Reference picture management in video coding

Abstract

To provide, e.g., a method of decoding a coded video bitstream.SOLUTION: The method includes parsing a parameter set represented in the coded video bitstream. The parameter set contains a set of syntax elements that include a set of reference picture list structures. The method also includes parsing a slice header of a current slice represented in the coded video bitstream. The slice header contains an index of a reference picture list structure in the set of reference picture list structures in the parameter set. The method further includes deriving, based on the set of syntax elements in the parameter set and the index of the reference picture list structure, a reference picture list of the current slice. The method also includes obtaining, based on the reference picture list, at least one reconstructed block of the current slice.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 62 / 719,360, entitled “Reference Picture Management in Video Coding,” by Ye-Kui Wang et al., filed Aug. 17, 2018, which is incorporated herein by reference. FIELD OF THE DISCLOSURE This disclosure relates generally to techniques for reference picture management in video coding. More particularly, this disclosure describes techniques for building reference picture lists and marking reference pictures. [Background technology]

[0002] The amount of video data required to depict even a relatively short video can be significant, which can pose difficulties when the data is to be streamed or otherwise conveyed over a communication network with limited bandwidth capacity. Thus, video data is generally compressed before being conveyed over modern communication networks. The size of the video can also be an issue when the video is stored on a storage device, since memory resources may also be limited. Often, a video compression device uses software and / or hardware at the source to code the video data before transmission or storage, thereby reducing the amount of data required to represent a digital video image. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and an ever-increasing demand for higher video quality, improved compression and decompression techniques that increase compression ratios with little or no sacrifice in image quality are desirable. Summary of the Invention [Means for solving the problem]

[0003] A first aspect relates to a method for decoding a coded video bitstream, the method including the steps of: parsing a parameter set indicated in the coded video bitstream, the parameter set including a set of syntax elements including a set of reference picture list structures, parsing a slice header of a current slice indicated in the coded video bitstream, the slice header including an index of a reference picture list structure from the set of reference picture list structures in the parameter set, deriving a reference picture list of the current slice based on the set of syntax elements in the parameter set and the index of the reference picture list structure, and obtaining at least one reconstructed block of the current slice based on the reference picture list.

[0004] The method provides techniques that make the signaling of reference picture lists simpler and more efficient, thus improving the overall coding process.

[0005] In a first implementation of the method according to the first aspect per se, the order of the entries of the reference picture list structure is the same as the order of the corresponding reference pictures in the reference picture list.

[0006] In the second implementation of the method according to the first aspect per se or any preceding implementation of the first aspect, the sequence is from zero to the indicated value.

[0007] In the third implementation of the method according to the first aspect itself or any of the preceding implementations of the first aspect, the indicated value is from zero to the value indicated by sps_max_dec_pic_buffering_minus1.

[0008] In the fourth implementation form of the method according to the first aspect itself or any of the preceding implementation forms of the first aspect, the reference picture list is the designated RefPictList[0].

[0009] In the fifth implementation form of the method according to the first aspect itself or any of the preceding implementation forms of the first aspect, the reference picture list is the designated RefPictList[1].

[0010] In a sixth implementation form of the method according to the first aspect itself or any of the aforementioned implementation forms of the first aspect, at least one reconstructed block is used to generate an image to be displayed on a display of the electronic device.

[0011] In a seventh implementation form of the method according to the first aspect itself or any of the preceding implementation forms of the first aspect, the reference picture list includes a list of reference pictures used for inter prediction.

[0012] In an eighth implementation form of the method according to the first aspect itself or any preceding implementation form of the first aspect, the inter prediction is for a P slice or for a B slice.

[0013] In a ninth implementation of the method according to the first aspect per se or any preceding implementation of the first aspect, the parameter set includes a sequence parameter set (SPS).

[0014] In a tenth implementation form of the method according to the first aspect itself or any of the aforementioned implementation forms of the first aspect, a set of syntax elements from the parameter set is placed in a Raw Byte Sequence Payload (RBSP) of a Network Abstraction Layer (NAL) unit.

[0015] In an eleventh implementation form of the method according to the first aspect itself or any of the aforementioned implementation forms of the first aspect, the reference picture list is designated RefPictList[0] or RefPictList[1], and the order of the entries in the reference picture list structure is the same as the order of the corresponding reference pictures in the reference picture list.

[0016] In a twelfth implementation form of the method according to the first aspect itself or any of the aforementioned implementation forms of the first aspect, the method further includes the steps of parsing a parameter set indicated in a coded video bitstream, wherein the parameter set includes a set of syntax elements including a set of reference picture list structures; obtaining a reference picture list structure indicated in the coded video bitstream; deriving a first reference picture list of the current slice based on the reference picture list structure, wherein the first reference picture list includes at least one active entry and at least one inactive entry, wherein the at least one inactive entry references a reference picture that is not used for inter prediction of the current slice but is referenced by an active entry of the second reference picture list, and the second reference picture list is a reference picture list of a slice that follows the current slice in decoding order or a reference picture list of a picture that follows the current picture in decoding order; and obtaining at least one reconstructed block of the current slice based on the at least one active entry of the first reference picture list.

[0017] A second aspect relates to a decoding device, the decoding device including: a receiver configured to receive a coded video bitstream; a memory connected to the receiver, the memory storing instructions; and a processor connected to the memory, configured to execute the instructions stored in the memory, the instructions causing the processor to: parse a parameter set indicated in the coded video bitstream, the parameter set including a set of syntax elements including a set of reference picture list structures; parse a slice header of a current slice indicated in the coded video bitstream, the slice header including an index of a reference picture list structure from the set of reference picture list structures in the parameter set; derive a reference picture list for the current slice based on the set of syntax elements in the parameter set and the index of the reference picture list structure; and obtain at least one reconstructed block of the current slice based on the reference picture list.

[0018] The decoding device provides techniques that make the signaling of reference picture lists simpler and more efficient, thus improving the overall coding process.

[0019] In a first implementation form of the decoding device according to the second aspect itself, the decoding device further includes a display configured to display the current picture generated based on the at least one reconstructed block.

[0020] A third aspect relates to a coding apparatus including: a receiver configured to receive a bitstream to be decoded; a transmitter connected to the receiver and configured to transmit a decoded image to a display; a memory connected to at least one of the receiver or the transmitter and configured to store instructions; and a processor connected to the memory and configured to execute the instructions stored in the memory to perform a method according to any of the preceding aspects or implementations.

[0021] A fourth aspect relates to a system including an encoder and a decoder in communication with the encoder, the encoder or decoder including a decoding device or coding apparatus of any of the preceding aspects or implementations.

[0022] The system provides techniques that make the signaling of reference picture lists simpler and more efficient, thus improving the overall coding process.

[0023] A fifth aspect relates to a means for coding, the means for coding comprising: a receiving means configured to receive a picture to be encoded or to receive a bitstream to be decoded; a transmitting means connected to the receiving means, configured to transmit the bitstream to a decoder or to transmit a decoded image to a display means; a storage means connected to at least one of the receiving means or the transmitting means, configured to store instructions; and a processing means connected to the storage means, configured to execute the instructions stored in the storage means to perform a method according to any of the previous aspects or implementations.

[0024] The solution for coding provides techniques that make the signaling of reference picture lists simpler and more efficient, thus improving the overall coding process.

[0025] 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]

[0026] [Figure 1] 1 is a block diagram illustrating an example coding system that may utilize bi-prediction techniques. [Diagram 2] 1 is a block diagram illustrating an example video encoder that may implement bi-prediction techniques. [Diagram 3] 1 is a block diagram illustrating an example of a video decoder that may implement bi-prediction techniques. [Figure 4] FIG. 2 is a schematic diagram showing a Reference Picture Set (RPS) with a picture, along with entries for all subsets of the RPS. [Diagram 5] 1 is a diagram of an embodiment of a method for decoding a coded video bitstream. [Figure 6] 1 is a schematic diagram of a video coding device. [Figure 7] FIG. 2 is a schematic diagram of an embodiment of a means for coding. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] FIG. 1 is a block diagram illustrating an example coding system 10 that may utilize video coding techniques as described herein. As shown in FIG. 1, coding system 10 includes an originating device 12 that provides encoded video data that is subsequently decoded by a destination device 14. In particular, originating device 12 may provide the video data to destination device 14 via a computer-readable medium 16. Destination device 12 and destination device 14 may include 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, originating device 12 and destination device 14 may be enabled for wireless communication.

[0028] The destination device 14 may receive the encoded video data to be decoded via a computer-readable medium 16. The computer-readable medium 16 may include any type of medium or device capable of moving the encoded video data from the source device 12 to the destination device 14. In one example, the computer-readable medium 16 may include a communication medium to enable the source device 12 to transmit the encoded video data directly to the 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 the destination device 14. The communication medium may include 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 help facilitate communication from the source device 12 to the destination device 14.

[0029] In some examples, the encoded data may be output from the output interface 22 to a storage device. Similarly, the encoded data may be accessed from the storage device by 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, a Blu-ray disc, a digital video disc (DVD), a compact disc read-only memory (CD-ROM), a flash memory, a volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data. In a further example, the storage device may correspond to a file server or another intermediate storage device that may store the encoded video generated by the source device 12. The destination device 14 may access the stored video data from the storage device by streaming or downloading. The file server may be any type of server capable of storing the encoded video data and transmitting the encoded video data to the destination device 14. Exemplary file servers include a web server (e.g., for a website), a file transfer protocol (FTP) server, a network attached storage (NAS) device, or a local disk drive. The destination device 14 may access the encoded video data through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., a digital subscriber line (DSL), a cable modem, etc.), or a combination of both, suitable for accessing the encoded video data stored on the file server. The transmission of the encoded video data from the storage device may be a streaming transmission, a download transmission, or a combination thereof.

[0030] The techniques of this disclosure are not necessarily limited to wireless applications or settings. The techniques may be applied to video coding in support of any of 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 on a data storage medium, decoding of digital video stored on a data storage medium, or other applications. In some examples, 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.

[0031] In the example of FIG. 1, source device 12 includes a video source 18, a video encoder 20, and an output interface 22. Destination device 14 includes an input interface 28, a video decoder 30, and a display device 32. According to this disclosure, video encoder 20 of source device 12 and / or video decoder 30 of 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, source device 12 may receive video data from an external video source, such as an external camera. Similarly, destination device 14 may interface with an external display device rather than including an integrated display device.

[0032] The depicted coding system 10 of FIG. 1 is only an example. The techniques for video coding may be performed by any digital video encoding and / or decoding device. Although the techniques of this disclosure are generally performed by a video coding device, the techniques may also be performed by a video encoder / decoder, commonly referred to as a "codec." Additionally, the techniques of this disclosure may also be performed by a video preprocessor. The video encoder and / or decoder may be a graphics processing unit (GPU) or similar device.

[0033] Source device 12 and destination device 14 are merely examples of such coding devices, with source device 12 generating coded video data for transmission to destination device 14. In some examples, source device 12 and destination device 14 may operate in a substantially symmetric manner, such that each of source and destination devices 12, 14 includes video encoding and decoding components. Thus, coding system 10 may support one-way or two-way video transmission between video devices 12, 14, for, e.g., video streaming, video playback, video broadcasting, or video telephony.

[0034] Video source 18 of originating 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, video source 18 may generate computer graphics based data as the source video, or generate a combination of live, archived, and computer-generated video.

[0035] In some cases, when video source 18 is a video camera, source device 12 and destination device 14 may form a so-called camera phone or video phone. However, as mentioned above, the techniques described in this disclosure may be applicable to video coding generally and may apply to wireless and / or wired applications. In each case, filmed, pre-filmed, or computer-generated video may be encoded by video encoder 20. The encoded video information may then be output by output interface 22 to computer-readable medium 16.

[0036] Computer-readable medium 16 may include a transitory medium, such as a wireless broadcast or wired network transmission, or a storage medium (i.e., a non-transitory storage medium), such as a hard disk, a flash drive, a compact disc, a digital video disc, a Blu-ray disc, or other computer-readable medium. In some examples, a network server (not shown) may receive the encoded video data from source device 12, for example, via a network transmission, and provide the encoded video data to destination device 14. Similarly, a computing device at a media production facility, such as a disc stamping facility, may receive the encoded video data from source device 12 and produce discs including the encoded video data. Thus, computer-readable medium 16 may be understood to include one or more computer-readable media of various forms in various examples.

[0037] An input interface 28 of destination device 14 receives information from computer-readable medium 16. The information on computer-readable medium 16 may include syntax information defined by video encoder 20 that is also used by video decoder 30, including syntax elements that describe characteristics and / or processing of blocks and other coded units, e.g., groups of pictures (GOPs). Display device 32 displays the decoded video data to a user and may include any of a variety of display devices, such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0038] Video encoder 20 and video decoder 30 may operate according to a video coding standard, such as the High Efficiency Video Coding (HEVC) standard currently being developed and may conform to the HEVC Test Model (HM). Alternatively, video encoder 20 and video decoder 30 may operate according to other proprietary or industry standards, such as the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) H.264 standard, also known as Moving Picture Expert Group (MPEG)-4, Part 10, Advanced Video Coding (AVC), H.265 / HEVC, or extensions of such standards. 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. 1, in some aspects, video encoder 20 and video decoder 30 may be integrated with audio encoders and decoders, respectively, and may include appropriate multiplexer-demultiplexer (MUX-DEMUX) units or other hardware and software to handle the encoding of both audio and video in a common or separate data stream. Where applicable, the MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol or other protocols, such as the User Datagram Protocol (UDP).

[0039] The video encoder 20 and the video decoder 30 may 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, software, hardware, firmware, or any combination thereof. When the techniques are implemented partially in software, the device may store instructions for the software on a suitable non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of the video encoder 20 and the video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder / decoder (codec) in the respective device. The device including the video encoder 20 and / or the video decoder 30 may include an integrated circuit, a microprocessor, and / or a wireless communication device, such as a cellular phone.

[0040] FIG. 2 is a block diagram illustrating an example of a video encoder 20 that may implement video coding techniques. The video encoder 20 may perform intra- and inter-coding of video blocks in a video slice. Intra-coding relies on spatial prediction to reduce or remove spatial redundancy of video within a given video frame or picture. Inter-coding relies on temporal prediction to reduce or remove temporal redundancy of video within nearby frames or pictures of a video sequence. An intra-mode (I-mode) may refer to any of several spatially-based coding modes. An inter-mode, such as uni-directional (aka uni prediction) prediction (P-mode) or bi-prediction (aka bi prediction) (B-mode), may refer to any of several temporal-based coding modes.

[0041] As shown in FIG. 2, video encoder 20 receives a current video block in a video frame to be encoded. In the example of FIG. 2, video encoder 20 includes a mode selection unit 40, a reference frame memory 64, a summer 50, a transform processing unit 52, a quantization unit 54, and an entropy coding unit 56. In addition, 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 partitioning unit 48. For reconstruction of video blocks, video encoder 20 also includes an inverse quantization unit 58, an inverse transform unit 60, and a summer 62. A deblocking filter (not shown in FIG. 2) may also be included to filter block boundaries to remove blockiness artifacts from the reconstructed video. If necessary, the deblocking filter generally filters the output of summer 62. Additional filters (in the loop or after the loop) may also be used in addition to the deblocking filter. Such a filter is not shown for simplicity, but could filter the output of summer 50 (as an in-loop filter) if desired.

