Video encoders, video decoders, and corresponding devices

Abstract

A method for decoding a coded video bitstream is provided. [Solution] The method includes the steps of parsing a flag, parsing a first reference picture list structure, determining that when the flag has a first value, an index to the second reference picture list structure does not exist in the slice header of the coded video bitstream and inferring that the index to the second reference picture list structure is the same as the index to the first reference picture list structure, determining that when the flag has a second value, an index to the second reference picture list structure exists in the slice header, generating a reference picture list using the first or second reference picture list structure, and performing interpretation based on the reference picture list to generate a reconstructed block.

Description

Technical Field

[0001] Cross - reference to Related Applications This patent application claims the benefit of U.S. Provisional Patent Application No. 62 / 730,172, filed Sep. 12, 2018, by Fnu Hendry et al. entitled "Bit Count Reduction for Reference Picture Management Based on Reference Picture Lists in Video Coding", and U.S. Provisional Patent Application No. 62 / 848,147, filed May 15, 2019, by Fnu Hendry et al. entitled "Bit Count Reduction for Reference Picture Management Based on Reference Picture Lists in Video Coding", each of which is incorporated herein by reference.

[0002] Generally, the present disclosure describes techniques for improving signaling efficiency for reference picture management in video coding. More specifically, the present disclosure describes techniques for improved signaling for the construction of reference picture lists and for the marking of reference pictures directly based on reference picture lists.

Background Art

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

[0004] The first aspect relates to a method for decoding a coded video bitstream, performed by a video decoder. The method comprises the steps of: parsing a flag from the coded video bitstream; parsing a first reference picture list structure from the coded video bitstream; determining that, when the flag has a first value, an index to a second reference picture list structure does not exist in the slice header of the coded video bitstream and inferring that the index to the second reference picture list structure is the same as the index to the first reference picture list structure; determining that, when the flag has a second value, an index to a second reference picture list structure exists in the slice header; generating a reference picture list using at least one of the first or second reference picture list structure; and performing interpretation based on the reference picture list to generate a reconstructed block.

[0005] The method provides techniques to simplify and make the coding process more efficient. By using a flag to specify whether the index for a second reference picture list structure can be inferred to be the same as the index for the first reference picture list structure, the coder / decoder (also known as a "codec") in video coding can be improved compared to the current codec (e.g., using fewer bits, requiring less bandwidth, being more efficient, etc.). In practical terms, an improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0006] In the first implementation of the method by the first aspect itself, the flag is called rpl1_idx_present_flag.

[0007] In a second implementation of the method, either in the first embodiment itself or in any preceding implementation of the first embodiment, the flag is included in the picture parameter set (PPS) of the video bitstream being coded.

[0008] In a third implementation of the method, either in the first embodiment itself or in any preceding implementation of the first embodiment, the flag is included in the sequence parameter set (SPS) of the coded video bitstream.

[0009] In the first embodiment itself or in the fourth implementation of the method in any preceding implementation of the first embodiment, the first reference picturelist structure is included in the slice header of the coded video bitstream.

[0010] In a fifth implementation of the method, either in the first embodiment itself or in any preceding implementation of the first embodiment, the flag is included in the picture parameter set (PPS) of the coded video bitstream, and the first reference picture list structure is included in the slice header of the coded video bitstream.

[0011] In the sixth implementation of the method, either in the first embodiment itself or in any preceding implementation of the first embodiment, the first value of the flag is 1.

[0012] In the seventh implementation of the method, either in the first embodiment itself or in any preceding implementation of the first embodiment, when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

[0013] In the eighth implementation of the method, either in the first embodiment itself or in any preceding implementation of the first embodiment, the second value of the flag is 0.

[0014] In the ninth implementation of the method, either in the first embodiment itself or in any preceding implementation of the first embodiment, when the second value of the flag is 0, ref_pic_list_sps_flag[0] and ref_pic_list_idx[0] are included in the slice header.

[0015] A second aspect relates to a method for encoding a video bitstream performed by a video encoder, the method comprising: encoding a flag into a video bitstream using a first value when the index for a second reference picture list structure is not encoded in the slice header of the video bitstream and the video decoder should infer that the index for the second reference picture list structure is the same as the index for a first reference picture list structure; encoding a flag into a video bitstream using a second value when the index for a second reference picture list structure is encoded in the slice header of the video bitstream; encoding a first reference picture list structure into a video bitstream when the flag is encoded using a first value; encoding a first reference picture list structure and a second reference picture list structure into a video bitstream when the flag is encoded using a second value; and transmitting the video bitstream to a video decoder.

[0016] The method provides techniques to simplify and make the coding process more efficient. By using a flag to specify whether the index for a second reference picture list structure can be inferred to be the same as the index for the first reference picture list structure, the coder / decoder (also known as a "codec") in video coding can be improved compared to the current codec (e.g., using fewer bits, requiring less bandwidth, being more efficient, etc.). In practical terms, an improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0017] In the first implementation of the method according to the second aspect itself, the flag is specified as rpl1_idx_present_flag.

[0018] In the second embodiment itself or in any prior implementation of the second embodiment, the flag is encoded in the picture parameter set (PPS) of the coded video bitstream.

[0019] In the third implementation of the method, either in the second embodiment itself or in any preceding implementation of the second embodiment, the first reference picturelist structure is encoded in the slice header of the coded video bitstream.

[0020] In the fourth implementation of the method, either in the second embodiment itself or in any preceding implementation of the second embodiment, the first reference picturelist structure and the second reference picturelist structure are encoded in the slice header of the coded video bitstream.

[0021] In the fifth implementation of the method, either in the second embodiment itself or in any preceding implementation of the second embodiment, the first value of the flag is 1 and the second value of the flag is 0.

[0022] In the sixth implementation of the method, either in the second embodiment itself or in any preceding implementation of the second embodiment, when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

[0023] A third aspect relates to a decoding device, the decoding device comprising a receiver configured to receive a coded video bitstream, a memory coupled to the receiver which stores instructions, and a processor coupled to the memory, the processor configured to execute instructions stored in memory to cause the processor to parse a flag from the coded video bitstream, to parse a first reference picture list structure from the coded video bitstream, to determine that when the flag has a first value, an index to a second reference picture list structure does not exist in the slice header of the coded video bitstream, to infer that the index to the second reference picture list structure is the same as the index to the first reference picture list structure, to determine that when the flag has a second value, an index to the second reference picture list structure exists in the slice header, to generate a reference picture list using at least one of the first or second reference picture list structure, and to perform inter prediction based on the reference picture list to generate a reconstructed block.

[0024] Decoding devices provide techniques to simplify and make the coding process more efficient. By using flags to specify whether the index for a second reference picture list structure can be inferred to be the same as the index for the first reference picture list structure, the coder / decoder (also known as a "codec") in video coding can be improved compared to the current codec (e.g., using fewer bits, requiring less bandwidth, being more efficient). In practical terms, an improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0025] In a first implementation form of the decoding device according to the third aspect itself, the decoding device includes a display configured to display an image generated using the reconstructed block.

[0026] In a second implementation form of the decoding device according to the third aspect itself or any preceding implementation form of the third aspect, the flag is designated as rpl1_idx_present_flag.

[0027] In a third implementation form of the decoding device according to the third aspect itself or any preceding implementation form of the third aspect, the flag is included in the picture parameter set (PPS) of the coded video bitstream.

[0028] In a fourth implementation form of the decoding device according to the third aspect itself or any preceding implementation form of the third aspect, the first reference picture list structure is included in the slice header of the coded video bitstream.

[0029] In a fifth implementation form of the decoding device according to the third aspect itself or any preceding implementation form of the third aspect, the first value of the flag is 1 and the second value of the flag is 0.

[0030] In a sixth implementation form of the decoding device according to the third aspect itself or any preceding implementation form of the third aspect, when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

[0031] A fourth aspect relates to an encoding device, the encoding device comprising a processor configured to encode a flag into a video bitstream using a first value when the index for a second reference picture list structure is not encoded in the slice header of the video bitstream and the video decoder should infer that the index for the second reference picture list structure is the same as the index for a first reference picture list structure; encode a flag into a video bitstream using a second value when the index for a second reference picture list structure is encoded in the slice header of the video bitstream; encode the first reference picture list structure into a video bitstream when the flag is encoded using the first value; and encode the first and second reference picture list structures into a video bitstream when the flag is encoded using the second value; and a transmitter coupled to the processor, configured to transmit a video bitstream toward a video decoder.

[0032] Encoding devices provide techniques to simplify and make the coding process more efficient. By using flags to specify whether the index for a second reference picture list structure can be inferred to be the same as the index for a first reference picture list structure, the coder / decoder (also known as a "codec") in video coding can be improved compared to the current codec (e.g., using fewer bits, requiring less bandwidth, being more efficient). In practical terms, an improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0033] In the first implementation of the encoding device according to the fourth aspect itself, the flag is specified as rpl1_idx_present_flag.

[0034] In the second implementation of the encoding device, either in the fourth embodiment itself or in any preceding implementation of the fourth embodiment, the flag is encoded in the picture parameter set (PPS) of the coded video bitstream.

[0035] In the third implementation of the encoding device, either in the fourth embodiment itself or in any preceding implementation of the fourth embodiment, the first reference picture list structure is encoded in the slice header of the coded video bitstream.

[0036] In the fourth implementation of the encoding device, either in the fourth embodiment itself or in any preceding implementation of the fourth embodiment, the first value of the flag is 1 and the second value of the flag is 0.

[0037] In the fifth implementation of the encoding device according to the fourth embodiment itself or any preceding implementation of the fourth embodiment, when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

[0038] A fifth aspect relates to a coding apparatus comprising: a receiver configured to receive a bitstream to be decoded; a transmitter coupled to the receiver, configured to transmit a decoded image to a display; a memory coupled to at least one of the receiver or transmitter, configured to store instructions; and a processor coupled to the memory, configured to execute instructions stored in the memory to perform a method in any of the embodiments disclosed herein.

[0039] Coding devices provide techniques to simplify and make the coding process more efficient. By using flags to specify whether the index for a second reference picture list structure can be inferred to be the same as the index for a first reference picture list structure, the coder / decoder (also known as a "codec") in video coding can be improved compared to the current codec (e.g., using fewer bits, requiring less bandwidth, being more efficient). In practical terms, an improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0040] A seventh aspect relates to a system comprising an encoder including an encoding device according to any embodiment disclosed herein, and a decoder communicating with the encoder, the decoder including a decoding device according to any embodiment disclosed herein.

[0041] The system provides techniques to simplify and make the coding process more efficient. By using a flag to specify whether the index for a second reference picture list structure can be inferred to be the same as the index for the first reference picture list structure, the coder / decoder (also known as a "codec") in video coding is improved compared to the current codec (e.g., uses fewer bits, requires less bandwidth, is more efficient, etc.). In practical terms, an improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0042] The eighth aspect relates to a coding means comprising: a receiving means configured to receive a bitstream to be decoded; a transmitting means coupled to the receiving means, configured to transmit a decoded image to a display means; a storage means coupled to at least one of the receiving means or the transmitting means, configured to store instructions; and a processing means coupled to the storage means, configured to execute instructions stored in the storage means in order to perform a method in any of the embodiments disclosed herein.

[0043] The means of coding provide techniques that simplify and make the coding process more efficient. By using flags to specify whether the index for a second reference picture list structure can be inferred to be the same as the index for a first reference picture list structure, the coder / decoder (also known as a "codec") in video coding can be improved compared to the current codec (e.g., using fewer bits, requiring less bandwidth, being more efficient, etc.). In practical terms, an improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0044] For a more complete understanding of this disclosure, references are made hereto to the following brief description in relation to the attached drawings and detailed description, where similar reference numbers represent similar parts. [Brief explanation of the drawing]

[0045] [Figure 1] A block diagram illustrating exemplary coding systems that can utilize two-sided prediction techniques. [Figure 2] This block diagram shows an exemplary video encoder capable of implementing a bilateral prediction technique. [Figure 3] This block diagram shows an example of a video decoder capable of implementing a two-sided prediction technique. [Figure 4]This is a schematic diagram showing the RPS (Reference Picture Set) with the current picture, including entries in all subsets of the RPS. [Figure 5] This is a schematic diagram of an embodiment of a video bitstream. [Figure 6] This is an embodiment of a method for decoding a coded video bitstream. [Figure 7] This is a diagram illustrating an embodiment of a method for encoding a video bitstream. [Figure 8] This is a schematic diagram of a video coding device. [Figure 9] This is a schematic diagram of an embodiment of a means for coding. [Modes for carrying out the invention]

[0046] The following are various acronyms used herein: Decoded Picture Buffer (DPB), Instantaneous Decoded Refresh (IDR), Intra-Random Access Point (IRAP), Least Significant Bit (LSB), Most Significant Bit (MSB), Network Abstraction Layer (NAL), Picture Order Count (POC), Low Byte Sequence Payload (RBSP), Sequence Parameter Set (SPS), and Working Draft (WD).

[0047] Figure 1 is a block diagram illustrating an exemplary coding system 10 that may utilize video coding techniques as described herein. As shown in Figure 1, the coding system 10 includes a source device 12 that provides encoded video data to be later decoded by a destination device 14. Specifically, the source device 12 may provide video data to the destination device 14 via a computer-readable medium 16. The source device 12 and destination device 14 may comprise any of a wide range of devices, including desktop computers, notebook (e.g., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called "smart" phones, so-called "smart" pads, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, and the like. In some cases, the source device 12 and destination device 14 may be compatible with wireless communication.

[0048] Destination device 14 may receive encoded video data, which will be decoded via computer-readable medium 16. Computer-readable medium 16 may comprise any type of medium or device capable of moving the encoded video data from source device 12 to destination device 14. For example, computer-readable medium 16 may comprise a communication medium that enables source device 12 to transmit the encoded video data directly to destination device 14 in real time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful in facilitating communication from source device 12 to destination device 14.

