sps_flag[i] equal to 1 specifies that the current picture's reference picture list i is derived based on one of the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures in the active SPS where listIdx is equal to i. A ref_pic_list_sps_flag[i] equal to 0 specifies that the current picture's reference picture list i is derived based on a ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure where listIdx is equal to i, which is directly included in the slice header of the current picture. When num_ref_pic_lists_in_sps[i] is equal to 0, the value of ref_pic_list_sps_flag[i] is considered to be equal to 0. ref_pic_list_idx[i] specifies an index to a list of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures in the active SPS where listIdx is equal to i, which is used to derive the reference picture list i of the current picture.The syntax element ref_pic_list_idx[i] is represented by the Ceil(Log2(num_ref_pic_lists_in_sps[i])) bit. If it does not exist, the value of ref_pic_list_idx[i] is presumed to be equal to 0. The value of ref_pic_list_idx[i] is assumed to be in the range of 0 to num_ref_pic_lists_in_sps[i]-1, including both ends. A num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] exists for P and B slices, and that the syntax element num_ref_idx_active_minus1[1] exists for B slices. A num_ref_idx_active_override_flag equal to 0 indicates that the syntax elements num_ref_idx_active_minus1[0] and num_ref_idx_active_minus1[1] do not exist. If num_ref_idx_active_minus1[i] exists, the value of the variable NumRefIdxActive[i] is specified as NumRefIdxActive[i] = num_ref_idx_active_minus1[i] + 1. The value of num_ref_idx_active_minus1[i] must be in the range of 0 to 14, including both endpoints.

[0123] The value of NumRefIdxActive[i]-1 specifies the maximum reference index to the reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, the reference index to the reference picture list i may not be used to decode the slice. For i equal to 0 or 1, if the current slice is a B slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is presumed to be equal to num_ref_idx_default_active_minus1[i]+1. If the current slice is a P slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[0] is presumed to be equal to num_ref_idx_default_active_minus1[0]+1. If the current slice is a P slice, NumRefIdxActive[i] is presumed to be equal to 0. When the current slice is an I slice, it is inferred that both NumRefIdxActive[0] and NumRefIdxActive[1] are equal to 0.

[0124] Alternatively, for i equal to 0 or 1, the following applies after the above: rplsIdx1 is set to equal ref_pic_list_sps_flag[i]?ref_pic_list_idx[i]:num_ref_pic_lists_in_sps[i], and numRpEntries[i] is equal to num_strp_entries[i][rplsIdx1]+num_ltrp_entries[i][rplsIdx1]. When NumRefIdxActive[i] is greater than numRpEntries[i], the value of NumRefIdxActive[i] is set to equal numRpEntries[i].

[0125] Reference Picture List Structure Semantics

[0126] The ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure can exist in either the SPS or the slice header. Depending on whether the syntax structure is in the slice header or the SPS, the following applies: If it is in the slice header, the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure specifies the reference picture listIdx of the current picture (the picture containing the slice). Otherwise (if present in an SPS), the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure specifies a candidate for the reference picture list listIdx, and the term “current picture” in the semantics specified for the remainder of this section refers to each picture that 1) has one or more slices containing ref_pic_list_idx[listIdx] equal to an index to a list of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures present in an SPS, and 2) is in a CVS that has an SPS as the active SPS. num_strp_entries[listIdx][rplsIdx] specifies the number of STRP entries in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. num_ltrp_entries[listIdx][rplsIdx] specifies the number of LTRP entries in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. If none exist, the value of num_ltrp_entries[listIdx][rplsIdx] is presumed to be equal to 0. The variable NumEntriesInList[listIdx][rplsIdx] is derived as follows: NumEntriesInList[listIdx][rplsIdx]=num_strp_entries[listIdx][rplsIdx]+num_ltrp_entries[listIdx][rplsIdx].The value of NumEntriesInList[listIdx][rplsIdx] is assumed to be between 0 and sps_max_dec_pic_buffering_minus1, including both ends. lt_ref_pic_flag[listIdx][rplsIdx][i] equal to 1 specifies that the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure is an LTRP entry. lt_ref_pic_flag[listIdx][rplsIdx][i] equal to 0 specifies that the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure is a STRP entry. If none exists, the value of lt_ref_pic_flag[listIdx][rplsIdx][i] is assumed to be equal to 0. A requirement for bitstream conformance is that the sum of lt_ref_pic_flag[listIdx][rplsIdx][i] for all values ​​of i in the range from 0 to NumEntriesInList[listIdx][rplsIdx]-1, including both ends, must be equal to num_ltrp_entries[listIdx][rplsIdx]. delta_poc_st[listIdx][rplsIdx][i] specifies the difference between the picture order count of the current picture and the picture order count of the picture referenced by the i-th entry, when the i-th entry is the first STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure, or when the i-th entry is a STRP entry but is not the first STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure, it specifies the difference between the picture order count of the picture referenced by the i-th entry and the picture order count of the picture referenced by a previous STRP entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure.The value of delta_poc_st[listIdx][rplsIdx][i] shall be in the range of -215 to 215-1, including both ends. poc_lsb_lt[listIdx][rplsIdx][i] specifies the picture order count modulo MaxLtPicOrderCntLsb value of the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. The length of the poc_lsb_lt[listIdx][rplsIdx][i] syntax element is Log2(MaxLtPicOrderCntLsb) bits.

[0127] The decryption process is discussed. The decryption process operates as follows for the current picture CurrPic: Decryption of NAL units is defined below. The following process defines the next decryption process using the slice header layer and the syntax elements described above. Variables and functions related to the picture order count are derived. This needs to be called only for the first slice of the picture. At the beginning of the decryption process for each slice of a non-IRAP picture, the decryption process for constructing the reference picture list is called to derive reference picture list 0 (RefPicList[0]) and reference picture list 1 (RefPicList[1]). The decryption process for reference picture marking is called, and reference pictures may be marked as "not used for reference" or "used for long-term reference". This needs to be called only for the first slice of the picture. The decryption process for coding tree units, scaling, transformation, in-loop filtering, etc. is called. After all slices of the current picture have been decrypted, the currently decrypted picture is marked as "used for short-term reference".

[0128] A NAL unit decoding process is discussed. The input to this process is the NAL unit of the current picture and any associated non-VCL NAL units. The output of this process is the parsed RBSP syntax structure encapsulated within the NAL unit. The decoding process for each NAL unit extracts the RBSP syntax structure from the NAL unit and then parses the RBSP syntax structure.

[0129] A slice decoding process is discussed, including a decoding process for picture order counting. The output of this process is PicOrderCntVal, which is the picture order count of the current picture. The picture order count is used to identify a picture for the derivation of motion parameters and prediction of motion vectors in merge mode, as well as for decoder compatibility verification. Each coded picture is associated with a picture order count variable denoted as PicOrderCntVal. When the current picture is not an IRAP picture, the variables prevPicOrderCntLsb and prevPicOrderCntMsb are derived as follows: prevTid0Pic is the previous picture in the decoding order, with a TemporalId equal to 0. The variable prevPicOrderCntLsb is set to equal slice_pic_order_cnt_lsb of prevTid0Pic. The variable prevPicOrderCntMsb is set to equal PicOrderCntMsb of prevTid0Pic.

[0130] The variable PicOrderCntMsb for the current picture is derived as follows: If the current picture is an IRAP picture, PicOrderCntMsb is set to equal to 0. Otherwise, PicOrderCntMsb is derived as follows: if((slice_pic_order_cnt_lsb <prevPicOrderCntLsb)&& ((prevPicOrderCntLsb-slice_pic_order_cnt_lsb)>=(MaxPicOrderCntLsb / 2))) PicOrderCntMsb=prevPicOrderCntMsb+MaxPicOrderCntLsb else if((slice_pic_order_cnt_lsb>prevPicOrderCntLsb)&& ((slice_pic_order_cnt_lsb-prevPicOrderCntLsb)>(MaxPicOrderCntLsb / 2))) PicOrderCntMsb=prevPicOrderCntMsb-MaxPicOrderCntLsb else PicOrderCntMsb=prevPicOrderCntMsb

[0131] PicOrderCntVal is derived as follows: PicOrderCntVal=PicOrderCntMsb+slice_pic_order_cnt_lsb

[0132] All IRAP pictures have a PicOrderCntVal equal to 0, because slice_pic_order_cnt_lsb is inferred to be equal to 0 for IRAP pictures, and prevPicOrderCntLsb and prevPicOrderCntMsb are both set to equal to 0. The value of PicOrderCntVal is assumed to be in the range of -231 to 231-1, including both ends. In a single CVS, the PicOrderCntVal values ​​for any two coded pictures are not assumed to be the same.

[0133] At any given moment during the decoding process, the values ​​of PicOrderCntVal&(MaxLtPicOrderCntLsb-1) for any two reference pictures in the DPB are not the same. The function PicOrderCnt(picX) is defined as PicOrderCnt(picX) = PicOrderCntVal of picture picX. The function DiffPicOrderCnt(picA,picB) is defined as DiffPicOrderCnt(picA,picB) = PicOrderCnt(picA) - PicOrderCnt(picB). The bitstream does not contain data that would result in a value of DiffPicOrderCnt(picA,picB) used in the decoding process that is not in the range of -215 to 215-1, including both ends. Let X be the current picture, and Y and Z be two other pictures in the same coded video sequence (CVS). Then Y and Z are considered to be in the same output order direction from X when DiffPicOrderCnt(X,Y) and DiffPicOrderCnt(X,Z) are both positive or both negative.

[0134] The decoding process for constructing the reference picture list is discussed. This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. Reference pictures are addressed through a reference index, which is an index to the reference picture list. When decoding an I slice, the reference picture list is not used when decoding the slice data. When decoding a P slice, only reference picture list 0 (i.e., RefPicList[0]) is used when decoding the slice data. When decoding a B slice, both reference picture list 0 and reference picture list 1 (i.e., RefPicList[1]) are used when decoding the slice data. At the beginning of the decoding process for each slice of a non-IRAP picture, the reference picture lists RefPicList[0] and RefPicList[1] are derived. The reference picture lists are used for marking the reference pictures or for decoding the slice data. For I-slices of non-IRAP pictures that are not the first slice of a picture, RefPicList[0] and RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but their derivation is not necessary for decoding the current picture or any picture that follows the current picture in the decoding order. For P-slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but its derivation is not necessary for decoding the current picture or any picture that follows the current picture in the decoding order. The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if (a reference picA is in DPB where PicOrderCntVal&(MaxLtPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } } }

[0135] For each i equal to 0 or 1, the following applies: The first NumRefIdxActive[i] entry in RefPicList[i] is called the active entry in RefPicList[i], and all other entries in RefPicList[i] are called inactive entries in RefPicList[i]. For each j in the range from 0 to NumEntriesInList[i][RplsIdx[i]]-1, including both ends, each entry in RefPicList[i][j] is called a STRP entry if lt_ref_pic_flag[i][RplsIdx[i]][j] is equal to 0, and an LTRP entry otherwise. A particular picture may be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. A particular picture may be referenced by more than one entry in RefPicList[0] or more than one entry in RefPicList[1]. Active entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that can be used for interpretation of the current picture, and one or more pictures that follow the current picture in the decoding order. Inactive entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that are not used for interpretation of the current picture, but can be used for interpretation of one or more pictures that follow the current picture in the decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equivalent to "no reference picture" because the corresponding picture does not exist in the DPB. Each inactive entry in RefPicList[0] or RefPicList[0] that is equivalent to "no reference picture" should be ignored. For each active entry in RefPicList[0] or RefPicList[1] that is equivalent to "no reference picture", an unintended picture loss should be inferred.

[0136] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is not less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] must exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of any inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: Inactive entries in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. STRP entries in RefPicList[0] or RefPicList[1] for a slice of a picture, and LTRP entries in RefPicList[0] or RefPicList[1] for the same slice or different slices of the same picture, shall not refer to the same picture. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics shall be the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics shall be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics shall be the same for all slices of a picture.

[0137] Decryption process for reference picture marking

[0138] This process is called once per picture, after the decoding of the slice header and the decoding process for building the reference picture list for the slice, but before decoding the slice data. This process may result in one or more reference pictures in the DPB being marked as "not used for reference" or "used for long-term reference". A decoded picture in the DPB can be marked as "not used for reference", "used for short-term reference", or "used for long-term reference", but only one of these three, at any given moment during the operation of the decoding process. Assigning one of these markings to a picture implicitly excludes another of these markings when applicable. When a picture is referred to as being marked as "used for reference", this collectively refers to the picture being marked as either "used for short-term reference" or "used for long-term reference" (but not both). When the current picture is an IRAP picture, all reference pictures (if any) currently in the DPB are marked as "not used for reference". STRPs are identified by their PicOrderCntVal values. LTRPs are identified by Log2(MaxLtPicOrderCntLsb) LSBs of their PicOrderCntVal values. The following applies: For each LTRP entry in RefPicList[0] or RefPicList[1], if the referenced picture is a STRP, the picture is marked as "Used for long-term reference". Each referenced picture in a DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as "Not used for reference".