[0042] During the encoding process, video encoder 20 receives a video frame or slice to be coded. The frame or slice may be divided into multiple video blocks. Motion estimation unit 42 and motion compensation unit 44 perform inter-predictive coding of the received video block relative to one or more blocks in one or more reference frames to provide temporal prediction. Intra prediction unit 46 may alternatively perform intra-predictive coding of the received video block relative to one or more neighboring blocks in the same frame or slice as the block to be coded to provide spatial prediction. Video encoder 20 may perform multiple coding passes to select an appropriate coding mode for each block of video data, for example.

[0043] Furthermore, partition unit 48 may partition blocks of video data into sub-blocks based on an evaluation of a previous partitioning scheme in a previous coding pass. For example, partition unit 48 may first partition a frame or slice into largest coding units (LCUs) and partition each of the LCUs into sub-coding units (sub-CUs) based on a rate-distortion analysis (e.g., rate-distortion optimization). Mode selection unit 40 may further generate a quadtree data structure indicating the partitioning of the LCUs into sub-CUs. A leaf-node CU of the quadtree may include one or more prediction units (PUs) and one or more transform units (TUs).

[0044] This disclosure uses the term "block" to refer to either a CU, PU, ​​or TU in the context of HEVC, or to refer to similar data structures in the context of other standards (e.g., macroblocks and their subblocks 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 a square shape. The size of a CU can range from 8x8 pixels up to the size of a treeblock of 64x64 pixels or more. Each CU can include one or more PUs and one or more TUs. Syntax data associated with a CU can, for example, describe the partitioning of the CU into one or more PUs. The partitioning mode can vary between whether the CU is coded in skip or direct mode, intra-prediction mode, or inter-prediction (aka inter prediction) mode. A PU can be partitioned to have a non-square shape. Syntax data associated with a CU can also describe the partitioning of a CU into one or more TUs, for example, by a quadtree. The TUs can be square or non-square (eg, rectangular) in shape.

[0045] Mode selection unit 40 may, for example, select one of the coding modes, intra or inter, based on an error result, and provide the resulting intra- or inter-coded block to summer 50 for generating residual block data and summer 62 for reconstructing a coded block for use as a reference frame. Mode selection unit 40 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information to entropy coding unit 56.

[0046] Motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are shown separately for conceptual purposes. Motion estimation performed by motion estimation unit 42 is a process of generating motion vectors that estimate motion for video blocks. A motion vector may indicate, for example, a displacement of a PU of a video block in a current video frame or picture relative to a predictive block in a reference frame (or other coded unit) relative to a current block being coded in the current frame (or other coded unit). A predictive block is a block that is found to be a good match for a block being coded in terms of pixel differences, which may be determined by sum of absolute differences (SAD), sum of squared differences (SSD), or other difference metrics. In some examples, video encoder 20 may calculate values ​​for sub-integer pixel locations of a reference picture stored in reference frame memory 64. For example, video encoder 20 may interpolate values ​​for quarter pixel locations, eighth pixel locations, or other fractional pixel locations of a reference picture. Thus, motion estimation unit 42 may perform motion searches relating to full pixel and fractional pixel locations, and output motion vectors with fractional pixel accuracy.

[0047] Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter-coded slice by comparing the position of the PU to the position of a predictive block of a 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 reference frame memory 64. Motion estimation unit 42 sends the calculated motion vector to entropy encoding unit 56 and motion compensation unit 44.

[0048] The motion compensation performed by motion compensation unit 44 may include retrieving or generating a predictive block based on the motion vector determined by motion estimation unit 42. Again, motion estimation unit 42 and motion compensation unit 44 may be functionally integrated in some examples. Upon receiving the motion vector for the PU of the current video block, motion compensation unit 44 may find the predictive block to which the motion vector points in one of the reference picture lists. Adder 50 forms a residual video block by subtracting pixel values ​​of the predictive block from pixel values ​​of the current video block being coded to form pixel difference values, as discussed below. In general, motion estimation unit 42 performs motion estimation related to the luma component, and motion compensation unit 44 uses the motion vector calculated based on the luma component for both the chroma and luma components. Mode selection unit 40 may also generate syntax elements related to the video blocks and video slices for use by video decoder 30 in decoding the video blocks of the video slices.

[0049] The intra prediction unit may inter predict the current block as an alternative to the inter prediction performed by the motion estimation unit 42 and the motion compensation unit 44 as described above. In particular, the intra prediction unit 46 may determine an intra prediction mode to use to encode the current block. In some examples, the intra prediction unit 46 may encode the current block using different intra prediction modes, for example, during separate encoding passes, and the intra prediction unit 46 (or the mode selection unit 40 in some examples) may select an appropriate intra prediction mode to use from the tested modes.

[0050] For example, intra prediction unit 46 may calculate a rate-distortion value using a rate-distortion analysis for various tested intra-prediction modes and select the intra-prediction mode with the best rate-distortion characteristics among the tested modes. The rate-distortion analysis generally determines the amount of distortion (or error) between the coded block and the original uncoded block that was coded to generate the coded block, and the bitrate (i.e., number of bits) used to generate the coded block. Intra prediction unit 46 may calculate a ratio from the distortion and rate for the various coded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block.

[0051] Further, the intra prediction unit 46 may be configured to code the depth blocks of the depth map using a depth modeling mode (DMM). The mode selection unit 40 may determine whether the available DMM modes produce better coding results than the intra prediction mode and other DMM modes, for example, using rate-distortion optimization (RDO). Data regarding texture images 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 the depth blocks of the depth map.

[0052] After selecting an intra-prediction mode for the block (e.g., one of a normal intra-prediction mode or a DMM mode), intra-prediction unit 46 may provide information indicating the selected intra-prediction mode for the block to entropy coding unit 56. Entropy coding unit 56 may encode the information indicating the selected intra-prediction mode. Video encoder 20 may include definitions of the coding contexts for the various blocks, as well as an indication of the most likely intra-prediction mode, intra-prediction mode index table, and modified intra-prediction mode index table to use for each of the contexts, in transmitted bitstream configuration data, which may include multiple intra-prediction mode index tables and multiple modified intra-prediction mode index tables (also referred to as codeword mapping tables).

[0053] Video encoder 20 forms a residual video block by subtracting the prediction data from mode select unit 40 from the original video block being coded. Summer 50 represents the component or components that perform this subtraction.

[0054] Transform processing unit 52 applies a transform, such as a discrete cosine transform (DCT) or a transform of similar concept, to the residual block to generate a video block that includes residual transform coefficient values. Transform processing unit 52 may perform other transforms of similar concept to the DCT. Wavelet transforms, integer transforms, subband transforms, or other types of transforms may also be used.

[0055] Transform processing unit 52 applies a transform to the residual block, generating a block of residual transform coefficients. The transform may convert the residual information from a pixel value domain to a transform domain, such as the frequency domain. Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54. Quantization unit 54 quantizes the transform coefficients to further reduce the bit rate. The quantization process may reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter. In some examples, quantization unit 54 may then perform a scan of a matrix including the quantized transform coefficients. Alternatively, entropy coding unit 56 may perform the scan.

[0056] After quantization, entropy coding unit 56 entropy codes the quantized transform coefficients. For example, entropy coding unit 56 may perform context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or another entropy coding technique. In the case of context-based entropy coding, the context may be based on neighboring blocks. After entropy coding by entropy coding unit 56, the encoded bitstream may be transmitted to another device (e.g., video decoder 30) or archived for later transmission or retrieval.

[0057] Inverse quantization unit 58 and inverse transform unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual block in the pixel domain, e.g., for later use as a reference block. Motion compensation unit 44 may calculate a reference block by adding the residual block to a predictive block of one of the frames in reference frame memory 64. Motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to calculate sub-integer pixel values ​​for use in motion estimation. Adder 62 adds the reconstructed residual block to the motion compensated predictive block generated by motion compensation unit 44 to generate a reconstructed video block for storage in reference frame memory 64. The reconstructed video block may be used by motion estimation unit 42 and motion compensation unit 44 as a reference block for inter-coding blocks of subsequent video frames.

[0058] 3 is a block diagram illustrating an example of a video decoder 30 that may implement a video coding technique. In the example of FIG. 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. The video decoder 30 may, in some examples, perform a decoding path that is generally reverse to the encoding path described in connection with the video encoder 20 (FIG. 2). The motion compensation unit 72 may generate prediction data based on a motion vector 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.

[0059] During the decoding process, video decoder 30 receives an encoded video bitstream representing video blocks of encoded video slices and associated syntax elements from video encoder 20. Entropy decoding unit 70 of video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements. Entropy decoding unit 70 forwards the motion vectors and other syntax elements to motion compensation unit 72. Video decoder 30 may receive syntax elements at the video slice level and / or at the video block level.

[0060] When a video slice is coded as an intra-coded (I) slice, intra prediction unit 74 may generate predictive data for video blocks of the current video slice based on the signaled intra prediction mode and data from already decoded blocks of the current frame or picture. When a video frame is coded as an inter-coded (e.g., B, P, or GPB) slice, motion compensation unit 72 generates predictive blocks for video blocks of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 70. The predictive blocks may be generated from one of the reference pictures in one of the reference picture lists. Video decoder 30 may construct reference frame lists List 0 and List 1 using a default construction technique based on reference pictures stored in reference frame memory 82.

[0061] Motion compensation unit 72 determines prediction information for video blocks of the current video slice by parsing the motion vectors and other syntax elements, and uses the prediction information to generate predictive blocks for the current video block being decoded. For example, motion compensation unit 72 uses some of the received syntax elements to determine the prediction mode (e.g., intra or inter prediction) used to code the video blocks of the video slice, the slice type for inter prediction (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, motion vectors for each inter coded video block of the slice, the status of inter prediction for each inter coded video block of the slice, and other information for decoding video blocks in the current video slice.

[0062] Motion compensation unit 72 may also perform the interpolation based on an interpolation filter. Motion compensation unit 72 may use the interpolation filter used by video encoder 20 during encoding of the video block to calculate interpolated values ​​for sub-integer pixels of the reference block. In this case, motion compensation unit 72 may determine the interpolation filter used by video encoder 20 from the received syntax elements and use the interpolation filter to generate the predictive block.

[0063] Data regarding texture images that correspond to the depth maps may be stored in reference frame memory 82. Motion compensation unit 72 may also be configured to inter-predict depth blocks of the depth maps.

[0064] Image and video compression has undergone rapid growth, resulting in a variety of coding standards. Such video coding standards include Advanced Video Coding (AVC), also known as ITU-T H.261, ISO / IEC Moving 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) and Multiview Video Coding plus Depth (MVC+D), as well as 3D AVC (3D-AVC). HEVC includes extensions such as Scalable HEVC (SHVC), Multi-view HEVC (MV-HEVC), and 3D HEVC (3D-HEVC).

[0065] Versatile Video Coding (VVC) is a new video coding standard being developed by the ITU-T and ISO / IEC joint video experts team (JVET). At the time of this writing, the latest Working Draft (WD) of VVC is contained in JVET-K1001-v1. JVET document JVET-K0325-v3 contains a revision of the high-level syntax of VVC.

[0066] Generally, this disclosure describes techniques based on the developing VVC standard, but the techniques are also compatible with other video / media codec specifications.

[0067] Video compression techniques perform spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as tree blocks, coding tree blocks (CTBs), coding tree units (CTUs), coding units (CUs), and / or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. A picture may be referred to as a frame, and a reference picture may be referred to as a reference frame.

[0068] Spatial or temporal prediction results in a predictive block for the block to be coded. The residual data represents pixel differences between the original block to be coded and the predictive block. Inter-coded blocks are coded by a motion vector pointing to a block of reference samples forming the predictive block and the residual data indicating the difference between the block to be coded and the predictive block. Intra-coded blocks are coded by an intra-coding mode and the residual data. For further compression, the residual data may be transformed from the pixel domain to a transform domain, resulting in residual transform coefficients, which may then be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, may be scanned to generate a one-dimensional vector of transform coefficients, and entropy coding may be applied to achieve further compression.

[0069] In video codec specifications, pictures are identified for multiple purposes, such as for use as reference pictures in inter prediction, for output of pictures from a decoded picture buffer (DPB), for motion vector scaling, for weighted prediction, etc. In AVC and HEVC, pictures may be identified by a picture order count (POC). In AVC and HEVC, pictures in the DPB may 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", the picture may no longer be used for prediction. When a picture is no longer needed for output, the picture may be removed from the DPB.

[0070] In AVC, there are two types of reference pictures: short-term and long-term. A reference picture can be marked as "not used for reference" when the reference picture is no longer needed for prediction reference. The transition between these three statuses (short-term, long-term, and not used for reference) is controlled by the decoded reference picture marking process. There are two alternative decoded reference picture marking mechanisms: an implicit sliding window process and an explicit memory management control operation (MMCO) process. The sliding window process marks a short-term reference picture as "not used for reference" when the number of reference frames is equal to a given maximum number (max_num_ref_frames in the sequence parameter set (SPS)). The short-term reference pictures are stored in a first-in-first-out order such that the most recently decoded short-term picture is retained in the DPB.

[0071] An explicit MMCO process may include multiple MMCO commands that may mark one or more short-term or long-term reference pictures as "not used for reference", may mark all pictures as "not used for reference", or 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 the long-term reference picture.

[0072] In AVC, the reference picture marking operation and the process for outputting and deleting pictures from the DPB are performed after the picture is decoded.

[0073] HEVC introduces a different approach for the management of reference pictures, called Reference Picture Set (RPS). The most fundamental difference of the RPS concept compared to AVC's MMCO / moving window process is that for each particular slice, a complete set of reference pictures to be 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 the current or future pictures is signaled. This differs from the AVC scheme, where only relative changes to the DPB are signaled. According to the RPS concept, no information from previous pictures in the decoding order is required to maintain the correct status of the reference pictures in the DPB.

[0074] The order of picture decoding and the operation of DPB in HEVC are changed compared to AVC to take advantage of RPS and improve error resilience. In AVC, picture marking and buffering operations (both outputting and deleting decoded pictures from DPB) are generally applied after the current picture is decoded. In HEVC, RPS is first decoded from the slice header of the current picture, and then picture marking and buffering operations are generally applied before decoding the current picture.

[0075] Each slice header in HEVC may contain parameters for signaling the RPS for the picture that contains the slice. The only exception is that for Instantaneous Decoding Refresh (IDR) slices, no RPS is signaled. Instead, the RPS is inferred to be empty. For I-slices that do not belong to an IDR picture, an RPS may be provided even if those I-slices belong to an I-picture, since there may be pictures following the I-picture in decoding order that use inter prediction from pictures that preceded the I-picture in decoding order. The number of pictures in the RPS does not exceed the size limit of the DPB specified by the sps_max_dec_pic_buffering syntax element of the SPS.

[0076] Each picture is associated with a POC value that represents the order of output. The slice header contains a fixed-length codeword pic_order_cnt_lsb that represents the least significant bits (LSBs) of the complete POC value, also known as the POC LSB. The length of the codeword is signaled within the SPS and can be, for example, between 4 and 16 bits. The RPS concept uses the POC to identify reference pictures. Besides its own POC value, each slice header either directly contains or inherits from the SPS a coded representation of the POC value (or LSBs) of each picture in the RPS.

[0077] The RPS of each picture consists of five different lists of reference pictures, also called five RPS subsets: RefPicSetStCurrBefore consists of all short-term reference pictures that are before the current picture in both decoding order and output order and may be used in inter prediction of the current picture; RefPicSetStCurrAfter consists of all short-term reference pictures that are before the current picture in decoding order and after the current picture in output order and may be used in inter prediction of the current picture; RefPicSetStFoll consists of all short-term reference pictures that may be used in inter prediction of one or more of the pictures that follow the current picture in decoding order and are not used in inter prediction of the current picture; RefPicSetLtCurr consists of all long-term reference pictures that may be used in inter prediction of the current picture. RefPicSetLtFoll consists of all long-term reference pictures that may be used in inter prediction of one or more of the pictures that follow the current picture in decoding order, but are not used in inter prediction of the current picture.