[0049] In some examples, encoded data may be output to a storage device via the output interface 22. Similarly, encoded data may be accessed from the storage device via the input interface. The storage device may include any of a variety of distributed or locally accessed data storage media, such as a hard drive, Blu-ray® disc, digital video disc (DVD), compact disc read-only memory (CD-ROM), flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data. In further examples, the storage device may correspond to a file server or another intermediate storage device capable of storing encoded video generated by the source device 12. The destination device 14 may access the stored video data from the storage device via streaming or download. The file server may be any type of server capable of storing encoded video data and transmitting encoded video data to the destination device 14. Exemplary file servers include web servers (e.g., for websites), file transfer protocol (FTP) servers, network-attached storage (NAS) devices, or local disk drives. The destination device 14 may access the encoded video data through any standard data connection, including an internet connection. This may include wireless channels (e.g., Wi-Fi connection), wired connections (e.g., digital subscriber line (DSL), cable modem, etc.), or a combination of both suitable for accessing encoded video data stored on a file server. Transmission of the encoded video data from the storage device may be streaming transmission, download transmission, or a combination thereof.

[0050] The techniques of this disclosure are not necessarily limited to wireless applications or configurations. These techniques may also be applied to video coding supporting a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, internet streaming video transmission such as dynamic adaptive streaming over HTTP (DASH), digital video encoded to a data storage medium, decoding of digital video stored to a data storage medium, or other applications. In some examples, the coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and / or video telephony.

[0051] In the example shown in Figure 1, the source device 12 includes a video source 18, a video encoder 20, and an output interface 22. The destination device 14 includes an input interface 28, a video decoder 30, and a display device 32. According to this disclosure, the video encoder 20 of the source device 12 and / or the video decoder 30 of the destination device 14 may be configured to apply techniques for video coding. In other examples, the source device and destination device may include other components or configurations. For example, the source device 12 may receive video data from an external video source, such as an external camera. Similarly, the destination device 14 may interface with an external display device rather than including an integrated display device.

[0052] The coding system 10 shown in Figure 1 is merely an example. The technique for video coding can be performed by any digital video coding and / or decoding device. While the technique of this disclosure is generally performed by a video coding device, it can also be performed by a video encoder / decoder, commonly referred to as a “codec.” Furthermore, the technique of this disclosure can also be performed by a video preprocessor. The video encoder and / or decoder may be a graphics processing unit (GPU) or a similar device.

[0053] The source device 12 and destination device 14 are merely examples of coding devices, such that the source device 12 generates coded video data for transmission to the destination device 14. In some examples, the source device 12 and destination device 14 may operate substantially symmetrically, such that each of the source device 12 and destination device 14 includes a video coding component and a video decoding component. Thus, the coding system 10 may support one-way or two-way video transmission between video devices 12 and 14 for, for example, video streaming, video playback, video broadcasting, or video phone calls.

[0054] The video source 18 of source device 12 may include a video capture device such as a video camera, a video archive containing previously captured video, and / or a video feed interface for receiving video from a video content provider. As a further alternative, the video source 18 may generate computer graphics-based data as source video, or generate a combination of live video, archived video, and computer-generated video.

[0055] In some cases, when the video source 18 is a video camera, the source device 12 and destination device 14 may form a so-called camera phone or video phone. However, as mentioned above, the techniques described herein may be applicable to video coding in general, and may be applicable to wireless and / or wired applications. In each case, captured, pre-captured, or computer-generated video may be encoded by the video encoder 20. The encoded video information may then be output to a computer-readable medium 16 via the output interface 22.

[0056] The computer-readable medium 16 may include temporary media such as wireless broadcast or wired network transmission, or storage media (i.e., non-temporary storage media) such as hard disks, flash drives, compact discs, digital video discs, Blu-ray® discs, or other computer-readable media. In some examples, a network server (not shown) may receive encoded video data from a source device 12 and provide the encoded video data to a destination device 14, for example, via network transmission. Similarly, a computing device in a media production facility, such as a disc stamping facility, may receive encoded video data from a source device 12 and produce discs containing the encoded video data. Thus, the computer-readable medium 16 may be understood to include one or more computer-readable media in various forms in various examples.

[0057] The input interface 28 of the destination device 14 receives information from the computer-readable medium 16. The information on the computer-readable medium 16 may include syntax information defined by the video encoder 20, which includes syntax elements that describe the characteristics and / or processing of blocks and other coded units, such as picture groups (GOPs), and which are also used by the video decoder 30. The display device 32 displays the decoded video data to the user and may comprise any of a variety of display devices, such as a cathode ray tube (CRT), liquid crystal display (LCD), plasma display, organic light-emitting diode (OLED) display, or another type of display device.

[0058] The video encoder 20 and video decoder 30 may operate in accordance with a video coding standard, such as the High Efficiency Video Coding (HEVC) standard currently under development, and may conform to the HEVC Test Model (HM). Alternatively, the video encoder 20 and video decoder 30 may operate in accordance with other proprietary or industry standards, such as the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) H.264 standard, H.265 / HEVC, or extensions of such standards, also known as Moving Picture Expert Group (MPEG)-4, Part 10, Advanced Video Coding (AVC). However, the techniques of this disclosure are not limited to any particular coding standard. Other examples of video coding standards include MPEG-2 and ITU-T H.263. Although not shown in Figure 1, in some embodiments, the video encoder 20 and video decoder 30 may be integrated with an audio encoder and decoder, respectively, and may include a suitable multiplexer-demultiplexer (MUX-DEMUX) unit or other hardware and software for handling the encoding of both audio and data in a common data stream and separate data streams. Where applicable, the MUX-DEMUX unit may conform to the ITU H.223 multiplexer protocol or other protocols such as the User Datagram Protocol (UDP).

[0059] The video encoder 20 and video decoder 30 can each be implemented as any of a variety of suitable encoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic circuits, software, hardware, firmware, or any combination thereof. When the technique is partially implemented in software, the device may store instructions for the software in a suitable non-temporary computer-readable medium and execute the instructions in hardware using one or more processors to perform the technique of this disclosure. Each of the video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, and any of them may be integrated as part of a composite encoder / decoder (codec) in their respective devices. A device including the video encoder 20 and / or video decoder 30 may include an integrated circuit, a microprocessor, and / or a wireless communication device such as a mobile phone.

[0060] Figure 2 is a block diagram showing an example of a video encoder 20 capable of performing video coding techniques. The video encoder 20 can perform intracoding and intercoding of video blocks within a video slice. Intracoding relies on spatial prediction to reduce or eliminate spatial redundancy in video within a given video frame or picture. Intercoding relies on temporal prediction to reduce or eliminate temporal redundancy in video within adjacent frames or pictures in a video sequence. Intra-mode (I-mode) can refer to any of several spatial-based coding modes. Inter-modes, such as unidirectional (also known as single prediction) prediction (P-mode) or bi-prediction (also known as bi-prediction) (B-mode), can refer to any of several temporal-based coding modes.

[0061] As shown in Figure 2, the video encoder 20 receives the current video block in the video frame to be encoded. In the example in Figure 2, the video encoder 20 includes a mode selection unit 40, a reference frame memory 64, an adder 50, a transformation unit 52, a quantization unit 54, and an entropy coding unit 56. The mode selection unit 40 includes a motion compensation unit 44, a motion estimation unit 42, an intra-prediction (also known as intra-prediction) unit 46, and a segmentation unit 48. For video block reconstruction, the video encoder 20 also includes an inverse quantization unit 58, an inverse transformation unit 60, and an adder 62. A deblocking filter (not shown in Figure 2) may also be included to filter block boundaries and remove blocking artifacts from the reconstructed video. If desired, the deblocking filter typically filters the output of the adder 62. Additional filters (in-loop or after-loop) may also be used in addition to the deblocking filter. For the sake of brevity, such a filter is not shown, but if desired, the output of adder 50 can be filtered (as an in-loop filter).

[0062] During the encoding process, the video encoder 20 receives video frames or slices to be coded. A frame or slice may be divided into multiple video blocks. Motion estimation units 42 and motion compensation units 44 perform inter-predictive coding of the received video blocks relative to one or more blocks in one or more reference frames to perform temporal prediction. Alternatively, an intra-predictive unit 46 may perform intra-predictive coding of the received video blocks relative to one or more neighboring blocks in the same frame or slice as the block to be coded to perform spatial prediction. The video encoder 20 may execute multiple coding paths, for example, to select an appropriate coding mode for each block of video data.

[0063] Furthermore, the partitioning unit 48 may partition blocks of video data into sub-blocks based on an evaluation of a previous partitioning method in a previous coding pass. For example, the partitioning unit 48 may first partition a frame or slice into a maximum coding unit (LCU), and then, based on rate distortion analysis (e.g., rate distortion optimization), partition each LCU into a sub-coding unit (sub-CU). The mode selection unit 40 may further generate a quadtree data structure that shows the partitioning of LCUs into sub-CUs. The leaf nodes CU of the quadtree may include one or more prediction units (PUs) and one or more transformation units (TUs).

[0064] This disclosure uses the term “block” to refer to a CU, PU, ​​or TU in the context of HEVC, or a similar data structure in the context of other standards (for example, macroblocks and subblocks of macroblocks in H.264 / AVC). A CU includes a coding node, a PU, and a TU associated with the coding node. The size of a CU corresponds to the size of the coding node and is square in shape. The size of a CU can range from 8x8 pixels to the size of a tree block of 64x64 pixels or more. Each CU may contain one or more PUs and one or more TUs. Syntax data associated with a CU may, for example, describe the division of the CU into one or more PUs. The division mode may differ depending on whether the CU is encoded in skip mode or direct mode, intra-prediction mode, or inter-prediction mode. A PU may be divided to have a non-square shape. The syntax data associated with a CU may also describe, for example, the division of the CU into one or more TUs according to a quadtree. The TUs may be square or non-square (for example, rectangular).

[0065] The mode selection unit 40 selects a coding mode, i.e., one of intra-coding mode or inter-coding mode, based, for example, on the result of an error, and provides the resulting intra-coded or inter-coded block to the adder 50 to generate residual block data, which is then provided to the adder 62 to reconstruct the encoded block for use as a reference frame. The mode selection unit 40 also provides syntax elements such as motion vectors, intra-mode indicators, segmentation information, and other such syntax information to the entropy coding unit 56.

[0066] The motion estimation unit 42 and the motion compensation unit 44 can be highly integrated, but are shown separately for conceptual purposes. The motion estimation performed by the motion estimation unit 42 is the process of generating motion vectors that estimate the motion of a video block. The motion vectors may, for example, show the PU deviation of a video block in the current video frame or picture from a predicted block in a reference frame (or other coded unit) to a current block coded in the current frame (or other coded unit). A predicted block is a block that is found to closely match the block to be coded with respect to pixel differences, which may be determined by the absolute difference sum (SAD), square difference sum (SSD), or other difference measures. In some examples, the video encoder 20 may calculate values ​​for sub-integer pixel positions of a reference picture stored in the reference frame memory 64. For example, the video encoder 20 may interpolate values ​​for quarter-pixel positions, eighth-pixel positions, or other fractional pixel positions of the reference picture. Thus, the motion estimation unit 42 may perform motion searches for all pixel positions and fractional pixel positions and output motion vectors with fractional pixel precision.

[0067] The motion estimation unit 42 calculates motion vectors for video blocks in the intercoded slice relative to the PU by comparing the PU's position with the predicted block's position in the reference picture. The reference picture may be selected from a first reference picture list (list 0) or a second reference picture list (list 1), each of which identifies one or more reference pictures stored in the reference frame memory 64. The motion estimation unit 42 transmits the calculated motion vectors to the entropy coding unit 56 and the motion compensation unit 44.

[0068] Motion compensation performed by the motion compensation unit 44 may involve fetching or generating a predicted block based on a motion vector determined by the motion estimation unit 42. Again, in some examples, the motion estimation unit 42 and the motion compensation unit 44 may be functionally integrated. Upon receiving the motion vector of the current video block, the motion compensation unit 44 may find the predicted block pointed to by the motion vector in one of the reference picture lists. As discussed below, the adder 50 forms a residual video block by subtracting the pixel values ​​of the predicted block from the pixel values ​​of the current video block being coded, which form the pixel difference value. Generally, the motion estimation unit 42 performs motion estimation for the lumens component, and the motion compensation unit 44 uses a motion vector calculated based on the lumens component for both the chromens and lumens components. The mode selection unit 40 may also generate syntax elements associated with video blocks and video slices for use by the video decoder 30 when decoding video blocks of video slices.

[0069] As described above, the intra-prediction unit 46 may intra-predict the current block as an alternative to the inter-prediction performed by the motion estimation unit 42 and the motion compensation unit 44. Specifically, the intra-prediction unit 46 may determine which intra-prediction mode should be used to encode the current block. In some examples, the intra-prediction unit 46 may encode the current block using various intra-prediction modes, for example, between separate encoding passes, and the intra-prediction unit 46 (or, in some examples, the mode selection unit 40) may select an appropriate intra-prediction mode to use from the tested modes.

[0070] For example, the intra-prediction unit 46 may calculate rate distortion values ​​using rate distortion analysis for various intra-prediction modes under test and select the intra-prediction mode with the best rate distortion characteristics from among the tested modes. Rate distortion analysis generally determines the amount of distortion (or error) between the encoded block and the original unencoded block encoded to produce the encoded block, as well as the bit rate (i.e., the number of bits) used to produce the encoded block. The intra-prediction unit 46 may calculate a ratio from the distortion and rate for various encoded blocks to determine which intra-prediction mode exhibits the best rate distortion value for a block.

[0071] In addition, the intra-prediction unit 46 may be configured to code depth blocks of the depth map using a depth modeling mode (DMM). The mode selection unit 40 may determine, for example, using rate distortion optimization (RDO), whether an available DMM mode produces better coding results than the intra-prediction mode and other DMM modes. Data for the texture image corresponding to the depth map may be stored in the reference frame memory 64. The motion estimation unit 42 and the motion compensation unit 44 may also be configured to inter-predict depth blocks of the depth map.

