Video Encoders, Video Decoders, and Counterparts

Abstract

To provide a method of decoding a coded video bitstream.SOLUTION: A method includes the steps of: parsing a flag; parsing a first reference picture list structure; determining that an index to a second reference picture list structure is not present in a slice header of a coded video bitstream and inferring that the index to the second reference picture list structure is the same as an index to the first reference picture list structure, when the flag has a first value; determining that the index to the second reference picture list structure is present in the slice header, when the flag has a second value; generating a reference picture list using the first reference picture list structure or the second reference picture list structure; and performing an inter-prediction based on the reference picture list to generate a reconstructed block.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0002] Generally, this disclosure describes techniques for improved signaling efficiency for reference picture management in video coding. More specifically, this disclosure describes techniques for improved signaling for building reference picture lists and marking reference pictures directly based on the reference picture lists. [Background technology]

[0003] The amount of video data required to render even a relatively short video can be substantial, which can pose challenges when data is streamed or otherwise communicated over communications networks with limited bandwidth capacity. Therefore, video data is typically compressed before being communicated over modern telecommunications networks. Because memory resources may be limited, video size can also be an issue when the video is stored on a storage device. Video compression devices often use software and / or hardware at the source to code the video data before transmission or storage, thereby reducing the amount of data needed to represent a digital video image. The compressed data is then received at the destination by a video decompression device, which decodes the video data. Due to limited network resources and an ever-increasing demand for higher quality video, improved compression and decompression techniques that increase compression ratios with little or no sacrifice in image quality are desirable. Summary of the Invention [Means for solving the problem]

[0004] A first aspect relates to a method for decoding a coded video bitstream, performed by a video decoder, comprising: parsing a flag from the coded video bitstream; parsing a first reference picture list structure from the coded video bitstream; determining, when the flag has a first value, that an index to a second reference picture list structure is not present in a 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, when the flag has a second value, that an index to the second reference picture list structure is present in the slice header; generating a reference picture list using at least one of the first reference picture list structure or the second reference picture list structure; and performing inter prediction 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 an index into a second reference picture list structure can be inferred to be the same as an index into a first reference picture list structure, coders / decoders (also known as "codecs") in video coding are improved (e.g., use fewer bits, require less bandwidth, are more efficient, etc.) compared to current codecs. In practical terms, the improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

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

[0007] In a second implementation of the method according to the first aspect itself or any preceding implementation of the first aspect, the flag is included in a Picture Parameter Set (PPS) of the video bitstream to be coded.

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

[0009] In a fourth implementation of the method according to the first aspect itself or any previous implementation of the first aspect, the first reference picture list structure is included in a slice header of the coded video bitstream.

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

[0011] In a sixth implementation of the method according to the first aspect itself or any preceding implementation of the first aspect, the first value of the flag is one.

[0012] In a seventh implementation of the method according to the first aspect itself or any preceding implementation of the first 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.

[0013] In an eighth implementation of the method according to the first aspect itself or any preceding implementation of the first aspect, the second value of the flag is 0.

[0014] In a ninth implementation form of the method according to the first aspect itself or any previous implementation form of the first aspect, 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 the video bitstream using a first value when an index for a second reference picture list structure is not encoded in a slice header of the video bitstream and the index for the second reference picture list structure should be inferred by the video decoder to be the same as the index for the first reference picture list structure; encoding a flag into the video bitstream using a second value when the index for the second reference picture list structure is encoded into the slice header of the video bitstream; encoding the first reference picture list structure into the video bitstream when the flag is encoded using the first value; encoding the first reference picture list structure and the second reference picture list structure into the video bitstream when the flag is encoded using the second value; and transmitting the video bitstream to the video decoder.

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

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

[0018] In a second implementation of the method according to the second aspect itself or any preceding implementation of the second aspect, the flag is encoded in a Picture Parameter Set (PPS) of the coded video bitstream.

[0019] In a third implementation of the method according to the second aspect itself or any preceding implementation of the second aspect, the first reference picture list structure is encoded in a slice header of the coded video bitstream.

[0020] In a fourth implementation form of the method according to the second aspect itself or any previous implementation form of the second aspect, the first reference picture list structure and the second reference picture list structure are encoded in a slice header of the coded video bitstream.

[0021] In a fifth implementation of the method according to the second aspect itself or any preceding implementation of the second aspect, the first value of the flag is 1 and the second value of the flag is 0.

[0022] In a sixth implementation of the method according to the second aspect itself or any preceding implementation of the second 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.

[0023] a processor coupled to the memory, the processor being configured to execute the instructions stored in the memory to cause the processor to parse a flag from the coded video bitstream; parse a first reference picture list structure from the coded video bitstream; determine, when the flag has a first value, that an index to a second reference picture list structure is not present in a slice header of the coded video bitstream and infer that the index to the second reference picture list structure is the same as the index to the first reference picture list structure; determine, when the flag has a second value, that an index to the second reference picture list structure is present in the slice header; generate a reference picture list using at least one of the first reference picture list structure or the second reference picture list structure; and perform inter prediction based on the reference picture list to generate a reconstructed block.

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

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

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

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

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

[0029] In a fifth implementation of a decoding device according to the third aspect itself or any preceding implementation 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 of a decoding device according to the third aspect itself or any preceding implementation 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]

[0013] A fourth aspect relates to an encoding device, comprising: a processor configured to: encode a flag into the video bitstream using a first value when an index for a second reference picture list structure is not coded in a slice header of the video bitstream and the index for the second reference picture list structure should be inferred by the video decoder to be the same as the index for the first reference picture list structure; encode a flag into the video bitstream using a second value when the index for the second reference picture list structure is coded into the slice header of the video bitstream; encode the first reference picture list structure into the video bitstream when the flag is coded using the first value; and encode the first reference picture list structure and the second reference picture list structure into the video bitstream when the flag is coded using the second value; and a transmitter coupled to the processor, configured to transmit the video bitstream towards the video decoder.

[0032] The encoding device provides techniques to simplify and make the coding process more efficient. By using a flag to specify whether an index into a second reference picture list structure can be inferred to be the same as an index into a first reference picture list structure, coders / decoders (also known as "codecs") in video coding are improved (e.g., use fewer bits, require less bandwidth, are more efficient, etc.) compared to current codecs. In practical terms, the improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

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

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

[0035] In a third implementation form of an encoding device according to the fourth aspect itself or any preceding implementation form of the fourth aspect, the first reference picture list structure is encoded in a slice header of the coded video bitstream.

[0036] In a fourth implementation of the encoding device according to the fourth aspect itself or any preceding implementation of the fourth aspect, the first value of the flag is 1 and the second value of the flag is 0.

[0037] In a fifth implementation of an encoding device according to the fourth aspect itself or any preceding implementation of the fourth 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.

[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, the transmitter configured to transmit a decoded image to a display; a memory coupled to at least one of the receiver or the transmitter, the memory configured to store instructions; and a processor coupled to the memory, the processor configured to execute the instructions stored in the memory to perform the method of any of the embodiments disclosed herein.

[0039] The coding apparatus provides techniques to simplify and make the coding process more efficient. By using a flag to specify whether an index into a second reference picture list structure can be inferred to be the same as an index into a first reference picture list structure, coders / decoders (also known as "codecs") in video coding are improved (e.g., use fewer bits, require less bandwidth, are more efficient, etc.) compared to current codecs. In practical terms, the improved video coding process provides users with a better user experience when the 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 of the embodiments disclosed herein, and a decoder in communication with the encoder, the decoder including a decoding device according to any of the embodiments disclosed herein.