[0078] The RPS is signaled using up to three loops repeated for different kinds of reference pictures, short-term reference pictures with smaller POC values ​​than the current picture, short-term reference pictures with larger POC values ​​than the current picture, and long-term reference pictures. Furthermore, a flag (used_by_curr_pic_X_flag) is sent for each picture to indicate whether the reference picture is used (included in one of the lists RefPicSetStCurrBefore, RefPicSetStCurrAfter, or RefPicSetLtCurr) or not (included in one of the lists RefPicSetStFoll or RefPicSetLtFoll) for referencing by the current picture.

[0079] 4 illustrates an RPS 400 with a current picture B14 along with the entries (e.g., pictures) of all subsets 402 of the RPS 400. In the example of FIG. 4, the current picture B14 includes exactly one picture in each of the five subsets 404 (aka RPS subsets). P8 is a picture in the subset 402 called RefPicSetStCurrBefore because the picture is before B14 in the order of output and is used by B14. P12 is a picture in the subset 402 called RefPicSetStCurrAfter because the picture is after B14 in the order of output and is used by B14. P13 is a picture in the subset 402 called RefPicSetStFoll because the picture is a short-term reference picture not used by B14 (but must be kept in the DPB because it is used by B15). P4 is a picture in subset 402 called RefPicSetLtCurr because the picture is a long-term reference picture used by B14. I0 is a picture in subset 402 called RefPicSetLtFoll because the picture is a long-term reference picture not used by the current picture (but must be kept in the DPB because it is used by B15).

[0080] The short-term part of the RPS 400 may be included directly in the slice header. Alternatively, the slice header may only include a syntax element representing an index that refers to a predefined list of RPSs transmitted in the active SPS. The short-term part of the RPS 402 may be signaled using two different schemes, either Inter-RPS, described below, or Intra-RPS, described here. When Intra-RPS is used, num_negative_pics and num_positive_pics are signaled, representing the length of two different lists of reference pictures. These lists contain reference pictures that have a negative POC difference and a positive POC difference, respectively, compared to the current picture. Each element of these lists is coded by a variable length coding that represents the difference of the POC value associated with the previous element in the list minus one. For the first picture of each list, the signaling relates to the POC value of the current picture minus one.

[0081] When coding a recurring RPS in a sequence parameter set, it is possible to code an element of one RPS (e.g., RPS 400) with reference to another RPS already coded in the sequence parameter set. This is called inter-RPS. Since all RPSs of a sequence parameter set are in the same network abstraction layer (NAL) unit, there is no error robustness problem associated with this method. The inter-RPS syntax exploits the fact that the RPS of the current picture can be predicted from the RPSs of already decoded pictures. This is because all reference pictures of the current picture must either be reference pictures of the previous picture or already decoded pictures themselves. It is only necessary to indicate which of these pictures is the reference picture and should be used for the prediction of the current picture. Thus, the syntax includes the following: an index pointing to the RPS to use as a predictor, a delta_POC that is added to the delta_POC of the predictor to obtain a delta POC of the current RPS, and a set of indicators indicating which pictures are reference pictures and whether those pictures are used only for predicting future pictures.

[0082] An encoder that wants to use 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 poc_lsb_lt, which represents the least significant bits of the complete POC value of the respective long-term picture. Each poc_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 LSB for the long-term picture can then be signaled in the slice header as an index into this list.

[0083] To enable calculation of the complete POC distance of a long-term reference picture relative to the current picture, the delta_poc_msb_cycle_lt_minus1 syntax element may be further signaled. 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.

[0084] Regarding the marking of reference pictures in HEVC, generally, some pictures are present in the DPB before the decoding of a picture. Some of the pictures may be available for prediction and therefore marked as "used for reference". Other pictures may not be available for prediction but are waiting for output and therefore marked as "not used for reference". When the slice header is parsed, the picture marking process is performed before the slice data is decoded. Pictures present in the DPB and marked as "used for reference" but not included in the RPS are marked as "not used for reference". When used_by_curr_pic_X_flag is equal to zero, pictures not present in the DPB but included in the reference picture set are ignored. However, when used_by_curr_pic_X_flag is instead equal to one, this reference picture was intended to be used for prediction in the current picture but is missing. Then, the loss of the unintended picture is inferred and the decoder should take appropriate action.

[0085] After decoding the current picture, it is marked as "used for short-term reference."

[0086] Next, the construction of reference picture lists in HEVC is considered. In HEVC, the term inter prediction is used to refer to prediction derived from data elements (e.g., sample values ​​or motion vectors) of reference pictures other than the currently decoded picture. Similar to AVC, a picture may be predicted from multiple reference pictures. The reference pictures used for inter prediction are organized into one or more reference picture lists. A reference index specifies which of the reference pictures in the list should be used to generate a prediction signal.

[0087] A single reference picture list, List 0, is used for P slices, and two reference picture lists, List 0 and List 1, are used for B slices. Similar to AVC, constructing a reference picture list in HEVC includes reference picture list initialization and reference picture list modification.

[0088] In AVC, the initialization process of List 0 is different for P slices (decoding order is used) and B slices (output order is used). In HEVC, output order is used in both cases.

[0089] The reference picture list initialization generates a default List 0 and List 1 (if the slice is a B slice) based on three RPS subsets: RefPicSetStCurrBefore, RefPicSetStCurrAfter, and RefPicSetLtCurr. First, the short-term pictures in earlier (later) output order are inserted into List 0 (List 1) in ascending order of POC distance with the current picture, then the short-term pictures in later (earlier) output order are inserted into List 0 (List 1) in ascending order of POC distance with the current picture, and finally the long-term pictures are inserted at the end. From the RPS point of view, for List 0, the RefPicSetStCurrBefore entry is inserted into the initial list, followed by the RefPicSetStCurrAfter entry. Then, if available, the RefPicSetLtCurr entry is appended to the end.

[0090] In HEVC, when the number of entries in the list is less than the target number of 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). When the number of entries is more than the target number, the list is truncated.

[0091] After the reference picture list is initialized, it may be modified based on the reference picture list modification command such that the reference pictures for the current picture may be arranged in any order, including the case where one particular reference picture may appear in more than one position in the list. When a flag indicating the presence of a list modification is set to 1, a fixed number of commands (equal to the target number of entries in the reference picture list) are signaled, each command inserting one entry for the reference picture list. The reference picture is identified in the command by an index into the list of reference pictures for the current picture derived from the signaling of the RPS. This is different from the modification of the reference picture list in H.264 / AVC, where the picture is identified either by picture number (derived from the frame_num syntax element) or by long-term reference picture index, and fewer commands may be required, for example, to swap the first two entries of the initial list or to insert one entry at the beginning of the initial list and shift the other entries.

[0092] A reference picture list is not allowed to contain any reference picture with a TemporalId greater than the current picture. An HEVC bitstream may consist of several temporal sublayers. Each NAL unit belongs to a particular sublayer, indicated by its TemporalId (equal to temporal_id_plus1 - 1).

[0093] The management of reference pictures is based directly on the reference picture list. JCT-VC document JCTVC-G643 includes an approach that directly uses three reference picture lists, reference picture list 0, reference picture list 1, and idle reference picture list, for the management of reference picture lists in the DPB, thereby avoiding the need for signaling and decoding processes that include either 1) the moving window and MMCO processes and reference picture list initialization and modification processes of AVC, or 2) the reference picture set and reference picture list initialization and modification processes of HEVC.

[0094] The approaches for reference picture management may have some problems. The AVC approach includes a complex moving window, MMCO process, and a reference picture list initialization and modification process. Furthermore, the loss of a picture may lead to a loss of the status of the DPB in terms of which pictures should have been in the DPB for further inter prediction reference purposes. The HEVC approach does not have the problem of the loss of the status of the DPB. However, the HEVC approach includes a complex reference picture set signaling and derivation process, and a complex reference picture list initialization and modification process. The approach of JCTVC-G643, which directly uses three reference picture lists, Reference Picture List 0, Reference Picture List 1, and Idle Reference Picture List, for managing reference pictures in the DPB, includes the following points: a third reference picture list, i.e., the Idle Reference Picture List, two-part coding of the difference of POC as a "short-term" part and a ue(v)-coded "long-term part", POC granularity based on TemporalId for coding the difference of POC, use of two-part coding of the difference of POC to decide marking between "used for short-term reference" or "used for long-term reference", description of a subset of reference picture lists that gives the ability to specify a reference picture by deleting a reference picture from the end of the description of a particular previous reference picture list, 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 above points unnecessarily complicates the approach. Furthermore, the decoding process for the reference picture list of JCTVC-G643 is also complicated: signaling of long-term reference pictures may require signaling of POC cycles in the slice header, which is not efficient.

[0095] To address the problems listed above, disclosed herein are the following solutions, each of which can be applied individually and some of which can be applied in combination: 1) The marking of reference pictures is based directly 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 can be signaled in the SPS, and each of the reference picture list structures can be referenced by an index from the slice header. 1b.ii) Each of the reference picture lists 0 and 1 can be signaled directly in the slice header. 2) Information for the derivation of two reference picture lists is signaled for all types of slices, i.e., B (bi-predictive), P (short-predictive), and I (intra) slices. The term slice refers to a set of coding tree units, such as slices in HEVC or the latest VVC WD, and the term slice can also refer to some other set of coding tree units, such as tiles in HEVC. 3) Two reference picture lists are generated for all types of slices, i.e., B, P, and I slices. 4) The two reference picture lists are directly constructed without using reference picture list initialization and reference picture list modification processes. 5) In each of the two reference picture lists, reference pictures that may be used for inter prediction of the current picture may only be referenced by the first few entries of the list. These entries are called active entries of the list, while the other entries are called inactive entries of the list. Both the number of all entries and the number of active entries of the list may be derived.6) A picture referenced by an inactive entry of a reference picture list is not allowed to be referenced by another entry of the reference picture list or any entry of other reference picture lists. 7) Long-term reference pictures are identified only by a certain number of POC LSBs, which may be larger than the number of POC LSBs signaled in the slice header for derivation of the POC value, which number is indicated 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 derivation of the POC value, and the number of bits used to represent the POC LSBs for identifying short-term and long-term reference pictures may be different. 9) The reference picture list structure is signaled only in the slice header and no distinction is made between short-term and long-term reference pictures, all reference pictures are simply called reference pictures and 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.

[0096] The first embodiment of the present disclosure is provided. The description is related to the latest VVC WD. In this embodiment, two sets of reference picture list structures are signaled in the SPS, one for each of reference picture list 0 and reference picture list 1.

[0097] Definitions are given for some of the terms used in this specification. Intra Random Access Point (IRAP) picture: A coded picture in which each video coding layer (VCL) NAL unit has nal_unit_type equal to IRAP_NUT. Non-IRAP picture: A coded picture in which each VCL NAL unit has nal_unit_type equal to NON_IRAP_NUT. Reference picture list: A list of reference pictures used for inter prediction of a P or B slice. Two reference picture lists, Reference Picture List 0 and Reference Picture List 1, are generated for each slice of a non-IRAP picture. The set of unique pictures referenced by all entries of the two reference picture lists associated with a picture consists of all reference pictures that may be used for inter prediction of the associated picture or any picture following the associated picture in decoding order. To decode slice data of a P slice, only Reference Picture List 0 is used for inter prediction. To decode slice data of a B slice, both reference picture lists are used for inter prediction. To decode slice data of an I slice, the reference picture list is not used for inter prediction. Long-term Reference Picture (LTRP): A picture that is marked as "used for long-term reference". Short-term Reference Picture (STRP): A picture that is marked as "used for short-term reference".

[0098] The terms "used for short-term reference", "used for long-term reference", or "not used for reference" are defined in VVC in section 8.3.3 Decoding process for reference picture marking, in HEVC in section 8.3.2 Decoding process for reference picture set, and in AVC in section 7.4.3.3 Decoded reference picture marking semantics. As used herein, the terms have the same meaning.

[0099] The relevant syntax and semantics for the first embodiment are given below.

[0100] NAL unit header syntax

[0101] [Table 1]

[0102] Sequence Parameter Set Raw Byte Sequence Payload (RBSP) Syntax

[0103] [Table 2]

[0104] Picture Parameter Set RBSP Syntax

[0105] [Table 3]

[0106] Slice Header Syntax

[0107] [Table 4]

[0108] Reference Picture List Structure Syntax

[0109] [Table 5]

[0110] NAL unit header semantics

[0111] forbidden_zero_bit is equal to 0. nal_unit_type specifies the type of RBSP data structure contained in the NAL unit.

[0112] [Table 6]

[0113] The value of nuh_temporal_id_plus1 minus 1 specifies the temporal identifier for the NAL unit. The value of nuh_temporal_id_plus1 is not equal to 0. The variable TemporalId is specified as follows: 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 of a coded picture or access unit is the value of TemporalId of 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 the access unit containing the NAL unit is equal to 0. 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 that contains the NAL unit. When the NAL unit is a non-VCL NAL unit, the value of TemporalId is equal to the minimum of the TemporalId values ​​of all access units to which the non-VCL NAL unit applies. When nal_unit_type is equal to PPS_NUT, then TemporalId may be greater than or equal to the TemporalId of the containing access unit since 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 an SEI NAL unit may contain information that applies to a subset of the bitstream that includes access units whose TemporalId value is greater than the TemporalId of the access unit that contains the SEI NAL unit. nuh_reserved_zero_7bits is equal to '0000000'. Other values ​​of nuh_reserved_zero_7bits may be specified in the future by ITU_T | ISO / IEC. Decoders shall ignore (i.e., remove from the bitstream and discard) NAL units that have a value of nuh_reserved_zero_7bits not equal to '0000000'.

[0114] Semantics of RBSP for sequence parameter sets

[0115] 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 ). The value of log2_max_pic_order_cnt_lsb_minus4 ranges from 0 to 12, inclusive. The value of sps_max_dec_pic_buffering_minus1 plus 1 specifies the maximum required size of the decoded picture buffer for CVS in units of picture storage buffer. The value of sps_max_dec_pic_buffering_minus1 ranges from 0 to MaxDpbSize - 1, inclusive, where MaxDpbSize is specified elsewhere. long_term_ref_pics_flag equal to 0 specifies that the LTRP is not used for inter prediction of any coded pictures in the CVS. long_term_ref_pics_flag equal to 1 specifies that the LTRP may be used for inter prediction 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_lt_poc_lsb ). The value of additional_lt_poc_lsb is in the range from 0 to 32 - log2_max_pic_order_cnt_lsb_minus4 - 4, inclusive. When not present, the value of additional_lt_poc_lsb is inferred 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 with listIdx equal to i contained in the SPS. The value of num_ref_pic_lists_in_sps[i] ranges from 0 to 64, inclusive. 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] + 1 ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structures, since there may be one ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure directly signaled in the slice header of the current picture.

[0116] Semantics of the RBSP of a picture parameter set

[0117] The value of num_ref_idx_default_active_minus1[i] plus 1 specifies the inferred value of the variable NumRefIdxActive[0] for a P or B slice with num_ref_idx_active_override_flag equal to 0 when i is equal to 0, and specifies the inferred value of NumRefIdxActive[1] for a B slice with num_ref_idx_active_override_flag equal to 0 when i is equal to 1. The value of num_ref_idx_default_active_minus1[i] lies in the range from 0 to 14, inclusive.