[0072] After selecting an intra-prediction mode for a block (for example, one of the conventional intra-prediction mode or DMM mode), the intra-prediction unit 46 may provide the entropy coding unit 56 with information indicating the selected intra-prediction mode for the block. The entropy coding unit 56 may encode the information indicating the selected intra-prediction mode. The video encoder 20 may include in the transmitted bitstream configuration data definitions for various blocks, instructions for the most probable intra-prediction mode, intra-prediction mode index tables, and modified intra-prediction mode index tables to be used for each context.

[0073] The video encoder 20 forms a residual video block by subtracting predicted data from the mode selection unit 40 from the original video block being coded. The adder 50 represents one or more components that perform this subtraction operation.

[0074] The transformation processing unit 52 applies a transformation, such as a discrete cosine transform (DCT) or a conceptually similar transformation, to the residual block to produce a video block containing residual transformation coefficient values. The transformation processing unit 52 may perform other transformations conceptually similar to the DCT. Wavelet transforms, integer transforms, subband transforms, or other types of transformations may also be used.

[0075] The conversion processing unit 52 applies the transformation to the residual block, generating a block of residual transformation coefficients. This transformation can convert the residual information from the pixel value domain to a transformation domain, such as the frequency domain. The conversion processing unit 52 may transmit the resulting transformation coefficients to the quantization unit 54. The quantization unit 54 quantizes the transformation coefficients to further reduce the bit rate. The quantization process can reduce the bit depth associated with some or all of the coefficients. The degree of quantization can be modified by adjusting the quantization parameters. In some examples, the quantization unit 54 may then perform a scan of the matrix containing the quantized transformation coefficients. Alternatively, the entropy coding unit 56 may perform the scan.

[0076] Following quantization, the entropy coding unit 56 codes the quantized transformation coefficients. For example, the entropy coding unit 56 may perform context-adaptive variable-length coding (CALVC), context-adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval piecewise entropy (PIPE) coding, or another entropy coding technique. In the case of context-based entropy coding, the context may be based on neighboring blocks. Following entropy coding by the entropy coding unit 56, the encoded bitstream may be transmitted to another device (e.g., video decoder 30) or stored for later transmission or retrieval.

[0077] The inverse quantization unit 58 and the inverse transform unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual block in the pixel region for later use, for example, as a reference block. The motion compensation unit 44 may compute a reference block by adding the residual block to a predicted block of one of the frames in the reference frame memory 64. The motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to compute sub-integer pixel values ​​for use in motion estimation. The adder 62 adds the reconstructed residual block to the motion-compensated predicted block produced by the motion compensation unit 44 to produce a reconstructed video block for storage in the reference frame memory 64. The reconstructed video block may be used as a reference block by the motion estimation unit 42 and the motion compensation unit 44 to intercode blocks in subsequent video frames.

[0078] Figure 3 is a block diagram showing an example of a video decoder 30 capable of performing video coding techniques. In the example in Figure 3, the video decoder 30 includes an entropy decoding unit 70, a motion compensation unit 72, an intra-prediction unit 74, an inverse quantization unit 76, an inverse transform unit 78, a reference frame memory 82, and an adder 80. In some examples, the video decoder 30 performs a decoding path that is generally the reverse of the coding path described with respect to the video encoder 20 (Figure 2). The motion compensation unit 72 may generate prediction data based on motion vectors received from the entropy decoding unit 70, while the intra-prediction unit 74 may generate prediction data based on an intra-prediction mode indicator received from the entropy decoding unit 70.

[0079] During the decoding process, the video decoder 30 receives an encoded video bitstream from the video encoder 20, representing the video blocks and associated syntax elements of the encoded video slice. The entropy decoding unit 70 of the video decoder 30 entropy-decodes the bitstream to generate quantized coefficients, motion vectors or intra-predictive mode indicators, and other syntax elements. The entropy decoding unit 70 transfers the motion vectors and other syntax elements to the motion compensation unit 72. The video decoder 30 may receive syntax elements at the video slice level and / or video block level.

[0080] When a video slice is coded as an intra-coded (I) slice, the intra-prediction unit 74 may generate prediction data for the video blocks of the current video slice based on the signaled intra-prediction mode and data from previously decoded blocks of the current frame or picture. When a video frame is coded as an intercoded (e.g., B, P, or GPB) slice, the motion compensation unit 72 generates prediction blocks for the video blocks of the current video slice based on motion vectors and other syntax elements received from the entropy decoding unit 70. The prediction blocks may be generated from one of the reference pictures in one of the reference picture lists. The video decoder 30 may construct reference frame lists, namely List 0 and List 1, using a default construction technique based on the reference pictures stored in the reference frame memory 82.

[0081] The motion compensation unit 72 determines prediction information for the video blocks of the current video slice by analyzing the motion vectors and other syntax elements, and uses the prediction information to generate prediction blocks for the current video blocks being decoded. For example, the motion compensation unit 72 uses some of the received syntax elements to determine the prediction mode used to code the video blocks of the video slice (e.g., intra-prediction or inter-prediction), the inter-prediction slice type (e.g., B-slice, P-slice, or GPB-slice), construction information for one or more of the reference picture lists for the slice, the motion vector for each inter-coded video block of the slice, the inter-prediction status for each inter-coded video block of the slice, and other information for decoding the video blocks in the current video slice.

[0082] The motion compensation unit 72 may also perform interpolation based on an interpolation filter. The motion compensation unit 72 may calculate interpolated values ​​for sub-integer pixels of a reference block using an interpolation filter such as the one used by the video encoder 20 during the encoding of the video block. In this case, the motion compensation unit 72 may determine the interpolation filter to be used by the video encoder 20 from the received syntax elements and use the interpolation filter to generate a predicted block.

[0083] Data for the texture image corresponding to the depth map can be stored in the reference frame memory 82. The motion compensation unit 72 can also be configured to interpret depth blocks of the depth map.

[0084] Image and video compression has grown rapidly, leading to various coding standards. Such video coding standards include International Telecommunication Union (ITU) Telecommunications Standardization Sector (ITU-T) H.261, ISO / IEC Motion Picture Experts Group (MPEG)-1 Part 2, ITU-T H.262 or ISO / IEC MPEG-2 Part 2, ITU-T H.263, ITU-T H.264 or ISO / IEC MPEG-4 Part 10 (also known as ISO / IEC MPEG-4 Part 10), Advanced Video Coding (AVC), and High Efficiency Video Coding (HEVC), also known as ITU-T H.265 or MPEG-H Part 2. AVC includes extensions such as Scalable Video Coding (SVC), Multiview Video Coding (MVC), Multiview Video Coding plus Depth (MVC+D), and 3D AVC (3D-AVC). HEVC includes extensions such as Scalable HEVC (SHVC), Multiview HEVC (MV-HEVC), and 3D HEVC (3D-HEVC).

[0085] Versatile Video Coding (VVC) is a new video coding standard under development by the ITU-T and ISO / IEC joint video expert team (JVET). As of this writing, the latest working draft (WD) of VVC is included in JVET-K1001-v1. JVET document JVET-K0325-v3 includes updates to the high-level syntax of VVC.

[0086] This disclosure describes techniques intended to address issues during the development of the VVC standard. However, these techniques may also be applicable to other video / media codec specifications.

[0087] Video compression techniques perform spatial (intra-picture) and / or temporal (inter-picture) prediction to reduce or eliminate redundancy inherent in a video sequence. In block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be divided into video blocks, which may also be called tree blocks, coding tree blocks (CTBs), coding tree units (CTUs), coding units (CUs), and / or coding nodes. A video block in an intra-coded (I) slice of a picture is coded using spatial prediction about a reference sample in a neighboring block within the same picture. A video block in an inter-coded (P or B) slice of a picture may use spatial prediction about a reference sample in a neighboring block within the same picture, or temporal prediction about a reference sample in another reference picture. A picture may be called a frame, and a reference picture may be called a reference frame.

[0088] Spatial or temporal prediction yields a predicted block for the block to be coded. Residual data represents the pixel difference between the original block to be coded and the predicted block. Intercoded blocks are coded according to a motion vector pointing to the reference sample block forming the predicted block and residual data showing the difference between the coded block and the predicted block. Intracoded blocks are coded according to the intracoded mode and residual data. For further compression, the residual data may be transformed from the pixel domain to the transformation domain, yielding residual transformation coefficients, which can then be quantized. The quantized transformation coefficients, initially arranged in a two-dimensional array, may be scanned to produce a one-dimensional vector of transformation coefficients, and entropy coding may be applied to achieve further compression.

[0089] In video codec specifications, pictures are identified for multiple purposes, including use as reference pictures in interpretation, output of pictures from the decoded picture buffer (DPB), scaling of motion vectors, and weighted prediction. In AVC and HEVC, pictures can be identified by picture order count (POC). In AVC and HEVC, pictures in the DPB can be marked as "used for short-term reference," "used for long-term reference," or "not used for reference." When a picture is marked as "not used for reference," it can no longer be used for prediction and can be removed from the DPB when it is no longer needed for output.

[0090] In AVC, there are two types of reference pictures: short-term and long-term. A reference picture can be marked as "not for reference" when it is no longer needed for predictive referencing. The conversion between these three statuses (short-term, long-term, and not for reference) is controlled by the decryption reference picture marking process. There are two alternative decryption reference picture marking mechanisms: the implicit sliding window process and the explicit memory management control operation (MMCO) process. The sliding window process marks a short-term reference picture as "not for reference" when the number of referenced frames equals a given maximum number (max_num_ref_frames in SPS). Short-term reference pictures are stored in a first-in, first-out manner so that the most recent decrypted short-term picture is held in the DPB.

[0091] An explicit MMCO process may include multiple MMCO commands. An MMCO command may mark one or more short-term or long-term reference pictures as “not used for reference,” or it may mark all pictures as “not used for reference,” or it may mark the current reference picture or an existing short-term reference picture as long-term and assign a long-term picture index to that long-term reference picture.

[0092] In AVC, the process of marking reference pictures, as well as the process of outputting and deleting pictures from the DPB, is performed after the pictures have been decoded.

[0093] HEVC introduces a different technique for managing reference pictures called the Reference Picture Set (RPS). The most fundamental difference between the RPS concept and AVC's MMCO / sliding window is that for each particular slice, a complete set of reference pictures used by the current picture or any subsequent pictures is provided. Thus, the complete set of all pictures that must be retained in the DPB for use by current or future pictures is signaled. This differs from the AVC method, where only changes relative to the DPB are signaled. With the RPS concept, information from earlier pictures in the decoding order is not needed to maintain the correct status of reference pictures in the DPB.

[0094] To leverage the advantages of RPS and enhance fault tolerance, the order of picture decoding and DPB operations in HEVC is modified compared to AVC. In AVC, picture marking and buffer operations (both outputting and deleting decoded pictures from the DPB) are generally applied after the current picture has been decoded. In HEVC, RPS is first decoded from the slice header of the current picture, and then picture marking and buffer operations are generally applied before the current picture is decoded.

[0095] Each slice header in HEVC must include parameters for signaling the RPS for the picture containing the slice. The only exception is that the RPS is not signaled for IDR slices; instead, the RPS is presumed to be empty. For I slices that do not belong to an IDR picture, an RPS may be provided even if the I slice belongs to an I picture, because there may be a picture that comes after the I picture in the decoding order, and the interpretation from the picture that came before the I picture in the decoding order is used for I slices that do not belong to an I picture. The number of pictures in the RPS should not exceed the DPB size limit, as specified by the sps_max_dec_pic_buffering syntax element in the SPS.

[0096] Each picture is associated with a POC value that represents the output order. The slice header contains a fixed-length codeword, pic_order_cnt_lsb, which represents the least significant bit of the complete POC value, also known as the POC LSB. The length of the codeword is signaled in the SPS and can be between 4 and 16 bits. The RPS concept uses the POC to identify the reference picture. In addition to its own POC value, each slice header directly contains, or inherits from, a coded representation of the POC value (or LSB) of each picture in the RPS.

[0097] The RPS for each picture includes five different sets of reference pictures, also known as the five RPS subsets. RefPicSetStCurrBefore includes all short-term reference pictures that are before the current picture in both the decoding and output order and that may be used in the interpretation of the current picture. RefPicSetStCurrAfter includes all short-term reference pictures that are before the current picture in the decoding order, after the current picture in the output order, and that may be used in the interpretation of the current picture. RefPicSetStFoll includes all short-term reference pictures that may be used in the interpretation of one or more pictures that are after the current picture in the decoding order, but are not used in the interpretation of the current picture. RefPicSetLtCurr includes all long-term reference pictures that may be used in the interpretation of the current picture. RefPicSetLtFoll includes all long-term reference pictures that may be used in the interpretation of one or more pictures that are after the current picture in the decoding order, but are not used in the interpretation of the current picture.

[0098] RPS is signaled using up to three loops that iterate through different types of reference pictures: short-term reference pictures with a lower POC value than the current picture, short-term reference pictures with a higher POC value than the current picture, and long-term reference pictures. In addition, a flag (used_by_curr_pic_X_flag) is sent for each reference picture indicating whether the reference picture is used for reference by the current picture (included in one of the lists RefPicSetStCurrBefore, RefPicSetStCurrAfter, or RefPicSetLtCurr) or not (included in one of the lists RefPicSetStFoll or RefPicSetLtFoll).

[0099] Figure 4 shows the RPS400 with the current picture B14, along with entries (e.g., pictures) from all subsets 402 of the RPS400. In the example in Figure 4, the current picture B14 contains exactly one picture from each of the five subsets 402 (also known as RPS subsets). P8 is a picture in subset 402 called RefPicSetStCurrBefore because the picture is earlier in the output order and used by B14. P12 is a picture in subset 402 called RefPicSetStCurrAfter because the picture is later in the output order and used by B14. P13 is a picture in subset 402 called RefPicSetStFoll because it is a short-term reference picture that is not used by B14 (but must be retained in the DPB because it is used by B15). P4 is a picture in subset 402 called RefPicSetLtCurr because it is a long-term reference picture used by B14. I0 is a picture in subset 402 called RefPicSetStLtFoll because it is a long-term reference picture that is not used by the current picture (but must be kept in DPB because it is used by B15).