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

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

[0043] The means for coding provide techniques that simplify and make the coding process more efficient. By using a flag to specify whether an index into a second reference picture list structure can be inferred to be the same as an index into a first reference picture list structure, coders / decoders (also known as "codecs") in video coding are improved (e.g., use fewer bits, require less bandwidth, are more efficient, etc.) compared to current codecs. In practical terms, the 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 the present disclosure, reference is now made to the following brief description, taken in conjunction with the accompanying drawings and detailed description, wherein like reference numerals represent like parts. [Brief explanation of the drawings]

[0045] [Figure 1] 1 is a block diagram illustrating an example coding system that may utilize bilateral prediction techniques. [Figure 2] 1 is a block diagram illustrating an example video encoder that may implement a bilateral prediction technique. [Figure 3] 1 is a block diagram illustrating an example of a video decoder that can implement a bilateral prediction technique. [Figure 4]1 is a schematic diagram illustrating a reference picture set (RPS) having a current picture with entries in all subsets of the RPS. [Figure 5] FIG. 1 is a schematic diagram of an embodiment of a video bitstream. [Figure 6] 1 is an embodiment of a method for decoding a coded video bitstream. [Figure 7] 1 is a diagram of an embodiment of a method for encoding a video bitstream. [Figure 8] 1 is a schematic diagram of a video coding device. [Figure 9] FIG. 1 is a schematic diagram of an embodiment of a means for coding. DETAILED DESCRIPTION OF THE INVENTION

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

[0047] 1 is a block diagram illustrating an example coding system 10 that may utilize video coding techniques as described herein. As shown in FIG. 1, coding system 10 includes a source device 12 that provides encoded video data to be subsequently decoded by a destination device 14. Specifically, source device 12 may provide the video data to destination device 14 via a computer-readable medium 16. 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, etc. In some cases, source device 12 and destination device 14 may be capable of wireless communication.

[0048] The destination device 14 may receive the encoded video data to be decoded via a computer-readable medium 16. The computer-readable medium 16 may comprise any type of medium or device capable of moving encoded video data from the source device 12 to the destination device 14. In one example, the computer-readable medium 16 may comprise a communication medium to enable the source device 12 to transmit the encoded video data directly to the destination device 14 in real time. The encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to the destination device 14. The communication medium may comprise any wireless or wired communication medium, such as the 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 the source device 12 to the destination device 14.

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

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

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

[0052] The depicted coding system 10 of FIG. 1 is merely an example. The techniques for video coding may be performed by any digital video encoding and / or decoding device. While the techniques of this disclosure are generally performed by a video coding device, the techniques may also be performed by a video encoder / decoder, commonly referred to as a "codec." Moreover, the techniques of this disclosure may also be performed by a video preprocessor. The video encoder and / or decoder may be a graphics processing unit (GPU) or similar device.

[0053] Source device 12 and destination device 14 are merely examples of coding devices, such that source device 12 generates coded video data for transmission to destination device 14. In some examples, source device 12 and destination device 14 may operate substantially symmetrically, such that source device 12 and destination device 14 each include video encoding and video decoding components. Thus, coding system 10 may support one-way or two-way video transmission between video devices 12 and 14, e.g., for video streaming, video playback, video broadcasting, or video telephony.

[0054] 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, video source 18 may generate computer-graphics-based data as the source video, or may generate a combination of live video, archived video, and computer-generated video.

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

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

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

[0058] 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, video encoder 20 and video decoder 30 may operate in accordance with other proprietary or industry standards, such as the International Telecommunication Union Telecommunications Standardization Sector (ITU-T) H.264 standard, H.265 / HEVC, or extensions of such standards, alternatively 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. 1, in some aspects, video encoder 20 and video decoder 30 may each be integrated with an audio encoder and decoder and may include an appropriate multiplexer-demultiplexer (MUX-DEMUX) unit or other hardware and software for handling the encoding of both audio and data in a common and separate data stream. 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] Video encoder 20 and video decoder 30 may each be implemented as any of a variety of suitable encoder circuits, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic circuits, software, hardware, firmware, or any combination thereof. When the techniques are implemented partially in software, a device may store instructions for the software on a suitable non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, any of which may be integrated as part of a composite encoder / decoder (codec) in the respective device. Devices including video encoder 20 and / or video decoder 30 may comprise integrated circuits, microprocessors, and / or wireless communication devices such as mobile phones.

[0060] 2 is a block diagram illustrating an example of a video encoder 20 that may implement video coding techniques. The video encoder 20 may perform intra-coding and inter-coding of video blocks within a video slice. Intra-coding relies on spatial prediction to reduce or remove spatial redundancy in video within a given video frame or picture. Inter-coding relies on temporal prediction to reduce or remove temporal redundancy in video within adjacent frames or pictures of a video sequence. Intra-mode (I-mode) may refer to any of several spatial-based coding modes. Inter-modes, such as uni-directional (also known as uni-prediction) prediction (P-mode) or bi-prediction (also known as bi-prediction) (B-mode), may refer to any of several temporal-based coding modes.

[0061] As shown in FIG. 2, video encoder 20 receives a current video block in a video frame to be encoded. In the example of FIG. 2, video encoder 20 includes a mode select unit 40, a reference frame memory 64, an adder 50, a transform processing unit 52, a quantization unit 54, and an entropy coding unit 56. Mode select unit 40 then includes a motion compensation unit 44, a motion estimation unit 42, an intra-prediction (also known as intra prediction) unit 46, and a partition unit 48. For video block reconstruction, video encoder 20 also includes an inverse quantization unit 58, an inverse transform unit 60, and an adder 62. A deblocking filter (not shown in FIG. 2) may also be included to filter block boundaries to remove blockiness artifacts from the reconstructed video. If desired, the deblocking filter typically filters the output of adder 62. Additional filters (in-loop or post-loop) may also be used in addition to the deblocking filter. The output of summer 50 may be filtered (as an in-loop filter) if desired, although such a filter is not shown for simplicity.

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

[0063] Moreover, partition unit 48 may partition blocks of video data into sub-blocks based on evaluation of previous partitioning schemes in previous coding passes. For example, partition unit 48 may first partition a frame or slice into largest coding units (LCUs) and then partition each of the LCUs into sub-coding units (sub-CUs) based on rate-distortion analysis (e.g., rate-distortion optimization). Mode selection unit 40 may further generate a quadtree data structure that indicates the partitioning of the LCUs into sub-CUs. A leaf-node CU of the quadtree may include one or more prediction units (PUs) and one or more transform units (TUs).

[0064] This disclosure uses the term "block" to refer to either a CU, PU, ​​or TU in the context of HEVC, or similar data structures in the context of other standards (e.g., 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 up to the size of a treeblock of 64x64 pixels or more. Each CU may include one or more PUs and one or more TUs. Syntax data associated with a CU may, for example, describe the partitioning of the CU into one or more PUs. The partitioning mode may differ depending on whether the CU is coded in skip mode or direct mode, in intra-prediction mode, or in inter-prediction (also known as inter-prediction) mode. A PU may be partitioned to be non-square in shape. Syntax data associated with a CU may also describe, for example, the partitioning of the CU into one or more TUs according to a quadtree. The TUs may be square or non-square (e.g., rectangular) in shape.

[0065] Mode select unit 40 selects a coding mode, i.e., one of intra-coding or inter-coding modes, based on, for example, the error result, and provides the resulting intra-coded or inter-coded block to summer 50 to generate residual block data and summer 62 to reconstruct a coded block for use as a reference frame. Mode select unit 40 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy coding unit 56.

[0066] Motion estimation unit 42 and motion compensation unit 44 may be highly integrated but are shown separately for conceptual purposes. Motion estimation performed by motion estimation unit 42 is the process of generating motion vectors that estimate the movement of video blocks. A motion vector may indicate, for example, the displacement of a video block within a current video frame or picture relative to a predictive block in a reference frame (or other coded unit) relative to a current block being coded within the current frame (or other coded unit). A predictive block is a block that is found to closely match a block to be coded in terms of pixel difference, which may be determined by sum of absolute differences (SAD), sum of squared differences (SSD), or other difference measure. In some examples, video encoder 20 may calculate values ​​for sub-integer pixel locations of a reference picture stored in reference frame memory 64. For example, video encoder 20 may interpolate values ​​for quarter-pixel positions, eighth-pixel positions, or other fractional pixel positions of a reference picture. Thus, motion estimation unit 42 may perform motion search for whole pixel positions and fractional pixel positions and output motion vectors with fractional pixel accuracy.