[0118] Slice header semantics

[0119] When present, the value of each of the syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb in the slice header shall be the same in all slice headers of a coded picture. ... slice_type specifies the coding type of the slice according to Table 7-3.

[0120] [Table 7]

[0121] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type is 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 in the range from 0 to MaxPicOrderCntLsb - 1, inclusive. When slice_pic_order_cnt_lsb is not present, slice_pic_order_cnt_lsb is inferred to be equal to 0. ref_pic_list_sps_flag[i] equal to 1 specifies that reference picture list i of the current picture is derived based on one of the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structures with listIdx equal to i in the active SPS. ref_pic_list_sps_flag[i] equal to 0 specifies that reference picture list i of the current picture is derived based on the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure with listIdx equal to i that 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 equal to 0. ref_pic_list_idx[i] specifies an index into a list of ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structures with listIdx equal to i contained in the active SPS, where ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structures with listIdx equal to i are used for deriving reference picture list i of the current picture.The syntax element ref_pic_list_idx[i] is represented by Ceil( Log2(num_ref_pic_lists_in_sps[i]) ) bits. When not present, the value of ref_pic_list_idx[i] is inferred to be equal to 0. The value of ref_pic_list_idx[i] is in the range from 0 to num_ref_pic_lists_in_sps[i] - 1, inclusive. num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that the syntax element num_ref_idx_active_minus1[1] is present for B slices. 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] are not present. num_ref_idx_active_minus1[i], when present, specifies the value of the variable NumRefIdxActive[i] as follows: NumRefIdxActive[i] = num_ref_idx_active_minus1[i] + 1. The value of num_ref_idx_active_minus1[i] is in the range from 0 to 14, inclusive.

[0122] The value of NumRefIdxActive[i] minus 1 specifies the highest reference index for reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, no reference index for reference picture list i may be used to decode the slice. For i equal to 0 or 1, when 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 inferred to be equal to num_ref_idx_default_active_minus1[0] + 1. When the current slice is a P slice, NumRefIdxActive[1] is inferred to be equal to 0. When the current slice is an I slice, both NumRefIdxActive[0] and NumRefIdxActive[1] are inferred to be equal to 0.

[0123] Alternatively, for i equal to 0 or 1, then the following applies: rplsIdx1 shall be set equal to ref_pic_list_sps_flag[i] ? ref_pic_list_idx[i] : num_ref_pic_lists_in_sps[i] and numRpEntries[i] shall be 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] shall be set equal to numRpEntries[i].

[0124] Reference Picture List Structure Semantics

[0125] The ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure may be present in the SPS or in the slice header. Depending on whether the syntax structure is included in the slice header or in the SPS, the following applies: If present in the slice header, the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure specifies the listIdx of a reference picture list for the current picture (the picture that contains the slice). Otherwise (present in the SPS), the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure specifies candidates for the reference picture list listIdx, and the term "current picture" in the semantics specified in the remainder of this section refers to each picture that 1) has one or more slices with ref_pic_list_idx[listIdx] equal to an index into the list of ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structures contained in the SPS, and 2) is in a CVS that has the SPS as its 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. When not present, the value of num_ltrp_entries[listIdx][rplsIdx] is inferred 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 in the range of 0 to sps_max_dec_pic_buffering_minus1, inclusive. lt_ref_pic_flag[listIdx][rplsIdx][i] equal to 1 specifies that the i-th entry of 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 of the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure is a STRP entry. When not present, the value of lt_ref_pic_flag[listIdx][rplsIdx][i] is inferred to be equal to 0. It is a compliance requirement of a bitstream 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, inclusive, is equal to num_ltrp_entries[listIdx][rplsIdx].delta_poc_st[listIdx][rplsIdx][i] specifies the difference between the value of the picture order count of the current picture and the value of the picture order count of the picture referenced by the i-th entry when the i-th entry is the first STRP entry of the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure, or specifies the difference between the value of the picture order count of the picture referenced by the i-th entry and the value of the picture order count of the picture referenced by the previous STRP entry of the ref_pic_list_struct(listIdx, rplsIdx, ltrpFlag) syntax structure when the i-th entry is a STRP entry of the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure but is not the first STRP entry. The value of delta_poc_st[listIdx][rplsIdx][i] is in the range of -215 to 215 - 1, inclusive. poc_lsb_lt[listIdx][rplsIdx][i] specifies the value of the picture order count modulo MaxLtPicOrderCntLsb of the picture referenced by the i-th entry of 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.

[0126] The decoding process is considered. The decoding process operates as follows for the current picture CurrPic. The decoding of NAL units is specified below. The process below specifies the following decoding process using syntax elements at slice header layer and above. Variables and functions related to picture order count are derived. This needs to be called only for the first slice of a picture. At the beginning of the decoding process for each slice of a non-IRAP picture, the decoding process for construction of reference picture lists is called for derivation of reference picture list 0 (RefPicList[0]) and reference picture list 1 (RefPicList[1]). The decoding process for marking of reference pictures is called, where 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 a picture. The decoding processes for coding tree units, scaling, transformation, in-loop filtering, etc. are called. After all slices of the current picture are decoded, the current decoded picture is marked as "used for short-term reference".

[0127] A NAL unit decoding process is considered. 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 structures encapsulated in 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.

[0128] A slice decoding process is considered, including a decoding process for picture order count. The output of this process is PicOrderCntVal, the picture order count of the current picture. The picture order count is used to identify pictures for deriving motion parameters in merge mode and motion vector prediction and for checking decoder compliance. 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: Let prevTid0Pic be the previous picture in decoding order with TemporalId equal to 0. The variable prevPicOrderCntLsb is set equal to slice_pic_order_cnt_lsb of prevTid0Pic. The variable prevPicOrderCntMsb is set equal to the PicOrderCntMsb of prevTid0Pic.

[0129] The variable PicOrderCntMsb for the current picture is derived as follows: If the current picture is an IRAP picture, PicOrderCntMsb is set 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

[0130] PicOrderCntVal is derived as follows: PicOrderCntVal = PicOrderCntMsb + slice_pic_order_cnt_lsb.

[0131] Since slice_pic_order_cnt_lsb is inferred to be 0 for IRAP pictures and both prevPicOrderCntLsb and prevPicOrderCntMsb are set equal to 0, all IRAP pictures have PicOrderCntVal equal to 0. The value of PicOrderCntVal is in the range of -231 to 231 - 1, inclusive. In one CVS, the PicOrderCntVal values ​​for any two coded pictures are not the same.

[0132] At any instant 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 specified as follows: PicOrderCnt(picX) = PicOrderCntVal of picture picX. The function DiffPicOrderCnt(picA, picB) is specified as follows: 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 within the range of -215 to 215 - 1, inclusive. If X is the current picture and Y and Z are 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 if DiffPicOrderCnt(X,Y) and DiffPicOrderCnt(X,Z) are both positive or both negative.

[0133] A decoding process for the construction of a reference picture list is considered. This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. A reference picture is addressed by a reference index. The reference index is an index into 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 in marking the reference pictures or in 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 checking bitstream conformance, but their derivation is not necessary for decoding of the current picture or pictures that follow the current picture in decoding order. For P slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of checking bitstream conformance, but its derivation is not necessary for decoding of the current picture or pictures that follow the current picture in 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( there exists a reference picture picA in DPB whose PicOrderCntVal is equal to RefPicPocList[i][j] ) RefPicList[i][j] = picA else RefPicList[i][j] = "no reference picture" pocBase = RefPicPocList[i][j] } else { if( there exists a reference picture picA 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" } } }

[0134] For each i equal to 0 or 1, the following applies: The first NumRefIdxActive[i] entries of RefPicList[i] are called active entries of RefPicList[i], and the other entries of RefPicList[i] are called inactive entries of RefPicList[i]. Each entry of RefPicList[i][j] for j in the range from 0 to NumEntriesInList[i][RplsIdx[i]] - 1, inclusive, is called a STRP entry if lt_ref_pic_flag[i][RplsIdx[i]][j] is equal to 0, and is called a LTRP entry otherwise. It is possible for a particular picture to be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. It is also possible that a particular picture is referenced by more than one entry in RefPicList[0] or by more than one entry in RefPicList[1]. The active entries in RefPicList[0] and the active entries in RefPicList[1] collectively refer to all reference pictures that may be used for inter-prediction of the current picture and one or more pictures that follow the current picture in decoding order. The inactive entries in RefPicList[0] and the inactive entries in RefPicList[1] collectively refer to all reference pictures that are not used for inter-prediction of the current picture but may be used in inter-prediction of one or more pictures that follow the current picture in decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equal 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 equal to "no reference picture" should be ignored.For each active entry in RefPicList[0] or RefPicList[1] that is equal to "no reference picture", an unintended picture loss should be inferred.

[0135] It is a requirement of bitstream compliance that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is greater than or equal to NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of 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: No inactive entry in RefPicList[0] or RefPicList[1] references the same picture as any other entry in RefPicList[0] or RefPicList[1]. A STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture do not reference the same picture. The current picture itself is not referenced by any entry in RefPicList[0] or RefPicList[1]. There is no LTRP entry in RefPicList[0] or RefPicList[1] such that the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is greater than or equal to 224. setOfRefPics shall be the set of unique pictures referenced by all entries of RefPicList[0] and all entries of RefPicList[1]. The number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1 and setOfRefPics is the same for all slices of the picture.

[0136] Decoding process for reference picture marking

[0137] This process is invoked once per picture after the decoding process for the decoding of the slice header and the construction of the reference picture list for the slice, but before the decoding of 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 may 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 removes another of these markings, if applicable. When a picture is said to be marked as "used for reference", this refers collectively to the picture being marked as "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 the Log2(MaxLtPicOrderCntLsb) LSB 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 reference picture in the DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as "not used for reference".

[0138] A detailed description of the second embodiment of the present disclosure is given. This section provides the document of the second embodiment of the present disclosure as described above. The description is related to 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.

[0139] Sequence Parameter Set RBSP Syntax

[0140] [Table 8]

[0141] Picture Parameter Set RBSP Syntax

[0142] [Table 9]

[0143] Slice Header Syntax

[0144] [Table 10]

[0145] Reference Picture List Structure Syntax

[0146] [Table 11]

[0147] The semantics of the NAL unit headers are considered.

[0148] Semantics of RBSP for sequence parameter sets

[0149] 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 ). The value of log2_max_pic_order_cnt_lsb_minus4 ranges from 0 to 12, inclusive. The value of sps_max_dec_pic_buffering_minus1 plus 1 specifies the maximum required size of the decoded picture buffer for CVS in units of picture storage buffer. The value of sps_max_dec_pic_buffering_minus1 ranges from 0 to MaxDpbSize - 1, inclusive, where MaxDpbSize is specified elsewhere. num_ref_pic_lists_in_sps specifies the number of ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structures contained in the SPS. The value of num_ref_pic_lists_in_sps is in the range of 0 to 128, inclusive. The decoder should allocate memory for a total of num_short_term_ref_pic_sets + 2 ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structures, since there can be two ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structures directly signaled in the slice header of the current picture. long_term_ref_pics_flag equal to 0 specifies that LTRP is not used for inter prediction of any coded pictures in the CVS. long_term_ref_pics_flag equal to 1 specifies that the LTRP may be used for inter prediction 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_lt_poc_lsb ). The value of additional_lt_poc_lsb is in the range from 0 to 32 - log2_max_pic_order_cnt_lsb_minus4 - 4, inclusive. When not present, the value of additional_lt_poc_lsb is inferred to be equal to 0.

[0150] The semantics of the RBSP of a picture parameter set is considered.

[0151] Slice header semantics

[0152] When present, the value of each of the syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb in the slice header shall be the same in all slice headers of a coded picture. slice_type specifies the coding type of the slice according to Table 7-3.

[0153] [Table 12]

[0154] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type is 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 in the range from 0 to MaxPicOrderCntLsb - 1, inclusive. When slice_pic_order_cnt_lsb is not present, slice_pic_order_cnt_lsb is inferred to be equal to 0. ref_pic_list_sps_flag[i] equal to 1 specifies that reference picture list i of the current picture is derived based on one of the ref_pic_list_struct(rplsIdx, ltrpFlag) in the active SPS. ref_pic_list_sps_flag[i] equal to 0 specifies that reference picture list i of the current picture is derived based on the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure directly included 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 equal to 0. ref_pic_list_idx[i] specifies an index into a list of ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structures contained in the active SPS that are used for the derivation of reference picture list i of the current picture. The syntax element ref_pic_list_idx[i] is represented by Ceil( Log2(num_ref_pic_lists_in_sps) ) bits.When not present, the value of ref_pic_list_idx[i] is inferred to be equal to 0. The value of ref_pic_list_idx[i] is in the range from 0 to num_ref_pic_lists_in_sps - 1, inclusive. num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that the syntax element num_ref_idx_active_minus1[1] is present for B slices. 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] are not present.

[0155] num_ref_idx_active_minus1[i], when present, specifies the value of the variable NumRefIdxActive[i] as follows: NumRefIdxActive[i] = num_ref_idx_active_minus1[i] + 1. The value of num_ref_idx_active_minus1[i] is in the range of 0 to 14, inclusive. The value of NumRefIdxActive[i] - 1 specifies the maximum reference index for reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, no reference index for reference picture list i may be used to decode the slice. For i equal to 0 or 1, when 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 inferred to be equal to num_ref_idx_default_active_minus1[0] + 1. When the current slice is a P slice, NumRefIdxActive[1] is inferred to be equal to 0. When the current slice is an I slice, both NumRefIdxActive[0] and NumRefIdxActive[1] are inferred to be equal to 0.

[0156] Alternatively, for i equal to 0 or 1, then the following applies: rplsIdx1 shall be set equal to ref_pic_list_sps_flag[i] ? ref_pic_list_idx[i] : num_ref_pic_lists_in_sps[i] and numRpEntries[i] shall be 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] shall be set equal to numRpEntries[i].

[0157] Reference Picture List Structure Semantics

[0158] The ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure may be present in an SPS or in a slice header. Depending on whether the syntax structure is included in a slice header or in an SPS, the following applies: If present in a slice header, the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure specifies a reference picture list for the current picture (the picture that contains the slice). Otherwise (present in an SPS), the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure specifies a candidate reference picture list, and the term "current picture" in the semantics specified in the remainder of this section refers to each picture that 1) has one or more slices with ref_pic_list_idx[i] equal to an index into the list of ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structures included in the SPS, and 2) is in a CVS that has the 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. When not present, the value of num_ltrp_entries[rplsIdx] is inferred to be equal to 0.

[0159] The variable NumEntriesInList[rplsIdx] is derived as follows: NumEntriesInList[rplsIdx] = num_strp_entries[rplsIdx] + num_ltrp_entries[rplsIdx]. The value of NumEntriesInList[rplsIdx] is in the range of 0 to sps_max_dec_pic_buffering_minus1, inclusive. 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 of the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure is a STRP entry. When not present, the value of lt_ref_pic_flag[rplsIdx][i] is inferred to be equal to 0. It is a compliance requirement of a bitstream that the sum of lt_ref_pic_flag[rplsIdx][i] for all values ​​of i in the range from 0 to NumEntriesInList[rplsIdx] - 1, inclusive, is equal to num_ltrp_entries[rplsIdx].delta_poc_st[rplsIdx][i] specifies the difference between the value of the picture order count of the current picture and the value of the picture order count of the picture referenced by the i-th entry when the i-th entry is the first STRP entry of the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure, or specifies the difference between the value of the picture order count of the picture referenced by the i-th entry and the value of the picture order count of the picture referenced by the previous STRP entry of the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure when the i-th entry is a STRP entry of the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure but is not the first STRP entry. The value of delta_poc_st[rplsIdx][i] is in the range from 0 to 215 - 1, inclusive. poc_lsb_lt[rplsIdx][i] specifies the value of the picture order count modulo MaxLtPicOrderCntLsb of the picture referenced by the i-th entry of the ref_pic_list_struct(rplsIdx, ltrpFlag) syntax structure. The length of the poc_lsb_lt[rplsIdx][i] syntax element is Log2(MaxLtPicOrderCntLsb) bits.