[0100] The short-term portion of RPS400 may be included directly in the slice header. Alternatively, the slice header may contain only a syntax element representing an index that references a predetermined list of RPSs transmitted in an active SPS. The short-term portion of RPS402 may be signaled using one of two different methods: interRPS as described below and intraRPS as described here. When intraRPS is used, num_negative_pics and num_positive_pics are signaled, representing the lengths of two different lists of reference pictures. These lists each contain reference pictures with negative and positive POC differences compared to the current picture. Each element in these lists is encoded using a variable-length code that represents the difference in POC value relative to the previous element in the list minus 1.

[0101] When encoding recurring RPS in a sequence parameter set, it is possible to encode elements of one RPS (e.g., RPS400) in relation to another RPS already encoded in the sequence parameter set. This is called interRPS. Since all RPS in a sequence parameter set are in the same Network Abstraction Layer (NAL) unit, there are no fault tolerance issues associated with this method. The interRPS syntax takes advantage of the fact that the RPS of the current picture can be predicted from the RPS of previously decoded pictures. This is because all reference pictures of the current picture must be either reference pictures of previous pictures or previously decoded pictures themselves. It is only necessary to indicate which of these pictures should be reference pictures and which should be used for predicting the current picture. Thus, the syntax comprises an index pointing to an RPS to be used as a predictor, a delta_POC to be added to the predictor's delta_POC to obtain the delta POC of the current RPS, and a set of indicators to show which pictures are reference pictures and whether they are used only for predicting future pictures. In one embodiment, Delta POC refers to the difference in POC values ​​between the current reference picture and another (e.g., previous) reference picture.

[0102] Encoders wishing to utilize long-term reference pictures must set the SPS syntax element long_term_ref_pics_present_flag to 1. Long-term reference pictures can then be signaled in the slice header by a fixed-length codeword pos_lst_lt representing the least significant bit of the complete POC value for each long-term picture. Each pos_lsb_lt is a copy of the pic_order_cnt_lsb codeword signaled for a particular long-term picture. It is also possible to signal a set of long-term pictures in the SPS as a list of POC LSB values. The POC LSBs for long-term pictures can then be signaled in the slice header as an index to this list.

[0103] The `delta_poc_msb_cycle_lt_minus1` syntax element may be additionally signaled to enable the calculation of the full POC distance of long-term reference pictures to the current picture. The codeword `delta_poc_msb_cycle_lt_minus1` is required to be signaled for each long-term reference picture that has the same POC LSB value as any other reference picture in the RPS.

[0104] For reference picture marking in HEVC, there are typically a number of pictures in the DPB before picture decoding. Some of these may be available for prediction and are therefore marked as "used for reference." Others may not be available for prediction but are waiting for output and are therefore marked as "not used for reference." Once the slice header is parsed, the picture marking process takes place before the slice data is decoded. Pictures that exist in the DPB and are marked as "used for reference" but are not included in the RPS are marked as "not used for reference." Pictures that do not exist in the DPB but are included in the reference picture set are ignored if used_by_curr_pic_X_flag is equal to 0. However, if used_by_curr_pic_X_flag is equal to 1 instead, this reference picture was intended to be used for prediction in the current picture but has been lost. An unintended loss of a picture is then inferred, and the decoder must take appropriate action.

[0105] After the current picture is decrypted, it will be marked as "to be used for short-term reference".

[0106] Next, the construction of the reference picture list in HEVC is discussed. In HEVC, the term inter-prediction is used to indicate a prediction derived from data elements (e.g., sample values ​​or motion vectors) of reference pictures other than the currently decoded picture. Like AVC, a picture can be predicted from multiple reference pictures. The reference pictures used for inter-prediction are organized in one or more reference picture lists. The reference index identifies which of the reference pictures in the list should be used to create the prediction signal.

[0107] A single reference picture list, list 0, is used for the P slice, and two reference picture lists, list 0 and list 1, are used for the B slice. Similar to AVC, reference picture list construction in HEVC involves reference picture list initialization and reference picture list modification.

[0108] In AVC, the initialization process for list 0 differs for P slices (where decoding order is used) and B slices (where output order is used). In HEVC, output order is used in both cases.

[0109] Reference picture list initialization creates default lists 0 and 1 (if the slice is a B slice) based on three RPS subsets: RefPicSetStCurrBefore, RefPicSetStCurrAfter, and RefPicSetLtCurr. Short-term pictures with earlier (later) output order are first inserted into list 0 (list 1) in ascending order of POC distance to the current picture, then short-term pictures with later (earlier) output order are inserted into list 0 (list 1) in ascending order of POC distance to the current picture, and finally, long-term pictures are inserted at the end. Regarding RPS, for list 0, entries in RefPicSetStCurrBefore are inserted into the initial list, followed by entries in RefPicSetStCurrAfter. Then, if available, entries in RefPicSetLtCurr are appended.

[0110] In HEVC, if the number of entries in the list is less than the number of target active reference pictures (signaled in the picture parameter set or slice header), the above process is repeated (reference pictures already added to the reference picture list are added again). If the number of entries is greater than the number of targets, the list is truncated.

[0111] After the referenced picture list is initialized, the referenced picture list can be modified based on referenced picture list modification commands so that the referenced pictures for the current picture can be arranged in any order, including cases where a particular referenced picture may appear at more than one position in the list. When the flag indicating the presence of list modification is set to 1, a fixed number of commands (equal to the target number of entries in the referenced picture list) are signaled, with each command inserting one entry into the referenced picture list. The referenced picture is identified in the command by its index to the list of referenced pictures for the current picture, derived from the RPS signaling. This differs from referenced picture list modification in H.264 / AVC, where pictures are identified by either a picture number (derived from the frame_num syntax element) or a long-term referenced picture index, and fewer commands may be required, for example, to swap the first two entries in the initial list, or to insert one entry at the beginning of the initial list and shift the other entry.

[0112] The reference picture list is allowed to contain any reference picture with a TemporalId greater than the current picture. An HEVC bitstream can consist of several temporal sublayers. Each NAL unit belongs to a specific sublayer, indicated by its TemporalId (equal to temporal_id_plus1-1).

[0113] Reference picture management is directly based on the reference picture list. The JCT-VC document JCTVC-G643 includes a method for directly using three reference picture lists—reference picture list 0, reference picture list 1, and idle reference picture list—for managing reference pictures in the DPB, thereby eliminating the need for signaling and decoding processes for either 1) the sliding window and MMCO process, as well as the reference picture list initialization and modification process in AVC, or 2) the reference picture set, as well as the reference picture list initialization and modification process in HEVC.

[0114] Unfortunately, Reference Picture List (RPL)-based reference picture management has drawbacks. For example, some RPL-based reference picture management schemes are not optimized in terms of signaling syntax elements in the bitstream. This results in such RPL-based methods requiring a larger bit count for signaling compared to other more obvious reference picture management methods, such as RPS-based methods. The signaling inefficiencies of RPL-based methods stem from several factors.

[0115] For example, some syntax elements in the RPL structure are coded using less efficient entropy coding. For instance, coding the syntax element representing the delta POC value of a short-circuit reference picture (STRP) uses a signed integer zero-order exponential Golomb coded syntax element (e.g., se(v)) where the left bit is first, since the delta POC value can be either positive or negative. To code any non-negative integer x using exponential Golomb coding, the first step is to write x+1 in binary. Then, count the bits written, subtract 1, and write the starting 0 bits of that number before the previous bit string. The first few values ​​of the sign are 0⇒1⇒1, 1⇒10⇒010, 2⇒11⇒011, 3⇒100⇒00100. However, this can be done more efficiently if the sign and absolute values ​​of the delta POC are coded separately.

[0116] Signaling RPL indices (for example, for reference picture list 0 and reference picture list 1) when they refer to a predetermined RPL structure in a parameter set (e.g., SPS) may not be as efficient as always signaling both indices. Often, the predetermined RPL structures for RPL0 and RPL1 can be such that the index for RPL0 and the index for RPL1 are the same when the picture's RPL refers to a predetermined RPL structure in a parameter set.

[0117] Furthermore, there is no inter-RPL coding for writing a reference picture list structure to a coded video bitstream. For example, an RPL structure can be coded without referencing a previously signaled RPL structure in the bitstream. In one embodiment, the RPL structure refers to a programming structure containing an indexed list of pointers to reference picture candidates.

[0118] Several embodiments, which can be applied individually and / or in combination, that solve the problems and address the shortcomings described herein are described herein. Each of these embodiments is described below in detail.

[0119] In one embodiment, when delta POC values ​​are coded for STRP, the sign value and absolute value are coded separately in the video bitstream. A flag is signaled in the same set of parameters (e.g., SPS, PPS) as a predetermined RPL structure to indicate whether the delta POC values ​​in each RPL structure have the same sign value (for example, all delta POCs in the same RPL structure are either positive or negative delta POC values). This flag may be called "all_rpl_entries_same_sign_flag".

[0120] When all_rpl_entries_same_sign_flag is equal to 1, the flag is signaled in the RPL structure to indicate the sign value of all entries in the RPL structure (e.g., the sign value of the delta POC value of the STRP). When all_rpl_entries_same_sign_flag is equal to 0, the flag is signaled in the RPL structure to indicate the sign value of each entry associated with a STRP in each RPL structure. In one embodiment, the absolute value of the delta POC value of a STRP entry in the RPL structure is coded using an unsigned integer zero-order exponential Golomb code (e.g., ue(v)).

[0121] Alternatively, instead of using a single flag called all_rpl_entries_same_sign_flag, two flags may be signaled, one for each RPL structure list (for example, an RPL structure list for RPL0 and an RPL structure list for RPL1).

[0122] When creating predetermined RPL structures for the RPL0 list and RPL1 list in the parameter set for encoding, the RPL structures in the lists for RPL0 and RPL1 can be made such that the RPL structure for list 0 and the RPL structure for list 1 are paired. Therefore, when a picture refers to a predetermined RPL structure in the parameter set, the index for RPL0 of that picture and the index for RPL0 are the same.

[0123] In relation to the above, the flag may indicate whether or not a syntax element for RPL1, which references a predetermined RPL structure, is present in the slice header. This flag may be called "rpl1_idx_present_flag". This flag may be signaled in the SPS or PPS, depending on the intended scope or persistence of the flag. In some embodiments, signaling of the flag in the PPS is preferred.

[0124] Based on the value of rpl1_idx_present_flag, the following applies: When rpl1_idx_present_flag is equal to 1, RPL1 in the slice header associated with the parameter set containing the flag refers to a predetermined RPL structure, and its index is not signaled in the slice header but rather inferred from the corresponding syntax element for RPL0 in the same slice. That is, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not signaled and are inferred (e.g., duplicated) from the values ​​of ref_pic_list_sps_flag[0] and ref_pic_list_idx[0], respectively. Otherwise, when rpl1_idx_present_flag is equal to 0, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] exist in the slice header associated with the parameter set containing the flag.

[0125] Alternatively, based on the value of rpl1_idx_present_flag, the following applies: When rpl1_idx_present_flag is equal to 1, the index of RPL1 is not signaled in the slice header when RPL1 in the slice header associated with the parameter set containing the flag refers to a predetermined RPL structure. Rather, the index of RPL1 is inferred from the corresponding syntax element for RPL0 in the same slice. That is, ref_pic_list_idx[1] is not signaled and is inferred (e.g., duplicated) from the value of ref_pic_list_idx[0], respectively. Otherwise, when rpl1_idx_present_flag is equal to 0, ref_pic_list_idx[1] exists in the slice header associated with the parameter set containing the flag.

[0126] A flag may be used to indicate whether the RPL structure in the list for RPL1 has the same content as the RPL structure in the list for RPL0. This flag may be called "rpl1_copy_from_rpl0_flag". This flag shall be signaled in the same parameter set as the predetermined RPL structure and shall be located before the signaling of the predetermined RPL structure.

[0127] Based on the value of rpl1_copy_from_rpl0_flag, the following applies: When rpl1_copy_from_rpl0_flag is equal to 1, the number of RPL structures for List 1 is not signaled; instead, it is inferred to be the same as the number of RPL structures for List 0. The RPL structures for List 1 are not signaled. Instead, after the predetermined RPL structures for List 0 are parsed and decoded in the decoder, a copy of the exact same RPL structure is created for each RPL structure for List 0, and the copy of the RPL structure is assigned as the RPL structure for List 1 with the same index. Otherwise, when rpl1_copy_from_rpl0_flag is equal to 0, the number of RPL structures for List 1 and the RPL structures for List 1 are signaled.

[0128] The contents of an RPL structure can be predicted from another RPL structure. When a predetermined RPL structure in a parameter set is divided into two lists (for example, an RPL structure list for List 0 and an RPL structure list for List 1), only the RPL structure in the list for List 0 can be used as a reference for interRPL. An RPL structure in the list for List 0 can only point to another RPL structure in the same list with an index less than the index of that RPL structure, while an RPL structure in the list for List 1 can point to any RPL structure in the list for List 0. An RPL structure explicitly signaled in a slice header can point to any of the predetermined RPL structures in the list for List 0. Alternatively, an RPL structure in the list for List 0 or List 1 can only point to another RPL structure in the list for List 0 with an index less than the index of that RPL structure. An RPL structure explicitly signaled in a slice header can point to any of the predetermined RPL structures in the list for List 0.

[0129] In one alternative form, when a predetermined RPL structure in the parameter set is divided into two lists (for example, an RPL structure list for List 0 and an RPL structure list for List 1), an RPL structure in the list for List 0 can only point to another RPL structure in the list for List 0 that has an index smaller than the index of that RPL structure. Similarly, an RPL structure in the list for List 1 can only point to another RPL structure in the list for List 1 that has an index smaller than the index of that RPL structure. An RPL structure explicitly signaled in the slice header for RPL0 can point to any of the predetermined RPL structures in the list for List 0, and an RPL structure explicitly signaled in the slice header for RPL1 can point to any of the predetermined RPL structures in the list for List 1.

[0130] In another alternative, when a predetermined RPL structure in the parameter set is not split into two lists (for example, the RPL structure list for list 0 and the RPL structure list for list 1 are signaled in a single list), an RPL structure can only point to another RPL structure in a list with an index smaller than its own. An RPL structure explicitly signaled in a slice header can point to any of the predetermined RPL structures.