[0067] Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter-coded slice by comparing the position of the PU with the position of a predictive block of a reference picture. The reference pictures may be selected from a first reference picture list (List 0) or a second reference picture list (List 1), each of which identifies one or more reference pictures stored in reference frame memory 64. Motion estimation unit 42 sends the calculated motion vector to entropy encoding unit 56 and motion compensation unit 44.

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

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

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

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

[0072] After selecting an intra-prediction mode for the block (e.g., one of a conventional intra-prediction mode or a DMM mode), intra-prediction unit 46 may provide information indicating the selected intra-prediction mode for the block to entropy coding unit 56. Entropy coding unit 56 may encode the information indicating the selected intra-prediction mode. Video encoder 20 may include definitions of the coding contexts for various blocks, an indication of the most probable intra-prediction mode, the intra-prediction mode index table, and the modified intra-prediction mode index table to use for each of the contexts in transmitted bitstream configuration data, which may include multiple intra-prediction mode index tables and multiple modified intra-prediction mode index tables (also referred to as codeword mapping tables).

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

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

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

[0076] Following quantization, entropy coding unit 56 codes the quantized transform coefficients. For example, 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 partitioned 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 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] Inverse quantization unit 58 and inverse transform unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual block in the pixel domain, e.g., for later use as a reference block. Motion compensation unit 44 may calculate a reference block by adding the residual block to a predictive block of one of the frames in reference frame memory 64. Motion compensation unit 44 may also apply one or more interpolation filters to the reconstructed residual block to calculate sub-integer pixel values ​​for use in motion estimation. Adder 62 adds the reconstructed residual block to the motion-compensated predictive block produced by motion compensation unit 44 to produce a reconstructed video block for storage in reference frame memory 64. The reconstructed video block may be used by motion estimation unit 42 and motion compensation unit 44 as a reference block for inter-coding blocks in subsequent video frames.

[0078] 3 is a block diagram illustrating an example of a video decoder 30 that may implement video coding techniques. In the example of FIG. 3, 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. Video decoder 30, in some examples, performs a decoding path that is generally inverse to the encoding path described with respect to video encoder 20 (FIG. 2). Motion compensation unit 72 may generate prediction data based on motion vectors received from entropy decoding unit 70, while intra prediction unit 74 may generate prediction data based on an intra-prediction mode indicator received from entropy decoding unit 70.

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

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

[0081] Motion compensation unit 72 determines prediction information for video blocks of the current video slice by analyzing the motion vectors and other syntax elements, and uses the prediction information to generate a predictive block for the current video block being decoded. For example, motion compensation unit 72 uses some of the received syntax elements to determine the prediction mode (e.g., intra-prediction or inter-prediction) used to code the video blocks of the video slice, 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, motion vectors for each inter-coded video block of the slice, inter-prediction status for each inter-coded video block of the slice, and other information for decoding video blocks in the current video slice.

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

[0083] Data for texture images corresponding to the depth maps may be stored in reference frame memory 82. Motion compensation unit 72 may also be configured to inter-predict depth blocks of the depth maps.

[0084] Image and video compression has experienced rapid growth, leading to a variety of coding standards, including 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, ISO / IEC MPEG-4 Part 2, also known as ITU-T H.264 or 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), and Multiview Video Coding plus Depth (MVC+D), as well as 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). At the time of writing, the latest working draft (WD) of VVC was included in JVET-K1001-v1. JVET document JVET-K0325-v3 contains updates to the high-level syntax of VVC.

[0086] This disclosure describes techniques intended to address the development of the VVC standard, however, the techniques may also be applied to other video / media codec specifications.

[0087] Video compression techniques perform spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. In block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be called tree blocks, coding tree blocks (CTBs), coding tree units (CTUs), coding units (CUs), and / or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. A picture may be referred to as a frame, and a reference picture may be referred to as a reference frame.

[0088] Spatial or temporal prediction results in a predictive block for the block to be coded. Residual data represents pixel differences between the original block to be coded and the predictive block. Inter-coded blocks are coded according to a motion vector pointing to a block of reference samples forming the predictive block and residual data indicating the difference between the coded block and the predictive block. Intra-coded blocks are coded according to an intra-coding mode and the residual data. For further compression, the residual data may be transformed from the pixel domain to a transform domain, resulting in residual transform coefficients, which may then be quantized. The quantized transform coefficients, initially arranged in a two-dimensional array, may be scanned to produce a one-dimensional vector of transform 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 inter prediction, output of pictures from a decoded picture buffer (DPB), motion vector scaling, weighted prediction, etc. In AVC and HEVC, pictures may be identified by a picture order count (POC). In AVC and HEVC, pictures in the DPB may be marked as "used for short-term reference," "used for long-term reference," or "not used for reference." When a picture is marked as "not used for reference," 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 used for reference" when it is no longer needed for prediction reference. The conversion between these three statuses (short-term, long-term, and not used for reference) is controlled by the decoded reference picture marking process. There are two alternative decoded reference picture marking mechanisms: 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 used for reference" when the number of reference frames is equal to a given maximum number (max_num_ref_frames in SPS). Short-term reference pictures are stored in a first-in, first-out manner, such that the most recently decoded short-term picture is kept in the DPB.

[0091] An explicit MMCO process may include multiple MMCO commands that may mark one or more short-term or long-term reference pictures as "unused for reference," may mark all pictures as "unused for reference," or 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 reference picture marking operation, as well as the process for outputting and deleting pictures from the DPB, are performed after the picture is decoded.

[0093] HEVC introduces a different approach to reference picture management, called Reference Picture Set (RPS). Compared to AVC's MMCO / sliding window, the most fundamental difference about the RPS concept is that for each particular slice, a complete set of reference pictures is provided to be used by the current picture or any subsequent pictures. Therefore, the complete set of all pictures that must be kept in the DPB for use by the current or future pictures is signaled. This differs from the AVC method, where only relative changes to the DPB are signaled. With the RPS concept, no information from earlier pictures in the decoding order is required to maintain the correct status of reference pictures in the DPB.

[0094] To take advantage of the RPS and improve error resilience, the order of picture decoding and DPB operations in HEVC is changed compared to AVC. In AVC, picture marking and buffer operations (both outputting and removing decoded pictures from the DPB) are generally applied after the current picture is decoded. In HEVC, the RPS is first decoded from the slice header of the current picture, and then picture marking and buffer operations are generally applied before decoding the current picture.

[0095] Each slice header in HEVC must contain parameters for signaling the RPS for the picture that contains the slice. The only exception is that no RPS is signaled for IDR slices. Instead, the RPS is inferred to be empty. For I-slices that do not belong to an IDR picture, an RPS may be provided even if the I-slice belongs to an I-picture, since there may be pictures after the I-picture in decoding order that use inter prediction from pictures that were before the I-picture in decoding order. The number of pictures in the RPS shall 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 its output order. The slice header contains a fixed-length codeword, pic_order_cnt_lsb, that represents the least significant bits 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 reference pictures. Besides its own POC value, each slice header either directly contains or inherits from the SPS a coded representation of the POC value (or LSB) of each picture in the RPS.

[0097] The RPS for each picture includes five different sets of reference pictures, also called five RPS subsets: RefPicSetStCurrBefore includes all short-term reference pictures that precede the current picture in both decoding order and output order and can be used in inter-prediction of the current picture; RefPicSetStCurrAfter includes all short-term reference pictures that precede the current picture in decoding order, follow the current picture in output order, and can be used in inter-prediction of the current picture; RefPicSetStFoll includes all short-term reference pictures that can be used in inter-prediction of one or more pictures that follow the current picture in decoding order, but are not used in inter-prediction of the current picture; RefPicSetLtCurr includes all long-term reference pictures that can be used in inter-prediction of one or more pictures that follow the current picture in decoding order, but are not used in inter-prediction of the current picture; and RefPicSetLtFoll includes all long-term reference pictures that can be used in inter-prediction of one or more pictures that follow the current picture in decoding order, but are not used in inter-prediction of the current picture.