[0160] The overall decoding process specified as part of the detailed description of the first embodiment of the present disclosure is applied. The NAL unit decoding process is described. The NAL unit decoding process specified as part of the detailed description of the first embodiment of the present disclosure is applied.

[0161] A slice decoding process is provided.

[0162] Decoding Process for Picture Order Count

[0163] The decoding process for picture order counting specified as part of the detailed description of the first embodiment of the present disclosure is applied.

[0164] Decoding process for constructing a reference picture list

[0165] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. A reference picture is addressed by a reference index. The reference index is an index into a 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 in marking the reference pictures or in 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 checking bitstream conformance, but their derivation is not necessary for decoding of the current picture or pictures that follow the current picture in decoding order. For P slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of checking bitstream conformance, but its derivation is not necessary for decoding of the current picture or pictures that follow the current picture in decoding order.

[0166] 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( there exists a reference picture picA in DPB whose PicOrderCntVal is equal to RefPicPocList[i][j] ) RefPicList[i][j] = picA else RefPicList[i][j] = "no reference picture" pocBase = RefPicPocList[i][j] } else { if( there exists a reference picA in DPB where PicOrderCntVal & ( MaxLtPicOrderCntLsb - 1 ) is equal to poc_lsb_lt[RplsIdx[i]][j] ) RefPicList[i][j] = picA else RefPicList[i][j] = "no reference picture" } } }

[0167] For each i equal to 0 or 1, the following applies: The first NumRefIdxActive[i] entries of RefPicList[i] are called active entries of RefPicList[i], and the other entries of RefPicList[i] are called inactive entries of RefPicList[i]. Each entry of RefPicList[i][j] for j in the range from 0 to NumEntriesInList[RplsIdx[i]] - 1, inclusive, is called a STRP entry if lt_ref_pic_flag[RplsIdx[i]][j] is equal to 0, and is called a LTRP entry otherwise. It is possible for a particular picture to be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. It is also possible that a particular picture is referenced by more than one entry in RefPicList[0] or by more than one entry in RefPicList[1]. The active entries in RefPicList[0] and the active entries in RefPicList[1] collectively refer to all reference pictures that may be used for inter-prediction of the current picture and one or more pictures that follow the current picture in decoding order. The inactive entries in RefPicList[0] and the inactive entries in RefPicList[1] collectively refer to all reference pictures that are not used for inter-prediction of the current picture but may be used in inter-prediction of one or more pictures that follow the current picture in decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equal 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 equal to "no reference picture" should be ignored.For each active entry in RefPicList[0] or RefPicList[1] that is equal to "no reference picture", an unintended picture loss should be inferred.

[0168] It is a requirement of bitstream compliance that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[RplsIdx[i]] is greater than or equal to NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of 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: No inactive entry in RefPicList[0] or RefPicList[1] references the same picture as any other entry in RefPicList[0] or RefPicList[1]. A STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture do not reference the same picture. The current picture itself is not referenced by any entry in RefPicList[0] or RefPicList[1]. There is no LTRP entry in RefPicList[0] or RefPicList[1] such that the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is greater than or equal to 224. setOfRefPics shall be the set of unique pictures referenced by all entries of RefPicList[0] and all entries of RefPicList[1]. The number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1 and setOfRefPics is the same for all slices of the picture.

[0169] The decoding process for reference picture marking is considered.

[0170] This process is invoked once per picture after the decoding process for the decoding of the slice header and the construction of the reference picture list for the slice, but before the decoding of 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 may 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 removes another of these markings, if applicable. When a picture is said to be marked as "used for reference", this refers collectively to the picture being marked as "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 the Log2(MaxLtPicOrderCntLsb) LSBs of their PicOrderCntVal values.

[0171] 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 reference picture in the DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as "not used for reference".

[0172] 5 is an embodiment of a method 500 for decoding a coded video bitstream implemented by a video decoder (e.g., video decoder 30). Method 500 may be performed after a decoded bitstream is received directly or indirectly from a video encoder (e.g., video encoder 20). Method 500 may be performed to improve the decoding process (e.g., make the decoding process more efficient, faster, etc. than a normal decoding process). Thus, as a practical matter, the performance of the codec may be improved, which leads to a better user experience.

[0173] A parameter set indicated in a coded video bitstream is parsed at block 502. In an embodiment, the parameter set includes a set of syntax elements including a set of reference picture list structures.

[0174] A slice header of a current slice indicated in the coded video bitstream is parsed at block 504. In an embodiment, the slice header includes an index of a reference picture list structure among a set of reference picture list structures in the parameter set.

[0175] At block 506, a reference picture list for the current slice is derived. In an embodiment, the reference picture list is derived based on a set of syntax elements in the parameter set and an index of the reference picture list structure. In an embodiment, the order of the entries in the reference picture list structure is the same as the order of the corresponding reference pictures in the reference picture list. In an embodiment, the order is from zero to the indicated value. In an embodiment, the indicated value is from zero to the value indicated by sps_max_dec_pic_buffering_minus1.

[0176] At least one reconstructed block of the current slice is obtained in block 508. In an embodiment, the at least one reconstructed block of the current slice is reconstructed based on the reference picture list. After the reconstruction process, the video decoder can output a video or image. In an embodiment, the video or image may be displayed on a display of an electronic device (e.g., a smartphone, a tablet, a laptop, etc.).

[0177] In an embodiment, the reference picture list is designated RefPictList[0] or RefPictList[1]. In an embodiment, the reference picture list includes a list of reference pictures used for inter prediction. In an embodiment, the inter prediction is for a P slice or for a B slice. In an embodiment, a set of syntax elements from a parameter set is placed in a raw byte sequence payload (RBSP) of a network abstraction layer (NAL) unit.

[0178] A summary of alternative embodiments based on the first and second embodiments is given.

[0179] This section provides a brief overview of other alternative embodiments of the present disclosure. The overview is related to the description of the first embodiment. However, the basic concepts of the present disclosure regarding the following alternative embodiments are also applicable for implementation with the knowledge of the present disclosure regarding the second embodiment. Such implementation is in the same spirit as the way aspects are implemented with the knowledge of the first embodiment.

[0180] Semantics of differential POC for short-term reference picture entries

[0181] In one alternative embodiment of the present disclosure, the semantic of a syntax element that specifies a differential POC of the i-th entry of the reference picture list structure ref_pic_list_struct( ) is defined as the difference in POC between the current picture and the reference picture associated with the i-th entry. Some of the descriptions used herein relate to current drafts of the standard (e.g., working drafts of VVC) where only differences are shown or described. Deleted text is indicated by a strikethrough and any added text is highlighted.

[0182] The semantics of delta_poc_st[listIdx][rplsIdx][i] are defined as follows: delta_poc_st[listIdx][rplsIdx][i] specifies the difference between the value of the picture order count of the current picture and the value of the picture order count 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, inclusive.

[0183] The equations for the reference picture list construction process need to be updated: The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows:

[0184]

number

[0185] Signaling an entry in a long-term reference picture

[0186] In one alternative embodiment of the present disclosure, the entries for long-term reference pictures are not signaled in the same reference picture list structure that contains the entries for short-term reference pictures: the entries for long-term reference pictures are signaled in a separate structure, and for each entry of the structure, there is a syntax element that describes the intended location of the long-term reference picture for derivation of the corresponding entry index in the final reference picture list.

[0187] Sequence Parameter Set RBSP Syntax

[0188] [Table 13]

[0189] Slice Header Syntax

[0190] [Table 14]

[0191] Reference Picture List Structure Syntax

[0192] [Table 15]

[0193] Long-term reference picture list structure syntax

[0194] [Table 16]

[0195] Semantics of RBSP for sequence parameter sets

[0196] num_ref_pic_lists_lt_in_sps specifies the number of ref_pic_list_lt_struct(ltRplsIdx) syntax structures contained in the SPS. The value of num_ref_pic_lists_lt_in_sps is in the range of 0 to 64, inclusive. When not present, the value of num_ref_pic_lists_lt_in_sps is inferred to be equal to 0.

[0197] Slice header semantics

[0198] ref_pic_list_lt_idx[i] specifies an index into a list of ref_pic_list_lt_struct(ltRplsIdx) syntax structures contained in the active SPS used for the derivation of reference picture list i for 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 lies in the range from 0 to num_ref_pic_lists_lt_in_sps - 1, inclusive.

[0199] Reference Picture List Structure Semantics

[0200] The ref_pic_list_struct(listIdx, rplsIdx) syntax structure may be present in an SPS or in a slice header. Depending on whether the syntax structure is included in a slice header or in an SPS, the following applies: If present in a slice header, the ref_pic_list_struct(listIdx, rplsIdx) syntax structure specifies the listIdx of a short-term reference picture list for the current picture (the picture that contains the slice). Otherwise (present in the SPS), the ref_pic_list_struct(listIdx, rplsIdx) syntax structure specifies candidates for listIdx of the short-term reference picture list, and the term "current picture" in the semantics specified in the remainder of this section refers to each picture that 1) has one or more slices with ref_pic_list_idx[listIdx] equal to an index into the list of ref_pic_list_struct(listIdx, rplsIdx) syntax structures contained in the SPS, and 2) is in a CVS that has the SPS as its active SPS. num_strp_entries[listIdx][rplsIdx] specifies the number of STRP entries in the ref_pic_list_struct(listIdx, rplsIdx) syntax structure.

[0201]

number

[0202]

number

[0203]

number

[0204]

number

[0205]

number

[0206]

number

[0207] delta_poc_st[listIdx][rplsIdx][i] specifies the difference between the value of the picture order count of the current picture and the value of the picture order count of the picture referenced by the i-th entry when the i-th entry is the first STRP entry of the ref_pic_list_struct(listIdx, rplsIdx) syntax structure, or specifies the difference between the value of the picture order count of the picture referenced by the i-th entry and the value of the picture order count of the picture referenced by the previous STRP entry of the ref_pic_list_struct(listIdx, rplsIdx) syntax structure when the i-th entry is a STRP entry of the ref_pic_list_struct(listIdx, rplsIdx) syntax structure but is not the first STRP entry. The value of delta_poc_st[listIdx][rplsIdx][i] is in the range of -215 to 215 - 1, inclusive.

[0208]

number

[0209] Semantics of the long-term reference picture list structure

[0210] The ref_pic_list_lt_struct(ltRplsIdx) syntax structure may be present in an SPS or in a slice header. Depending on whether the syntax structure is included in a slice header or in an SPS, the following applies: If present in a slice header, the ref_pic_list_lt_struct(ltRplsIdx) syntax structure specifies the long-term reference picture list of the current picture (the picture that contains the slice). Otherwise (present in an SPS), the ref_pic_list_struct(listIdx, rplsIdx) syntax structure specifies candidates for the long-term reference picture list, and the term "current picture" in the semantics specified in the remainder of this section refers to each picture that 1) has one or more slices with ref_pic_list_lt_idx[i] equal to an index into the list of ref_pic_list_lt_struct(ltRplsIdx) syntax structures included in the SPS, and 2) is in a CVS that has the 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 value of the picture order count modulo MaxLtPicOrderCntLsb of the picture referenced by the i-th entry of 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 of the ref_pic_list_lt_struct(rplsIdx) syntax structure in the reference picture list after construction of the reference picture list. The length of the lt_pos_idx[rplsIdx][i] syntax element is Log2( sps_max_dec_pic_buffering_minus1 + 1 ) bits.When num_ltrp_entries[ltRplsIdx] exceeds 1, poc_lsb_lt[rplsIdx][i] and lt_pos_idx[rplsIdx][i] are in descending order of the values ​​of lt_pos_idx[rplsIdx][i].

[0211] The decoding process is explained.

[0212] Decoding process for constructing a reference picture list

[0213] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. A reference picture is addressed by a reference index. The reference index is an index into a 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 in marking the reference pictures or in 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 checking bitstream conformance, but their derivation is not necessary for decoding of the current picture or pictures that follow the current picture in decoding order. For P slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of checking bitstream conformance, but its derivation is not necessary for decoding of the current picture or pictures that follow the current picture in decoding order. The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows:

[0214]

number

[0215] For each i equal to 0 or 1, the following applies: The first NumRefIdxActive[i] entries of RefPicList[i] are called active entries of RefPicList[i], and the other entries of RefPicList[i] are called inactive entries of RefPicList[i]. Each entry of RefPicList[i][j] for j in the range from 0 to NumEntriesInList[i][RplsIdx[i]] - 1, inclusive, is called a STRP entry if lt_ref_pic_flag[i][RplsIdx[i]][j] is equal to 0, and is called a LTRP entry otherwise. It is possible for a particular picture to be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. It is also possible that a particular picture is referenced by more than one entry in RefPicList[0] or by more than one entry in RefPicList[1]. The active entries in RefPicList[0] and the active entries in RefPicList[1] collectively refer to all reference pictures that may be used for inter-prediction of the current picture and one or more pictures that follow the current picture in decoding order. The inactive entries in RefPicList[0] and the inactive entries in RefPicList[1] collectively refer to all reference pictures that are not used for inter-prediction of the current picture but may be used in inter-prediction of one or more pictures that follow the current picture in decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equal 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 equal to "no reference picture" should be ignored.For each active entry in RefPicList[0] or RefPicList[1] that is equal to "no reference picture", an unintended picture loss should be inferred.

[0216] It is a requirement of bitstream compliance that the following constraints apply: For each i equal to 0 or 1, the number of entries in RefPicList[i] is greater than or equal to NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of 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: No inactive entry in RefPicList[0] or RefPicList[1] references the same picture as any other entry in RefPicList[0] or RefPicList[1]. A STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture do not reference the same picture. The current picture itself is not referenced by any entry in RefPicList[0] or RefPicList[1]. There is no LTRP entry in RefPicList[0] or RefPicList[1] such that the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is greater than or equal to 224. setOfRefPics shall be the set of unique pictures referenced by all entries of RefPicList[0] and all entries of RefPicList[1]. The number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1 and setOfRefPics is the same for all slices of the picture.

[0217] Signaling of the number of short-term reference picture entries is considered.

[0218] In one alternative embodiment of the present disclosure, the syntax element specifying the number of entries related to 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]. The change has two effects on the signaling of reference picture lists. The change may save bits for signaling the number of entries related to short-term reference pictures in the reference picture list structure since the element is coded using ue(v). The change implicitly imposes a constraint such that each reference picture list contains at least one short-term reference picture. To accommodate this idea, some changes are needed relative to the first embodiment.