[0131] In interRPL, the index for a reference RPL structure is coded as the delta of the current RPL structure index minus 1, and can be coded using ue(v) coding. In one alternative form, the reference RPL index is coded directly using u(v) coding. The number of bits used to represent the index is set as the binary logarithm of the number of RPL structures in the list suitable for reference. For example, when only RPL structures in the list for list 0 can be used as references, the number of bits to represent the reference RPL index is the binary logarithm of the number of RPL structures in the list for list 0. In another alternative form, the index for a reference RPL structure can be coded using either ue(v) or u(v), depending on the interRPL mode.

[0132] To support interRPL, each RPL structure is coded using one of the modes described below. Note that the order of the modes below does not necessarily mean the order of the mode values. Mode indications can be coded as follows: In one embodiment, a mode indication can be coded simply using ue(v). In one embodiment, a mode indication can be coded using u(v) with the number of bits to represent the mode, which is the binary logarithm of the total number of defined modes.

[0133] The first RLP coding mode is intracoding mode. This mode functions similarly to other mechanisms for signaling the contents of an RPL structure. See, for example, the method described in U.S. Provisional Application No. 62 / 719,360, titled "Reference Picture Management in Video Coding," filed August 17, 2018. Alternatively, an integer value greater than 0 may be signaled for each RPL structure and called granularity_val. The value of granularity_val is used to scale or divide each value representing the POC delta value of the STRP in the RPL structure.

[0134] The second RPL coding mode is an intercoding mode that utilizes delta POC values ​​for STRPs in the reference RPL structure and the current RPL structure, which have the same or equal difference. To code the RPL using this mode, the following information is signaled in the bitstream:

[0135] First, the coding mode and reference index are signaled in the bitstream. The reference index is the index of the reference RPL structure. The reference index can be coded as described above. However, the mechanism may also code the reference index as the delta between the current RPL structure index and the reference RPL structure index minus 1, which is coded as ue(v). The offset is also signaled in the bitstream. The offset is the difference between the delta POC of the STRP in the reference RPL structure and the delta POC of the STRP in the current RPL structure. The value of the offset may be restricted to positive values ​​only (for example, if the delta POC value of the STRP in the reference RPL structure is less than the delta POC value of the STRP in the current RPL structure, this mode cannot be used to code the current RPL structure), restricted to negative values ​​only, or be either positive or negative. The offset may be signaled using term_minus1 when coded as ue(v). A flag is also signaled in the bitstream for each entry in the referenced RPL structure to indicate whether the entry is to be used as an entry in the current RPL structure. When an entry is a STRP entry in the referenced RPL structure and is used as an entry in the current RPL structure, the entry is also a STRP entry in the current RPL structure, and its value is the entry value in the referenced RPL structure minus the offset (plus 1 if the _minus1 term is used to code the offset). When an entry is a Long-Term Reference Picture (LTRP) entry in the referenced RPL structure and is used as an entry in the current RPL structure, the entry is also an LTRP entry in the current RPL structure, and its value is simply duplicated for the entry in the referenced RPL structure.

[0136] The third RPL coding mode is an intercoding mode that takes advantage of the fact that entries in the current RPL structure (e.g., STRP and LTRP) are a superset of entries in the reference RPL structure. That is, all entries in the reference RPL structure are the same as the first X entries (replace X with the number of entries in the reference RPL structure) with zero or more additional entries. To code the RPL using this mode, the following information is signaled in the bitstream:

[0137] First, the coding mode and reference index are signaled in the bitstream. The reference index is the index of the reference RPL structure. The reference index can be coded as described above. The number of additional entries is also signaled in the bitstream. The number of additional entries is the difference between the number of entries in the current RPL structure and the number of entries in the reference RPL structure. When an entry is a STRP entry in the reference RPL structure, the entry is also a STRP entry in the current RPL structure, and its value is simply duplicated for the entry in the reference RPL structure. When an entry is an LTRP entry in the reference RPL structure, the entry is also an LTRP entry in the current RPL structure, and its value is simply duplicated for the entry in the reference RPL structure. After all entries have been duplicated from the reference RPL structure to the current RPL structure, the following information is signaled for each additional entry. When a long-term reference picture is used in a bitstream (i.e., this can be indicated by a flag in the same parameter set), the flag is signaled to indicate whether the additional entry is an LTRP entry or a STRP entry. If the entry is an LTRP entry, the LTRP entry's POC LSB is signaled. Otherwise, the STRP entry's delta POC is signaled. The value of the delta POC can be signaled as the delta from a previous STRP entry, or simply as the delta from the current picture's POC.

[0138] The fourth RPL coding mode is an intercoding mode that takes advantage of the fact that entries in the current RPL structure (e.g., STRP and LTRP) are either exactly the same as entries in the reference RPL structure, or exactly the same with their sign values ​​reversed. To code an RPL using this mode, the following information is signaled in the bitstream:

[0139] First, the coding mode and reference index are signaled. The reference index is the index of the reference RPL structure. The reference index can be coded as described above. Optionally, a flag indicating whether the sign value is inverted is also signaled in the bitstream.

[0140] When a bitstream is coded using forward interpretation (e.g., interpretation for pictures with a POC value smaller than the current picture's POC value) and backward interpretation (e.g., interpretation for pictures with a POC value greater than the current picture's POC value), the following constraints apply to reference pictures in RPLs: For each RPL of a picture, all reference pictures in the RPL must have the same interpretation direction, for example, all reference pictures are reference pictures for forward interpretation, or all reference pictures are reference pictures for backward interpretation. For a pair of RPLs of a picture, there are no reference pictures that are included in both RPL0 and RPL1 unless the following condition is true: both RPL0 and RPL1 contain the same reference pictures in the same order. In such a condition, all reference pictures except the first picture in RPL1 (i.e., the picture with the lowest index) are removed from RPL1. As an alternative, all referenced pictures in RPL0 except the first picture (i.e., the picture with the lowest index) are removed from RPL0.

[0141] A video coding technique is disclosed herein that uses a flag to indicate whether the index for a second reference picture list structure can be inferred to be the same as the index for a first reference picture list structure. That is, when the flag has a first value, the index for the second reference picture list structure is not present in the slice header of the coded video bitstream and is inferred to be the same as the index for the first reference picture list structure. On the other hand, when the flag has a second value, the index for the second reference picture list structure is present in the slice header. By utilizing the flag in this manner, the coder / decoder (also known as the "codec") in video coding is improved compared to the current code (e.g., uses fewer bits, requires less bandwidth, is more efficient, etc.). In practice, an improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0142] Figure 5 is a schematic diagram of an embodiment of the video bitstream 500. In this specification, the video bitstream 500 may also be referred to as a coded video bitstream, a bitstream, or a variation thereof. As shown in Figure 5, the bitstream 500 comprises a sequence parameter set (SPS) 510, a picture parameter set (PPS) 512, a slice header 514, and image data 520.

[0143] SPS510 contains data common to all pictures in a sequence of pictures (SOP). In contrast, PPS512 contains data common to all pictures. The slice header 514 contains information about the current slice, such as the slice type and which of the reference pictures is used. SPS510 and PPS512 can be collectively referred to as parameter sets. SPS510, PPS512, and slice header 514 are types of network abstraction layer (NAL) units. Image data 520 comprises data associated with the image or video being encoded or decoded. Image data 520 can simply be referred to as the payload or data being carried in the bitstream 500.

[0144] In one embodiment, the SPS510, PPS512, slice header 514, or another part of the bitstream 500 carries a plurality of reference picture list structures, each containing a plurality of reference picture entries. Those skilled in the art will understand that the bitstream 500 may contain other parameters and information in actual applications.

[0145] Figure 6 shows an embodiment of method 600 for decoding a coded video bitstream (e.g., bitstream 500) implemented by a video decoder (e.g., video decoder 30). Method 600 can be performed after the decoded bitstream has been received directly or indirectly from a video encoder (e.g., video encoder 20). Method 600 improves the decoding process (e.g., makes the decoding process more efficient and faster than conventional decoding processes) because, when a flag is set to a certain value, it can be inferred that the index for a second reference picture list structure is the same as the index for a first reference picture list structure. That is, the second reference picture list structure does not need to be signaled in the coded video bitstream in all situations, as in HEVC and AVC. Therefore, in practice, the performance of the codec is improved, which leads to a better user experience.

[0146] In block 602, a flag is parsed from the coded video bitstream (e.g., video bitstream 500). In one embodiment, this flag is specified as rpl1_idx_present_flag. In one embodiment, this flag is included in the PPS of the coded video bitstream (e.g., PPS512). In one embodiment, this flag is included in the SPS of the coded video bitstream (e.g., SPS510).

[0147] In one embodiment, the first value of the flag is 1. In one embodiment, when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header. In one embodiment, the second value of the flag is 0. In one embodiment, when the second value of the flag is 0, ref_pic_list_sps_flag[0] and ref_pic_list_idx[0] are included in the slice header.

[0148] In block 604, the first reference picture list structure is parsed from the coded video bitstream. In one embodiment, the first reference picture list structure is contained in the slice header of the coded video bitstream (e.g., slice header 514). In one embodiment, the flag and the first reference picture list structure are parsed separately from each other; that is, the flag is parsed first, then the first reference picture list structure, or vice versa.

[0149] In block 606, when the flag has a first value, it is determined that the index for the second reference picture list structure does not exist in the slice header of the coded video bitstream, and it is inferred that the index for the second reference picture list structure is the same as the index for the first reference picture list structure. In block 608, when the flag has a second value, it is determined that the index for the second reference picture list structure exists in the slice header.

[0150] In block 610, the reference picture list is generated using a first reference picture list structure, a second reference picture list structure, or any combination thereof. The reference picture list may identify one or more pictures, such as the picture illustrated and described in relation to Figure 4.

[0151] In block 612, interpretation is performed based on the reference picture list to generate a reconstructed block. In one embodiment, the reconstructed block may be used to generate or create an image for display to a user on the display or screen of an electronic device (e.g., a smartphone, tablet, laptop, personal computer, etc.).

[0152] Figure 7 shows an embodiment of method 700 for encoding a video bitstream (e.g., bitstream 500) performed by a video encoder (e.g., video encoder 20). Method 700 can be performed when pictures (e.g., from video) are encoded into a video bitstream and then sent to a video decoder (e.g., video decoder 30). Method 700 improves the encoding process (e.g., makes the encoding process more efficient and faster than conventional encoding processes) because, when a flag is set to a certain value, it can be inferred that the index for a second reference picture list structure is the same as the index for a first reference picture list structure. That is, the second reference picture list structure does not need to be signaled in the encoded video bitstream in all situations, as in HEVC and AVC. Therefore, in practice, the performance of the codec is improved, which leads to a better user experience.

[0153] In block 702, when the index for the second reference picture list structure is not encoded in the slice header of the video bitstream, and the video decoder should infer that the index for the second reference picture list structure is the same as the index for the first reference picture list structure, the flag is encoded into the video bitstream using the first value. In one embodiment, this flag is specified as rpl1_idx_present_flag. In one embodiment, this flag is encoded in the PPS (e.g., PPS512) of the coded video bitstream (e.g., video bitstream 500). In one embodiment, the first reference picture list structure is encoded in the slice header of the video bitstream (e.g., slice header 514).

[0154] In block 704, when the index for the second reference picture list structure is encoded into the slice header of the video bitstream, the flag is encoded into the video bitstream using the second value. In one embodiment, the first reference picture list structure and the second reference picture list are encoded in the slice header of the coded video bitstream.

[0155] In block 706, when the flag is encoded with a first value, the first reference picture list structure is encoded into a video bitstream. In block 708, when the flag is encoded with a second value, the first and second reference picture list structures are encoded into a video bitstream. In some embodiments, the first value of the flag is 1 and the second value of the flag is 0. In some embodiments, when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

[0156] In block 710, the video bitstream is transmitted toward a video decoder (for example, video decoder 30). Upon receipt by the video decoder, the encoded video bitstream can be decoded (for example, as described above) to generate or create an image for display to a user on the display or screen of an electronic device (for example, a smartphone, tablet, laptop, personal computer, etc.).

[0157] A description of the techniques disclosed herein is given in relation to the latest VVC WD. In addition, definitions, syntax, and semantics suitable for implementing the techniques disclosed herein are also provided.

[0158] First, some definitions are given. An intra-random access point (IRAP) picture is a coded picture in which each video coding layer (VCL) NAL unit has a nal_unit_type equal to IRAP_NUT. A long-term reference picture (LTRP) is a picture marked as "used for long-term reference". A non-IRAP picture is a coded picture in which each VCL NAL unit has a nal_unit_type equal to NON_IRAP_NUT. A reference picture list is a list of reference pictures used for interpretation of P or B slices. Two reference picture lists, reference picture list 0 and reference picture list 1, are generated for each slice of a non-IRAP picture. The set of unique pictures referenced by all entries in the two reference picture lists associated with a picture includes all reference pictures that can be used for interpretation of the associated picture, or any picture that follows the associated picture in the decoding order. To decode the slice data of a P slice, only reference picture list 0 is used for interpretation. To decode the slice data of a B slice, both reference picture lists are used for interpretation. To decode the slice data of an I slice, the reference picture lists are not used for interpretation. A short-term reference picture (STRP) is a picture marked as "used for short-term reference".

[0159] Next, several abbreviations are given. In this specification, LTRP means long-term reference picture, and STRP means short-term reference picture.

[0160] The following portions of this disclosure provide syntax and semantics suitable for carrying out the techniques disclosed herein.

[0161] NAL Unit Header Syntax

[0162] [Table 1]

[0163] Sequence parameter set RBSP syntax

[0164] [Table 2]

[0165] Picture parameter set RBSP syntax

[0166] [Table 3]

[0167] Slice header syntax

[0168] [Table 4]

[0169] Reference picture list structure syntax

[0170] [Table 5]

[0171] NAL Unit Header Semantics

[0172] `forbidden_zero_bit` is assumed to be equal to 0. `nal_unit_type` specifies the type of RBSP data structure included in the NAL unit.