[0098] The RPS is signaled using up to three loops that iterate over different types of reference pictures: short-term reference pictures with lower POC values ​​than the current picture, short-term reference pictures with higher POC values ​​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 referencing 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 an RPS 400 with a current picture B14 with entries (e.g., pictures) in all subsets 402 of the RPS 400. In the example of Figure 4, the current picture B14 includes exactly one picture in each of the five subsets 402 (also known as RPS subsets). P8 is a picture in the subset 402 called RefPicSetStCurrBefore because the picture is earlier in the output order and used by B14. P12 is a picture in the subset 402 called RefPicSetStCurrAfter because the picture is later in the output order and used by B14. P13 is a picture in the subset 402 called RefPicSetStFoll because the picture is a short-term reference picture not used by B14 (but must be kept in the DPB because it is used by B15). P4 is a picture in a subset 402 called RefPicSetLtCurr because it is a long-term reference picture used by B14. I0 is a picture in a subset 402 called RefPicSetStLtFoll because it is a long-term reference picture not used by the current picture (but must be kept in the DPB because it is used by B15).

[0100] The short-term portion of the RPS 400 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 the active SPS. The short-term portion of the RPS 402 may be signaled using one of two different schemes: inter-RPS, as described below, or intra-RPS, as described herein. When intra-RPS is used, num_negative_pics and num_positive_pics are signaled, representing the lengths of two different lists of reference pictures. These lists contain reference pictures with negative and positive POC differences compared to the current picture, respectively. 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 one.

[0101] When encoding a recurring RPS in a sequence parameter set, it is possible to encode elements of one RPS (e.g., RPS 400) relative to another RPS already encoded in the sequence parameter set. This is called inter-RPS. Because all RPSs of a sequence parameter set are in the same network abstraction layer (NAL) unit, there are no error resilience issues associated with this method. The inter-RPS 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 used for prediction of the current picture. Thus, the syntax comprises an index indicating the RPS to use as a predictor, a delta_POC to be added to the delta_POC of the predictor to obtain the delta_POC of the current RPS, and a set of indicators to indicate which pictures are reference pictures and whether they are used only for prediction of future pictures. In an embodiment, delta POC refers to the difference in POC value between a current reference picture and another (eg, earlier) reference picture.

[0102] Encoders that want to exploit the use of 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 fixed-length codewords pos_lst_lt, which represent the least significant bits of the complete POC value of 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 the set of long-term pictures in an SPS as a list of POC LSB values. The POC LSB for a long-term picture can be signaled in the slice header as an index into this list.

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

[0104] For reference picture marking in HEVC, there are usually a certain number of pictures in the DPB before picture decoding. Some of them 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." When the slice header is parsed, the picture marking process occurs before the slice data is decoded. Pictures that are present in the DPB and marked as "used for reference" but not included in the RPS are marked as "not used for reference." Pictures that are not in the DPB but 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 instead equal to 1, this reference picture was intended to be used for prediction in the current picture but has been lost. Then, unintentional picture loss is inferred and the decoder must take appropriate action.

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

[0106] Next, reference picture list construction in HEVC is discussed. In HEVC, the term inter-prediction is used to indicate 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. A 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 P slices, and two reference picture lists, List 0 and List 1, are used for B slices. Similar to AVC, reference picture list construction in HEVC includes reference picture list initialization and reference picture list modification.

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

[0109] Reference picture list initialization creates default list 0 and list 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 inserted into list 0 (list 1) first 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. In terms of RPS, for list 0, entries in RefPicSetStCurrBefore are inserted into the initial list, followed by entries in RefPicSetStCurrAfter. Then, entries in RefPicSetLtCurr are added, if available.

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

[0111] After the reference picture list is initialized, the reference picture list may be modified based on a reference picture list modification command so that the reference pictures for the current picture can be arranged in any order, including cases where one particular reference picture may appear in more than one position in the list. When a flag indicating the presence of a list modification is set to 1, a fixed number of commands (equal to the target number of entries in the reference picture list) are signaled, with each command inserting one entry into the reference picture list. The reference picture is identified in the command by an index into the list of reference pictures for the current picture derived from RPS signaling. This differs from reference 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 reference 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 include any reference picture with a TemporalId greater than the current picture. An HEVC bitstream may consist of several temporal sub-layers. Each NAL unit belongs to a particular sub-layer as indicated by its TemporalId (equal to temporal_id_plus1-1).

[0113] Reference picture management is based directly on reference picture lists. JCT-VC document JCTVC-G643 includes a technique for directly using three reference picture lists, Reference Picture List 0, Reference Picture List 1, and Idle Reference Picture List, for managing reference pictures in a DPB, thereby eliminating the need for signaling and decoding processes for either 1) the sliding window and MMCO processes and the reference picture list initialization and modification processes in AVC, or 2) the reference picture set and the reference picture list initialization and modification processes 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 leads to higher signaling bit counts for such RPL-based approaches compared to other explicit reference picture management approaches, such as RPS-based approaches. The signaling inefficiency of RPL-based approaches is due to several aspects.

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

[0116] Signaling RPL indices (e.g., 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. In many cases, the predetermined RPL structures of RPL0 and RPL1 may be arranged such that when the RPL of a picture refers to a predetermined RPL structure in a parameter set, the index of RPL0 and the index of RPL1 are the same.

[0117] Furthermore, there is no inter-RPL coding for writing reference picture list structures into the coded video bitstream. For example, an RPL structure may be coded without reference to a previously signaled RPL structure in the bitstream. In one embodiment, an RPL structure refers to a programming construct that contains an indexed list of pointers to candidate reference pictures.

[0118] Described herein are several aspects that may be applied individually and / or in combination to solve the problems and address the shortcomings described herein, each of which is described in more detail below.

[0119] In one aspect, 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 parameter set (e.g., SPS, PPS) as the predefined RPL structure to indicate whether the delta POC values ​​in each RPL structure have the same sign value (e.g., all delta POCs in the same RPL structure are either positive delta POC values ​​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, a flag is signaled in the RPL structure to indicate the sign values ​​of all entries in the RPL structure (e.g., the sign values ​​of the delta POC values ​​of the STRP). When all_rpl_entries_same_sign_flag is equal to 0, a flag is signaled in the RPL structure to indicate the sign values ​​of each of the entries associated with the STRP in each RPL structure. In an embodiment, the absolute values ​​of the delta POC values ​​of the STRP entries in the RPL structure are coded using an unsigned integer zeroth-order exponential-Golomb code (e.g., ue(v)).

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

[0122] When creating predetermined RPL structures for the RPL0 list and the RPL1 list in the parameter set for encoding, the RPL structures in the lists for RPL0 and RPL1 may be made such that the RPL structure for list 0 and the RPL structure for list 1 are paired. Thus, when a picture references 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 point, a flag may indicate whether a syntax element for RPL1 referencing a predefined RPL structure is present or absent in the slice header. This flag may be referred to as "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 certain embodiments, signaling 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 of the slice header associated with the parameter set containing the flag refers to a predefined RPL structure, the index of which is not signaled in the slice header but is instead 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 but 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] are present 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 of the slice header associated with the parameter set containing the flag refers to a predefined 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 but 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] is present 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 identical content to 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 that contains the predefined RPL structure and shall be located before the signaling of the predefined 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, and instead 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, for each RPL structure for list 0, a copy of the exact same RPL structure is created, 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 structure for list 1 are signaled.

[0128] The contents of an RPL structure can be predicted from another RPL structure. When the predefined RPL structures in a parameter set are divided into two lists (e.g., an RPL structure list for list 0 and an RPL structure list for list 1), only the RPL structures in the list for list 0 can be used as a reference for inter-RPL. 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 predefined 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 predefined RPL structures in the list for list 0.

[0129] In one alternative, when the predefined RPL structures in a parameter set are divided into two lists (e.g., 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 with an index smaller than its index. Similarly, an RPL structure in the list for list 1 can only point to another RPL structure in the list for list 1 with an index smaller than its index. An RPL structure explicitly signaled in a slice header for RPL0 can point to any of the predefined RPL structures in the list for list 0, and an RPL structure explicitly signaled in a slice header for RPL1 can point to any of the predefined RPL structures in the list for list 1.