[0219] Regarding the signaling of reference picture lists in the slice header, only the necessary reference picture lists are signaled according to the slice type, i.e., one reference picture list (i.e., reference picture list 0) is signaled for an I or P slice, and two reference picture lists (i.e., both reference picture list 0 and reference picture list 1) are signaled for a B slice. The syntax of the slice header is modified as follows:

[0220] [Table 17]

[0221] By applying the above modification of the slice header (i.e., reference picture list 0 for I or P slices and reference picture 0 and reference picture 1 for B slices), it prevents the scheme from running into problems when there is only one short-term reference picture for a P slice. However, duplicate short-term reference pictures cannot be signaled in reference picture list 0 and reference picture list 1, and the entries of reference picture list 1 are inactive entries, since the number of active entries of reference picture list 1 must be equal to 0. The semantics of num_strp_entries_minus1[listIdx][rplsIdx] are modified as follows: num_strp_entries_minus1[listIdx][rplsIdx] plus 1 specifies the number of STRP entries of 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 + num_ltrp_entries[listIdx][rplsIdx]. The value of NumRefPicEntries[listIdx][rplsIdx] is in the range 1 to sps_max_dec_pic_buffering_minus1, inclusive.

[0222] Allowing inclusion of the current picture in the reference picture list

[0223] In one alternative embodiment of the present disclosure, the current picture is allowed to be included in its reference picture list. To support this feature, no syntax and semantic changes are required relative to those described in the first and second embodiments. However, the bitstream compliance constraints described in the decoding process for constructing the reference picture list need to be modified as follows. It is a bitstream compliance requirement that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is greater than or equal to NumRefIdxActive[i]. The picture referenced by each active entry of RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of the current picture. Optionally, the following constraints may be further specified: The entry index of any inactive entry of RefPicList[0] or RefPicList[1] is not used as a reference index for the decoding of the current picture. Optionally, the following constraints may be further specified. An inactive entry in RefPicList[0] or RefPicList[1] does not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. An STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture do not reference the same picture.

number

[0224] Using different POC LSB bits for LTRP entries in the reference picture list

[0225] In one alternative embodiment of the present disclosure, the number of bits used to identify long-term reference pictures in the reference picture list structure is allowed to differ between Reference Picture List 0 and Reference Picture List 1. To support this feature, the following modifications are required:

[0226] [Table 18]

[0227] additional_lt_poc_lsb[i] specifies the value of the variable MaxLtPicOrderCntLsb[i] used in the decoding process for the reference picture list listIdx equal to i as follows: 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 in the range from 0 to 32 - log2_max_pic_order_cnt_lsb_minus4 - 4, inclusive. When not present, the value of additional_lt_poc_lsb[i] is inferred to be equal to 0.

[0228] poc_lsb_lt[listIdx][rplsIdx][i] specifies the value of the picture order count modulo MaxLtPicOrderCntLsb[listIdx] of the picture referenced by the i-th entry of 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.

[0229] 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( there exists a reference picture picA in DPB whose PicOrderCntVal is equal to RefPicPocList[i][j] ) RefPicList[i][j] = picA else RefPicList[i][j] = "no reference picture" pocBase = RefPicPocList[i][j] } else { if( there exists a reference picA in DPB where PicOrderCntVal & ( MaxLtPicOrderCntLsb[i] - 1 ) is equal to poc_lsb_lt[i][RplsIdx[i]][j] ) RefPicList[i][j] = picA else RefPicList[i][j] = "no reference picture" } } }

[0230] Use the same ref_pic_list_sps_flag for reference picture lists 0 and 1

[0231] 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 picture lists. Such an alternative constrains that either both reference picture lists are derived based on the 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 modifications are needed:

[0232] [Table 19]

[0233]

number

[0234] The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows.

[0235]

number

[0236] Signaling Differential POC Most Significant Bit (MSB) for Long-Term Reference Picture Entries

[0237] In one alternative embodiment of the present disclosure, instead of using additional bits to represent the POC LSB of the entries of long-term reference pictures 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 points to 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:

[0238] [Table 20]

[0239] [Table 21]

[0240] [Table 22]

[0241]

number

[0242]

number

[0243]

number

[0244] The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows.

[0245]

number

[0246] Alternatively, the semantics of delta_poc_msb_cycle_lt[listIdx][i] can be expressed as a difference of differences, such that the construction of the reference picture lists can be updated as follows: The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows:

[0247]

number

[0248] It is a requirement of bitstream compliance that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is greater than or equal to NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of 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: No inactive entry in RefPicList[0] or RefPicList[1] references the same picture as any other entry in RefPicList[0] or RefPicList[1]. A STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture do not reference the same picture. The current picture itself is not referenced by any entry in RefPicList[0] or RefPicList[1]. There is no LTRP entry in RefPicList[0] or RefPicList[1] such that the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is greater than or equal to 224. setOfRefPics shall be the set of unique pictures referenced by all entries of RefPicList[0] and all entries of RefPicList[1]. The number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1 and setOfRefPics is the same for all slices of the picture.

[0249] 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] with delta_poc_msb_present_flag[listIdx][i] equal to 1, then the LTRP is identified by its PicOrderCntVal value, otherwise the LTRP is identified by the Log2(MaxPicOrderCntLsb) LSB of its PicOrderCntVal value.

[0250] Alternative 1 for signaling differential POC MSB for long-term reference picture entries

[0251] This embodiment provides an alternative to the embodiment described in the previous section. Similar to the idea of ​​the previous section, instead of using additional bits to represent the POC LSB of a long-term reference picture in ref_pic_list_struct( ), the POC MSB cycle is signaled to distinguish long-term reference pictures. However, in this alternative, when signaled, the POC MSB cycle information is not signaled in ref_pic_list_struct( ), instead, when the POC MSB cycle information is needed, the POC MSB cycle information is signaled in the slice header. The ref_pic_list_struct( ) syntax structure may be signaled in the SPS and in the slice header.

[0252] [Table 23]

[0253] [Table 24A] [Table 24B]

[0254] A delta_poc_msb_present_flag[i][j] equal to 1 specifies that delta_poc_msb_cycle_lt[i][j] is present. A delta_poc_msb_present_flag[i][j] equal to 0 specifies that delta_poc_msb_cycle_lt[i][j] is not present. When NumLtrpEntries[i] is greater than 0 and for the j-th LTRP entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure, there are two or more reference pictures in the DPB whose PicOrderCntVal modulo MaxPicOrderCntLsb is equal to poc_lsb_lt[i][rplsIdx][jj] when the slice header is decoded, where jj is the entry index of the entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure that is the j-th LTRP entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure, then delta_poc_msb_present_flag[i][j] is equal to 1. Otherwise, the value of delta_poc_msb_cycle_lt[i][j] is inferred 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 of the jth LTRP entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure. When delta_poc_msb_cycle_lt[i][j] is not present, delta_poc_msb_cycle_lt[i][j] is inferred to be equal to 0.

[0255] [Table 25A] [Table 25B]

[0256] delta_poc_msb_present_flag[i][j] equal to 1 specifies that delta_poc_msb_cycle_lt[i][j] is present. delta_poc_msb_present_flag[i][j] equal to 0 specifies that delta_poc_msb_cycle_lt[i][j] is not present. When NumLtrpEntries[i] is greater than 0 and there are two or more reference pictures in the DPB with PicOrderCntVal modulo MaxPicOrderCntLsb equal to poc_lsb_lt[i][rplsIdx][j] when the slice header is decoded, delta_poc_msb_present_flag[i][j] is equal to 1. When not present, the value of delta_poc_msb_cycle_lt[i][j] is inferred 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 of the jth entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure. When delta_poc_msb_cycle_lt[i][j] is not present, delta_poc_msb_cycle_lt[i][j] is inferred to be equal to 0.

number

[0257] Modifications to the decoding process regarding picture order counting.

number

[0258] For slice header design 1, reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows:

[0259]

number

[0260] Alternatively, for slice header design 1, the semantics of delta_poc_msb_cycle_lt[listIdx][i] can be expressed as a difference of differences, such that the construction of the reference picture lists can be updated as follows: The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows:

[0261]

number

[0262] For slice header design 2, reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows:

[0263]

number

[0264] Alternatively, for slice header design 2, the semantics of delta_poc_msb_cycle_lt[listIdx][i] can be expressed as a difference of differences, such that the construction of the reference picture lists can be updated as follows: The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows:

[0265]

number

[0266] It is a requirement of bitstream compliance that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is greater than or equal to NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of 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: No inactive entry in RefPicList[0] or RefPicList[1] references the same picture as any other entry in RefPicList[0] or RefPicList[1]. A STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture do not reference the same picture. The current picture itself is not referenced by any entry in RefPicList[0] or RefPicList[1]. There is no LTRP entry in RefPicList[0] or RefPicList[1] such that the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is greater than or equal to 224. setOfRefPics shall be the set of unique pictures referenced by all entries of RefPicList[0] and all entries of RefPicList[1]. The number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1 and setOfRefPics is the same for all slices of the picture.

[0267] 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] with delta_poc_msb_present_flag[i][j] equal to 1, then the LTRP is identified by its PicOrderCntVal value; otherwise, the LTRP is identified by the Log2(MaxPicOrderCntLsb) LSB of its PicOrderCntVal value.

[0268] Alternative 2 for signaling differential POC MSB for long-term reference picture entries

[0269] In one alternative embodiment of the present disclosure, the disclosure described in the first embodiment or the second embodiment may be combined with the above-mentioned embodiments referred to as "signaling of differential POC MSB for long-term reference picture entries" and "alternative 1 of signaling of differential POC MSB for long-term reference picture entries", respectively. The aspects of the present disclosure that are combined are the signaling of additional_lt_poc_lsb (i.e., from the first embodiment or the second embodiment) and POC MSB cycle information (i.e., from the above-mentioned embodiments referred to as "signaling of differential POC MSB for long-term reference picture entries" and "alternative 1 of signaling of differential POC MSB for long-term reference picture entries"). An example of how the combination of the first embodiment and the above-mentioned embodiment referred to as "alternative 1 of signaling of differential POC MSB for long-term reference picture entries" may be performed is shown as follows:

[0270] [Table 26A] [Table 26B]

[0271] A delta_poc_msb_present_flag[i][j] equal to 1 specifies that delta_poc_msb_cycle_lt[i][j] is present. A delta_poc_msb_present_flag[i][i] equal to 0 specifies that delta_poc_msb_cycle_lt[i][j] is not present. When NumLtrpEntries[i] is greater than 0 and for the j-th LTRP entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure, there are two or more reference pictures in the DPB whose PicOrderCntVal modulo MaxPicOrderCntLsb is equal to poc_lsb_lt[i][rplsIdx][jj] when the slice header is decoded, where jj is the entry index of the entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure that is the j-th LTRP entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure, then delta_poc_msb_present_flag[i][j] is equal to 1. Otherwise, the value of delta_poc_msb_cycle_lt[i][j] is inferred 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 of the jth LTRP entry of the ref_pic_list_struct(i, rplsIdx, 1) syntax structure. When delta_poc_msb_cycle_lt[i][j] is not present, delta_poc_msb_cycle_lt[i][j] is inferred to be equal to 0.

[0272] Modifications to the decoding process regarding picture order counting.

number

[0273] 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( there exists a reference picture picA in DPB whose PicOrderCntVal is equal to 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 && PicOrderCntVal & ( MaxLtPicOrderCntLsb - 1 ) is equal to poc_lsb_lt[i][RplsIdx[i]][j] there exists reference picture picA in DPB ) RefPicList[i][j] = picA else if( delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 1 && there exists a reference picture picA in DPB whose 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" } } }

[0274] Alternatively, the semantics of delta_poc_msb_cycle_lt[listIdx][i] can be expressed as a difference of differences, such that the construction of the reference picture lists 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( there exists a reference picture picA in DPB whose PicOrderCntVal is equal to 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 && PicOrderCntVal & ( MaxLtPicOrderCntLsb - 1 ) is equal to poc_lsb_lt[i][RplsIdx[i]][j] there exists reference picture picA in DPB ) RefPicList[i][j] = picA else if( delta_poc_msb_cycle_lt[i][msbCycleIdx] is equal to 1 && there exists a reference picture picA in DPB whose 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" } } }

[0275] It is a requirement of bitstream compliance that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is greater than or equal to NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of 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: No inactive entry in RefPicList[0] or RefPicList[1] references the same picture as any other entry in RefPicList[0] or RefPicList[1]. A STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture do not reference the same picture. The current picture itself is not referenced by any entry in RefPicList[0] or RefPicList[1]. There is no LTRP entry in RefPicList[0] or RefPicList[1] such that the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is greater than or equal to 224. setOfRefPics shall be the set of unique pictures referenced by all entries of RefPicList[0] and all entries of RefPicList[1]. The number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1 and setOfRefPics is the same for all slices of the picture.

[0276] 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] with delta_poc_msb_present_flag[i][j] equal to 1, then the LTRP is identified by its PicOrderCntVal value, otherwise the LTRP is identified by the Log2(MaxLtPicOrderCntLsb) LSB of its PicOrderCntVal value.

[0277] Signaling the reference picture list in the slice header always in a way that distinguishes between short-term and long-term reference pictures

[0278] This section describes another alternative embodiment of the present disclosure. The description is related to the latest VVC WD (i.e., only the differences to the latest VVC WD of JVET-K1001-v1 are described, but the text of the latest VVC WD that is not described below applies as is). This alternative embodiment is 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 reference pictures' 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. Furthermore, the number of bits used to represent the POC LSBs for identifying short-term and long-term reference pictures may be different.

[0279] NAL unit header syntax

[0280] [Table 27]

[0281] Sequence Parameter Set RBSP Syntax

[0282] [Table 28]

[0283] Picture Parameter Set RBSP Syntax

[0284] [Table 29]

[0285] Slice Header Syntax

[0286] [Table 30]

[0287] Reference Picture List Structure Syntax

[0288] [Table 31]

[0289] NAL unit header semantics

[0290] forbidden_zero_bit is equal to 0. nal_unit_type specifies the type of RBSP data structure contained in the NAL unit.

[0291] [Table 32]

[0292] The value of nuh_temporal_id_plus1 minus 1 specifies a temporal identifier for the NAL unit. The value of nuh_temporal_id_plus1 is not equal to 0. The variable TemporalId is specified as follows: TemporalId = nuh_temporal_id_plus1 - 1.

[0293] 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 of a coded picture or access unit is the value of TemporalId of the VCL NAL units 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 the access unit containing the 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 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 of the TemporalId values ​​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 an SEI NAL unit may contain information that applies to a subset of the bitstream that includes access units whose TemporalId value is greater than the TemporalId of the access unit that contains the supplemental enhancement information (SEI) NAL unit. nuh_reserved_zero_7bits is equal to '0000000'.Other values ​​of nuh_reserved_zero_7bits may be specified in the future by ITU_T | ISO / IEC. Decoders shall ignore (i.e., remove from the bitstream and discard) NAL units that have a value of nuh_reserved_zero_7bits that is not equal to '0000000'.

[0294] Semantics of RBSP for sequence parameter sets

[0295] 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 )

[0296] The value of log2_max_pic_order_cnt_lsb_minus4 ranges from 0 to 12, inclusive. The value of sps_max_dec_pic_buffering_minus1 plus 1 specifies the maximum required size of the decoded picture buffer for CVS in units of picture storage buffer. The value of sps_max_dec_pic_buffering_minus1 ranges from 0 to MaxDpbSize - 1, inclusive, where MaxDpbSize is specified elsewhere. additional_st_poc_lsb specifies the value of the variable MaxStPicOrderCntLsb used in the decoding process for the reference picture list, as follows: MaxStPicOrderCntLsb = 2 ( log2_max_pic_order_cnt_lsb_minus4 + 4 + additional_st_poc_lsb )

[0297] The value of additional_st_poc_lsb is in the range from 0 to 32 - log2_max_pic_order_cnt_lsb_minus4 - 4, inclusive. long_term_ref_pics_flag equal to 0 specifies that the LTRP is not used for inter prediction of any coded pictures in the CVS. long_term_ref_pics_flag equal to 1 specifies that the LTRP may be used for inter prediction 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 in the range from 0 to 32 - log2_max_pic_order_cnt_lsb_minus4 - 4 - additional_st_poc_lsb, inclusive. When not present, the value of additional_lt_poc_lsb is inferred to be equal to 0.