[0173] [Table 6]

[0174] The value obtained by subtracting 1 from nuh_temporal_id_plus1 specifies the time identifier for the NAL unit. The value of nuh_temporal_id_plus1 must not be equal to 0. The variable TemporalId is specified as TemporalId=nuh_temporal_id_plus1-1. When nal_unit_type is equal to IRAP_NUT, the coded slice belongs to an IRAP picture, and TemporalId is equal to 0. The value of TemporalId is the same for all VCL NAL units of an access unit. The value of TemporalId for a coded picture or access unit is the value of TemporalId for the VCL NAL unit of the coded picture or access unit. The value of TemporalId for non-VCL NAL units is constrained as follows: When nal_unit_type is equal to SPS_NUT, TemporalId is equal to 0, and the TemporalId of an access unit containing a NAL unit is equal to 0. Instead, if nal_unit_type is equal to EOS_NUT or EOB_NUT, TemporalId shall be equal to 0. Otherwise, TemporalId shall be greater than or equal to the TemporalId of the access unit containing the NAL unit. When the NAL unit is a non-VCL NAL unit, the value of TemporalId shall be equal to the minimum TemporalId value of all access units to which the non-VCL NAL unit applies. When nal_unit_type is equal to PPS_NUT, TemporalId may be greater than or equal to the TemporalId of the access unit containing it, because all Picture Parameter Sets (PPS) may be included at the beginning of the bitstream, and the first coded picture shall have a TemporalId equal to 0.When nal_unit_type is equal to PREFIX_SEI_NUT or SUFFIX_SEI_NUT, the TemporalId may be greater than or equal to the TemporalId of the containing access unit, because an SEI NAL unit may contain information applicable to a subset of the bitstream that contains access units with a TemporalId value greater than the TemporalId of the access unit containing the SEI NAL unit. nuh_reserved_zero_7bits shall be equal to "0000000". Other values ​​for nuh_reserved_zero_7bits may be specified in the future by ITU-T|ISO / IEC. The decoder shall ignore (i.e., remove and discard from the bitstream) any NAL unit with a nuh_reserved_zero_7bits value that is not equal to "0000000".

[0175] Sequence parameter set RBSP semantics

[0176] log2_max_pic_order_cnt_lsb_minus4 specifies the value of the variable MaxPicOrderCntLsb, which is used in the decoding process for picture order counting, as MaxPicOrderCntLsb=2(log2_max_pic_order_cnt_lsb_minus4+4). The value of log2_max_pic_order_cnt_lsb_minus4 should be in the range of 0 to 12, including both ends. sps_max_dec_pic_buffering_minus1 plus 1 specifies the maximum required size of the decoded picture buffer for the Coding Video Sequence (CVS), in units of picture storage buffers. The value of sps_max_dec_pic_buffering_minus1 should be in the range of 0 to MaxDpbSize-1, including both ends, where MaxDpbSize is as specified elsewhere. long_term_ref_pics_flag equal to 0 specifies that LTRP is not used for interpretation of any coded pictures in CVS. A long_term_ref_pics_flag equal to 1 specifies that LTRP may be used for interpretation of one or more coded pictures in CVS. additional_lt_poc_lsb specifies the value of the variable MaxLtPicOrderCntLsb used in the decoding process for the reference picture list, as MaxLtPicOrderCntLsb=2(log2_max_pic_order_cnt_lsb_minus4+4+additional_lt_poc_lsb). The value of additional_lt_poc_lsb should be in the range of 0 to 32-log2_max_pic_order_cnt_lsb_minus4-4, including both ends. If it does not exist, the value of additional_lt_poc_lsb is presumed to be equal to 0.

[0177] A flag equal to 1, all_rpl_entries_same_sign_flag, specifies that all STRP entries in each ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) have the same sign value, where the sign can be positive or negative. A flag equal to 0, all_rpl_entries_same_sign_flag, specifies that STRP entries in each ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) may or may not have the same sign value. A flag equal to 1, rpl1_copy_from_rpl0_flag, specifies that num_ref_pic_lists_in_sps[1] and ref_pic_list_struct(1,rplsIdx,ltrpFlag) do not exist, and the following applies: the value of num_ref_pic_lists_in_sps[1] is set to be equal to the value of num_ref_pic_lists_in_sps[0]. It is inferred that the syntax structure ref_pic_list_struct(1,rplsIdx,ltrpFlag) is identical to the value of ref_pic_list_struct(0,rplsIdx,ltrpFlag). Subsequently, it is inferred that the syntax elements within ref_pic_list_struct(1,rplsIdx,ltrpFlag) are equivalent to the syntax elements within ref_pic_list_struct(0,rplsIdx,ltrpFlag).

[0178] num_ref_pic_lists_in_sps[i] specifies the number of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures in the SPS where listIdx is equal to i. The value of num_ref_pic_lists_in_sps[i] is in the range of 0 to 64, including both ends. For each value of listIdx (equal to 0 or 1), the decoder should allocate memory for a total of num_ref_pic_lists_in_sps[i] ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures, because there may be one ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure that is directly signaled in the slice header of the current picture.

[0179] Picture parameter set RBSP semantics

[0180] The value of num_ref_idx_default_active_minus1[i] plus 1 specifies the inferred value of the variable NumRefIdxActive[0] for P or B slices where num_ref_idx_active_override_flag is equal to 0 when i is equal to 0, and the inferred value of NumRefIdxActive[1] for B slices where num_ref_idx_active_override_flag is equal to 0 when i is equal to 1. The value of num_ref_idx_default_active_minus1[i] is assumed to be in the range of 0 to 14, including both ends. A rpl1_idx_present_flag equal to 0 specifies that ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] do not exist in the slice header. A value of 1 for rpl1_idx_present_flag indicates that ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] may be present in the slice header.

[0181] Slice header semantics

[0182] If present, the values ​​of the slice header syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb, respectively, shall be the same for all slice headers of the coded picture. slice_type specifies the coding type of the slice according to Table 7-3.

[0183] [Table 7]

[0184] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type is assumed to be equal to 2. slice_pic_order_cnt_lsb specifies the picture order count modulo MaxPicOrderCntLsb for the current picture. The length of the slice_pic_order_cnt_lsb syntax element is log2_max_pic_order_cnt_lsb_minus4+4 bits. The value of slice_pic_order_cnt_lsb is assumed to be in the range of 0 to MaxPicOrderCntLsb-1, including both ends. If slice_pic_order_cnt_lsb does not exist, it is assumed to be equal to 0. A ref_pic_list_sps_flag[i] equal to 1 specifies that the current picture's reference picture list i is derived based on one of the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures in the active SPS where listIdx is equal to i. A ref_pic_list_sps_flag[i] equal to 0 specifies that the current picture's reference picture list i is derived based on a ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure where listIdx is equal to i, which is directly included in the slice header of the current picture. When num_ref_pic_lists_in_sps[i] is equal to 0, the value of ref_pic_list_sps_flag[i] is assumed to be equal to 0. When rpl1_idx_present_flag is equal to 0 and ref_pic_list_sps_flag[0] exists, the value of ref_pic_list_sps_flag[1] is presumed to be equal to the value of ref_pic_list_sps_flag[0].ref_pic_list_idx[i] specifies the index to a list of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures in the active SPS where listIdx is equal to i, which is used to derive the reference picture list i of the current picture. The syntax element ref_pic_list_idx[i] is represented by Ceil(Log2(num_ref_pic_lists_in_sps[i])) bits. If it does not exist, the value of ref_pic_list_idx[i] is presumed to be equal to 0. The value of ref_pic_list_idx[i] is assumed to be in the range of 0 to num_ref_pic_lists_in_sps[i]-1, including both ends. When rpl1_idx_present_flag is equal to 0 and ref_pic_list_sps_flag[0] exists, the value of ref_pic_list_idx[1] is presumed to be equal to the value of ref_pic_list_idx[0]. A num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] exists for P and B slices, and that the syntax element num_ref_idx_active_minus1[1] exists for B slices. A num_ref_idx_active_override_flag equal to 0 specifies that the syntax elements num_ref_idx_active_minus1[0] and num_ref_idx_active_minus1[1] do not exist. If num_ref_idx_active_minus1[i] exists, the value of the variable NumRefIdxActive[i] is specified as NumRefIdxActive[i] = num_ref_idx_active_minus1[i] + 1. The value of num_ref_idx_active_minus1[i] is assumed to be in the range of 0 to 14, including both endpoints.

[0185] The value of NumRefIdxActive[i]-1 specifies the maximum reference index to the reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, the reference index to the reference picture list i may not be used to decode the slice. For i equal to 0 or 1, if the current slice is a B slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is presumed to be equal to num_ref_idx_default_active_minus1[i]+1. If the current slice is a P slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[0] is presumed to be equal to num_ref_idx_default_active_minus1[0]+1. If the current slice is a P slice, NumRefIdxActive[i] is presumed to be equal to 0. When the current slice is an I slice, it is inferred that both NumRefIdxActive[0] and NumRefIdxActive[1] are equal to 0.

[0186] Alternatively, for i equal to 0 or 1, the following applies after the above: rplsIdx1 is set to equal ref_pic_list_sps_flag[i]?ref_pic_list_idx[i]:num_ref_pic_lists_in_sps[i], and numRpEntries[i] is equal to num_strp_entries[i][rplsIdx1]+num_ltrp_entries[i][rplsIdx1]. When NumRefIdxActive[i] is greater than numRpEntries[i], the value of NumRefIdxActive[i] is set to equal numRpEntries[i].

[0187] Reference Picture List Structure Semantics

[0188] The ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure can exist in either the SPS or the slice header. Depending on whether the syntax structure is in the slice header or the SPS, the following applies: If it is in the slice header, the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure specifies the reference picture listIdx of the current picture (the picture containing the slice). Otherwise (if present in an SPS), the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure specifies a candidate for the reference picture list listIdx, and the term “current picture” in the semantics specified for the remainder of this section refers to each picture that 1) has one or more slices containing ref_pic_list_idx[listIdx] equal to an index to a list of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures present in an SPS, and 2) is in a CVS that has an SPS as the active SPS. rpl_mode[listIdx][rplsIdx] specifies the coding mode of the syntax elements in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. num_strp_entries[listIdx][rplsIdx] specifies the number of STRP entries in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. num_ltrp_entries[listIdx][rplsIdx] specifies the number of LTRP entries in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. If none exist, the value of num_ltrp_entries[listIdx][rplsIdx] is presumed to be equal to 0.The variable NumEntriesInList[listIdx][rplsIdx] is derived as follows: NumEntriesInList[listIdx][rplsIdx]=num_strp_entries[listIdx][rplsIdx]+num_ltrp_entries[listIdx][rplsIdx]. The value of NumEntriesInList[listIdx][rplsIdx] is assumed to be in the range of 0 to sps_max_dec_pic_buffering_minus1, including both ends. strp_entries_sign_flag[listIdx][rplsIdx] equal to 1 specifies that all STRP entries in ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) have a value of 0 or greater. A strp_entries_sign_flag[listIdx][rplsIdx] equal to 0 specifies that all STRP entries in ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) have a value less than 0.

[0189] A value of 1 for lt_ref_pic_flag[listIdx][rplsIdx][i] indicates that the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure is an LTRP entry. A value of 0 for lt_ref_pic_flag[listIdx][rplsIdx][i] indicates that the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure is a STRP entry. If it does not exist, the value of lt_ref_pic_flag[listIdx][rplsIdx][i] is presumed to be equal to 0. A bitstream conformance requirement is that the sum of lt_ref_pic_flag[listIdx][rplsIdx][i] for all values ​​of i in the range from 0 to NumEntriesInList[listIdx][rplsIdx]-1, including both ends, must be equal to num_ltrp_entries[listIdx][rplsIdx]. strp_entry_sign_flag[listIdx][rplsIdx][i] equal to 1 specifies that the i-th entry in ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) has a value of 0 or greater. strp_entries_sign_flag[listIdx][rplsIdx] equal to 0 specifies that the i-th entry in ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) has a value of less than 0. If it does not exist, the value of strp_entries_sign_flag[listIdx][rplsIdx][i] is presumed to be equal to the value of strp_entries_sign_flag[listIdx][rplsIdx].

[0190] delta_poc_st[listIdx][rplsIdx][i] specifies the difference between the picture order count of the current picture and the picture order count of the picture referenced by the i-th entry, when the i-th entry is the first STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure, or when the i-th entry is a STRP entry but is not the first STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure, it specifies the difference between the picture order count of the picture referenced by the i-th entry and the picture order count of the picture referenced by a previous STRP entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. The value of delta_poc_st[listIdx][rplsIdx][i] shall be in the range of -215 to 215-1, including both ends. poc_lsb_lt[listIdx][rplsIdx][i] specifies the picture order count modulo MaxLtPicOrderCntLsb value of the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. The length of the poc_lsb_lt[listIdx][rplsIdx][i] syntax element is Log2(MaxLtPicOrderCntLsb) bits. The array DeltaPocSt[listIdx][rplsIdx] is derived as follows: for(i=0;i <NumEntriesInList[listIdx][rplsIdx];i++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ DeltaPocSt[listIdx][rplsIdx][i]=(strp_entry_sign_flag[listIdx][rplsIdx][i])? delta_poc_st[listIdx][rplsIdx][i]:0- delta_poc_st[listIdx][rplsIdx][i] } }

[0191] Adding 1 to model_ref_rpl_idx_delta_minus1[listIdx][rplsIdx] specifies the difference between the value of rplsIdx and the index of the reference ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag). When rpl_mode[listIdx][rplsIdx] is equal to 1, the variable RefRplIdx is derived as follows: RefRplIdx=rplsIdx-(model_ref_rpl_idx_delta_minus1[listIdx][rplsIdx]+1)

[0192] Adding 1 to strp_offset_val_minus1[listIdx][rplsIdx] specifies the value to be subtracted from each STRP entry in the reference ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) in order to calculate the value of delta_poc_st[listIdx][rplsIdx][i] in the current ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag). ref_entry_used_flag[listIdx][rplsIdx][i] equal to 1 specifies that the i-th entry in ref_pic_list_struct(0,RefRplIdx,ltrpFlag) is used as the entry in ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag). A ref_entry_used_flag[listIdx][rplsIdx] equal to 0 specifies that the i-th entry in ref_pic_list_struct(0,RefRplIdx,ltrpFlag) is not used as an entry in ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag).