[0139] A detailed description of a second embodiment of the present disclosure is given. This section describes in detail the second embodiment of the present disclosure as described above. The description is for the latest VVC WD. In this embodiment, one set of reference picture list structures is signaled in the SPS and shared by reference picture list 0 and reference picture list 1.

[0140] Sequence parameter set RBSP syntax

[0141] [Table 8]

[0142] Picture parameter set RBSP syntax

[0143] [Table 9]

[0144] Slice header syntax

[0145] [Table 10]

[0146] Reference picture list structure syntax

[0147] [Table 11]

[0148] NAL unit header semantics will be discussed.

[0149] Sequence parameter set RBSP semantics

[0150] log2_max_pic_order_cnt_lsb_minus4 specifies the value of the variable MaxPicOrderCntLsb, which is used in the decryption process for picture order counting, as MaxPicOrderCntLsb=2(log2_max_pic_order_cnt_lsb_minus4+4). The value of log2_max_pic_order_cnt_lsb_minus4 should be in the range of 0 to 12, including both ends. sps_max_dec_pic_buffering_minus1 plus 1 specifies the maximum required size of the decrypted picture buffer for CVS, in units of picture storage buffers. The value of sps_max_dec_pic_buffering_minus1 should be in the range of 0 to MaxDpbSize-1, including both ends, where MaxDpbSize is as specified elsewhere. num_ref_pic_lists_in_sps specifies the number of ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structures included in the SPS. The value of num_ref_pic_lists_in_sps should be in the range of 0 to 128, including both ends. The decoder should allocate memory for num_short_term_ref_pic_sets + 2 ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structures in total, because there may be two ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structures that are directly signaled in the slice header of the current picture. A long_term_ref_pics_flag equal to 0 specifies that LTRP is not used for interpretation of any coded pictures in the CVS. A long_term_ref_pics_flag equal to 1 indicates that LTRP may be used for interpretation of one or more coded pictures in CVS.`additional_lt_poc_lsb` specifies the value of the variable `MaxLtPicOrderCntLsb`, which is used in the decoding process for the reference picture list, as `MaxLtPicOrderCntLsb=2(log2_max_pic_order_cnt_lsb_minus4+4+additional_lt_poc_lsb)`. The value of `additional_lt_poc_lsb` should be in the range of 0 to 32-log2_max_pic_order_cnt_lsb_minus4-4, including both ends. If it does not exist, the value of `additional_lt_poc_lsb` is presumed to be equal to 0.

[0151] Picture parameter set RBSP semantics will be discussed.

[0152] Slice header semantics

[0153] If present, the values ​​of the slice header syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb, respectively, shall be the same for all slice headers of the coded picture. slice_type specifies the coding type of the slice according to Table 7-3 (Table 12).

[0154] [Table 12]

[0155] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type is assumed to be equal to 2. slice_pic_order_cnt_lsb specifies the picture order count modulo MaxPicOrderCntLsb for the current picture. The length of the slice_pic_order_cnt_lsb syntax element is log2_max_pic_order_cnt_lsb_minus4+4 bits. The value of slice_pic_order_cnt_lsb is assumed to be in the range of 0 to MaxPicOrderCntLsb-1, including both ends. If slice_pic_order_cnt_lsb does not exist, it is assumed to be equal to 0. A ref_pic_list_sps_flag[i] equal to 1 specifies that the current picture's reference picture list i is derived based on one of the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structures in the active SPS. A ref_pic_list_sps_flag[i] equal to 0 specifies that the current picture's reference picture list i is derived based on the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure directly contained in the slice header of the current picture. When num_ref_pic_lists_in_sps is equal to 0, the value of ref_pic_list_sps_flag[i] is considered to be equal to 0. ref_pic_list_idx[i] specifies the index of the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure used to derive the reference picture list i of the current picture into a list of ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structures contained in the active SPS. The syntax element ref_pic_list_idx[i] is represented by Ceil(Log2(num_ref_pic_lists_in_sps)) bits. If it does not exist, the value of ref_pic_list_idx[i] is presumed to be equal to 0.The value of ref_pic_list_idx[i] is to be in the range of 0 to num_ref_pic_lists_in_sps-1, including both ends. A num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] exists for P and B slices, and that the syntax element num_ref_idx_active_minus1[1] exists for B slices. A num_ref_idx_active_override_flag equal to 0 specifies that the syntax elements num_ref_idx_active_minus1[0] and num_ref_idx_active_minus1[1] do not exist.

[0156] num_ref_idx_active_minus1[i], if it exists, specifies the value of the variable NumRefIdxActive[i] as NumRefIdxActive[i]=num_ref_idx_active_minus1[i]+1. The value of num_ref_idx_active_minus1[i] is assumed to be in the range of 0 to 14, including both ends. The value of NumRefIdxActive[i]-1 specifies the maximum reference index to the reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, the reference index to the reference picture list i may not be used to decode the slice. For i equal to 0 or 1, if the current slice is a B slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is inferred to be equal to num_ref_idx_default_active_minus1[i]+1. When the current slice is a P slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[0] is presumed to be equal to num_ref_idx_default_active_minus1[0]+1. When the current slice is a P slice, NumRefIdxActive[1] is presumed to be equal to 0. When the current slice is an I slice, both NumRefIdxActive[0] and NumRefIdxActive[1] are presumed to be equal to 0.

[0157] Alternatively, for i equal to 0 or 1, the following applies after the above: rplsIdx1 is set to equal ref_pic_list_sps_flag[i]?ref_pic_list_idx[i]:num_ref_pic_lists_in_sps[i], and numRpEntries[i] is set to equal num_strp_entries[i][rplsIdx1]+num_ltrp_entries[i][rplsIdx1]. When NumRefIdxActive[i] is greater than numRpEntries[i], the value of NumRefIdxActive[i] is set to equal numRpEntries[i].

[0158] Reference Picture List Structure Semantics

[0159] The ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure can exist in an SPS or a slice header. Depending on whether the syntax structure is in a slice header or an SPS, the following applies: If it is in a slice header, the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure specifies the reference picture list listIdx of the current picture (the picture containing the slice). Otherwise (if it is in an SPS), the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure specifies a reference picture list candidate, and the term “current picture” in the semantics specified for the remainder of this section refers to each picture that 1) has one or more slices containing ref_pic_list_idx[i] equal to an index to a list of ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structures in an SPS, and 2) is in a CVS that has an SPS as the active SPS. num_strp_entries[rplsIdx] specifies the number of STRP entries in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure. num_ltrp_entries[rplsIdx] specifies the number of LTRP entries in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure. If none exist, the value of num_ltrp_entries[rplsIdx] is presumed to be equal to 0.

[0160] The variable NumEntriesInList[rplsIdx] is derived as follows: NumEntriesInList[rplsIdx]=num_strp_entries[rplsIdx]+num_ltrp_entries[rplsIdx]. The value of NumEntriesInList[rplsIdx] is assumed to be in the range of 0 to sps_max_dec_pic_buffering_minus1, including both ends. lt_ref_pic_flag[rplsIdx][i] equal to 1 specifies that the i-th entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure is an LTRP entry. lt_ref_pic_flag[rplsIdx][i] equal to 0 specifies that the i-th entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure is a STRP entry. If it does not exist, the value of lt_ref_pic_flag[rplsIdx][i] is presumed to be equal to 0. A requirement for bitstream conformance is that the sum of lt_ref_pic_flag[rplsIdx][i] for all values ​​of i in the range from 0 to NumEntriesInList[rplsIdx]-1, including both ends, must be equal to num_ltrp_entries[rplsIdx]. delta_poc_st[rplsIdx][i] specifies the difference between the picture order count of the current picture and the picture order count of the picture referenced by the i-th entry, when the i-th entry is the first STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure, or when the i-th entry is a STRP entry but is not the first STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure, it specifies the difference between the picture order count of the picture referenced by the i-th entry and the picture order count of the picture referenced by a previous STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure.The value of delta_poc_st[rplsIdx][i] is in the range of 0 to 215-1, including both ends. poc_lsb_lt[rplsIdx][i] specifies the picture order count modulo MaxLtPicOrderCntLsb value of the picture referenced by the i-th entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure. The length of the poc_lsb_lt[rplsIdx][i] syntax element is Log2(MaxLtPicOrderCntLsb) bits.

[0161] A general decoding process, as defined as part of the detailed description of the first embodiment of this disclosure, is applied. A NAL unit decoding process is described. A NAL unit decoding process, as defined as part of the detailed description of the first embodiment of this disclosure, is applied.

[0162] A slice decoding process is provided.

[0163] Decoding process for picture order counting

[0164] A decoding process for picture sequence counting, as defined as part of the detailed description of the first embodiment of this disclosure, is applied.

[0165] Decryption process for building the reference picture list

[0166] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. The reference picture is addressed through a reference index, which is an index to the reference picture list. When decoding an I slice, the reference picture list is not used in decoding the slice data. When decoding a P slice, only reference picture list 0 (i.e., RefPicList[0]) is used in decoding the slice data. When decoding a B slice, both reference picture list 0 and reference picture list 1 (i.e., RefPicList[1]) are used in decoding the slice data. At the beginning of the decoding process for each slice of a non-IRAP picture, the reference picture lists RefPicList[0] and RefPicList[1] are derived. The reference picture lists are used for marking the reference picture and decoding the slice data. For I-slices of non-IRAP pictures that are not the first slice of a picture, RefPicList[0] and RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but their derivation is not necessary for decoding the current picture or any picture that follows the current picture in the decoding order. For P-slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but its derivation is not necessary for decoding the current picture or any picture that follows the current picture in the decoding order.

[0167] The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps for(j=0,pocBase=PicOrderCntVal;j< NumEntriesInList[RplsIdx[i]];j++){ if(!lt_ref_pic_flag[RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if (a reference picA in DPB is equal to PicOrderCntVal&(MaxLtPicOrderCntLsb-1) poc_lsb_lt[RplsIdx[i]][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } } }

[0168] For each i equal to 0 or 1, the following applies: The first NumRefIdxActive[i] entry in RefPicList[i] is called the active entry in RefPicList[i], and all other entries in RefPicList[i] are called inactive entries in RefPicList[i]. Each entry RefPicList[i][j] for j in the range of 0 to NumEntriesInList[RplsIdx[i]]-1, including both ends, is called a STRP entry if lt_ref_pic_flag[RplsIdx[i]][j] is equal to 0, and an LTRP entry otherwise. A particular picture may be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. A particular picture may be referenced by more than one entry in RefPicList[0] or more than one entry in RefPicList[1]. Active entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that can be used for interpretation of the current picture, and one or more pictures that follow the current picture in the decoding order. Inactive entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that are not used for interpretation of the current picture, but can be used for interpretation of one or more pictures that follow the current picture in the decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equivalent to "no reference picture" because the corresponding picture does not exist in the DPB. Each inactive entry in RefPicList[0] or RefPicList[1] that is equivalent to "no reference picture" should be ignored. For each active entry in RefPicList[0] or RefPicList[1] that is equivalent to "no reference picture", an unintended picture loss should be inferred.

[0169] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, NumEntriesInList[RplsIdx[i]] is not less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] must exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of any inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: Inactive entries in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. STRP entries in RefPicList[0] or RefPicList[1] for a slice of a picture, and LTRP entries in RefPicList[0] or RefPicList[1] for the same slice or different slices of the same picture, shall not refer to the same picture. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics shall be the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics shall be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics shall be the same for all slices of a picture.

[0170] The decoding process for reference picture marking is discussed.

[0171] This process is called once per picture, after the decoding of the slice header and the decoding process for constructing the slice's reference picture list, but before decoding the slice data. This process may result in one or more reference pictures in the DPB being marked as "not used for reference" or "used for long-term reference". A decoded picture in the DPB can be marked as "not used for reference", "used for short-term reference", or "used for long-term reference", but only one of these three, at any given moment during the operation of the decoding process. Assigning one of these markings to a picture implicitly excludes another of these markings when applicable. When a picture is referred to as being marked as "used for reference", this collectively refers to the picture being marked as either "used for short-term reference" or "used for long-term reference" (but not both). When the current picture is an IRAP picture, all reference pictures (if any) currently in the DPB are marked as "not used for reference". STRPs are identified by their PicOrderCntVal values. The LTRP is identified by the Log2(MaxLtPicOrderCntLsb) LSBs of those PicOrderCntVal values.

[0172] The following applies: For each LTRP entry in RefPicList[0] or RefPicList[1], if the referenced picture is a STRP, the picture is marked as “Used for long-term reference.” Each referenced picture in a DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as “Not used for reference.”

[0173] Figure 5 shows an embodiment of method 500 for decoding a coded video bitstream, which is performed by a video decoder (e.g., video decoder 30). Method 500 may be performed after the decoded bitstream has been received directly or indirectly from a video encoder (e.g., video encoder 20). Method 500 may also be performed to improve the decoding process (e.g., to make the decoding process more efficient or faster than conventional decoding processes, etc.) because a reference picture list structure is included in the coded video bitstream for all types of slices. Thus, the performance of the codec can be improved, which leads to a better user experience.