[0298] Semantics of the RBSP of a picture parameter set

[0299] The value of num_ref_idx_default_active_minus1[i] plus 1 specifies the inferred value of the variable NumRefIdxActive[0] for a P or B slice with num_ref_idx_active_override_flag equal to 0 when i is equal to 0, and specifies the inferred value of NumRefIdxActive[1] for a B slice with num_ref_idx_active_override_flag equal to 0 when i is equal to 1. The value of num_ref_idx_default_active_minus1[i] lies in the range from 0 to 14, inclusive.

[0300] Slice header semantics

[0301] When present, the value of each of the syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb in the slice header shall be the same in all slice headers of a coded picture. slice_type specifies the coding type of the slice according to Table 7-3.

[0302] [Table 33]

[0303] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type is equal to 2.

[0304] 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 in the range from 0 to MaxPicOrderCntLsb - 1, inclusive. When slice_pic_order_cnt_lsb is not present, slice_pic_order_cnt_lsb is inferred to be equal to 0. num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that the syntax element num_ref_idx_active_minus1[1] is present for B slices. 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] are not present. num_ref_idx_active_minus1[i], when present, specifies the value of the variable NumRefIdxActive[i] as follows: NumRefIdxActive[i] = num_ref_idx_active_minus1[i] + 1

[0305] The value of num_ref_idx_active_minus1[i] is in the range of 0 to 14, inclusive. A value of NumRefIdxActive[i] minus 1 specifies the maximum reference index for reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, no reference index for reference picture list i may be used to decode the slice. For i equal to 0 or 1, when 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 inferred to be equal to num_ref_idx_default_active_minus1[0] + 1. When the current slice is a P slice, NumRefIdxActive[1] is inferred to be equal to 0. When the current slice is an I slice, both NumRefIdxActive[0] and NumRefIdxActive[1] are inferred to be equal to 0. Alternatively, for i equal to 0 or 1, after the above the following applies: Let rplsIdx1 be set equal to ref_pic_list_sps_flag[i] ? ref_pic_list_idx[i] : num_ref_pic_lists_in_sps[i], and let numRpEntries[i] be 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 equal to numRpEntries[i].

[0306] Reference Picture List Structure Semantics

[0307] The ref_pic_list_struct(listIdx, ltrpFlag) syntax structure may be present in the slice header. If the ref_pic_list_struct(listIdx, ltrpFlag) syntax structure is present in the slice header, it specifies the listIdx of the reference picture list of the current picture (the picture that contains 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] is inferred to be equal to 0. The variable NumEntriesInList[listIdx] is derived as follows: NumEntriesInList[listIdx] = num_strp_entries[listIdx] + num_ltrp_entries[listIdx]

[0308] The value of NumEntriesInList[listIdx] is in the range of 0 to sps_max_dec_pic_buffering_minus1, inclusive. lt_ref_pic_flag[listIdx][i] equal to 1 specifies that the i-th entry of 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 of the ref_pic_list_struct(listIdx, ltrpFlag) syntax structure is a STRP entry. When not present, the value of lt_ref_pic_flag[listIdx][i] is inferred to be equal to 0. It is a conforming bitstream requirement that the sum of lt_ref_pic_flag[listIdx][i] for all values ​​of i in the range from 0 to NumEntriesInList[listIdx] - 1, inclusive, is equal to num_ltrp_entries[listIdx]. poc_lsb_st[listIdx][i] specifies the value of the picture order count modulo MaxStPicOrderCntLsb of the picture referenced by the i-th entry of 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 value of the picture order count modulo MaxLtPicOrderCntLsb of the picture referenced by the i-th entry of 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.

[0309] The decoding process is considered.

[0310] Overall Decoding Process

[0311] The decoding process operates as follows for the current picture CurrPic. The decoding of NAL units is specified below. The process below specifies the following decoding process using syntax elements from the slice header layer and above. Variables and functions related to picture order count are derived. This needs to be called only for the first slice of a picture. At the beginning of the decoding process for each slice of a non-IRAP picture, the decoding process for construction of reference picture lists is called for the derivation of reference picture list 0 (RefPicList[0]) and reference picture list 1 (RefPicList[1]). The decoding process for marking of reference pictures is called, where 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 a picture. The decoding processes for coding tree units, scaling, transform, in-loop filtering, etc. are called. After all slices of the current picture are decoded, the current decoded picture is marked as "used for short-term reference".

[0312] NAL unit decoding process

[0313] 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 structures encapsulated in 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.

[0314] Slice Decoding Process

[0315] Decoding Process for Picture Order Count

[0316] The output of this process is PicOrderCntVal, the picture order count of the current picture. The picture order count is used to identify the picture for deriving motion parameters in merge mode and motion vector prediction and for decoder compliance checking. Each coded picture is associated with a picture order count variable, denoted PicOrderCntVal. When the current picture is not an IRAP picture, the variables prevPicOrderCntLsb and prevPicOrderCntMsb are derived as follows: Let prevTid0Pic be the previous picture in decoding order with TemporalId equal to 0. The variable prevPicOrderCntLsb is set equal to slice_pic_order_cnt_lsb of prevTid0Pic. The variable prevPicOrderCntMsb is set equal to 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 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

[0317] PicOrderCntVal is derived as follows: PicOrderCntVal = PicOrderCntMsb + slice_pic_order_cnt_lsb

[0318] Since slice_pic_order_cnt_lsb is inferred to be 0 for IRAP pictures and both prevPicOrderCntLsb and prevPicOrderCntMsb are set equal to 0, all IRAP pictures have PicOrderCntVal equal to 0. The value of PicOrderCntVal is in the range of -231 to 231 - 1, inclusive. In one CVS, the PicOrderCntVal values ​​for any two coded pictures are not the same. At any instant during the decoding process, the values ​​of PicOrderCntVal & (MaxStPicOrderCntLsb - 1) for any two short-term reference pictures in the DPB are not the same. At any instant during the decoding process, the values ​​of PicOrderCntVal & (MaxLtPicOrderCntLsb - 1) for any two reference pictures in the DPB are not the same.

[0319] The function PicOrderCnt(picX) is specified as follows: PicOrderCnt(picX) = PicOrderCntVal of picture picX

[0320] The function DiffPicOrderCnt(picA, picB) is specified as follows: DiffPicOrderCnt(picA, picB) = PicOrderCnt(picA) - PicOrderCnt(picB)

[0321] The bit stream is -2 15 and 2 15 - 1 including -2 15 From 2 15 - It does not include data that would result in a value of DiffPicOrderCnt(picA, picB) used in the decoding process that is not within the range of 1 to 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.

[0322] Decoding process for constructing a reference picture list

[0323] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. A reference picture is addressed by a reference index. The reference index is an index into a 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 in marking the reference pictures or in 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 checking bitstream conformance, but their derivation is not necessary for decoding of the current picture or pictures that follow the current picture in decoding order. For P slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of checking bitstream conformance, but its derivation is not necessary for decoding of the current picture or pictures that follow the current picture in decoding order.

[0324] 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( there exists a reference picA in DPB where PicOrderCntVal & ( MaxLtPicOrderCntLsb - 1 ) is equal to 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( there exists a short-term reference picture picA in DPB with PicOrderCntVal & ( MaxStPicOrderCntLsb - 1 ) equal to poc_lsb_st[i][j] ) RefPicList[i][j] = picA else RefPicList[i][j] = "no reference picture" } } }

[0325] For each i equal to 0 or 1, the following applies:

[0326] The first NumRefIdxActive[i] entries of RefPicList[i] are called active entries of RefPicList[i], and the other entries of RefPicList[i] are called inactive entries of RefPicList[i]. Each entry of RefPicList[i][j], for j in the range from 0 to NumEntriesInList[i] - 1, inclusive, is called a STRP entry if lt_ref_pic_flag[i][j] is equal to 0, and a LTRP entry otherwise. It is possible for a particular picture to be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. It is also possible for a particular picture to be referenced by more than one entry in RefPicList[0] or by more than one entry in RefPicList[1]. The active entries of RefPicList[0] and the active entries of RefPicList[1] collectively refer to all reference pictures that may be used for inter-prediction of the current picture and one or more pictures following the current picture in decoding order. The inactive entries of RefPicList[0] and the inactive entries of RefPicList[1] collectively refer to all reference pictures that are not used for inter-prediction of the current picture but may be used in inter-prediction of one or more pictures following the current picture in decoding order. There may be one or more entries of RefPicList[0] or RefPicList[1] that are equal to "no reference picture" because the corresponding picture does not exist in the DPB. Each inactive entry of RefPicList[0] or RefPicList[0] that is equal to "no reference picture" should be ignored.For each active entry in RefPicList[0] or RefPicList[1] that is equal to "no reference picture", an unintended picture loss should be inferred.

[0327] It is a requirement of bitstream compliance that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[i] is greater than or equal to NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of 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: No inactive entry in RefPicList[0] or RefPicList[1] references the same picture as any other entry in RefPicList[0] or RefPicList[1]. A STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture do not reference the same picture. The current picture itself is not referenced by any entry in RefPicList[0] or RefPicList[1]. There is no LTRP entry in RefPicList[0] or RefPicList[1] such that the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is greater than or equal to 224. setOfRefPics shall be the set of unique pictures referenced by all entries of RefPicList[0] and all entries of RefPicList[1]. The number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1 and setOfRefPics is the same for all slices of the picture.

[0328] Decoding process for reference picture marking

[0329] This process is invoked once per picture after the decoding process for the decoding of the slice header and the construction of the reference picture list for the slice, but before the decoding of 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 may 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 removes another of these markings, if applicable. When a picture is said to be marked as "used for reference", this refers collectively to the picture being marked as "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". The STRPs are identified by the Log2(MaxStPicOrderCntLsb) LSBs of their PicOrderCntVal values. The LTRPs are identified by the Log2(MaxLtPicOrderCntLsb) LSBs of their PicOrderCntVal values.

[0330] 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 reference picture in the DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as "not used for reference".

[0331] Signaling the reference picture list always in the slice header without distinguishing between short-term and long-term reference pictures

[0332] This section describes another alternative embodiment of the present disclosure. The description is related to the latest VVC WD (i.e., only the differences to the latest VVC WD of JVET-K1001-v1 are described, but the text of the latest VVC WD that is not described below applies as is). This alternative embodiment is summarized as follows: The reference picture list structure is signaled only in the slice header. No distinction is made between short-term and long-term reference pictures. All reference pictures are simply called reference pictures. 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.

[0333] Abbreviations. The text of section 4 of the VVC WD applies.

[0334] NAL unit header syntax

[0335] [Table 34]

[0336] Sequence Parameter Set RBSP Syntax

[0337] [Table 35]

[0338] Picture Parameter Set RBSP Syntax

[0339] [Table 36]

[0340] Slice Header Syntax

[0341] [Table 37]

[0342] Reference Picture List Structure Syntax

[0343] [Table 38]

[0344] NAL unit header semantics

[0345] forbidden_zero_bit is equal to 0. nal_unit_type specifies the type of RBSP data structure contained in the NAL unit.

[0346] [Table 39]

[0347] The value of nuh_temporal_id_plus1 minus 1 specifies a temporal identifier for the NAL unit. The value of nuh_temporal_id_plus1 is not equal to 0. The variable TemporalId is specified as follows: TemporalId = nuh_temporal_id_plus1 - 1

[0348] 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 of a coded picture or access unit is the value of TemporalId of the VCL NAL unit of the coded picture or access unit. The value of TemporalId for non-VCL NAL units is constrained as follows:

[0349] If nal_unit_type is equal to SPS_NUT, 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, 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 of the TemporalId values ​​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 since 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 an SEI NAL unit may contain information that applies to a subset of the bitstream that includes access units whose TemporalId value is greater than the TemporalId of the access unit that contains the SEI NAL unit. nuh_reserved_zero_7bits is equal to '0000000'. Other values ​​of nuh_reserved_zero_7bits may be specified in the future by ITU_T | ISO / IEC. Decoders shall ignore (i.e., remove from the bitstream and discard) NAL units that have a value of nuh_reserved_zero_7bits not equal to '0000000'.

[0350] Semantics of RBSP for sequence parameter sets

[0351] 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 )

[0352] The value of log2_max_pic_order_cnt_lsb_minus4 ranges from 0 to 12, inclusive. The value of sps_max_dec_pic_buffering_minus1 plus 1 specifies the maximum required size of the decoded picture buffer for CVS in units of picture storage buffer. The value of sps_max_dec_pic_buffering_minus1 ranges from 0 to MaxDpbSize - 1, inclusive, where MaxDpbSize is specified elsewhere. additional_ref_poc_lsb specifies the value of the variable MaxRefPicOrderCntLsb used in the decoding process for the reference picture list, as follows: MaxRefPicOrderCntLsb = 2 ( log2_max_pic_order_cnt_lsb_minus4 + 4 + additional_ref_poc_lsb )

[0353] The value of additional_ref_poc_lsb is in the range 0 to 32 - log2_max_pic_order_cnt_lsb_minus4 - 4, inclusive.

[0354] Semantics of the RBSP of a picture parameter set

[0355] The value of num_ref_idx_default_active_minus1[i] plus 1 specifies the inferred value of the variable NumRefIdxActive[0] for a P or B slice with num_ref_idx_active_override_flag equal to 0 when i is equal to 0, and specifies the inferred value of NumRefIdxActive[1] for a B slice with num_ref_idx_active_override_flag equal to 0 when i is equal to 1. The value of num_ref_idx_default_active_minus1[i] lies in the range from 0 to 14, inclusive.

[0356] Slice header semantics

[0357] When present, the value of each of the slice header syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb shall be the same in all slice headers of a coded picture. ... slice_type specifies the coding type of the slice according to Table 7-3.

[0358] [Table 40]

[0359] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type is 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 in the range from 0 to MaxPicOrderCntLsb - 1, inclusive. When slice_pic_order_cnt_lsb is not present, slice_pic_order_cnt_lsb is inferred to be equal to 0. num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that the syntax element num_ref_idx_active_minus1[1] is present for B slices. 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] are not present. num_ref_idx_active_minus1[i], when present, specifies the value of the variable NumRefIdxActive[i] as follows: NumRefIdxActive[i] = num_ref_idx_active_minus1[i] + 1

[0360] The value of num_ref_idx_active_minus1[i] is in the range of 0 to 14, inclusive. A value of NumRefIdxActive[i] minus 1 specifies the maximum reference index for reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, no reference index for reference picture list i may be used to decode the slice. For i equal to 0 or 1, when 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 inferred to be equal to num_ref_idx_default_active_minus1[0] + 1. When the current slice is a P slice, NumRefIdxActive[1] is inferred to be equal to 0. When the current slice is an I slice, both NumRefIdxActive[0] and NumRefIdxActive[1] are inferred to be equal to 0. Alternatively, for i equal to 0 or 1, after the above the following applies: Let rplsIdx1 be set equal to ref_pic_list_sps_flag[i] ? ref_pic_list_idx[i] : num_ref_pic_lists_in_sps[i], and let numRpEntries[i] be 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 equal to numRpEntries[i].