[0193] When rpl_mode[listIdx][rplsIdx] is equal to 1, the following applies to the interference of the value of the syntax element lt_ref_pic_flag[listIdx][rplsIdx][i], and when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 1, the following applies to the interference of the value of poc_lsb_lt[listIdx][rplsIdx][i], and to the derivation of the variable DeltaPocSt[listIdx][rplsIdx][i] (when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 0) and the variable NumEntriesInList[listIdx][rplsIdx]. currEntryIdx=0 for(i=0;i <NumEntriesInList[0][RefRplsIdx];i++){ if(ref_entry_used_flag[listIdx][rplsIdx][i]){ lt_ref_pic_flag[listIdx][rplsIdx][currEntryIdx])=lt_ref_pic_flag[0][RefRplsIdx][i]) if(!lt_ref_pic_flag[0][RefRplsIdx][i]) DeltaPocSt[listIdx][rplsIdx][currEntryIdx]=DeltaPocSt[0][RefRplsIdx][i] else poc_lsb_lt[listIdx][rplsIdx][currEntryIdx]=poc_lsb_lt[0][RefRplsIdx][i] currEntryIdx++ } } NumEntriesInList[listIdx][rplsIdx]=currEntryIdx

[0194] mode2_ref_rpl_idx[listIdx][rplsIdx] specifies the index of the reference ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag). The syntax element mode2_ref_rpl_idx[listIdx][rplsIdx] is represented by Ceil(Log2(num_ref_pic_lists_in_sps[0])) bits. When rpl_mode[listIdx][rplsIdx] is equal to 2, the variable RefRplIdx is derived as follows: RefRplIdx=mode2_ref_rpl_idx[listIdx][rplsIdx]

[0195] num_additional_entries[listIdx][rplsIdx] specifies the delta between NumEntriesInList[listIdx][rplsIdx] and NumEntriesInList[0][RefRplIdx]. add_lt_ref_pic_flag[listIdx][rplsIdx][i] is used to infer the value of lt_ref_pic_flag[listIdx][rplsIdx][NumEntriesInList[0][RefRplIdx]+i]. If it does not exist, the value of add_lt_ref_pic_flag[listIdx][rplsIdx][i] is inferred to be equal to 0. The parameter `add_strp_entry_sign_flag[listIdx][rplsIdx][i]` is used to guess the value of `strp_entry_sign_flag[listIdx][rplsIdx][NumEntriesInList[0][RefRplIdx]+i]`. If it does not exist, the value of `add_strp_entries_sign_flag[listIdx][rplsIdx][i]` is set to be equal to the value of `strp_entries_sign_flag[listIdx][rplsIdx]`.

[0196] The syntax element `add_delta_poc_st[listIdx][rplsIdx][i]` is used to guess the value of `delta_poc_st[listIdx][rplsIdx][NumEntriesInList[0][RefRplIdx]+i]`. The value of `add_delta_poc_st[listIdx][rplsIdx][i]` is assumed to be in the range of -215 to 215-1, including both ends. The syntax element `add_poc_lsb_lt[listIdx][rplsIdx][i]` is used to guess the value of `poc_lst_lt[listIdx][rplsIdx][NumEntriesInList[0][RefRplIdx]+i]`. The length of the `add_poc_lsb_lt[listIdx][rplsIdx][i]` is Log2(MaxLtPicOrderCntLsb) bits.

[0197] When rpl_mode[listIdx][rplsIdx] is equal to 2, the following applies to infer the values ​​of the syntax elements strp_entries_sign_flag[listIdx][rplsIdx] and lt_ref_pic_flag[listIdx][rplsIdx][i], and when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 1, the following applies to infer the value of poc_lsb_lt[listIdx][rplsIdx][i], and to derive the variable DeltaPocSt[listIdx][rplsIdx][i] (when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 0) and the variable NumEntriesInList[listIdx][rplsIdx]. strp_entries_sign_flag[listIdx][rplsIdx]=strp_entries_sign_flag[0][RefRplsIdx] for(i=0;i <NumEntriesInList[0][RefRplsIdx];i++){ lt_ref_pic_flag[listIdx][rplsIdx][i])=lt_ref_pic_flag[0][RefRplsIdx][i]) if(!lt_ref_pic_flag[0][RefRplsIdx][i]) DeltaPocSt[listIdx][rplsIdx][i]=DeltaPocSt[0][RefRplsIdx][i] else poc_lsb_lt[listIdx][rplsIdx][i]=poc_lsb_lt[0][RefRplsIdx][i] } currEntryIdx=NumEntriesInList[0][RefRplsIdx] for(i=0;i <num_additional_entries[listIdx][rplsIdx];i++,currEntryIdx++){ lt_ref_pic_flag[listIdx][rplsIdx][currEntryIdx])=add_lt_ref_pic_flag[listIdx][rplsIdx][i]) if(!add_lt_ref_pic_flag[listIdx][rplsIdx][i]) DeltaPocSt[listIdx][rplsIdx][currEntryIdx]=(add_strp_entry_sign_flag[listIdx][rplsIdx][i])? add_delta_poc_st[listIdx][rplsIdx][i]: 0-add_delta_poc_st[listIdx][rplsIdx][i] else poc_lsb_lt[listIdx][rplsIdx][currEntryIdx]=add_poc_lsb_lt[listIdx][rplsIdx][i] } NumEntriesInList[listIdx][rplsIdx]=currEntryIdx

[0198] mode3_ref_rpl_idx[listIdx][rplsIdx] specifies the index of the reference ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag). The syntax element mode3_ref_rpl_idx[listIdx][rplsIdx] is represented by Ceil(Log2(num_ref_pic_lists_in_sps[0])) bits. When rpl_mode[listIdx][rplsIdx] is equal to 3, the variable RefRplIdx is derived as follows: RefRplIdx=mode3_ref_rpl_idx[listIdx][rplsIdx]

[0199] When rpl_mode[listIdx][rplsIdx] is equal to 3, the following applies to infer the value of the syntax element lt_ref_pic_flag[listIdx][rplsIdx][i], when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 1, the following applies to infer the value of poc_lsb_lt[listIdx][rplsIdx][i], and the following applies to derive the variable DeltaPocSt[listIdx][rplsIdx][i] (when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 0) and the variable NumEntriesInList[listIdx][rplsIdx]. for(i=0;i <NumEntriesInList[0][RefRplsIdx];i++){ lt_ref_pic_flag[listIdx][rplsIdx][i])=lt_ref_pic_flag[0][RefRplsIdx][i]) if(!lt_ref_pic_flag[0][RefRplsIdx][i]) DeltaPocSt[listIdx][rplsIdx][i]=0-DeltaPocSt[0][RefRplsIdx][i] else poc_lsb_lt[listIdx][rplsIdx][i]=poc_lsb_lt[0][RefRplsIdx][i] } NumEntriesInList[listIdx][rplsIdx]=NumEntriesInList[0][RefRplsIdx]

[0200] A general decryption process is provided.

[0201] For the current picture CurrPic, the decryption process operates as follows: Decryption of NAL units is defined below. The following process defines the next decryption process using the slice header layer and the syntax elements described above. Variables and functions related to the picture order count are derived. This is called only for the first slice of the picture. At the beginning of the decryption process for each slice of a non-IRAP picture, the decryption process for constructing the reference picture list is called to derive reference picture list 0 (RefPicList[0]) and reference picture list 1 (RefPicList[1]). The decryption process for reference picture marking is called, and reference pictures may be marked as "not used for reference" or "used for long-term reference". This is called only for the first slice of the picture. The decryption process for coding tree units, scaling, transformation, in-loop filtering, etc. is called. After all slices of the current picture have been decrypted, the currently decrypted picture is marked as "used for short-term reference".

[0202] A NAL unit decoding process is provided.

[0203] The input to this process is the NAL unit of the current picture and any associated non-VCL NAL units. The output of this process is the parsed RBSP syntax structure encapsulated within the NAL unit. The decoding process for each NAL unit extracts the RBSP syntax structure from the NAL unit and then parses the RBSP syntax structure.

[0204] A slice decoding process is provided.

[0205] The decoding process for picture order counting is as follows:

[0206] The output of this process is PicOrderCntVal, which is the picture order count of the current picture. The picture order count is used to identify a picture for the derivation of motion parameters and prediction of motion vectors in merge mode, as well as for decoder compatibility verification. Each coded picture is associated with a picture order count variable denoted as PicOrderCntVal. When the current picture is not an IRAP picture, the variables prevPicOrderCntLsb and prevPicOrderCntMsb are derived as follows: prevTid0Pic is the previous picture in the decoding order with a TemporalId equal to 0. The variable prevPicOrderCntLsb is set to equal slice_pic_order_cnt_lsb of prevTid0Pic. The variable prevPicOrderCntMsb is set to equal PicOrderCntMsb of prevTid0Pic.

[0207] The variable PicOrderCntMsb for the current picture is derived as follows: If the current picture is an IRAP picture, PicOrderCntMsb is set to equal to 0. Otherwise, PicOrderCntMsb is derived as follows: if((slice_pic_order_cnt_lsb <prevPicOrderCntLsb)&& ((prevPicOrderCntLsb-slice_pic_order_cnt_lsb)>=(MaxPicOrderCntLsb / 2))) PicOrderCntMsb=prevPicOrderCntMsb+MaxPicOrderCntLsb else if((slice_pic_order_cnt_lsb>prevPicOrderCntLsb)&& ((slice_pic_order_cnt_lsb-prevPicOrderCntLsb)>(MaxPicOrderCntLsb / 2))) PicOrderCntMsb=prevPicOrderCntMsb-MaxPicOrderCntLsb else PicOrderCntMsb=prevPicOrderCntMsb

[0208] PicOrderCntVal is derived as follows: PicOrderCntVal=PicOrderCntMsb+slice_pic_order_cnt_lsb

[0209] All IRAP pictures have a PicOrderCntVal equal to 0, because slice_pic_order_cnt_lsb is inferred to be equal to 0 for IRAP pictures, and prevPicOrderCntLsb and prevPicOrderCntMsb are both set to equal to 0. The value of PicOrderCntVal is assumed to be in the range of -231 to 231-1, including both ends. In a single CVS, the PicOrderCntVal values ​​for any two coded pictures are not assumed to be the same.

[0210] At any given moment during the decoding process, the values ​​of PicOrderCntVal&(MaxLtPicOrderCntLsb-1) for any two reference pictures in the DPB are not the same. The function PicOrderCnt(picX) is defined as PicOrderCnt(picX) = PicOrderCntVal of picture picX. The function DiffPicOrderCnt(picA,picB) is defined as DiffPicOrderCnt(picA,picB) = PicOrderCnt(picA) - PicOrderCnt(picB). The bitstream does not contain data that would result in a value of DiffPicOrderCnt(picA,picB) used in the decoding process that is not in the range of -215 to 215-1, including both ends. Let X be the current picture, and Y and Z be two other pictures in the same 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.

[0211] A decoding process is provided for constructing the reference picture list.

[0212] This process is called at the beginning of the decoding process for each slice of a non-IRAP picture. The reference picture is addressed through a reference index, which is an index to the reference picture list. When decoding an I slice, the reference picture list is not used when decoding the slice data. When decoding a P slice, only reference picture list 0 (i.e., RefPicList[0]) is used when decoding the slice data. When decoding a B slice, both reference picture list 0 and reference picture list 1 (i.e., RefPicList[1]) are used when decoding the slice data. At the beginning of the decoding process for each slice of a non-IRAP picture, the reference picture lists RefPicList[0] and RefPicList[1] are derived. The reference picture lists are used for marking the reference picture or decoding the slice data. For I-slices of non-IRAP pictures that are not the first slice of a picture, RefPicList[0] and RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but their derivation is not required for decoding the current picture or any picture that follows the current picture in the decoding order. For P-slices that are not the first slice of a picture, RefPicList[1] may be derived for the purpose of bitstream compatibility verification, but its derivation is not required for decoding the current picture or any picture that follows the current picture in the decoding order. The reference picture lists RefPicList[0] and RefPicList[1] are constructed as follows: for(i=0;i<2;i++){ if(ref_pic_list_sps_flag[i]) RplsIdx[i]=ref_pic_list_idx[i] else RplsIdx[i]=num_ref_pic_lists_in_sps[i] for(j=0,pocBase=PicOrderCntVal;j <NumEntriesInList[i][RplsIdx[i]];j++){ if(!lt_ref_pic_flag[i][RplsIdx[i]][j]){ RefPicPocList[i][j]=pocBase-DeltaPocSt[i][RplsIdx[i]][j] if (the reference picture picA in DPB is equal to PicOrderCntVal in RefPicPocList[i][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" pocBase=RefPicPocList[i][j] else{ if (a reference picA is in DPB where PicOrderCntVal&(MaxLtPicOrderCntLsb-1) is equal to poc_lsb_lt[i][RplsIdx[i]][j]) RefPicList[i][j]=picA else RefPicList[i][j]="No reference picture" } } }

[0213] For each i equal to 0 or 1, the following applies: The first NumRefIdxActive[i] entry in RefPicList[i] is called the active entry in RefPicList[i], and all other entries in RefPicList[i] are called inactive entries in RefPicList[i]. For each j in the range from 0 to NumEntriesInList[i][RplsIdx[i]]-1, including both ends, each entry in RefPicList[i][j] is called a STRP entry if lt_ref_pic_flag[i][RplsIdx[i]][j] is equal to 0, and an LTRP entry otherwise. A particular picture may be referenced by both an entry in RefPicList[0] and an entry in RefPicList[1]. A particular picture may be referenced by more than one entry in RefPicList[0] or more than one entry in RefPicList[1]. Active entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that can be used for interpretation of the current picture, and one or more pictures that follow the current picture in the decoding order. Inactive entries in RefPicList[0] and RefPicList[1] collectively refer to all reference pictures that are not used for interpretation of the current picture, but can be used for interpretation of one or more pictures that follow the current picture in the decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equivalent to "no reference picture" because the corresponding picture does not exist in the DPB. Each inactive entry in RefPicList[0] or RefPicList[0] that is equivalent to "no reference picture" should be ignored. For each active entry in RefPicList[0] or RefPicList[1] that is equivalent to "no reference picture", an unintended picture loss should be inferred.