[0174] In block 502, a first reference picture list structure and a second reference picture list structure are obtained, which are represented in the coded video bitstream. In one embodiment, the first and second reference picture list structures are obtained by parsing the coded video bitstream.

[0175] In some embodiments, the order of entries in the first and second reference picture list structures is the same as the order of the corresponding reference pictures in the reference picture list. In some embodiments, the order ranges from 0 to a specified value. In some embodiments, the specified value ranges from 0 to a value specified by sps_max_dec_pic_buffering_minus1.

[0176] In block 504, a first reference picture list and a second reference picture list for the current slice are derived based on the first and second reference picture list structures. In some embodiments, the first and second reference picture lists are derived for all types of slices, not just for bipredictive or bidirectional (B) slices. In some embodiments, the current slice comprises an intra (I) slice or a single-predictive (P) slice. In some embodiments, the reference picture lists are referred to as RefPictList[0] or RefPictList[1].

[0177] In block 506, following the derivation of the first and second reference picture lists, at least one reconstructed block of the current slice is obtained. In one embodiment, at least one reconstructed block is used to generate an image to be displayed on the display of an electronic device.

[0178] In one embodiment, the reference picture list comprises a list of reference pictures used for interpretation. In one embodiment, the interpretation is for P-slice or B-slice.

[0179] In one embodiment, the slice header includes a Reference Picture List Sequence Parameter Set (SPS) flag called ref_pic_list_sps_flag[i]. When this flag is equal to 1, the i-th reference picture list, i.e., RefPictList[i], is not directly signaled in the slice header but is referenced from the SPS. When this flag is equal to 0, the i-th reference picture list, i.e., RefPictList[i], is directly signaled in the slice header but is not referenced from the SPS. In one embodiment, the slice header includes a numbered reference index active override flag specified by num_ref_idx_active_override_flag. When this flag is equal to 1, the number of active entries in each reference picture list is the default value signaled in the PPS. When this flag is equal to 0, the number of active entries in each reference picture list is explicitly signaled in the slice header.

[0180] In one embodiment, the reference picture list is called RefPictList[0] or RefPictList[1], and the order of entries in the first reference picture list structure or the second reference picture list syntax structure is the same as the order of the corresponding reference pictures in the reference picture list.

[0181] An outline of alternative embodiments based on the first and second embodiments is provided.

[0182] This section provides a brief overview of other alternative embodiments of the present disclosure. The overview is for the purposes of the description of the first embodiment. However, the basic concepts of the present disclosure for the following alternative embodiments are applicable to implementations in addition to the disclosure for the second embodiment. Such implementations are in the same sense as how the embodiments are implemented in addition to the first embodiment.

[0183] Semantics of Delta POC for Short-Term Reference Picture Entries

[0184] In one alternative embodiment of this disclosure, the semantics of a syntax element specifying the delta POC of the i-th entry in a reference picture list structure ref_pic_list_struct() are defined as the POC difference between the current picture and the reference picture associated with its i-th entry. Some of the descriptions used herein are relative to the current standard draft (e.g., the VVC Working Draft), and only differences are shown or described. Deleted text is indicated by strikethrough, and any added text is highlighted.

[0185] The semantics of delta_poc_st[listIdx][rplsIdx][i] are defined as follows: delta_poc_st[listIdx][rplsIdx][i] specifies the difference between the picture order count value of the current picture and the picture order count value of the picture referenced by the i-th entry. The value of delta_poc_st[listIdx][rplsIdx][i] is in the range of -215 to 215-1, including both ends.

[0186] The formulas in the reference picture list construction process need to be updated. The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] for(j=0;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=PicOrderCntVal-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" else{ if (a reference picA is in DPB where PicOrderCntVal&(MaxLtPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } } }

[0187] Signaling of long-term reference picture entries

[0188] In one alternative embodiment of the present disclosure, long-term reference picture entries are not signaled in the same reference picture list structure that includes short-term reference picture entries. Long-term reference picture entries are signaled in a separate structure, and for each entry in the structure, there is a syntax element that describes the intended location of the long-term reference picture entry for the derivation of the corresponding entry index in the final reference picture list.

[0189] Sequence parameter set RBSP syntax

[0190] [Table 13]

[0191] Slice header syntax

[0192] [Table 14]

[0193] Reference picture list structure syntax

[0194] [Table 15]

[0195] Long-term reference picture list structure syntax

[0196] [Table 16]

[0197] Sequence parameter set RBSP semantics

[0198] num_ref_pic_lists_lt_in_sps specifies the number of ref_pic_list_lt_struct(ltRplsIdx) syntax structures included in the SPS. The value of num_ref_pic_lists_lt_in_sps is expected to be in the range of 0 to 64, including both endpoints. If none exist, the value of num_ref_pic_lists_lt_in_sps is presumed to be equal to 0.

[0199] Slice header semantics

[0200] ref_pic_list_lt_idx[i] specifies an index to a list of ref_pic_list_lt_struct(ltRplsIdx) syntax structures contained in the active SPS, which are used to derive the reference picture list i of the current picture. The syntax element ref_pic_list_lt_idx[i] is represented by Ceil(Log2(num_ref_pic_lists_lt_in_sps)) bits. The value of ref_pic_list_lt_idx is to be in the range of 0 to num_ref_pic_lists_lt_in_sps-1, including both ends.

[0201] Reference Picture List Structure Semantics

[0202] The ref_pic_list_struct(listIdx,rplsIdx) syntax structure can exist in either the SPS or the slice header. Depending on whether the syntax structure is in the slice header or the SPS, the following applies: If it is in the slice header, the ref_pic_list_struct(listIdx,rplsIdx) syntax structure specifies the reference picture list listIdx of the current picture (the picture containing the slice). Otherwise (if present in an SPS), the ref_pic_list_struct(listIdx,rplsIdx) syntax structure specifies candidates for the short-term reference picture list listIdx, and the term “current picture” in the semantics specified for the remainder of this section refers to each picture that 1) has one or more slices containing ref_pic_list_idx[listIdx] equal to an index to a list of ref_pic_list_struct(listIdx,rplsIdx) syntax structures present in an SPS, and 2) is in a CVS that has an SPS as the active SPS. num_strp_entries[listIdx][rplsIdx] specifies the number of STRP entries in the ref_pic_list_struct(listIdx,rplsIdx) syntax structure.

[0203] delta_poc_st[listIdx][rplsIdx][i] specifies the difference between the picture order count of the current picture and the picture order count of the picture referenced by the i-th entry, when the i-th entry is the first STRP entry in the ref_pic_list_struct(listIdx,rplsIdx) syntax structure, or when the i-th entry is a STRP entry but is not the first STRP entry in the ref_pic_list_struct(listIdx,rplsIdx) syntax structure, it specifies the difference between the picture order count of the picture referenced by the i-th entry and the picture order count of the picture referenced by a previous STRP entry in the ref_pic_list_struct(listIdx,rplsIdx) syntax structure. The value of delta_poc_st[listIdx][rplsIdx][i] shall be in the range of -215 to 215-1, including both ends.

[0204] Long-term reference picture list structure semantics

[0205] The ref_pic_list_lt_struct(ltRplsIdx) syntax structure can exist in an SPS or a slice header. Depending on whether the syntax structure is in a slice header or an SPS, the following applies: If it is in a slice header, the ref_pic_list_lt_struct(ltRplsIdx) syntax structure specifies a long-term reference picture list for the current picture (the picture containing the slice). Otherwise (if it is in an SPS), the ref_pic_list_struct(listIdx,rplsIdx) syntax structure specifies a candidate for the long-term reference picture list, and the term “current picture” in the semantics specified for the remainder of this section refers to each picture that 1) has one or more slices containing ref_pic_list_lt_idx[i] equal to an index to a list of ref_pic_list_lt_struct(ltRplsIdx) syntax structures in an SPS, and 2) is in a CVS that has an SPS as the active SPS. num_ltrp_entries[ltRplsIdx] specifies the number of LTRP entries in the ref_pic_list_lt_struct(ltRplsIdx) syntax structure. poc_lsb_lt[rplsIdx][i] specifies the picture order count modulo MaxLtPicOrderCntLsb value of the picture referenced by the i-th entry in the ref_pic_list_lt_struct(rplsIdx) syntax structure. The length of the poc_lsb_lt[rplsIdx][i] syntax element is Log2(MaxLtPicOrderCntLsb) bits. lt_pos_idx[rplsIdx][i] specifies the index of the i-th entry in the ref_pic_list_lt_struct(rplsIdx) syntax structure in the referenced picture list after the referenced picture list construction. The length of the syntax element lt_pos_idx[rplsIdx][i] is Log2(sps_max_dec_pic_buffering_minus1+1) bits.When num_ltrp_entries[ltRplsIdx] is greater than 1, poc_lsb_lt[rplsIdx][i] and lt_pos_idx[rplsIdx][i] are assumed to be in descending order of the lt_pos_idx[rplsIdx][i] value.

[0206] The decryption process is explained.

[0207] Decryption process for building the reference picture list

[0208] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. The reference picture is addressed through a reference index, which is an index to the reference picture list. When decoding an I slice, the reference picture list is not used when decoding the slice data. When decoding a P slice, only reference picture list 0 (i.e., RefPicList[0]) is used when decoding the slice data. When decoding a B slice, both reference picture list 0 and reference picture list 1 (i.e., RefPicList[1]) are used when decoding the slice data. At the beginning of the decoding process for each slice of a non-IRAP picture, the reference picture lists RefPicList[0] and RefPicList[1] are derived. The reference picture lists are used for marking the reference picture or decoding the slice data. For I-slices of non-IRAP pictures that are not the first slice of a picture, RefPicList[0] and RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but their derivation is not required for decoding the current picture or any picture that follows the current picture in the decoding order. For P-slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but its derivation is not required for decoding the current picture or any picture that follows the current picture in the decoding order. The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] } if(ref_pic_list_lt_sps_flag[i]) LtRplsIdx=ref_pic_list_lt_idx[i] else LtRplsIdx=num_ref_pic_lists_lt_in_sps[i] for(j=0;j <num_ltrp_entries[LtRplsIdx[i]];j++){ if (a reference picA in DPB is equal to PicOrderCntVal&(MaxLtPicOrderCntLsb-1) is poc_lsb_lt[LtRplsIdx[i]][j]) for(k=sps_max_dec_pic_buffering_minus1;k>lt_pos_idx[LtRplsIdx[i]][j];k--) RefPicList[i][k]=RefPicList[i][k-1] RefPicList[i][lt_pos_idx[LtRplsIdx[i]][j]]=picA }else{ for(k=sps_max_dec_pic_buffering_minus1;k>lt_pos_idx[LtRplsIdx[i]][j];k--) RefPicList[i][k]=RefPicList[i][k-1] RefPicList[i][lt_pos_idx[RplsIdx[i]][j]]="refrigerateピクチャしし" } } }

[0209] For each i equal to 0 or 1, the following applies: The first NumRefIdxActive[i] entry in RefPicList[i] is called the active entry in RefPicList[i], and all other entries in RefPicList[i] are called inactive entries in RefPicList[i]. For each j in the range from 0 to NumEntriesInList[i][RplsIdx[i]]-1, including both ends, each entry in RefPicList[i][j] is called a STRP entry if lt_ref_pic_flag[i][RplsIdx[i][j]] is equal to 0, and an LTRP entry otherwise. A particular picture may be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. A particular picture may be referenced by more than one entry in RefPicList[0] or more than one entry in RefPicList[1]. The active entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that can be used for interpretation of the current picture, and one or more pictures that follow the current picture in the decoding order. The inactive entries in RefPicList[0] and RefPicList[1] refer to all reference pictures that are not used for interpretation of the current picture, but can be used for interpretation of one or more pictures that follow the current picture in the decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equivalent to "no reference picture" because the corresponding picture does not exist in the DPB. Each inactive entry in RefPicList[0] or RefPicList[0] that is equivalent to "no reference picture" should be ignored. For each active entry in RefPicList[0] or RefPicList[1] that is equivalent to "no reference picture", an unintended picture loss should be inferred.

[0210] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, the number of entries in RefPicList[i] shall not be less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] shall exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of an inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: An inactive entry in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. STRP entries in RefPicList[0] or RefPicList[1] for a slice of a picture, and LTRP entries in RefPicList[0] or RefPicList[1] for the same slice or different slices of the same picture, shall not refer to the same picture. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics shall be the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics shall be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics shall be the same for all slices of a picture.

[0211] Signaling of the number of short-term reference picture entries is discussed.

[0212] In one alternative embodiment of this disclosure, the syntax element specifying the number of entries associated with short-term reference pictures in the reference picture list structure ref_pic_list_struct() is defined as num_strp_entries_minus1[listIdx][rplsIdx] instead of num_strp_entries[listIdx][rplsIdx]. This change has two effects on the signaling of reference picture lists. Namely, it can save bits for signaling the number of entries associated with short-term reference pictures in the reference picture list structure, since the element is coded using ue(v). This implicitly imposes the constraint that each reference picture list contains at least one short-term reference picture. Addressing this proposal requires several modifications to the first embodiment.