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

[0131] In inter-RPL, the index for the reference RPL structure is coded as the delta between the current RPL structure index and the reference RPL structure index minus one, and may be coded using ue(v) coding. In one alternative, 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 that qualify 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, the index for the reference RPL structure may be coded using either ue(v) or u(v), depending on the mode of inter-RPL.

[0132] To support inter-RPL, each RPL structure is coded using one of the modes described below. Note that the order of the modes below does not necessarily imply an order of the mode values. An indication of the mode may be coded as follows: In one embodiment, the indication of the mode may simply be coded using ue(v). In one embodiment, the indication of the mode may be coded using u(v), with the number of bits to represent the mode being the binary logarithm of the total number of defined modes.

[0133] The first RLP coding mode is the intra-coding 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, entitled "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 referred to as granularity_val. The value of granularity_val is used to scale or divide each value representing the STRP's POC delta value in the RPL structure.

[0134] The second RPL coding mode is an inter-coding mode that utilizes delta POC values ​​for STRPs in the reference RPL structure and the current RPL structure that have the same or even difference. To code an 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 may 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, coded as ue(v). An 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 constrained to only positive values ​​(e.g., 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, then this mode cannot be used to code the current RPL structure), may be constrained to only negative values, or may be either positive or negative. When coded as ue(v), the offset may be signaled using term_minus1. A flag for each entry in the reference RPL structure is also signaled in the bitstream to indicate whether the entry is used as an entry in the current RPL structure. When an entry is a STRP entry in the reference 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 reference RPL structure minus an 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 reference 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 reference RPL structure.

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

[0137] First, the coding mode and the reference index are signaled in the bitstream. The reference index is an index of the reference RPL structure. The reference index may 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 to 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 to the entry in the reference RPL structure. After all entries from the reference RPL structure are duplicated to the current RPL structure, the following information is signaled for each additional entry: If long-term reference pictures are used in the bitstream (i.e., this may be indicated by a flag in the same parameter set), a 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 POC LSB of the LTRP entry is signaled. Otherwise, the delta POC of the STRP entry is signaled. The value of the delta POC may be signaled as a delta from the previous STRP entry or simply as a delta from the POC of the current picture.

[0138] The fourth RPL coding mode is an inter-coding 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 the code values ​​reversed. To code the RPL using this mode, the following information is signaled in the bitstream:

[0139] First, the coding mode and the reference index are signaled. The reference index is an index into the reference RPL structure. The reference index may be coded as described above. Optionally, a flag to indicate whether the code value is inverted is also signaled in the bitstream.

[0140] When a bitstream is coded using forward inter-prediction (e.g., inter-prediction for pictures with a POC value smaller than that of the current picture) and backward inter-prediction (e.g., inter-prediction for pictures with a POC value larger than that of the current picture), the following constraints on reference pictures in the RPL apply: For each RPL of a picture, all reference pictures in the RPL have the same inter-prediction direction, e.g., all reference pictures are reference pictures for forward inter-prediction or all reference pictures are reference pictures for backward inter-prediction. For a pair of RPLs of a picture, no reference picture shall be 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. Alternatively, all reference pictures except the first picture in RPL0 (ie the picture with the lowest index) are removed from RPL0.

[0141] Disclosed herein is a video coding technique that uses a flag to indicate whether an index for a second reference picture list structure can be inferred to be the same as an 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, coders / decoders (also known as "codecs") in video coding are improved (e.g., use fewer bits, require less bandwidth, are more efficient, etc.) compared to current codes. In practical terms, the improved video coding process provides users with a better user experience when video is transmitted, received, and / or viewed.

[0142] 5 is a schematic diagram of an embodiment of a video bitstream 500. Herein, the video bitstream 500 may also be referred to as a coded video bitstream, a bitstream, or variations thereof. As shown in FIG. 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] The SPS 510 contains data common to all pictures in a sequence of pictures (SOP). In contrast, the PPS 512 contains data common to the entire picture. The slice header 514 contains information about the current slice, such as the slice type, which of the reference pictures are used, etc. The SPS 510 and the PPS 512 may be collectively referred to as a parameter set. The SPS 510, the PPS 512, and the slice header 514 are types of Network Abstraction Layer (NAL) units. The image data 520 comprises data associated with the image or video being encoded or decoded. The image data 520 may simply be referred to as the payload or data being carried in the bitstream 500.

[0144] In an embodiment, the SPS 510, the PPS 512, the slice header 514, or another portion of the bitstream 500 carries multiple reference picture list structures, each of which contains multiple reference picture entries. Those skilled in the art will understand that the bitstream 500 may include other parameters and information in actual applications.

[0145] 6 is an embodiment of a method 600 for decoding a coded video bitstream (e.g., bitstream 500) implemented by a video decoder (e.g., video decoder 30). Method 600 may be performed after a decoded bitstream is received directly or indirectly from a video encoder (e.g., video encoder 20). Method 600 improves the decoding process (e.g., making the decoding process more efficient, faster, etc. than conventional decoding processes) because, when the flag is set to a certain value, indexes to the second reference picture list structure may be inferred to be the same as indexes to the 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 circumstances, as in HEVC and AVC. Thus, in practical terms, codec performance is improved, which translates into a better user experience.

[0146] In block 602, a flag is parsed from a coded video bitstream (e.g., video bitstream 500). In one embodiment, this flag is designated as rpl1_idx_present_flag. In one embodiment, this flag is included in a PPS (e.g., PPS 512) of the coded video bitstream. In one embodiment, this flag is included in an SPS (e.g., SPS 510) of the coded video bitstream.

[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 an embodiment, the first reference picture list structure is included in a slice header (e.g., slice header 514) of the coded video bitstream. In an 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 is parsed, or vice versa.

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

[0150] At block 610, a reference picture list is generated using the first reference picture list structure, the second reference picture list structure, or some combination thereof. The reference picture list may identify one or more pictures, such as, for example, the pictures shown and described in connection with FIG.

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

[0152] 7 is an embodiment of a method 700 for encoding a video bitstream (e.g., bitstream 500) performed by a video encoder (e.g., video encoder 20). Method 700 may be executed when pictures (e.g., from a video) are to be encoded into a video bitstream and then transmitted toward a video decoder (e.g., video decoder 30). Method 700 improves the encoding process (e.g., making the encoding process more efficient, faster, etc. than conventional encoding processes) because, when a flag is set to a certain value, it can be inferred that an index to a second reference picture list structure is the same as an index to 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. Thus, in practice, codec performance is improved, which translates into a better user experience.

[0153] In block 702, a flag is coded into the video bitstream using a first value when an index to the second reference picture list structure is not coded in a slice header of the video bitstream and the index to the second reference picture list structure should be inferred by the video decoder to be the same as the index to the first reference picture list structure. In an embodiment, the flag is designated as rpl1_idx_present_flag. In an embodiment, the flag is coded in a PPS (e.g., PPS 512) of the coded video bitstream (e.g., video bitstream 500). In an embodiment, the first reference picture list structure is coded in a slice header (e.g., slice header 514) of the video bitstream.

[0154] A flag is encoded into the video bitstream using the second value when an index to the second reference picture list structure is encoded into the slice header of the video bitstream in block 704. In an 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 coded using a first value, the first reference picture list structure is coded into the video bitstream. In block 708, when the flag is coded using a second value, the first reference picture list structure and the second reference picture list structure are coded into the video bitstream. In an embodiment, the first value of the flag is 1 and the second value of the flag is 0. In an 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.

[0156] At block 710, the video bitstream is transmitted toward a video decoder (e.g., video decoder 30). Once received by the video decoder, the encoded video bitstream may be decoded (e.g., as described above) to generate or create images for display to a user on a display or screen of an electronic device (e.g., a smartphone, tablet, laptop, personal computer, etc.).