[0214] The following constraints apply to the requirements for bitstream conformance: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] is not less than NumRefIdxActive[i]. The pictures referenced by each active entry in RefPicList[0] or RefPicList[1] must exist in the DPB and have a TemporalId less than or equal to the current picture. Optionally, the following constraints may be further specified: The entry index of any inactive entry in RefPicList[0] or RefPicList[1] shall not be used as a reference index for decoding the current picture. Optionally, the following constraints may be further specified: Inactive entries in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. STRP entries in RefPicList[0] or RefPicList[1] for a slice of a picture, and LTRP entries in RefPicList[0] or RefPicList[1] for the same slice or different slices of the same picture, shall not refer to the same picture. The current picture itself shall not be referenced by any entry in RefPicList[0] or RefPicList[1]. There shall be no LTRP entries in RefPicList[0] or RefPicList[1] where the difference between the PicOrderCntVal of the current picture and the PicOrderCntVal of the picture referenced by the entry is 224 or greater. setOfRefPics shall be the set of unique pictures referenced by all entries in RefPicList[0] and all entries in RefPicList[1]. The number of pictures in setOfRefPics shall be less than or equal to sps_max_dec_pic_buffering_minus1, and setOfRefPics shall be the same for all slices of a picture.

[0215] A decryption process for reference picture marking is provided.

[0216] This process is called once per picture, after the decoding of the slice header and the decoding process for building the reference picture list for the slice, but before decoding the slice data. This process may result in one or more reference pictures in the DPB being marked as "not used for reference" or "used for long-term reference". A decoded picture in the DPB can be marked as "not used for reference", "used for short-term reference", or "used for long-term reference", but only one of these three, at any given moment during the operation of the decoding process. Assigning one of these markings to a picture implicitly excludes another of these markings when applicable. When a picture is referred to as being marked as "used for reference", this collectively refers to the picture being marked as either "used for short-term reference" or "used for long-term reference" (but not both). When the current picture is an IRAP picture, all reference pictures (if any) currently in the DPB are marked as "not used for reference". STRPs are identified by their PicOrderCntVal values. LTRPs are identified by Log2(MaxLtPicOrderCntLsb) LSBs of their PicOrderCntVal values. The following applies: For each LTRP entry in RefPicList[0] or RefPicList[1], if the referenced picture is a STRP, the picture is marked as "Used for long-term reference". Each referenced picture in a DPB that is not referenced by any entry in RefPicList[0] or RefPicList[1] is marked as "Not used for reference".

[0217] Figure 8 is a schematic diagram of a video coding device 800 (e.g., a video encoder 20 or a video decoder 30) according to one embodiment of the present disclosure. The video coding device 800 is suitable for carrying out the disclosed embodiments as described herein. The video coding device 800 comprises an inlet port 810 and a receiver unit (Rx) 820 for receiving data, a processor, logic unit, or central processing unit (CPU) 830 for processing data, a transmitter unit (Tx) 840 and an exit port 850 for transmitting data, and a memory 860 for storing data. The video coding device 800 may also comprise optical-electronic (OE) components and electron-optical (EO) components coupled to the exit port 810, the receiver unit 820, the transmitter unit 840, and the exit port 850 for the input and output of optical or electrical signals.

[0218] The processor 830 is implemented by hardware and software. The processor 830 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 830 communicates with the input port 810, the receiver unit 820, the transmitter unit 840, the output port 850, and the memory 860. The processor 830 includes a coding module 870. The coding module 870 implements the disclosed embodiments described above. For example, the coding module 870 implements, processes, prepares, or provides various networking functions. Thus, including the coding module 870 results in a significant improvement to the functionality of the video coding device 800, producing conversions of the video coding device 800 to different states. Alternatively, the coding module 870 is implemented as instructions stored in the memory 860 and executed by the processor 830.

[0219] The video coding device 800 may also include input and / or output (I / O) devices 880 for exchanging data with the user. The I / O devices 880 may include output devices such as a display for displaying video data and speakers for outputting audio data. The I / O devices 880 may also include input devices such as a keyboard, mouse, or trackball, and / or corresponding interfaces for interface with such output devices.

[0220] Memory 860 comprises one or more disks, tape drives, and solid-state drives and may be used as an overflow data storage device for storing a program when such a program is selected for execution, and for storing instructions and data to be read during program execution. Memory 860 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).

[0221] Figure 9 is a schematic diagram of one embodiment of the coding means 900. In this embodiment, the coding means 900 is implemented in a video coding device 902 (for example, a video encoder 20 or a video decoder 30). The video coding device 902 includes a receiving means 901. The receiving means 901 is configured to receive a picture to be coded or a bitstream to be decoded. The video coding device 902 includes a transmitting means 907 coupled to the receiving means 901. The transmitting means 907 is configured to transmit a bitstream to a decoder or to a display means (for example, one of the I / O devices 880).

[0222] The video coding device 902 includes a storage means 903. The storage means 903 is coupled to at least one of the receiving means 901 or the transmitting means 907. The storage means 903 is configured to store instructions. The video coding device 902 also includes a processing means 905. The processing means 905 is coupled to the storage means 903. The processing means 905 is configured to execute instructions stored in the storage means 903 in order to perform the method disclosed herein.

[0223] It should also be understood that the steps of the exemplary methods described herein do not necessarily have to be performed in the order described, and the order of the steps of such methods should be understood to be merely illustrative. Similarly, additional steps may be included in such methods, and some steps may be omitted or combined in a manner consistent with the various embodiments of this disclosure.

[0224] While several embodiments are provided in this disclosure, it should be understood that the disclosed systems and methods can be embodied in many other specific forms without departing from the spirit or scope of this disclosure. These examples should be considered illustrative rather than restrictive, and the intent is not limited to the details given herein. For example, different systems may combine or integrate various elements and components, or some features may be omitted or not implemented.

[0225] In addition, techniques, systems, subsystems, and methods described and illustrated individually or separately in various embodiments may be combined with or integrated with other systems, modules, techniques, or methods without departing from the scope of this disclosure. Other items shown or discussed as being coupled, directly coupled, or communicating with one another may be indirectly coupled or communicating through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of modifications, substitutions, and variations that are recognizable to those skilled in the art may be made without departing from the spirit and scope disclosed herein. [Explanation of symbols]

[0226] 12 Source Devices 14 Destination Devices 16 Computer-readable media 18 Video Sources 20 Video Encoders 22 Output Interfaces 28 Input Interfaces 30 video decoders 32 Display Devices 40 Mode Selection Unit 42 Motion Estimation Unit 44 Motion compensation unit 46 Intra Prediction Units 48 division units 52 Conversion Processing Unit 54 Quantization Units 56 Entropy Coding Unit 58 Inverse Quantization Unit 60 Reverse Conversion Unit 64 Reference frame memory 70 Entropy Decoding Unit 72 Motion Compensation Unit 74 Intra Prediction Units 76 Inverse Quantization Unit 78 Reverse Conversion Unit 82 Reference frame memory 510 SPS 512 PPS 514 slice header 520 image data 810 Entrance Port 820 Receiver Unit 830 Processor 840 Transmitter Unit 850 Exit Port 860 memory 870 Coding Modules 880 I / O devices 901 Receiving means 902 Video Coding Device 903 Memory means 905 Processing means 907 Transmission method

Claims

1. A method for decoding a coded video bitstream performed by a video decoder, The steps include parsing the flags from the coded video bitstream, The steps include parsing a first reference picture list structure from the coded video bitstream, When the flag has a first value, the steps include determining that an index for the second reference picture list structure does not exist in the slice header of the coded video bitstream, and inferring that the index for the second reference picture list structure is the same as the index for the first reference picture list structure, When the flag has a second value, the step of determining that the index for the second reference picture list structure exists in the slice header, A step of generating a reference picture list from the coded video bitstream using at least one of the first reference picture list structure or the second reference picture list structure, A method comprising the step of performing interpretation based on the reference picture list to generate reconstructed blocks.

2. The method according to claim 1, wherein the flag is specified as rpl1_idx_present_flag.

3. The method according to either claim 1 or 2, wherein the flag is included in the picture parameter set (PPS) of the coded video bitstream.

4. The method according to any one of claims 1 to 3, wherein the flag is included in the sequence parameter set (SPS) of the coded video bitstream.

5. The method according to any one of claims 1 to 4, wherein the first reference picture list structure is included in the slice header of the coded video bitstream.

6. The method according to claim 1, wherein the flag is included in the picture parameter set (PPS) of the coded video bitstream, and the first reference picture list structure is included in the slice header of the coded video bitstream.

7. The method according to any one of claims 1 to 6, wherein the first value of the flag is 1.

8. The method according to any one of claims 1 to 7, wherein when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

9. The method according to claim 1, wherein the second value of the flag is 0.

10. The method according to claim 9, wherein when the second value of the flag is 0, ref_pic_list_sps_flag[0] and ref_pic_list_idx[0] are included in the slice header.

11. A method for encoding a video bitstream performed by a video encoder, When the index for the second reference picture list structure is not encoded in the slice header of the video bitstream, and the video decoder should infer that the index for the second reference picture list structure is the same as the index for the first reference picture list structure, the steps are to encode a flag into the video bitstream using a first value, When the index for the second reference picture list structure is encoded into the slice header of the video bitstream, the steps include encoding a flag into the video bitstream using the second value, When the flag is encoded using the first value, the first reference picture list structure is encoded into the video bitstream. When the flag is encoded using the second value, the first reference picture list structure and the second reference picture list structure are encoded into the video bitstream. A method comprising the steps of transmitting the video bitstream toward the video decoder.

12. The method according to claim 11, wherein the flag is specified as rpl1_idx_present_flag.

13. The method according to any one of claims 11 to 12, wherein the flag is encoded in the picture parameter set (PPS) of the coded video bitstream.

14. The method according to any one of claims 11 to 13, wherein the first reference picture list structure is encoded in the slice header of the coded video bitstream.

15. The method according to any one of claims 11 to 14, wherein the first reference picture list structure and the second reference picture list are encoded in the slice header of the coded video bitstream.

16. The method according to any one of claims 11 to 15, wherein the first value of the flag is 1 and the second value of the flag is 0.

17. The method according to any one of claims 11 to 16, wherein when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

18. A receiver configured to receive an coded video bitstream, A memory coupled to the receiver, which stores instructions, The system comprises a processor coupled to the memory, and the processor has, From the coded video bitstream, the flags are parsed syntactically. From the coded video bitstream, a first reference picture list structure is parsed, When the flag has a first value, it is determined that the index for the second reference picture list structure does not exist in the slice header of the coded video bitstream, and it is inferred that the index for the second reference picture list structure is the same as the index for the first reference picture list structure. When the flag has a second value, it is determined that the index for the second reference picture list structure exists in the slice header. A reference picture list is generated using at least one of the first reference picture list structure or the second reference picture list structure. Perform interpretation based on the aforementioned reference picture list to generate the reconstructed blocks. A decoding device configured to execute the instructions stored in the memory for this purpose.

19. The decoding device according to claim 18, further comprising a display configured to display an image generated using the reconstructed blocks.

20. The decoding device according to any one of claims 18 to 19, wherein the flag is specified as rpl1_idx_present_flag.

21. The decoding device according to any one of claims 18 to 20, wherein the flag is included in the picture parameter set (PPS) of the coded video bitstream.

22. The decoding device according to any one of claims 18 to 21, wherein the first reference picture list structure is included in the slice header of the coded video bitstream.

23. The decoding device according to any one of claims 18 to 22, wherein the first value of the flag is 1 and the second value of the flag is 0.

24. The encoding device according to any one of claims 18 to 23, wherein when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

25. When the index for the second reference picture list structure is not encoded in the slice header of the video bitstream, and the video decoder should infer that the index for the second reference picture list structure is the same as the index for the first reference picture list structure, the flag is encoded into the video bitstream using the first value. When the index for the second reference picture list structure is encoded into the slice header of the video bitstream, the flag is encoded into the video bitstream using the second value. When the flag is encoded using the first value, the first reference picture list structure is encoded into the video bitstream. When the flag is encoded using the second value, the first reference picture list structure and the second reference picture list structure are encoded into the video bitstream. A processor configured as follows, An encoding device comprising a transmitter coupled to the processor, configured to transmit the video bitstream toward the video decoder.

26. The encoding device according to claim 25, wherein the flag is specified as rpl1_idx_present_flag.

27. The encoding device according to any one of claims 25 to 26, wherein the flag is encoded in the picture parameter set (PPS) of the coded video bitstream.

28. The encoding device according to any one of claims 25 to 27, wherein the first reference picture list structure is encoded in the slice header of the coded video bitstream.

29. The encoding device according to any one of claims 25 to 28, wherein the first value of the flag is 1 and the second value of the flag is 0.

30. The encoding device according to any one of claims 25 to 29, wherein when the first value of the flag is 1, ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not included in the slice header.

31. A receiver configured to receive a bitstream to be decoded, A transmitter coupled to the receiver, configured to transmit the decoded image to a display, A memory connected to at least one of the receiver or the transmitter, configured to store instructions, A coding device comprising a processor coupled to the memory, configured to execute the instructions stored in the memory in order to perform the method according to any one of claims 1 to 17.

32. An encoder comprising the encoding device according to any one of claims 25 to 30, A system comprising a decoder communicating with an encoder, the decoder comprising a decoding device according to any one of claims 18 to 24.

33. A receiving means configured to receive a bitstream to be decoded, A transmitting means coupled to the receiving means, configured to transmit the decoded image to a display means, A storage means coupled to at least one of the receiving means or the transmitting means, configured to store instructions, A means for coding, comprising: a processing means coupled to the storage means, configured to execute the instructions stored in the storage means in order to perform the method described in any one of claims 1 to 17.

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