[0213] For reference picture list signaling in slice headers, the required reference picture lists—namely, one reference picture list for I or P slices (i.e., reference picture list 0) and two reference picture lists for B slices (i.e., both reference picture list 0 and reference picture list 1)—are signaled according to the slice type. The slice header syntax is changed as follows:

[0214] [Table 17]

[0215] By applying the above changes to the slice header (i.e., reference picture list 0 for I or P slices, reference picture 0 and reference picture 1 for B slices), the problem of having only one short-term reference picture for a P slice is avoided in this scheme. However, duplicate short-term reference pictures cannot be signaled in reference picture list 0 and reference picture list 1, and the number of active entries in reference picture list 1 must be equal to 0, so entries in reference picture list 1 are inactive entries. The semantics of num_strp_entries_minus1[listIdx][rplsIdx] are changed as follows: num_strp_entries_minus1[listIdx][rplsIdx] plus 1 specifies the number of STRP entries in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. The variable NumEntriesInList[listIdx][rplsIdx] is derived as follows: NumRefPicEntriesInRpl[listIdx][rplsIdx]=num_strp_entries_minus1[listIdx][rplsIdx]+1+numb_ltrp_entries[listIdx][rplsIdx]. The value of NumRefPicEntries[listIdx][rplsIdx] is assumed to be in the range of 1 to sps_max_dec_pic_buffering_minus1, including both ends.

[0216] Allow the current picture to be included in the reference picture list.

[0217] In one alternative embodiment of this disclosure, the current picture is permitted to be included in its reference picture list. To support this feature, no syntax and semantic changes are required for the descriptions of the first and second embodiments. However, the bitstream conformance constraints described in the decoding process for constructing the reference picture list must be modified as follows: The following constraints apply to the bitstream conformance requirements: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is not less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] reside in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of any inactive entry in RefPicList[0] or RefPicList[1] is not used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: An inactive entry in RefPicList[0] or RefPicList[1] shall not refer to the same picture as any other entry in RefPicList[0] or RefPicList[1]. A STRP entry in RefPicList[0] or RefPicList[1] for a slice of picture, and an LTRP entry in RefPicList[0] or RefPicList[1] for the same slice or a different slice of the same picture, shall not refer to the same picture. When the current picture is referenced by an entry in RefPicList[i], for i equal to 0 or 1, the entry index shall be less than NumRefIdxActive[i]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater.setOfRefPics is the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. If the current picture is not included in setOfRefPics, the number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1; otherwise, the number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1+1. setOfRefPics is the same for all slices of a picture.

[0218] Use different POC LSB bits for LTRP entries in the reference picture list.

[0219] In one alternative embodiment of the present disclosure, the number of bits used to identify a long-term reference picture in the reference picture list structure may be the difference between reference picture list 0 and reference picture list 1. To support this feature, the following modifications are required:

[0220] [Table 18]

[0221] `additional_lt_poc_lsb[i]` specifies the value of the variable `MaxLtPicOrderCntLsb[i]` used in the decoding process for a reference picture list `listIdx` equal to `i`, such as `MaxLtPicOrderCntLsb[i]=2(log2_max_pic_order_cnt_lsb_minus4+4+additional_lt_poc_lsb[i])`. The value of `additional_lt_poc_lsb[i]` is assumed to be in the range of 0 to 32-log2_max_pic_order_cnt_lsb_minus4-4, including both endpoints. If it does not exist, the value of `additional_lt_poc_lsb[i]` is assumed to be equal to 0.

[0222] poc_lsb_lt[listIdx][rplsIdx][i] specifies the picture order count modulo MaxLtPicOrderCntLsb[listIdx] value of the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. The length of the poc_lsb_lt[listIdx][rplsIdx][i] syntax element is Log2(MaxLtPicOrderCntLsb[listIdx]) bits.

[0223] The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the referenced picture picA, whose PicOrderCntVal is RefPicPocList[i][j], exists in the DPB) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if (PicOrderCntVal & (MaxLtPicOrderCntLsb[i] - 1) is equal to poc_lsb_lt[i][RplsIdx[i]][j] and the reference picA is in the DPB) RefPicList[i][j] = picA else RefPicList[i][j] = "No reference picture" } } }

[0224] Use the same ref_pic_list_sps_flag for reference picture lists 0 and 1

[0225] In one alternative embodiment of the present disclosure, instead of using two flags to indicate whether reference picture list 0 and reference picture list 1 are derived based on the ref_pic_list_struct() syntax structure in the active SPS, one flag is used for both reference pictures. Such an alternative form has either the constraint that both reference picture lists are derived based on ref_pic_list_struct() in the active SPS, or they are derived based on the ref_pic_list_struct() syntax structure directly included in the slice header of the current picture. To support this feature, the following changes are required.

[0226]

Table 19

[0227] A ref_pic_list_sps_flag equal to 1 specifies that the current picture's referenced picture list is derived based on the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) in the active SPS. A ref_pic_list_sps_flag equal to 0 specifies that the current picture's referenced picture list is derived based on the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) directly included in the current picture's slice header. If either num_ref_pic_lists_in_sps[0] or num_ref_pic_lists_in_sps[1] is equal to 0, the value of ref_pic_list_sps_flag is equal to 0. If pic_lists_in_sps[1] is equal to 0, the value of ref_pic_list_sps_flag is equal to 0.

[0228] The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if (a reference picA is in DPB where PicOrderCntVal&(MaxLtPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } } }

[0229] Signaling of the most significant bit (MSB) of the Delta POC for long-term reference picture entries

[0230] In one alternative embodiment of this disclosure, instead of using additional bits to represent the POC LSB of long-term reference picture entries in ref_pic_list_struct(), the POC MSB cycle is signaled to distinguish long-term reference pictures. When signaled, the POC MSB cycle information is signaled for each entry in ref_pic_list_struct() that references a long-term reference picture. The ref_pic_list_struct() syntax structure is not signaled in the SPS, but only in the slice header. To support this feature, the following modifications are required:

[0231] [Table 20]

[0232] [Table 21]

[0233]

Table 22

[0234] The ref_pic_list_struct(listIdx, ltrpFlag) syntax structure may be present in the slice header. When present in the slice header, the ref_pic_list_struct(listIdx, ltrpFlag) syntax structure specifies the reference picture list listIdx of the current picture (the picture containing the slice). num_strp_entries[listIdx] specifies the number of STRP entries in the ref_pic_list_struct(listIdx, ltrpFlag) syntax structure. num_ltrp_entries[listIdx] specifies the number of LTRP entries in the ref_pic_list_struct(listIdx, ltrpFlag) syntax structure. When not present, the value of num_ltrp_entries[listIdx][rplsIdx] is presumed to be equal to 0.

[0235] The variable NumEntriesInList[listIdx] is derived as follows. It is derived as NumRefPicEntriesInRpl[listIdx]=num_strp_entries[listIdx]+num_ltrp_entries[listIdx].

[0236] The value of NumRefPicEntries[listIdx] is assumed to be between 0 and sps_max_dec_pic_buffering_minus1, including both ends. lt_ref_pic_flag[listIdx][i] equal to 1 specifies that the i-th entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure is an LTRP entry. lt_ref_pic_flag[listIdx][i] equal to 0 specifies that the i-th entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure is a STRP entry. If none exists, the value of lt_ref_pic_flag[listIdx][i] is assumed to be equal to 0. A requirement for bitstream conformance is that the sum of lt_ref_pic_flag[listIdx][i] for all values ​​of i in the range from 0 to NumRefPicEntries[listIdx]-1, including both ends, must be equal to num_ltrp_entries[listIdx]. delta_poc_st[listIdx][i] specifies the difference between the picture order count of the current picture and the picture order count of the picture referenced by the i-th entry, when the i-th entry is the first STRP entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure, or when the i-th entry is a STRP entry but is not the first STRP entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure, it specifies the difference between the picture order count of the picture referenced by the i-th entry and the picture order count of the picture referenced by a previous STRP entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure. The value of delta_poc_st[listIdx][i] is -2 including both ends. 15 From 2 15It is assumed to be in the range of -1. poc_lsb_lt[listIdx][i] specifies the picture order count modulo MaxLtPicOrderCntLsb value of the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure. The length of the poc_lsb_lt[listIdx][i] syntax element is Log2(MaxPicOrderCntLsb) bits. delta_poc_msb_present_flag[listIdx][i] equal to 1 specifies that delta_poc_msb_cycle_lt[listIdx][i] exists. delta_poc_msb_present_flag[listIdx][i] equal to 0 specifies that delta_poc_msb_cycle_lt[listIdx][i] does not exist. If num_ltrp_entries[listIdx] is greater than 0, and when this slice header is decoded, there is more than one reference picture in the DPB where PicOrderCntVal modulo MaxPicOrderCntLsb is equal to poc_lsb_lt[listIdx][i], then delta_poc_msb_present_flag[listIdx][i] is assumed to be equal to 1. If none exist, the value of delta_poc_msb_cycle_lt[listIdx][i] is assumed to be equal to 0. delta_poc_msb_cycle_lt[listIdx][i] is used to determine the value of the most significant bit of the picture order count value for the i-th entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure. If delta_poc_msb_cycle_lt[listIdx][i] does not exist, it is assumed to be equal to 0. Changes to the decoding process for picture order count:

[0237] The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i];j++){ if(!lt_ref_pic_flag[i][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if(delta_poc_msb_cycle_lt[i][j] is equal to 0 && (If PicOrderCntVal&(MaxPicOrderCntLsb-1) is equal to poc_lsb_lt[i][j], then the referenced picture picA is in DPB.) RefPicList[i][j]=picA else if(delta_poc_msb_cycle_lt[i][j] is equal to 1 && (There is a reference picture picA in DPB where PicOrderCntVal is equal to (MaxPicOrderCntLsb*delta_poc_msb_cycle_lt[i][j])+poc_lsb_lt[i][j])) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } } }

[0238] Alternatively, the semantics of delta_poc_msb_cycle_lt[listIdx][i] can be expressed as a difference of differences, so that the construction of the reference picture list can be updated as follows: The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ prevMsbCycle=0 for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i];j++){ (8-5) if(!lt_ref_pic_flag[i][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if(delta_poc_msb_cycle_lt[i][j] is equal to 0 && (If PicOrderCntVal&(MaxPicOrderCntLsb-1) is equal to poc_lsb_lt[i][j], then the referenced picture picA is in DPB.) RefPicList[i][j]=picA else if(delta_poc_msb_cycle_lt[i][j] is equal to 1 && If PicOrderCntVal is equal to (MaxPicOrderCntLsb*(delta_poc_msb_cycle_lt[i][j]+ prevMsbCycle))+poc_lsb_lt[i][j]), then there is a reference picA in DPB){ RefPicList[i][j]=picA prevMsbCycle+=delta_poc_msb_cycle_lt[i][j] else RefPicList[i][j]="No reference picture" } } }

[0239] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] shall not be less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] shall exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of an inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: An inactive entry in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. STRP entries in RefPicList[0] or RefPicList[1] for a slice of a picture, and LTRP entries in RefPicList[0] or RefPicList[1] for the same slice or different slices of the same picture, shall not refer to the same picture. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics shall be the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics shall be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics shall be the same for all slices of a picture.

[0240] Each STRP is identified by its PicOrderCntVal value. For each LTRP, if the LTRP is referenced by an entry in RefPicList[0] or RefPicList[1] where delta_poc_msb_present_flag[listIdx][i] is equal to 1, it is identified by its PicOrderCntVal value; otherwise, it is identified by Log2(MaxPicOrderCntLsb) LSBs of its PicOrderCntVal value.

[0241] Alternative Form 1 of Delta POC MSB Signaling for Long-Term Reference Picture Entries

[0242] This embodiment provides an alternative to the embodiment described in the previous section. Similar to the approach in the previous section, instead of using additional bits to represent the POC LSB of long-term reference pictures within ref_pic_list_struct(), the POC MSB cycle is signaled to distinguish long-term reference pictures. However, in this alternative, once signaled, the POC MSB cycle information is not signaled within ref_pic_list_struct(), but instead is signaled in the slice header when the POC MSB cycle information is needed. The ref_pic_list_struct() syntax structure can be signaled in the SPS and slice header.

[0243] [Table 23]

[0244] [Table 24]

[0245] A delta_poc_msb_present_flag[i][j] equal to 1 indicates that delta_poc_msb_cycle_lt[i][j] exists. A delta_poc_msb_present_flag[i][j] equal to 0 indicates that delta_poc_msb_cycle_lt[i][j] does not exist. If NumLtrpEntries[i] is greater than 0, and when this slice header is decoded for the j-th LTRP entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure, there is more than one reference picture in the DPB where PicOrderCntVal modulo MaxPicOrderCntLsb is equal to poc_lsb_lt[i][rplsIdx][jj], and jj is the entry index of the entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure that is the j-th LTRP entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure, then delta_poc_msb_present_flag[i][j] is equal to 1. If it does not exist, the value of delta_poc_msb_cycle_lt[i][j] is presumed to be equal to 0. delta_poc_msb_cycle_lt[i][j] is used to determine the value of the most significant bit of the picture order count value for the j-th LTRP entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure. When delta_poc_msb_cycle_lt[i][j] does not exist, it is presumed to be equal to 0.