[0157] A description of the techniques disclosed herein is provided in the context of 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 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 nal_unit_type equal to NON_IRAP_NUT. A reference picture list is a list of reference pictures used for inter prediction of a P or B slice. Two reference picture lists, Reference Picture List 0 and Reference Picture List 1, are generated for each slice of a non-IRAP picture. The set of unique pictures referenced by all entries in the two reference picture lists associated with a picture includes all reference pictures that can be used for inter prediction of the associated picture or any picture that follows the associated picture in decoding order. To decode slice data of a P slice, only Reference Picture List 0 is used for inter prediction. To decode slice data of a B slice, both reference picture lists are used for inter prediction. To decode slice data of an I slice, no reference picture list is used for inter prediction. A short-term reference picture (STRP) is a picture marked as "used for short-term reference."

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

[0160] The remainder of this disclosure provides syntax and semantics suitable for implementing 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 shall be equal to 0. nal_unit_type specifies the type of RBSP data structure contained in the NAL unit.

[0173] [Table 6]

[0174] nuh_temporal_id_plus1 minus 1 specifies the temporal identifier for the NAL unit. The value of nuh_temporal_id_plus1 shall not be equal to 0. The variable TemporalId is specified as follows: TemporalId = nuh_temporal_id_plus1 - 1. When nal_unit_type is equal to IRAP_NUT, the coded slice belongs to an IRAP picture and TemporalId shall be equal to 0. The value of TemporalId shall be the same for all VCL NAL units of an access unit. The value of TemporalId of a coded picture or access unit is the value of TemporalId of the VCL NAL units of the coded picture or access unit. The value of TemporalId for non-VCL NAL units is constrained as follows: If nal_unit_type is equal to SPS_NUT, TemporalId shall be equal to 0 and the TemporalId of the access unit containing the NAL unit shall be equal to 0. Otherwise, if nal_unit_type is equal to EOS_NUT or EOB_NUT, then TemporalId shall be equal to 0. Otherwise, TemporalId shall be greater than or equal to the TemporalId of the access unit that contains the NAL unit. When the NAL unit is a non-VCL NAL unit, the value of TemporalId is equal to the minimum of the TemporalId values ​​of all access units to which the non-VCL NAL unit applies. When nal_unit_type is equal to PPS_NUT, TemporalId may be greater than or equal to the TemporalId of the containing access unit, since all picture parameter sets (PPS) may be included at the beginning of the bitstream, and the first coded picture has TemporalId equal to 0.When nal_unit_type is equal to PREFIX_SEI_NUT or SUFFIX_SEI_NUT, TemporalId may be greater than or equal to the TemporalId of the containing access unit, because the SEI NAL unit may contain information that applies to bitstream subsets that include access units with TemporalId values ​​greater than the TemporalId of the access unit that contains the SEI NAL unit. nuh_reserved_zero_7bits shall be equal to '0000000'. Other values ​​of nuh_reserved_zero_7bits may be specified in the future by ITU-T|ISO / IEC. Decoders shall ignore (i.e., remove from the bitstream and discard) NAL units with a value of nuh_reserved_zero_7bits 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 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 shall be in the range of 0 to 12, inclusive. 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 buffer. The value of sps_max_dec_pic_buffering_minus1 shall be in the range of 0 to MaxDpbSize-1, inclusive, where MaxDpbSize is as specified elsewhere. long_term_ref_pics_flag equal to 0 specifies that LTRP is not used for inter prediction of any coded pictures in the CVS. long_term_ref_pics_flag equal to 1 specifies that LTRP may be used for inter prediction 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 shall be in the range from 0 to 32-log2_max_pic_order_cnt_lsb_minus4-4, inclusive. When not present, the value of additional_lt_poc_lsb is inferred to be equal to 0.

[0177] all_rpl_entries_same_sign_flag equal to 1 specifies that all STRP entries in each ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) have the same sign value, where sign indicates a positive or negative value. all_rpl_entries_same_sign_flag equal to 0 specifies that STRP entries in each ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) may or may not have the same sign value. rpl1_copy_from_rpl0_flag equal to 1 specifies that num_ref_pic_lists_in_sps[1] and ref_pic_list_struct(1,rplsIdx,ltrpFlag) are not present, and the following applies: The value of num_ref_pic_lists_in_sps[1] is set equal to the value of num_ref_pic_lists_in_sps[0]. The syntax structure ref_pic_list_struct(1,rplsIdx,ltrpFlag) is inferred to be identical to the value of ref_pic_list_struct(0,rplsIdx,ltrpFlag). Subsequently, the syntax elements in ref_pic_list_struct(1,rplsIdx,ltrpFlag) are inferred to be equal to the syntax elements in ref_pic_list_struct(0,rplsIdx,ltrpFlag), respectively.

[0178] num_ref_pic_lists_in_sps[i] specifies the number of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures contained in the SPS, with listIdx equal to i. The value of num_ref_pic_lists_in_sps[i] shall be in the range of 0 to 64, inclusive. For each value of listIdx (equal to 0 or 1), the decoder should allocate memory for a total of num_ref_pic_lists_in_sps[i] ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures, since there can be one ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure signaled directly in the slice header of the current picture.

[0179] Picture Parameter Set RBSP Semantics

[0180] num_ref_idx_default_active_minus1[i] plus 1 specifies the inferred value of the variable NumRefIdxActive[0] for P or B slices with num_ref_idx_active_override_flag equal to 0 when i is equal to 0, and specifies the inferred value of NumRefIdxActive[1] for B slices with num_ref_idx_active_override_flag equal to 0 when i is equal to 1. The value of num_ref_idx_default_active_minus1[i] shall be in the range 0 to 14, inclusive. rpl1_idx_present_flag equal to 0 specifies that ref_pic_list_sps_flag[1] and ref_pic_list_idx[1] are not present in the slice header. rpl1_idx_present_flag equal to 1 specifies 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] When present, the value of each of the slice header syntax elements slice_pic_parameter_set_id and slice_pic_order_cnt_lsb shall be the same in all slice headers of a coded picture. slice_type specifies the coding type of the slice according to Table 7-3.

[0183] [Table 7]

[0184] When nal_unit_type is equal to IRAP_NUT, i.e., the picture is an IRAP picture, slice_type shall 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 shall be in the range from 0 to MaxPicOrderCntLsb-1, inclusive. When slice_pic_order_cnt_lsb is not present, slice_pic_order_cnt_lsb is inferred to be equal to 0. ref_pic_list_sps_flag[i] equal to 1 specifies that reference picture list i of the current picture is derived based on one of the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures in the active SPS with listIdx equal to i. ref_pic_list_sps_flag[i] equal to 0 specifies that reference picture list i of the current picture is derived based on the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure with listIdx equal to i that is directly included in the slice header of the current picture. When num_ref_pic_lists_in_sps[i] is equal to 0, the value of ref_pic_list_sps_flag[i] shall be equal to 0. When rpl1_idx_present_flag is equal to 0 and ref_pic_list_sps_flag[0] is present, the value of ref_pic_list_sps_flag[1] is inferred to be equal to the value of ref_pic_list_sps_flag[0].ref_pic_list_idx[i] specifies an index into the list of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures with listIdx equal to i contained in the active SPS, of which ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures with listIdx equal to i are used to derive reference picture list i for the current picture. The syntax element ref_pic_list_idx[i] is represented by Ceil(Log2(num_ref_pic_lists_in_sps[i])) bits. When not present, the value of ref_pic_list_idx[i] is inferred to be equal to 0. The value of ref_pic_list_idx[i] shall lie in the range from 0 to num_ref_pic_lists_in_sps[i] - 1, inclusive. When rpl1_idx_present_flag is equal to 0 and ref_pic_list_sps_flag[0] is present, the value of ref_pic_list_idx[1] is inferred to be equal to the value of ref_pic_list_idx[0]. num_ref_idx_active_override_flag equal to 1 specifies that the syntax element num_ref_idx_active_minus1[0] is present for P and B slices and that the syntax element num_ref_idx_active_minus1[1] is present for B slices. num_ref_idx_active_override_flag equal to 0 specifies that the syntax elements num_ref_idx_active_minus1[0] and num_ref_idx_active_minus1[1] are not present. num_ref_idx_active_minus1[i], when present, specifies the value of the variable NumRefIdxActive[i], where NumRefIdxActive[i] = num_ref_idx_active_minus1[i] + 1. The value of num_ref_idx_active_minus1[i] shall be in the range 0 to 14, inclusive.