[0361] Reference Picture List Structure Semantics

[0362] The ref_pic_list_struct(listIdx) syntax structure may be present in a slice header. If the ref_pic_list_struct(listIdx) syntax structure is present in a slice header, it specifies the listIdx of the reference picture list of the current picture (the picture that contains 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: NumRefPicEntriesInRpl[listIdx] = num_ref_entries[listIdx]

[0363] The value of NumRefPicEntries[listIdx] is in the range of 0 to sps_max_dec_pic_buffering_minus1, inclusive. poc_ref_lsb[listIdx][i] specifies the value of MaxRefPicOrderCntLsb, modulo the picture order count of the picture referenced by the i-th entry of the ref_pic_list_struct(listIdx) syntax structure. The length of the poc_ref_lsb[listIdx][i] syntax element is Log2(MaxRefPicOrderCntLsb) bits.

[0364] The decoding process is considered.

[0365] Overall Decoding Process

[0366] The decoding process operates as follows for the current picture CurrPic: The decoding of NAL units is specified below. The process below specifies the following decoding process using syntax elements from the slice header layer and above: Variables and functions related to picture order count are derived. This needs to be called only for the first slice of a picture. At the beginning of the decoding process for each slice of a non-IRAP picture, the decoding process for construction of reference picture lists is called for the derivation of reference picture list 0 (RefPicList[0]) and reference picture list 1 (RefPicList[1]). The decoding process for marking of reference pictures is called, where reference pictures may be marked as "not used for reference". This needs to be called only for the first slice of a picture. The decoding processes for coding tree units, scaling, transform, in-loop filtering, etc. are called. After all slices of the current picture are decoded, the current decoded picture is marked as "used for reference".

[0367] NAL unit decoding process

[0368] 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 structures encapsulated in 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.

[0369] Slice Decoding Process

[0370] Decoding Process for Picture Order Count

[0371] The output of this process is PicOrderCntVal, the picture order count of the current picture. The picture order count is used to identify the picture for deriving motion parameters in merge mode and motion vector prediction and for decoder compliance checking. Each coded picture is associated with a picture order count variable, denoted PicOrderCntVal. When the current picture is not an IRAP picture, the variables prevPicOrderCntLsb and prevPicOrderCntMsb are derived as follows: Let prevTid0Pic be the previous picture in decoding order with TemporalId equal to 0. The variable prevPicOrderCntLsb is set equal to slice_pic_order_cnt_lsb of prevTid0Pic. The variable prevPicOrderCntMsb is set equal to 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 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

[0372] PicOrderCntVal is derived as follows: PicOrderCntVal = PicOrderCntMsb + slice_pic_order_cnt_lsb

[0373] Since slice_pic_order_cnt_lsb is inferred to be 0 for IRAP pictures and both prevPicOrderCntLsb and prevPicOrderCntMsb are set equal to 0, all IRAP pictures have PicOrderCntVal equal to 0. The value of PicOrderCntVal is in the range of -231 to 231 - 1, inclusive. In one CVS, the PicOrderCntVal values ​​for any two coded pictures are not the same. At any instant during the decoding process, the values ​​of PicOrderCntVal & (MaxRefPicOrderCntLsb - 1) for any two reference pictures in the DPB are not the same.

[0374] The function PicOrderCnt(picX) is specified as follows: PicOrderCnt(picX) = PicOrderCntVal of picture picX

[0375] The function DiffPicOrderCnt(picA, picB) is specified as follows: DiffPicOrderCnt(picA, picB) = PicOrderCnt(picA) - PicOrderCnt(picB)

[0376] The bitstream does not contain data that would result in a value of DiffPicOrderCnt(picA, picB) used in the decoding process that is not within the range of -215 to 215 - 1, inclusive. 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.

[0377] Decoding process for constructing a reference picture list

[0378] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. A reference picture is addressed by a reference index. The reference index is an index into a 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 in marking the reference pictures or in 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 checking bitstream conformance, but their derivation is not necessary for decoding of the current picture or pictures that follow the current picture in decoding order. For P slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of checking bitstream conformance, but its derivation is not necessary for decoding of the current picture or pictures that follow the current picture in 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( there exists a reference picA in DPB where PicOrderCntVal & ( MaxRefPicOrderCntLsb - 1 ) is equal to poc_ref_lsb[i][j] ) RefPicList[i][j] = picA else RefPicList[i][j] = "no reference picture" } }

[0379] For each i equal to 0 or 1, the first NumRefIdxActive[i] entries of RefPicList[i] are called active entries of RefPicList[i], and the other entries of RefPicList[i] are called inactive entries of RefPicList[i]. A particular picture may be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. It is also possible that a particular picture may be referenced by more than one entry in RefPicList[0] or by more than one entry in RefPicList[1]. The active entries of RefPicList[0] and the active entries of RefPicList[1] collectively refer to all reference pictures that may be used for inter prediction of the current picture and one or more pictures that follow the current picture in decoding order. Inactive entries of RefPicList[0] and inactive entries of RefPicList[1] collectively refer to all reference pictures that are not used for inter prediction of the current picture, but may be used in inter prediction of one or more pictures following the current picture in decoding order. There may be one or more entries of RefPicList[0] or RefPicList[1] that are equal to "no reference picture" because no corresponding picture exists in the DPB. An inactive entry of RefPicList[0] or RefPicList[0], respectively, that is equal to "no reference picture" should be ignored. For an active entry of RefPicList[0] or RefPicList[1], respectively, that is equal to "no reference picture", an unintended picture loss should be inferred.

[0380] It is a requirement of bitstream compliance that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[i] is greater than or equal to NumRefIdxActive[i]. A picture referenced by each active entry in RefPicList[0] or RefPicList[1] is present in the DPB and has a TemporalId less than or equal to the TemporalId of 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 the decoding of the current picture. Optionally, the following constraints may be further specified: No inactive entry in RefPicList[0] or RefPicList[1] references the same picture as any other entry in RefPicList[0] or RefPicList[1]. The current picture itself is not referenced by any entry in RefPicList[0] or RefPicList[1]. There are no entries in RefPicList[0] or RefPicList[1] such that the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is greater than or equal to 224. setOfRefPics shall be the set of unique pictures referenced by all entries of RefPicList[0] and all entries of RefPicList[1]. The number of pictures in setOfRefPics is less than or equal to sps_max_dec_pic_buffering_minus1 and setOfRefPics is the same for all slices of the picture.

[0381] Decoding process for reference picture marking

[0382] This process is invoked once per picture after the decoding process for the decoding of the slice header and the construction of the reference picture list for the slice, but before the decoding of the slice data. This process may result in one or more reference pictures in the DPB being marked as "not used for reference". A decoded picture in the DPB may be marked as "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 removes the other of these markings, if 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 the Log2(MaxRefPicOrderCntLsb) LSB of their PicOrderCntVal values. Each reference picture in the DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as "unused for reference."

[0383] Yet another alternative embodiment

[0384] This section describes an alternative embodiment of the approach detailed above called "Always signaling reference picture lists in slice headers with distinction between short-term and long-term reference pictures". In this alternative embodiment, in slice headers, POC MSB cycle may be signaled for each LTRP entry, similar to HEVC or the approach described above, and the following constraint is removed: At any instant during the decoding process, the values ​​of PicOrderCntVal & (MaxLtPicOrderCntLsb - 1) for any two reference pictures in the DPB are not the same.

[0385] 6 is a schematic diagram of a video coding device 600 (e.g., video encoder 20 or video decoder 30) according to an embodiment of the present disclosure. The video coding device 600 is suitable for implementing the disclosed embodiments as described herein. The video coding device 600 includes an incoming 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 outgoing port 650 for transmitting data, and a memory 660 for storing data. The video coding device 600 may also include optical-electrical (OE) and electrical-optical (EO) components connected to the incoming port 610, the receiver unit 620, the transmitter unit 640, and the outgoing port 650 for the incoming or outgoing optical or electrical signals.

[0386] 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 incoming port 610, the receiver unit 620, the transmitter unit 640, the outgoing port 650, and the memory 660. The processor 630 includes a coding module 670. The coding module 670 implements the above-disclosed embodiments. For example, the coding module 670 implements, processes, prepares, or provides various networking functions. Thus, the inclusion of the coding module 670 significantly improves the functionality of the video coding device 600 and realizes the transition 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.

[0387] Video coding device 600 may also include input and / or output (I / O) devices 680 for communicating data to and from a user. I / O devices 680 may include output devices such as a display for displaying video data, speakers for outputting audio data, etc. I / O devices 680 may also include input devices such as a keyboard, mouse, trackball, etc., and / or corresponding interfaces for interacting with such output devices.

[0388] Memory 660 may include one or more disks, tape drives, and solid state drives, and may be used as an over-flow data storage device for storing programs when such programs are selected for execution as well as for storing instructions and data read during execution of the programs. 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).

[0389] 7 is a schematic diagram of an embodiment of a means for coding 700. In an embodiment, the means for coding 700 is implemented in a video coding device 702 (e.g., video encoder 20 or video decoder 30). The video coding device 702 includes a receiving means 701. The receiving means 701 is configured to receive a picture to encode or a bitstream to decode. The video coding device 702 includes a transmitting means 707 connected to the receiving means 701. The transmitting means 707 is configured to transmit the bitstream to a decoder or transmit a decoded image to a display means (e.g., one of the I / O devices 680).

[0390] The video coding device 702 includes a storage means 703. The storage means 703 is connected 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 connected to the storage means 703. The processing means 705 is configured to execute the instructions stored in the storage means 703 for performing the methods disclosed herein.

[0391] Although several embodiments have been provided in this disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the disclosure. These examples should be considered illustrative and not limiting, and the intention should not be limited to the details given herein. For example, various elements or components may be combined or integrated into another system, or certain features may be omitted or not implemented.

[0392] Additionally, techniques, systems, subsystems, and methods described and illustrated in various embodiments as separate or distinct may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the disclosure. Others shown or discussed as being coupled or directly coupled to each other, or in communication with each other, may be indirectly coupled or in communication through some interface, device, or intermediate component, whether electrical, mechanical, or otherwise. Other examples of changes, substitutions, and alterations may occur to those skilled in the art and may be made without departing from the spirit and scope disclosed herein. [Explanation of symbols]

[0393] 10 Coding Systems 12 Source Device 14 Destination Device 16 Computer-Readable Media 18 Video Sources 20 Video Encoder 22 Output Interface 28 Input Interface 30 Video Decoder 32 Display Devices 40 Mode Selection Unit 42 Motion Estimation Unit 44 Motion Compensation Unit 46 intra prediction units 48 Division Unit 50 Adder 52 Conversion Processing Unit 54 Quantization Units 56 Entropy Coding Units 58 Inverse Quantization Unit 60 Reverse conversion unit 62 Adder 64 Reference Frame Memory 70 Entropy Decoding Unit 72 Motion Compensation Unit 74 intra prediction units 76 Inverse Quantization Unit 78 Reverse conversion unit 80 Adder 82 Reference Frame Memory 400 Reference Picture Sets (RPS) 402 Subset 500 ways 600 Video Coding Device 610 Incoming Port 620 Receiver Unit (Rx) 630 Processor, Logic Unit, Central Processing Unit (CPU) 640 Transmitter Unit (Tx) 650 Outgoing Port 660 Memory 670 Coding Module 680 Input and / or Output (I / O) Devices 700 Coding Tools 701 Receiving means 702 Video Coding Device 703 Memory means 705 Processing Means 707 Transmission Method

Claims

1. 1. A method for decoding a coded video bitstream, performed by a video decoder, comprising: parsing a parameter set indicated in the coded video bitstream, the parameter set including a set of syntax elements including a set of reference picture list structures; parsing a slice header of a current slice indicated in the coded video bitstream, the slice header including an index of a reference picture list structure among the set of reference picture list structures in the parameter set; deriving a reference picture list for the current slice based on the set of syntax elements in the parameter set and the index of the reference picture list structure; obtaining at least one reconstructed block of the current slice based on the reference picture list; The method includes:

2. The method of claim 1 , wherein the order of entries in the reference picture list structure is the same as the order of corresponding reference pictures in the reference picture list.

3. 3. The method of claim 1 or 2, wherein the order of the entries is from zero to the indicated value.

4. The method of claim 3 , wherein the indicated value is from zero to a value indicated by sps_max_dec_pic_buffering_minus1.

5. The method according to claim 1 , wherein the reference picture list is a designated RefPictList[0].

6. The method according to claim 1 , wherein the reference picture list is a designated RefPictList[1].

7. The method of claim 1 , wherein the at least one reconstructed block is used to generate an image that is displayed on a display of an electronic device.

8. The method according to claim 1 , wherein the reference picture list comprises a list of reference pictures used for inter prediction.

9. The method according to any one of claims 1 to 8, wherein inter prediction is for P slices or for B slices.

10. The method of claim 1 , wherein the parameter set comprises a sequence parameter set (SPS).

11. 11. The method of claim 1, wherein the set of syntax elements from the parameter set is placed in a Raw Byte Sequence Payload (RBSP) of a Network Abstraction Layer (NAL) unit.

12. 12. The method of claim 7, wherein the reference picture list is a designated RefPictList[0] or RefPictList[1], and the order of entries in the reference picture list structure is the same as the order of corresponding reference pictures in the reference picture list.

13. parsing a parameter set indicated in the coded video bitstream, the parameter set including a set of syntax elements including a set of reference picture list structures; obtaining a reference picture list structure indicated in the coded video bitstream; Deriving a first reference picture list for a current slice based on the reference picture list structure, the first reference picture list including at least one active entry and at least one inactive entry, the at least one inactive entry referring to a reference picture that is not used for inter prediction of the current slice but is referenced by an active entry of a second reference picture list, the second reference picture list being a reference picture list of a slice following the current slice in decoding order or a reference picture list of a picture following the current picture in decoding order; obtaining at least one reconstructed block of the current slice based on at least one active entry of the first reference picture list; 13. The method of any one of claims 1 to 12, further comprising:

14. a receiver configured to receive a coded video bitstream; a memory coupled to the receiver for storing instructions; a processor, coupled to the memory, configured to execute the instructions stored in the memory; Including, The instructions cause the processor to: parsing a parameter set indicated in the coded video bitstream, the parameter set including a set of syntax elements including a set of reference picture list structures; parsing a slice header of a current slice indicated in the coded video bitstream, the slice header including an index of a reference picture list structure among the set of reference picture list structures in the parameter set; deriving a reference picture list for the current slice based on the set of syntax elements in the parameter set and the index of the reference picture list structure; obtaining at least one reconstructed block of the current slice based on the reference picture list; A decryption device that causes

15. a display configured to display an image based on the at least one reconstructed block. The decoding device of claim 14, further comprising:

16. 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, the memory configured to store instructions; A processor coupled to the memory and configured to execute the instructions stored in the memory to perform the method of any one of claims 1 to 13. A coding device comprising:

17. An encoder; a decoder in communication with the encoder; Including, A system, wherein the decoder comprises a decoding device according to claim 14 or 15 or a coding apparatus according to claim 16.

18. receiving means configured to receive a bitstream to be decoded; a transmitting means connected to said receiving means, configured to transmit the decoded image to a display means; a storage means coupled to at least one of said receiving means or said transmitting means, said storage means configured to store instructions; processing means connected to said storage means, said processing means being configured to execute the instructions stored in said storage means to perform the method according to any one of claims 1 to 13; A means for coding, including

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