[0246] [Table 25]

[0247] A delta_poc_msb_present_flag[i][j] equal to 1 indicates that delta_poc_msb_cycle_lt[i][j] exists. A delta_poc_msb_present_flag[i][j] equal to 0 indicates that delta_poc_msb_cycle_lt[i][j] does not exist. If NumLtrpEntries[i] is greater than 0 and there is more than one referenced picture in the DPB where PicOrderCntVal modulo MaxPicOrderCntLsb is equal to poc_lsb_lt[i][rplsIdx][j] when this slice header is decoded, then delta_poc_msb_present_flag[i][j] is assumed to be equal to 1. If it does not exist, the value of delta_poc_msb_cycle_lt[i][j] is assumed to be equal to 0. delta_poc_msb_cycle_lt[i][j] is used to determine the value of the most significant bit of the picture order count value for the j-th entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure. When delta_poc_msb_cycle_lt[i][j] does not exist, it is presumed to be equal to 0. poc_lsb_lt[listIdx][rplsIdx][i] specifies the value of the picture order count modulo MaxPicOrderCntLsb for the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. The length of the poc_lsb_lt[listIdx][rplsIdx][i] syntax element is Log2(MaxPicOrderCntLsb) bits.

[0248] Changes to the decoding process for picture order counting:

[0249] For slice header design 1, the reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[ i ]=ref_pic_list_idx[ i ] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] msbCycleIdx=0 for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 0 && (If PicOrderCntVal&(MaxPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j], then the referenced picture picA is in DPB.) RefPicList[i][j]=picA else if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 1 && If there is a reference picture picA in DPB where PicOrderCntVal is equal to (MaxPicOrderCntLsb*delta_poc_msb_cycle_lt[i][msbCycleIdx])+poc_lsb_lt[i][RplsIdx[i]][j]){ RefPicList[i][j]=picA msbCycleIdx++ else RefPicList[i][j]="No reference picture" } } }

[0250] Alternatively, for slice header design 1, the semantics of delta_poc_msb_cycle_lt[listIdx][i] can be expressed as a difference of differences, so that the reference picture list construction may be updated as follows: The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] pevMsbCycle=0 msbCycleIdx=0 for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 0 && (If PicOrderCntVal&(MaxPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j], then the referenced picture picA is in DPB.) RefPicList[i][j]=picA else if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 1 && If there is a reference picture picA in DPB where PicOrderCntVal is equal to (MaxPicOrderCntLsb*(delta_poc_msb_cycle_lt[i][msbCycleIdx]+prevMsbCycle)+poc_lsb_lt[i][RplsIdx[i]][j]) { RefPicList[i][j]=picA prevMsbCycle+=delta_poc_msb_cycle_lt[i][msbCycleIdx] msbCycleIdx++ else RefPicList[i][j]="No reference picture" } } }

[0251] For slice header design 2, the reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if(delta_poc_msb_cycle_lt[i][j] is equal to 0 && (If PicOrderCntVal&(MaxPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j], then the referenced picture picA is in DPB.) RefPicList[i][j]=picA else if(delta_poc_msb_cycle_lt[i][j] is equal to 1 && (There is a reference picture picA in DPB where PicOrderCntVal is equal to (MaxPicOrderCntLsb*delta_poc_msb_cycle_lt[i][j])+poc_lsb_lt[i][RplsIdx[i]][j])) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture"} } }

[0252] Alternatively, for slice header design 2, the semantics of delta_poc_msb_cycle_lt[listIdx][i] can be expressed as a difference of differences so that the reference picture list construction can be updated as follows: The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] prevMsbCycle=0 for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if(delta_poc_msb_cycle_lt[i][j] is equal to 0 && (If PicOrderCntVal&(MaxPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j], then the referenced picture picA is in DPB.) RefPicList[i][j]=picA else if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 1 && If there is a reference picture picA in DPB where PicOrderCntVal is equal to (MaxPicOrderCntLsb*(delta_poc_msb_cycle_lt[i][j]+ prevMsbCycle)+poc_lsb_lt[i][RplsIdx[i]][j]){ RefPicList[i][j]=picA prevMsbCycle+=delta_poc_msb_cycle_lt[i][j] else RefPicList[i][j]="No reference picture" } } }

[0253] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is not less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] must exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of any inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: Inactive entries in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. STRP entries in RefPicList[0] or RefPicList[1] for a slice of a picture, and LTRP entries in RefPicList[0] or RefPicList[1] for the same slice or different slices of the same picture, shall not refer to the same picture. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics shall be the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics shall be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics shall be the same for all slices of a picture.

[0254] Each STRP is identified by its PicOrderCntVal value. For each LTRP, if the LTRP is referenced by an entry in RefPicList[0] or RefPicList[1] where delta_poc_msb_present_flag[i][j] is equal to 1, it is identified by its PicOrderCnVal value; otherwise, it is identified by Log2(MaxPicOrderCntLsb) LSBs of its PicOrderCntVal value.

[0255] Alternative Form 2 of Delta POC MSB Signaling for Long-Term Reference Picture Entries

[0256] In one alternative embodiment of the present disclosure, the disclosure described in the first or second embodiment is combined with the embodiments described above and may be named “Signaling Delta POC MSB for Long-Term Reference Picture Entries” and “Alternative Form 1 of Signaling Delta POC MSB for Long-Term Reference Picture Entries,” respectively. The aspects of the present disclosure to be combined are the signaling of additional_lt_poc_lsb (i.e., from the first or second embodiment) and POC MSB cycle information (i.e., from the embodiment described above and named “Signaling Delta POC MSB for Long-Term Reference Picture Entries” or “Alternative Form 1 of Signaling Delta POC MSB for Long-Term Reference Picture Entries”). An example of how this combination, i.e., the combination of the first embodiment and the embodiment described above and named “Alternative Form 1 of Signaling Delta POC MSB for Long-Term Reference Picture Entries” may be made is described below.

[0257] [Table 26]

[0258] A delta_poc_msb_present_flag[i][j] equal to 1 indicates that delta_poc_msb_cycle_lt[i][j] exists. A delta_poc_msb_present_flag[i][i] equal to 0 indicates that delta_poc_msb_cycle_lt[i][j] does not exist. If NumLtrpEntries[i] is greater than 0, and when this slice header is decoded for the j-th LTRP entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure, there is more than one reference picture in the DPB where PicOrderCntVal modulo MaxPicOrderLtCntLsb is equal to poc_lsb_lt[i][rplsIdx][jj], and jj is the entry index of the entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure that is the j-th LTRP entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure, then delta_poc_msb_present_flag[i][j] is equal to 1. If it does not exist, the value of delta_poc_msb_cycle_lt[i][j] is presumed to be equal to 0. delta_poc_msb_cycle_lt[i][j] is used to determine the value of the most significant bit of the picture order count value for the j-th LTRP entry in the ref_pic_list_struct(i,rplsIdx,1) syntax structure. When delta_poc_msb_cycle_lt[i][j] does not exist, it is presumed to be equal to 0.

[0259] Changes to the decoding process for picture order counting:

[0260] The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] msbCycleIdx=0 for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 0 && (If PicOrderCntVal&(MaxLtPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j], then there is a reference picture picA in DPB.) RefPicList[i][j]=picA else if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 1 && If there is a reference picture picA in DPB where PicOrderCntVal is equal to (MaxLtPicOrderCntLsb*delta_poc_msb_cycle_lt[i][msbCycleIdx])+poc_lsb_lt[i][RplsIdx[i]][j]){ RefPicList[i][j]=picA msbCycleIdx++ else RefPicList[i][j]="No reference picture" } } }

[0261] Alternatively, the semantics of delta_poc_msb_cycle_lt[listIdx][i] can be expressed as a difference of differences, so that the construction of the reference picture list can be updated as follows: The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] prevMsbCycle=0 msbCycleIdx=0 for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-delta_poc_st[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 0 && (If PicOrderCntVal&(MaxLtPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j], then there is a reference picture picA in DPB.) RefPicList[i][j]=picA else if(delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 1 && If there is a reference picture picA in DPB where PicOrderCntVal is equal to (MaxLtPicOrderCntLsb*(delta_poc_msb_cycle_lt[i][msbCycleIdx]+prevMsbCycle)+poc_lsb_lt[i][RplsIdx[i]][j]) { RefPicList[i][j]=picA prevMsbCycle+=delta_poc_msb_cycle_lt[i][msbCycleIdx] msbCycleIdx++ else RefPicList[i][j]="No reference picture" } } }

[0262] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is not less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] must exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of any inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: Inactive entries in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. STRP entries in RefPicList[0] or RefPicList[1] for a slice of a picture, and LTRP entries in RefPicList[0] or RefPicList[1] for the same slice or different slices of the same picture, shall not refer to the same picture. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics shall be the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics shall be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics shall be the same for all slices of a picture.

[0263] Each STRP is identified by its PicOrderCntVal value. For each LTRP, if the LTRP is referenced by an entry in RefPicList[0] or RefPicList[1] where delta_poc_msb_present_flag[i][j] is equal to 1, it is identified by its PicOrderCntVal value; otherwise, it is identified by Log2(MaxLtPicOrderCntLsb) LSBs of its PicOrderCntVal value.

[0264] Distinguish between short-term and long-term reference pictures and always signal the list of reference pictures in the slice header.

[0265] This section describes another alternative embodiment of the present disclosure. This description is for the most recent VVC WD (i.e., only the differences to the most recent VVC WD of JVET-K1001-v1 are described, but the text of the most recent VVC WD not mentioned below remains applicable). This alternative embodiment can be summarized as follows: The reference picture list structure is signaled only in the slice header. Both short-term and long-term reference pictures are identified by their POC LSBs, which may be represented by a different number of bits than the number of bits used to represent the POC LSBs signaled in the slice header for the derivation of the POC values. Furthermore, the number of bits used to represent the POC LSB for identifying short-term reference pictures may be different from the number of bits used to represent the POC LSB for identifying long-term reference pictures.

[0266] NAL Unit Header Syntax

[0267] [Table 27]

[0268] Sequence parameter set RBSP syntax

[0269] [Table 28]

[0270] Picture parameter set RBSP syntax

[0271] [Table 29]

[0272] Slice header syntax

[0273] [Table 30]

[0274] Reference picture list structure syntax

[0275] [Table 31]

[0276] NAL Unit Header Semantics

[0277] `forbidden_zero_bit` is assumed to be equal to 0. `nal_unit_type` specifies the type of RBSP data structure included in the NAL unit.

[0278] [Table 32]

[0279] The value obtained by subtracting 1 from nuh_temporal_id_plus1 specifies the time identifier for the NAL unit. The value of nuh_temporal_id_plus1 must not be equal to 0. The variable TemporalId is specified as TemporalId=nuh_temporal_id_plus1-1.

[0280] When nal_unit_type is equal to IRAP_NUT, the coded slice belongs to an IRAP picture and its TemporalId is equal to 0. The value of TemporalId is the same for all VCL NAL units in an access unit. The value of TemporalId for a coded picture or access unit is the value of TemporalId for the VCL NAL unit of the coded picture or access unit. The value of TemporalId for non-VCL NAL units is constrained as follows: If nal_unit_type is equal to SPS_NUT, TemporalId is equal to 0, and the TemporalId of an access unit containing a NAL unit is equal to 0. Otherwise, if nal_unit_type is equal to EOS_NUT or EOB_NUT, TemporalId is equal to 0. Otherwise, TemporalId is greater than or equal to the TemporalId of an access unit containing a NAL unit. When a NAL unit is a non-VCL NAL unit, the value of TemporalId is equal to the minimum TemporalId value of all access units to which the non-VCL NAL unit applies. When nal_unit_type is equal to PPS_NUT, TemporalId may be greater than or equal to the TemporalId of the containing access unit because all Picture Parameter Sets (PPS) may be included at the beginning of the bitstream, and the first coded picture has a TemporalId equal to 0. When nal_unit_type is equal to PREFIX_SEI_NUT or SUFFIX_SEI_NUT, TemporalId may be greater than or equal to the TemporalId of the containing access unit because a Supplementary Enhancement Information (SEI) NAL unit may contain information that applies to a subset of the bitstream that includes access units with a TemporalId value greater than the TemporalId of the access unit containing the SEI NAL unit. nuh_reserved_zero_7bits shall be equal to "0000000".Other values ​​for nuh_reserved_zero_7bits may be specified in the future by ITU-T|ISO / IEC. The decoder shall ignore (i.e., remove and discard from the bitstream) any NAL units with a nuh_reserved_zero_7bits value that is not equal to "0000000".