[0185] The value of NumRefIdxActive[i]-1 specifies the highest reference index for reference picture list i that may be used to decode the slice. When the value of NumRefIdxActive[i] is equal to 0, no reference index for reference picture list i may be used to decode the slice. For i equal to 0 or 1, when the current slice is a B slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[i] is inferred to be equal to num_ref_idx_default_active_minus1[i]+1. When the current slice is a P slice and num_ref_idx_active_override_flag is equal to 0, NumRefIdxActive[0] is inferred to be equal to num_ref_idx_default_active_minus1[0]+1. When the current slice is a P slice, NumRefIdxActive[i] is inferred to be equal to 0. When the current slice is an I slice, both NumRefIdxActive[0] and NumRefIdxActive[1] are inferred to be equal to 0.

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

[0187] Reference Picture List Structure Semantics

[0188] The ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure can be present in an SPS or a slice header. Depending on whether the syntax structure is included in a slice header or an SPS, the following applies: When present in a slice header, the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure specifies the reference picture list listIdx of the current picture (the picture that contains the slice). Otherwise (if present in the SPS), the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure specifies candidates for the reference picture list listIdx, and the term "current picture" in the semantics specified in the rest of this section refers to each picture that 1) has one or more slices with ref_pic_list_idx[listIdx] equal to an index into the list of ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structures contained in the SPS, and 2) is in a CVS that has the SPS as its active SPS. 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. When not present, the value of num_ltrp_entries[listIdx][rplsIdx] is inferred to be equal to 0.The variable NumEntriesInList[listIdx][rplsIdx] is derived as follows: NumEntriesInList[listIdx][rplsIdx] = num_strp_entries[listIdx][rplsIdx] + num_ltrp_entries[listIdx][rplsIdx]. The value of NumEntriesInList[listIdx][rplsIdx] shall be in the range 0 to sps_max_dec_pic_buffering_minus1, inclusive. strp_entries_sign_flag[listIdx][rplsIdx] equal to 1 specifies that all STRP entries in ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) have values ​​greater than or equal to 0. strp_entries_sign_flag[listIdx][rplsIdx] equal to 0 specifies that all STRP entries in ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) have values ​​less than 0.

[0189] lt_ref_pic_flag[listIdx][rplsIdx][i] equal to 1 specifies that the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure is an LTRP entry. lt_ref_pic_flag[listIdx][rplsIdx][i] equal to 0 specifies that the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure is a STRP entry. When not present, the value of lt_ref_pic_flag[listIdx][rplsIdx][i] is inferred to be equal to 0. It is a bitstream conformance requirement that the sum of lt_ref_pic_flag[listIdx][rplsIdx][i] for all values ​​of i in the range 0 to NumEntriesInList[listIdx][rplsIdx]-1, inclusive, must equal 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 greater than or equal to 0. 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 less than 0. When not present, the value of strp_entries_sign_flag[listIdx][rplsIdx][i] is inferred 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 value of the current picture and the picture order count value of the picture referenced by the ith entry when the ith entry is the first STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure, or specifies the difference between the picture order count value of the picture referenced by the ith entry and the picture order count value of the picture referenced by the previous STRP entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure when the ith entry is a STRP entry but is not the first STRP entry in the ref_pic_list_struct(rplsIdx,ltrpFlag) syntax structure. The value of delta_poc_st[listIdx][rplsIdx][i] shall be in the range of -215 to 215-1, inclusive. poc_lsb_lt[listIdx][rplsIdx][i] specifies the value of the picture order count modulo MaxLtPicOrderCntLsb for the picture referenced by the i-th entry in the ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) syntax structure. The length of the poc_lsb_lt[listIdx][rplsIdx][i] syntax element is Log2(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] model_ref_rpl_idx_delta_minus1[listIdx][rplsIdx] plus 1 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] strp_offset_val_minus1[listIdx][rplsIdx] plus 1 specifies the value to be subtracted from each STRP entry in the reference ref_pic_list_struct(listIdx,rplsIdx,ltrpFlag) to calculate the value of delta_poc_st[listIdx][rplsIdx][i] of 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). 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] The following applies to the interaction of values ​​of the syntax element lt_ref_pic_flag[listIdx][rplsIdx][i] when rpl_mode[listIdx][rplsIdx] is equal to 1, and the following applies to the interaction of values ​​of poc_lsb_lt[listIdx][rplsIdx][i] when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 1, 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]. When not present, the value of add_lt_ref_pic_flag[listIdx][rplsIdx][i] is inferred to be equal to 0. 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]. When not present, the value of add_strp_entries_sign_flag[listIdx][rplsIdx][i] is set equal to the value of strp_entries_sign_flag[listIdx][rplsIdx].

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

[0197] The following applies for inferring the values ​​of the syntax elements strp_entries_sign_flag[listIdx][rplsIdx], lt_ref_pic_flag[listIdx][rplsIdx][i] when rpl_mode[listIdx][rplsIdx] is equal to 2, and for inferring the value of poc_lsb_lt[listIdx][rplsIdx][i] when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 1, as well as for 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]: 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] The following applies for guessing the value of the syntax element lt_ref_pic_flag[listIdx][rplsIdx][i] when rpl_mode[listIdx][rplsIdx] is equal to 3, the following applies for guessing the value of poc_lsb_lt[listIdx][rplsIdx][i] when lt_ref_pic_flag[listIdx][rplsIdx][i] is equal to 1, and the following applies for 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]: 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 decoding process is provided.

[0201] For the current picture, CurrPic, the decoding process operates as follows: The decoding of NAL units is specified below. The following process, using the syntax elements in the slice header layer and above, specifies the next decoding process: The variables and functions for the picture order count are derived. This is called only for the first slice of the picture. At the beginning of the decoding process for each slice of a non-IRAP picture, the decoding process for reference picture list construction is called to derive reference picture list 0 (RefPicList[0]) and reference picture list 1 (RefPicList[1]). The decoding 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 decoding processes for coding tree units, scaling, transform, in-loop filtering, etc. are called. After all slices of the current picture have been decoded, the currently decoded 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 units of the current picture and 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, the picture order count of the current picture. The picture order count is used to identify pictures for motion parameter derivation and motion vector prediction in merge mode, as well as for decoder conformance checking. Each coded picture is associated with a picture order count variable, denoted PicOrderCntVal. When the current picture is not an IRAP picture, the variables prevPicOrderCntLsb and prevPicOrderCntMsb are derived as follows: Let prevTid0Pic be the previous picture in decoding order with TemporalId equal to 0. The variable prevPicOrderCntLsb is set equal to slice_pic_order_cnt_lsb of prevTid0Pic. The variable prevPicOrderCntMsb is set equal to PicOrderCntMsb of prevTid0Pic.

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

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

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

[0210] At any instant during the decoding process, the values ​​of PicOrderCntVal & (MaxLtPicOrderCntLsb-1) for any two reference pictures in the DPB shall not be the same. The function PicOrderCnt(picX) is defined as follows: PicOrderCnt(picX) = PicOrderCntVal of picture picX. The function DiffPicOrderCnt(picA,picB) is defined as follows: DiffPicOrderCnt(picA,picB) = PicOrderCnt(picA) - PicOrderCnt(picB). The bitstream shall not contain data that results in a value of DiffPicOrderCnt(picA,picB) used in the decoding process that is not in the range of -215 to 215-1, inclusive. 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 if DiffPicOrderCnt(X,Y) and DiffPicOrderCnt(X,Z) are both positive or both negative.