[0281] Sequence parameter set RBSP semantics

[0282] log2_max_pic_order_cnt_lsb_minus4 specifies the value of the variable MaxPicOrderCntLsb, which is used in the decoding process for picture order counting, as follows: MaxPicOrderCntLsb=2 (log2_max_pic_order_cnt_lsb_minus4+4)

[0283] The value of log2_max_pic_order_cnt_lsb_minus4 shall be in the range of 0 to 12, including both ends. Adding 1 to sps_max_dec_pic_buffering_minus1 specifies the maximum required size of the decrypted picture buffer for CVS in units of picture storage buffers. The value of sps_max_dec_pic_buffering_minus1 shall be in the range of 0 to MaxDpbSize-1, including both ends, where MaxDpbSize is as specified elsewhere. additional_st_poc_lsb specifies the value of the variable MaxStPicOrderCntLsb used in the decryption process for the reference picture list as follows: MaxStPicOrderCntLsb=2 (log2_max_pic_order_cnt_lsb_minus4+4+additional_st_poc_lsb)

[0284] The value of additional_st_poc_lsb shall be in the range of 0 to 32-log2_max_pic_order_cnt_lsb_minus4-4, including both ends. A long_term_ref_pics_flag equal to 0 specifies that LTRP will not be used for interpretation of any coded pictures in the CVS. A long_term_ref_pics_flag equal to 1 specifies that LTRP may be used for interpretation of one or more coded pictures in the CVS. additional_lt_poc_lsb specifies the value of the variable MaxLtPicOrderCntLsb used in the decoding process for the reference picture list as follows: MaxLtPicOrderCntLsb=2 (log2_max_pic_order_cnt_lsb_minus4+4+additional_st_poc_lsb+additional_lt_poc_lsb) The value of additional_lt_poc_lsb is assumed to be within the range of 0 to 32-log2_max_pic_order_cnt_lsb_minus4-4-additional_st_poc_lsb, including both endpoints. If it does not exist, the value of additional_lt_poc_lsb is presumed to be equal to 0.

[0285] Picture parameter set RBSP semantics

[0286] The value of num_ref_idx_default_active_minus1[i] plus 1 specifies the inferred value of the variable NumRefIdxActive[0] for P or B slices where num_ref_idx_active_override_flag is equal to 0 when i is equal to 0, and specifies the inferred value of NumRefIdxActive[1] for B slices where num_ref_idx_active_override_flag is equal to 0 when i is equal to 1. The value of num_ref_idx_default_active_minus1[i] is assumed to be in the range of 0 to 14, including both endpoints.

[0287] Slice header semantics

[0288] If present, the values ​​of the slice header syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb, respectively, shall be the same for all slice headers of the coded picture. slice_type specifies the coding type of the slice according to Table 7-3 (Table 33).

[0289] [Table 33]

[0290] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, then slice_type is equal to 2.

[0291] `slice_pic_order_cnt_lsb` specifies the picture order count modulo `MaxPicOrderCntLsb` for the current picture. The length of the `slice_pic_order_cnt_lsb` syntax element is log2_max_pic_order_cnt_lsb_minus4+4 bits. The value of `slice_pic_order_cnt_lsb` is assumed to be in the range of 0 to `MaxPicOrderCntLsb-1`, including both ends. If `slice_pic_order_cnt_lsb` does not exist, it is assumed to be equal to 0. A `num_ref_idx_active_override_flag` equal to 1 specifies that the syntax element `num_ref_idx_active_minus1[0]` exists for P and B slices, and the syntax element `num_ref_idx_active_minus1[1]` exists for B slices. A num_ref_idx_active_override_flag equal to 0 indicates that the syntax elements num_ref_idx_active_minus1[0] and num_ref_idx_active_minus1[1] do not exist. If num_ref_idx_active_minus1[i] exists, it specifies the value of the variable NumRefIdxActive[i] as follows: NumRefIdxActive[i]=num_ref_idx_active_minus1[i]+1

[0292] The value of num_ref_idx_active_minus1[i] is assumed to be in the range of 0 to 14, including both ends. The value of NumRefIdxActive[i]-1 specifies the maximum reference index to reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, the reference index to reference picture list i may not be used to decode the slice. For i equal to 0 or 1, if the current slice is a B slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is inferred to be equal to num_ref_idx_default_active_minus1[i]+1. If the current slice is a P slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[0] is inferred to be equal to num_ref_idx_default_active_minus1[0]+1. When the current slice is a P slice, NumRefIdxActive[1] is presumed to be equal to 0. When the current slice is an I slice, both NumRefIdxActive[0] and NumRefIdxActive[1] are presumed to be equal to 0. Alternatively, for i equal to 0 or 1, the following applies after the above: Assume that rplsIdx1 is set to equal to ref_pic_list_sps_flag[i]?ref_pic_list_idx[i]:num_ref_pic_lists_in_sps[i], and numRpEntries[i] is equal to num_strp_entries[i][rplsIdx1]+num_ltrp_entries[i][rplsIdx1]. When NumRefIdxActive[i] is greater than numRpEntries[i], the value of NumRefIdxActive[i] is set to equal to numRpEntries[i].

[0293] Reference Picture List Structure Semantics

[0294] The ref_pic_list_struct(listIdx,ltrpFlag) syntax structure can exist in the slice header. When it exists in the slice header, the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure specifies the reference picture list listIdx of the current picture (the picture containing the slice). num_strp_entries[listIdx] specifies the number of STRP entries in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure. num_ltrp_entries[listIdx] specifies the number of LTRP entries in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure. When it does not exist, the value of num_ltrp_entries[listIdx] is presumed to be equal to 0. The variable NumEntriesInList[listIdx] is derived as follows: NumEntriesInList[listIdx]=num_strp_entries[listIdx]+num_ltrp_entries[listIdx]

[0295] The value of NumEntriesInList[listIdx] is assumed to be between 0 and sps_max_dec_pic_buffering_minus1, including both ends. lt_ref_pic_flag[listIdx][i] equal to 1 specifies that the i-th entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure is an LTRP entry. lt_ref_pic_flag[listIdx][i] equal to 0 specifies that the i-th entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure is a STRP entry. If none exists, the value of lt_ref_pic_flag[listIdx][i] is assumed to be equal to 0. A bitstream conformance requirement is that the sum of lt_ref_pic_flag[listIdx][i] for all values ​​of i in the range from 0 to NumEntriesInList[listIdx]-1, including both ends, is equal to num_ltrp_entries[listIdx]. poc_lsb_st[listIdx][i] specifies the value of the picture order count modulo MaxStPicOrderCntLsb for the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure when lt_ref_pic_flag[listIdx][i] is equal to 0. The length of the poc_lsb_st[listIdx][i] syntax element is Log2(MaxStPicOrderCntLsb) bits. poc_lsb_lt[listIdx][i] specifies the modulo MaxLtPicOrderCntLsb value of the picture order count of the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx,ltrpFlag) syntax structure, when lt_ref_pic_flag[listIdx][i] is equal to 1. The length of the poc_lsb_lt[listIdx][i] syntax element is Log2(MaxLtPicOrderCntLsb) bits.

[0296] The decryption process will be discussed.

[0297] Typical decryption process

[0298] For the current picture CurrPic, the decryption process operates as follows: Decryption of NAL units is defined below. The following process defines the next decryption process using the slice header layer and the syntax elements described above. Variables and functions related to the picture order count are derived. This needs to be called only for the first slice of the picture. At the beginning of the decryption process for each slice of a non-IRAP picture, the decryption process for constructing the reference picture list is called to derive reference picture list 0 (RefPicList[0]) and reference picture list 1 (RefPicList[1]). The decryption process for reference picture marking is called, and reference pictures may be marked as "not used for reference" or "used for long-term reference". This needs to be called only for the first slice of the picture. The decryption process for coding tree units, scaling, transformation, in-loop filtering, etc. is called. After all slices of the current picture have been decrypted, the currently decrypted picture is marked as "used for short-term reference".

[0299] NAL unit decoding process

[0300] The input to this process is the NAL units of the current picture and their associated non-VCL NAL units. The output of this process is the parsed RBSP syntax structure encapsulated within the NAL units. The decoding process for each NAL unit extracts the RBSP syntax structure from the NAL unit and then parses the RBSP syntax structure.

[0301] Slice decoding process

[0302] Decoding process for picture order counting

[0303] The output of this process is PicOrderCntVal, which is the picture order count of the current picture. The picture order count is used to identify the picture for the derivation of motion parameters and prediction of motion vectors in merge mode, as well as for decoder compatibility verification. Each coded picture is associated with a picture order count variable denoted as PicOrderCntVal. When the current picture is not an IRAP picture, the variables prevPicOrderCntLsb and prevPicOrderCntMsb are derived as follows: prevTid0Pic is the previous picture in the decoding order with a TemporalId equal to 0. The variable prevPicOrderCntLsb is set to equal slice_pic_order_cnt_lsb of prevTid0Pic. The variable prevPicOrderCntMsb is set to equal PicOrderCntMsb of prevTid0Pic. The variable PicOrderCntMsb of the current picture is derived as follows: If the current picture is an IRAP picture, PicOrderCntMsb is set to equal to 0. Otherwise, PicOrderCntMsb is derived as follows: if((slice_pic_order_cnt_lsb <prevPicOrderCntLsb)&& ((prevPicOrderCntLsb-slice_pic_order_cnt_lsb)>=(MaxPicOrderCntLsb / 2))) PicOrderCntMsb=prevPicOrderCntMsb+MaxPicOrderCntLsb else if((slice_pic_order_cnt_lsb>prevPicOrderCntLsb)&& ((slice_pic_order_cnt_lsb-prevPicOrderCntLsb)>(MaxPicOrderCntLsb / 2))) PicOrderCntMsb=prevPicOrderCntMsb-MaxPicOrderCntLsb else PicOrderCntMsb=prevPicOrderCntMsb

[0304] PicOrderCntVal is derived as follows: PicOrderCntVal=PicOrderCntMsb+slice_pic_order_cnt_lsb

[0305] All IRAP pictures have a PicOrderCntVal equal to 0, because slice_pic_order_cnt_lsb is presumed to be equal to 0 for IRAP pictures, and prevPicOrderCntLsb and prevPicOrderCntMsb are both set to equal to 0. The value of PicOrderCntVal is assumed to be in the range of -231 to 231-1, including both ends. In a single CVS, the PicOrderCntVal values ​​for any two coded pictures are not assumed to be the same. At any moment during the decoding process, the values ​​of PicOrderCntVal&(MaxStPicOrderCntLsb-1) for any two short-term reference pictures in the DPB are not assumed to be the same. At any moment during the decoding process, the values ​​of PicOrderCnvVal&(MaxLtPicOrderCntLsb-1) for any two reference pictures in the DPB are not assumed to be the same.

[0306] The function PicOrderCnt(picX) is defined as follows: PicOrderCnt(picX) = PicOrderCntVal of picture picX

[0307] The function DiffPicOrderCnt(picA,picB) is defined as follows: DiffPicOrderCnt(picA,piB)=PicOrderCnt(picA)-PicOrderCnt(picB)

[0308] The bitstream is -2 including both ends. 15 From 2 15 Assume that the decoding process does not contain data that would result in a DiffPicOrderCnt(picA,picB) value that is not in the range of -1. If X is the current picture and Y and Z are two other pictures in the same CVS, then Y and Z are considered to be in the same output order direction from X when DiffPicOrderCnt(X,Y) and DiffPicOrderCnt(X,Z) are both positive or both negative.

[0309] Decryption process for building the reference picture list

[0310] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. The reference picture is addressed through a reference index, which is an index to the reference picture list. When decoding an I slice, the reference picture list is not used when decoding the slice data. When decoding a P slice, only reference picture list 0 (i.e., RefPicList[0]) is used when decoding the slice data. When decoding a B slice, both reference picture list 0 and reference picture list 1 (i.e., RefPicList[1]) are used when decoding the slice data. At the beginning of the decoding process for each slice of a non-IRAP picture, the reference picture lists RefPicList[0] and RefPicList[1] are derived. The reference picture lists are used for marking the reference picture or decoding the slice data. For I-slices of non-IRAP pictures that are not the first slice of a picture, RefPicList[0] and RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but their derivation is not necessary for decoding the current picture or any picture that follows the current picture in the decoding order. For P-slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but its derivation is not necessary for decoding the current picture or any picture that follows the current picture in the decoding order.

[0311] The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ for(j=0;j <NumEntriesInList[i];j++){ if(lt_ref_pic_flag[i][j]){ if (a reference picA in DPB is equal to PicOrderCntVal&(MaxLtPicOrderCntLsb-1) is poc_lsb_lt[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } } } for(i=0;i<2;i++){ for(j=0;j <NumEntriesInList[i];j++){ if(!lt_ref_pic_flag[i][j]){ if (PicOrderCntVal&(MaxStPicOrderCntLsb-1) is equal to poc_lsb_st[i][j] and there is a short-term reference picture picA in DPB) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } } }

[0312] For each i that is equal to 0 or 1, the following holds true:

[0313] The first NumRefIdxActive[i] entry in RefPicList[i] is called the active entry in RefPicList[i], and all other entries in RefPicList[i] are called inactive entries in RefPicList[i]. Each entry in RefPicList[i][j] for j in the range of 0 to NumEntriesInList[i]-1, including both ends, is called a STRP entry if lt_ref_pic_flag[i][j] is equal to 0, and an LTRP entry otherwise. A particular picture may be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. A particular picture may be referenced by more than one entry in RefPicList[0] or more than one entry in RefPicList[1]. Active entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that can be used for interpretation of the current picture, and one or more pictures that follow the current picture in the decoding order. Inactive entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that are not used for interpretation of the current picture, but can be used for interpretation of one or more pictures that follow the current picture in the decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equivalent to "no reference picture" because the corresponding picture does not exist in the DPB. Each inactive entry in RefPicList[0] or RefPicList[0] that is equivalent to "no reference picture" should be ignored. For each active entry in RefPicList[0] or RefPicList[1] that is equivalent to "no reference picture", an unintended picture loss should be inferred.

[0314] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, NumEntriesInList[i] shall not be less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] shall exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of an inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: An inactive entry in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. STRP entries in RefPicList[0] or RefPicList[1] for a slice of a picture, and LTRP entries in RefPicList[0] or RefPicList[1] for the same slice or different slices of the same picture, shall not refer to the same picture. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics shall be the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics shall be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics shall be the same for all slices of a picture.

[0315] Decryption process for reference picture marking

[0316] This process is called once per picture, after the decoding of the slice header and the decoding process for building the reference picture list for the slice, but before decoding the slice data. This process may result in one or more reference pictures in the DPB being marked as "not used for reference" or "used for long-term reference". A decoded picture in the DPB can be marked as "not used for reference", "used for short-term reference", or "used for long-term reference", but only one of these three, at any given moment during the operation of the decoding process. Assigning one of these markings to a picture implicitly excludes another of these markings when applicable. When a picture is referred to as being marked as "used for reference", this collectively refers to the picture being marked as either "used for short-term reference" or "used for long-term reference" (but not both). When the current picture is an IRAP picture, all reference pictures (if any) currently in the DPB are marked as "not used for reference". STRPs are identified by the Log2(MaxStPicOrderCntLsb) LSBs of their PicOrderCntVal values. LTRPs are identified by the Log2(MaxLtPicOrderCntLsb) LSBs of their PicOrderCntVal values.

[0317] The following applies: For each LTRP entry in RefPicList[0] or RefPicList[1], if the referenced picture is a STRP, the picture is marked as “Used for long-term reference.” Each referenced picture in a DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as “Not used for reference.”

[0318] Always signal the list of referenced pictures in the slice header without distinguishing between short-term and long-term referenced pictures.

[0319] This section describes another alternative embodiment of the present disclosure. This description is for the most recent VVC WD (i.e., only the differences for the most recent VVC WD of JVET-K1001-v1 are described, but the text of the most recent VVC WD not mentioned below remains applicable). This alternative embodiment can be summarized as follows: The reference picture list structure is signaled only in the slice header. Short-term and long-term reference pictures are not distinguished. All reference pictures are simply named reference pictures. Reference pictures are identified by their POC LSB, which may be represented by a number of bits different from the number of bits used to represent the POC LSB that is signaled in the slice header for the derivation of the POC value.

[0320] Abbreviation. The text of section 4 of VVC WD applies.

[0321] NAL Unit Header Syntax

[0322] [Table 34]

[0323] Sequence parameter set RBSP syntax

[0324] [Table 35]

[0325] Picture parameter set RBSP syntax

[0326] [Table 36]

[0327] Slice header syntax

[0328] [Table 37]

[0329] Reference picture list structure syntax

[0330] [Table 38]

[0331] NAL Unit Header Semantics

[0332] `forbidden_zero_bit` is assumed to be equal to 0. `nal_unit_type` specifies the type of RBSP data structure included in the NAL unit.

[0333] [Table 39]

[0334] The value obtained by subtracting 1 from nuh_temporal_id_plus1 specifies the time identifier for the NAL unit. The value of nuh_temporal_id_plus1 must not be equal to 0. The variable TemporalId is specified as follows: TemporalId=nuh_temporal_id_plus1-1

[0335] When nal_unit_type is equal to IRAP_NUT, the coded slice belongs to an IRAP picture and its TemporalId is equal to 0. The value of TemporalId is the same for all VCL NAL units of an access unit. The value of TemporalId for a coded picture or access unit is the value of TemporalId for the VCL NAL unit of the coded picture or access unit. The value of TemporalId for non-VCL NAL units is constrained as follows:

[0336] If nal_unit_type is equal to SPS_NUT, then TemporalId is equal to 0, and the TemporalId of the access unit containing the NAL unit is equal to 0. Otherwise, if nal_unit_type is equal to EOS_NUT or EOB_NUT, then TemporalId is equal to 0. Otherwise, TemporalId is greater than or equal to the TemporalId of the access unit containing the NAL unit. When the NAL unit is a non-VCL NAL unit, the value of TemporalId is equal to the minimum TemporalId value of all access units to which the non-VCL NAL unit applies. When nal_unit_type is equal to PPS_NUT, TemporalId may be greater than or equal to the TemporalId of the containing access unit because all Picture Parameter Sets (PPS) may be included at the beginning of the bitstream, and the first coded picture has a TemporalId equal to 0. When nal_unit_type is equal to PREFIX_SEI_NUT or SUFFIX_SEI_NUT, the TemporalId may be greater than or equal to the TemporalId of the containing access unit, because an SEI NAL unit may contain information applicable to a subset of the bitstream that contains access units with a TemporalId value greater than the TemporalId of the access unit containing the SEI NAL unit. nuh_reserved_zero_7bits shall be equal to "0000000". Other values ​​for nuh_reserved_zero_7bits may be specified in the future by ITU-T|ISO / IEC. The decoder shall ignore (i.e., remove and discard from the bitstream) any NAL unit with a nuh_reserved_zero_7bits value that is not equal to "0000000".

[0337] Sequence parameter set RBSP semantics

[0338] log2_max_pic_order_cnt_lsb_minus4 specifies the value of the variable MaxPicOrderCntLsb used in the decoding process for picture order count as follows. MaxPicOrderCntLsb = 2 (log2_max_pic_order_cnt_lsb_minus4+4)

[0339] The value of log2_max_pic_order_cnt_lsb_minus4 shall be in the range from 0 to 12 inclusive. Adding 1 to sps_max_dec_pic_buffering_minus1 specifies the maximum required size of the decoded picture buffer for CVS in picture storage buffer units. The value of sps_max_dec_pic_buffering_minus1 shall be in the range from 0 to MaxDpbSize - 1 inclusive, where MaxDpbSize is as specified elsewhere. additional_ref_poc_lsb specifies the value of the variable MaxRefPicOrderCntLsb used in the decoding process for reference picture lists as follows. MaxRefPicOrderCntLsb = 2 (log2_max_pic_order_cnt_lsb_minus4+4+additional_ref_poc_lsb)

[0340] The value of additional_ref_poc_lsb shall be in the range from 0 to 32 - log2_max_pic_order_cnt_lsb_minus4 - 4 inclusive.

[0341] Picture Parameter Set RBSP Semantics

[0342] The value of num_ref_idx_default_active_minus1[i] plus 1 specifies the inferred value of the variable NumRefIdxActive[0] for P or B slices where num_ref_idx_active_override_flag is equal to 0 when i is equal to 0, and specifies the inferred value of NumRefIdxActive[1] for B slices where num_ref_idx_active_override_flag is equal to 0 when i is equal to 1. The value of num_ref_idx_default_active_minus1[i] is assumed to be in the range of 0 to 14, including both endpoints.

[0343] Slice header semantics

[0344] If present, the values ​​of the slice header syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb, respectively, shall be the same for all slice headers of the coded picture. slice_type specifies the coding type of the slice according to Table 7-3 (Table 40).

[0345] [Table 40]

[0346] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type is assumed to be equal to 2. slice_pic_order_cnt_lsb specifies the picture order count modulo MaxPicOrderCntLsb for the current picture. The length of the slice_pic_order_cnt_lsb syntax element is log2_max_pic_order_cnt_lsb_minus4+4 bits. The value of slice_pic_order_cnt_lsb is assumed to be in the range of 0 to MaxPicOrderCntLsb-1, including both ends. If slice_pic_order_cnt_lsb does not exist, it is assumed to be equal to 0. A num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] exists for P and B slices, and the syntax element num_ref_idx_active_minus1[1] exists for B slice. A num_ref_idx_active_override_flag equal to 0 specifies that the syntax elements num_ref_idx_active_minus1[0] and num_ref_idx_active_minus1[1] do not exist. When num_ref_idx_active_minus1[i] exists, it specifies the value of the variable NumRefIdxActive[i] as follows: NumRefIdxActive[i]=num_ref_idx_active_minus1[i]+1

[0347] The value of num_ref_idx_active_minus1[i] is assumed to be in the range of 0 to 14, including both ends. The value of NumRefIdxActive[i]-1 specifies the maximum reference index to reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, the reference index to reference picture list i may not be used to decode the slice. For i equal to 0 or 1, if the current slice is a B slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is inferred to be equal to num_ref_idx_default_active_minus1[i]+1. If the current slice is a P slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[0] is inferred to be equal to num_ref_idx_default_active_minus1[0]+1. When the current slice is a P slice, NumRefIdxActive[i] is presumed to be equal to 0. When the current slice is an I slice, both NumRefIdxActive[0] and NumRefIdxActive[1] are presumed to be equal to 0. Alternatively, for i equal to 0 or 1, the following applies after the above: Assume that rplsIdx1 is set to equal to ref_pic_list_sps_flag[i]?ref_pic_list_idx[i]:num_ref_pic_lists_in_sps[i], and numRpEntries[i] is equal to num_strp_entries[i][rplsIdx1]+num_ltrp_entries[i][rplsIdx1]. When NumRefIdxActive[i] is greater than numRpEntries[i], the value of NumRefIdxActive[i] is set to equal to numRpEntries[i].

[0348] Reference Picture List Structure Semantics

[0349] The ref_pic_list_struct(listIdx) syntax structure can exist in a slice header. When it exists in a slice header, the ref_pic_list_struct(listIdx) syntax structure specifies the reference picture listIdx of the current picture (the picture containing the slice). num_ref_entries[listIdx] specifies the number of entries in the ref_pic_list_struct(listIdx) syntax structure. The variable NumEntriesInList[listIdx] is derived as follows: NumRefEntriesInRpl[listIdx]=num_ref_entries[listIdx]

[0350] The value of NumRefPicEntries[listIdx] is assumed to be in the range of 0 to sps_max_dec_pic_buffering_minus1, including both ends. poc_ref_lsb[listIdx][i] specifies the picture order count modulo MaxRefPicOrderCntLsb of the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx) syntax structure. The length of the poc_ref_lsb[listIdx][i] syntax element is Log2(MaxRefPicOrderCntLsb) bits.

[0351] The decryption process will be discussed.

[0352] Typical decryption process

[0353] For the current picture CurrPic, the decryption process operates as follows: Decryption of NAL units is defined below. The following process defines the next decryption process using the slice header layer and the syntax elements described above. Variables and functions related to the picture order count are derived. This needs to be called only for the first slice of the picture. At the beginning of the decryption process for each slice of a non-IRAP picture, the decryption process for constructing the reference picture list is called to derive reference picture list 0 (RefPicList[0]) and reference picture list 1 (RefPicList[1]). The decryption process for reference picture marking is called, and reference pictures may be marked as "not used for reference". This needs to be called only for the first slice of the picture. The decryption process for coding tree units, scaling, transformations, in-loop filtering, etc. is called. After all slices of the current picture have been decrypted, the currently decrypted picture is marked as "used for reference".

[0354] NAL unit decoding process

[0355] The input to this process is the NAL units of the current picture and their associated non-VCL NAL units. The output of this process is the parsed RBSP syntax structure encapsulated within the NAL units. The decoding process for each NAL unit extracts the RBSP syntax structure from the NAL unit and then parses the RBSP syntax structure.

[0356] Slice decoding process

[0357] Decoding process for picture order counting

[0358] The output of this process is PicOrderCntVal, which is the picture order count of the current picture. The picture order count is used to identify the picture for the derivation of motion parameters and prediction of motion vectors in merge mode, as well as for decoder compatibility verification. Each coded picture is associated with a picture order count variable denoted as PicOrderCntVal. When the current picture is not an IRAP picture, the variables prevPicOrderCntLsb and prevPicOrderCntMsb are derived as follows: prevTid0Pic is the previous picture in the decoding order with a TemporalId equal to 0. The variable prevPicOrderCntLsb is set to equal slice_pic_order_cnt_lsb of prevTid0Pic. The variable prevPicOrderCntMsb is set to equal PicOrderCntMsb of prevTid0Pic. The variable PicOrderCntMsb of the current picture is derived as follows: If the current picture is an IRAP picture, PicOrderCntMsb is set to equal to 0. Otherwise, PicOrderCntMsb is derived as follows: if((slice_pic_order_cnt_lsb <prevPicOrderCntLsb)&& ((prevPicOrderCntLsb-slice_pic_order_cnt_lsb)>=(MaxPicOrderCntLsb / 2))) PicOrderCntMsb=prevPicOrderCntMsb+MaxPicOrderCntLsb else if((slice_pic_order_cnt_lsb>prevPicOrderCntLsb)&& ((slice_pic_order_cnt_lsb-prevPicOrderCntLsb)>(MaxPicOrderCntLsb / 2))) PicOrderCntMsb=prevPicOrderCntMsb-MaxPicOrderCntLsb else PicOrderCntMsb=prevPicOrderCntMsb

[0359] PicOrderCntVal is derived as follows: PicOrderCntVal=PicOrderCntMsb+slice_pic_order_cnt_lsb

[0360] All IRAP pictures have a PicOrderCntVal equal to 0, because slice_pic_order_cnt_lsb is presumed to be equal to 0 for IRAP pictures, and prevPicOrderCntLsb and prevPicOrderCntMsb are both set to equal to 0. The value of PicOrderCntVal is assumed to be in the range of -231 to 231-1, including both ends. In a single CVS, the PicOrderCntVal values ​​for any two coded pictures are not assumed to be the same. At any moment during the decoding process, the values ​​of PicOrderCntVal&(MaxRefPicOrderCntLsb-1) for any two reference pictures in the DPB are not assumed to be the same.

[0361] The function PicOrderCnt(picX) is defined as follows: PicOrderCnt(picX) = PicOrderCntVal of picture picX

[0362] The function DiffPicOrderCnt(picA,picB) is defined as follows: DiffPicOrderCnt(picA,piB)=PicOrderCnt(picA)-PicOrderCnt(picB)

[0363] The bitstream is assumed to contain no data that would result in a DiffPicOrderCnt(picA,picB) value used in the decoding process that is not in the range of -215 to 215-1, including both ends. If X is the current picture and Y and Z are two other pictures in the same CVS, then Y and Z are considered to be in the same output order direction from X when DiffPicOrderCnt(X,Y) and DiffPicOrderCnt(X,Z) are both positive or both negative.

[0364] Decryption process for building the reference picture list

[0365] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. The reference picture is addressed through a reference index, which is an index to the reference picture list. When decoding an I slice, the reference picture list is not used when decoding the slice data. When decoding a P slice, only reference picture list 0 (i.e., RefPicList[0]) is used when decoding the slice data. When decoding a B slice, both reference picture list 0 and reference picture list 1 (i.e., RefPicList[1]) are used when decoding the slice data. At the beginning of the decoding process for each slice of a non-IRAP picture, the reference picture lists RefPicList[0] and RefPicList[1] are derived. The reference picture lists are used for marking the reference picture or decoding the slice data. For I-slices of non-IRAP pictures that are not the first slice of a picture, RefPicList[0] and RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but their derivation is not required for decoding the current picture or any picture that follows the current picture in the decoding order. For P-slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but its derivation is not required for decoding the current picture or any picture that follows the current picture in the decoding order. The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i];j++){ if (PicOrderCntVal&(MaxRefPicOrderCntLsb-1) is equal to poc_ref_lsb[i][j] and there is a reference picA in DPB) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } }

[0366] For each i equal to 0 or 1, the first NumRefIdxActive[i] entry in RefPicList[i] is called the active entry in RefPicList[i], and all other entries in RefPicList[i] are called inactive entries in RefPicList[i]. A particular picture may be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. A particular picture may be referenced by more than one entry in RefPicList[0] or more than one entry in RefPicList[1]. The active entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that can be used for interpretation of the current picture, and one or more pictures that come after the current picture in the decoding order. Inactive entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that are not used for interpretation of the current picture but may be used for interpretation of one or more pictures that follow the current picture in the decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equivalent to "no reference picture" because the corresponding picture does not exist in the DPB. Each inactive entry in RefPicList[0] or RefPicList[0] that is equivalent to "no reference picture" should be ignored. For each active entry in RefPicList[0] or RefPicList[1] that is equivalent to "no reference picture", an unintended loss of a picture should be inferred.

[0367] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, NumEntriesInList[i] shall not be less than NumRefIdxActive[i]. Pictures referenced by each active entry in RefPicList[0] or RefPicList[1] shall exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of an inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: An inactive entry in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. Entries in RefPicList[0] or RefPicList[1] are assumed to be not present in RefPicList[0] or RefPicList[1] if the difference between the current picture's PicOrderCntVal and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics is the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics is assumed to be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics is assumed to be the same for all slices of pictures.

[0368] Decryption process for reference picture marking

[0369] This process is called once per picture, after the decoding of the slice header and the decoding process for constructing the reference picture list for the slice, but before decoding the slice data. This process may cause one or more reference pictures in the DPB to be marked as "not used for reference". A decoded picture in the DPB may be marked as either "not used for reference" or "used for reference", but only one of these two, at any given moment during the operation of the decoding process. Assigning one of these markings to a picture implicitly excludes the other of these markings when applicable. When the current picture is an IRAP picture, all reference pictures (if any) currently in the DPB are marked as "not used for reference". Reference pictures in the DPB are identified by Log2(MaxRefPicOrderCntLsb) LSBs of their PicOrderCntVal values. Each referenced picture in the DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as "not used for reference".

[0370] Yet another alternative embodiment

[0371] This section describes an alternative embodiment to the technique specified as “always signaling the reference picture list in the slice header without distinguishing between short-term and long-term reference pictures.” In this alternative embodiment, the POC MSB cycle may be signaled for each LTRP entry in the slice header, similar to HEVC or the technique described above, but the following constraint is removed: namely, that at any given moment during the decoding process, the values ​​of PicOrderCntVal&(MaxLtPicOrderCntLsb-1) for any two reference pictures in the DPB are not the same.

[0372] Figure 6 is a schematic diagram of a video coding device 600 (for example, a video encoder 20 or a video decoder 30) according to one embodiment of the present disclosure. The video coding device 600 is suitable for carrying out the disclosed embodiments as described herein. The video coding device 600 comprises an inlet port 610 and a receiver unit (Rx) 620 for receiving data, a processor, logic unit, or central processing unit (CPU) 630 for processing data, a transmitter unit (Tx) 640 and an exit port 650 for transmitting data, and memory 660 for storing data. The video coding device 600 may also comprise optical-electronic (OE) components and electron-optical (EO) components coupled to the inlet port 610, the receiver unit 620, the transmitter unit 640, and the exit port 650 for the input and output of optical or electrical signals.

[0373] The processor 630 is implemented by hardware and software. The processor 630 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), field-programmable gate arrays (FPGAs), application-specific integrated circuits (ASICs), and digital signal processors (DSPs). The processor 630 communicates with the inlet port 610, the receiver unit 620, the transmitter unit 640, the exit port 650, and the memory 660. The processor 630 includes a coding module 670. The coding module 670 implements the disclosed embodiments described above. For example, the coding module 670 implements, processes, prepares, or provides various networking functions. Thus, including the coding module 670 results in a significant improvement to the functionality of the video coding device 600, producing conversions of the video coding device 600 to different states. Alternatively, the coding module 670 is implemented as instructions stored in the memory 660 and executed by the processor 630.

[0374] The video coding device 600 may also include input and / or output (I / O) devices 680 for exchanging data with the user. The I / O devices 680 may include output devices such as a display for displaying video data and speakers for outputting audio data. The I / O devices 680 may also include input devices such as a keyboard, mouse, and trackball, and / or corresponding interfaces for interface with such output devices.

[0375] Memory 660 comprises one or more disks, tape drives, and solid-state drives and may be used as an overflow data storage device for storing a program when such a program is selected for execution, and for storing instructions and data to be read during program execution. Memory 660 may be volatile and / or non-volatile and may be read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), and / or static random-access memory (SRAM).

[0376] Figure 7 is a schematic diagram of one embodiment of the coding means 700. In this embodiment, the coding means 700 is implemented in a video coding device 702 (for example, a video encoder 20 or a video decoder 30). The video coding device 702 includes a receiving means 701. The receiving means 701 is configured to receive a picture to be coded or a bitstream to be decoded. The video coding device 702 includes a transmitting means 707 coupled to the receiving means 701. The transmitting means 707 is configured to transmit a bitstream to a decoder or to a display means (for example, one of the I / O devices 680).

[0377] The video coding device 702 includes a storage means 703. The storage means 703 is coupled to at least one of the receiving means 701 or the transmitting means 707. The storage means 703 is configured to store instructions. The video coding device 702 also includes a processing means 705. The processing means 705 is coupled to the storage means 703. The processing means 705 is configured to execute instructions stored in the storage means 703 in order to perform the method disclosed herein.

[0378] While several embodiments are provided in this disclosure, it should be understood that the disclosed systems and methods can be embodied in many other specific forms without departing from the spirit or scope of this disclosure. These examples should be considered illustrative rather than restrictive, and the intent is not limited to the details given herein. For example, different systems may combine or integrate various elements and components, or some features may be omitted or not implemented.

[0379] In addition, techniques, systems, subsystems, and methods described and illustrated individually or separately in various embodiments may be combined with or integrated with other systems, modules, techniques, or methods without departing from the scope of this disclosure. Other items shown or discussed as being coupled, directly coupled, or communicating with one another may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of modifications, substitutions, and variations that are recognizable to those skilled in the art may be made without departing from the spirit and scope disclosed herein. [Explanation of Symbols]

[0380] 12 Source Devices 14 Destination Devices 16 Computer-readable media 18 Video Sources 20 Video Encoders 22 Output Interfaces 28 Input Interfaces 30 video decoders 32 Display Devices 40 Mode Selection Unit 42 Motion Estimation Unit 44 Motion compensation unit 46 Intra Prediction Units 48 division units 52 Conversion Processing Unit 54 Quantization Units 56 Entropy Coding Unit 58 Inverse Quantization Unit 60 Reverse Conversion Unit 64 Reference frame memory 70 Entropy Decoding Unit 72 Motion Compensation Unit 74 Intra Prediction Units 76 Inverse Quantization Unit 78 Reverse Conversion Unit 82 Reference frame memory 610 Entrance Port 620 Receiver Unit 630 Processor 640 Transmitter Unit 650 Exit Port 660 memory 670 Coding Modules 680 I / O devices 701 Receiving means 702 Video Coding Device 703 Memory means 705 Processing means 707 Transmission method

Claims

1. Steps to obtain video data from a video source, A step of generating an encoded bitstream based on the video data, wherein the encoded bitstream comprises a first ref_pic_list_struct(listIdx, rplsIdx) syntax structure and a second ref_pic_list_struct(listIdx, rplsIdx) syntax structure, wherein the first ref_pic_list_struct(listIdx, rplsIdx) syntax structure comprises a first number of entries used to derive the reference picture list 0 (RPL 0) of the current slice, and the second ref_pic_list_struct(listIdx, rplsIdx) syntax structure comprises a second number of entries used to derive the reference picture list 1 (RPL 1) of the current slice, An encoding method comprising: a step, where the syntax structure (rplsIdx) has an index along with the value of rplsIdx, which indicates a reference picture list listIdx of the current slice, and the current slice is an intra(I) slice, a single predictive (P) slice, or a double predictive (B) slice.

2. The encoding method according to claim 1, wherein the order of entries in the first syntax structure is the same as the order of reference pictures in RPL 0, or the order of entries in the second syntax structure is the same as the order of reference pictures in RPL 1.

3. The encoding method according to claim 1 or 2, wherein each entry in the first ref_pic_list_struct(listIdx, rplsIdx) syntax structure describes a corresponding reference picture in RPL 0, and each entry in the second ref_pic_list_struct(listIdx, rplsIdx) syntax structure describes a corresponding reference picture in RPL 1.

4. A storage device configured to generate at least one encoded bitstream by an encoding method according to any one of claims 1 to 3, wherein the storage device comprises at least one storage medium and at least one communication interface, The at least one communication interface is configured to transmit the at least one encoded bitstream, A storage device in which at least one storage medium is configured to store at least one encoded bitstream.

5. A step of generating at least one encoded bitstream by the encoding method described in any one of Claims 1 to 3, The steps include transmitting the at least one encoded bitstream through a communication interface, A storage method comprising the steps of storing the at least one encoded bitstream in one or more storage media.

6. A transmitting device configured to generate at least one encoded bitstream by the encoding method described in any one of claims 1 to 3, A transmitting device comprising at least one storage medium configured to store the at least one encoded bitstream.

7. A processing system comprising a source device, an encoding device, one or more storage media, and a destination device, The source device is configured to provide video data, The encoding device is configured to acquire the video data through an interface, encode the video data, and acquire one or more encoded bitstreams generated by the encoding method described in any one of claims 1 to 3. The one or more storage mediums are used to store the one or more encoded bitstreams. A system in which the destination device is used to decode one or more encoded bitstreams and obtain reconstructed video data.

8. A processing system comprising a server and a source device, The source device is configured to acquire video data from the server, and the source device is further configured to encode the video data and acquire one or more encoded bitstreams generated by the encoding method described in any one of claims 1 to 3. The system further comprises one or more storage media and / or destination devices, A processing system wherein the source device is further configured to store the one or more encoded bitstreams in the one or more storage mediums, and / or the source device is further configured to transmit the one or more encoded bitstreams to the destination device via a communication interface, and the destination device is configured to decode the one or more encoded bitstreams and obtain reconstructed video data.

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