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

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

[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 the other entries in RefPicList[i] are called inactive entries in RefPicList[i]. Each entry in RefPicList[i][j], for j in the range from 0 to NumEntriesInList[i][RplsIdx[i]]-1, inclusive, is called a STRP entry if lt_ref_pic_flag[i][RplsIdx[i]][j] is equal to 0, and 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 also be referenced by more than one entry in RefPicList[0] or more than one entry in RefPicList[1]. The active entries in RefPicList[0] and the active entries in RefPicList[1] collectively refer to all reference pictures that can be used for inter-prediction of the current picture and one or more pictures that follow the current picture in decoding order. The inactive entries in RefPicList[0] and the inactive entries in RefPicList[1] collectively refer to all reference pictures that are not used for inter-prediction of the current picture but can be used in inter-prediction for one or more pictures that follow the current picture in decoding order. There may be one or more entries in RefPicList[0] or RefPicList[1] that are equal to "No Reference Picture" because no corresponding picture exists in the DPB. Each inactive entry in RefPicList[0] or RefPicList[0] that is equal to "No Reference Picture" should be ignored. For each active entry in RefPicList[0] or RefPicList[1] that is equal to "No Reference Picture," an unintentional picture loss should be inferred.

[0214] It is a bitstream conformance requirement that the following constraints apply: For each i equal to 0 or 1, NumEntriesInList[i][RplsIdx[i]] shall not be less than NumRefIdxActive[i]. The picture referenced by each active entry in RefPicList[0] or RefPicList[1] shall be present in the DPB and shall have a TemporalId less than or equal to the current picture. Optionally, the following constraint 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 constraint may be further specified: An inactive entry in RefPicList[0] or RefPicList[1] shall not reference the same picture as any other entry in RefPicList[0] or RefPicList[1]. An STRP entry in RefPicList[0] or RefPicList[1] of a slice of a picture and an LTRP entry in RefPicList[0] or RefPicList[1] of the same slice or a different slice of the same picture shall not reference 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 more. Let setOfRefPics 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 decoding process for reference picture marking is provided.

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

[0217] 8 is a schematic diagram of a video coding device 800 (e.g., video encoder 20 or video decoder 30) according to an embodiment of the present disclosure. The video coding device 800 is suitable for implementing the disclosed embodiments as described herein. The video coding device 800 includes an ingress 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 egress port 850 for transmitting data, and a memory 860 for storing data. The video coding device 800 may also include optical-electronic (OE) and electro-optical (EO) components coupled to the egress port 810, the receiver unit 820, the transmitter unit 840, and the egress port 850 for inputting and outputting 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 is in communication with the ingress port 810, the receiver unit 820, the transmitter unit 840, the egress 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, the inclusion of the coding module 870 significantly improves the functionality of the video coding device 800 and produces transformations of the video coding device 800 into different states. Alternatively, the coding module 870 is implemented as instructions stored in the memory 860 and executed by the processor 830.

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

[0220] Memory 860 may comprise one or more disks, tape drives, and solid-state drives and may be used as overflow data storage devices for storing programs when such programs are selected for execution and for storing instructions and data 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] 9 is a schematic diagram of an embodiment of a means for coding 900. In an embodiment, the means for coding 900 is implemented in a video coding device 902 (e.g., video encoder 20 or video decoder 30). The video coding device 902 includes a means for receiving 901. The means for receiving 901 is configured to receive a picture to be encoded or a bitstream to be decoded. The video coding device 902 includes a means for transmitting 907 coupled to the means for receiving 901. The means for transmitting 907 is configured to transmit the bitstream to a decoder or transmit a decoded image to a display means (e.g., one of 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 the instructions stored in the storage means 903 in order to perform the methods 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 steps of such methods should be understood as merely exemplary. Similarly, additional steps may be included in such methods, and some steps may be omitted or combined in a manner consistent with various embodiments of the present disclosure.

[0224] Although several embodiments have been provided in this disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the disclosure. These examples should be considered illustrative rather than limiting, and the intention is not to be limited to the details provided herein. For example, various elements and components may be combined or integrated in another system, or certain features may be omitted or not implemented.

[0225] Additionally, techniques, systems, subsystems, and methods described and illustrated as separate or distinct in various embodiments may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or in communication with each other may also be indirectly coupled or in communication, whether electrically, mechanically, or otherwise, through some interface, device, or intermediate component. Other examples of changes, substitutions, and variations will be recognizable by those skilled in the art and may be made without departing from the spirit and scope disclosed herein. [Explanation of symbols]

[0226] 12 Source Devices 14 Destination Device 16 Computer-Readable Medium 18 Video Sources 20 Video Encoder 22 Output Interface 28 Input Interface 30 Video Decoder 32 Display Devices 40 Mode Selection Unit 42 Motion Estimation Unit 44 Motion Compensation Unit 46 intra prediction units 48 division units 52 Conversion Processing Unit 54 quantization units 56 Entropy Coding Units 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 Inlet Port 820 receiver unit 830 processor 840 Transmitter Unit 850 Exit Port 860 memory 870 Coding Module 880 I / O Devices 901 Receiving means 902 Video Coding Device 903 Memory means 905 Processing means 907 Transmission Method

Claims

1. 1. A method for decoding a coded video bitstream, performed by a video decoder, comprising: parsing a picture parameter set (PPS) level flag from the coded video bitstream; parsing a first reference picture list (RPL) flag and a first RPL index to a first RPL syntax structure from the coded video bitstream; determining, when the PPS level flag has a first value, that a second RPL flag and a second RPL index for a second RPL syntax structure are not present in a slice header of the coded video bitstream, and that the value of the second RPL flag and the second RPL index for the second RPL syntax structure are inferred to be equal to the value of the first RPL flag and the first RPL index for the first RPL syntax structure, respectively; The first RPL flag equal to 1 specifies that the first reference picture list of the current picture is derived based on one of the RPL syntax structures with listIdx equal to 0 in a sequence parameter set (SPS), and the first RPL flag equal to 0 specifies that the first reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 0; the second RPL flag equal to 1 specifies that the second reference picture list of the current picture is derived based on one of the RPL syntax structures in the SPS with listIdx equal to 1, and the second RPL flag equal to 0 specifies that the second reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 1; the first RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 0, that is used to derive the first reference picture list of the current picture to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 0; the second RPL index specifies an index of the RPL syntax structure, having listIdx equal to 1, that is used to derive the second reference picture list for the current picture, to a list of the RPL syntax structures that are included in the SPS and have listIdx equal to 1, and the method further comprises: parsing the second RPL flag and the second RPL index for the second RPL syntax structure from the slice header when the PPS level flag has a second value; parsing a first syntax element from the coded video bitstream, the first syntax element specifying a number of RPL syntax structures for the first reference picture list included in the SPS; parsing an SPS level flag from the coded video bitstream; determining, when the SPS level flag is equal to 1, that a second syntax element is absent from the coded video bitstream and is inferred to be equal to the first syntax element, the second syntax element specifying the number of RPL syntax structures for the second reference picture list included in the SPS; and parsing the second syntax element from the coded video bitstream when the SPS level flag is equal to 0.

2. The method of claim 1 , wherein the PPS level flag is designated as rpl1_idx_present_flag.

3. The method according to claim 1 , wherein the first RPL flag is expressed as ref_pic_list_sps_flag[0] and the first RPL index is expressed as ref_pic_list_idx[0].

4. 4. The method of claim 3, wherein the second RPL flag is expressed as ref_pic_list_sps_flag[1] and the second RPL index is expressed as ref_pic_list_idx[1].

5. 5. The method of claim 1, wherein the first syntax element is expressed as num_ref_pic_lists_in_sps[0] and the second syntax element is expressed as num_ref_pic_lists_in_sps[1].

6. 1. A method for encoding a coded video bitstream, performed by a video encoder, comprising: encoding a picture parameter set (PPS) level flag into the coded video bitstream; encoding a first reference picture list (RPL) flag and a first RPL index for a first RPL syntax structure into the coded video bitstream; When the PPS level flag is equal to a first value, a second RPL flag and a second RPL index for a second RPL syntax structure are not coded into a slice header of the coded video bitstream, and the value of the second RPL flag and the second RPL index for the second RPL syntax structure are inferred to be equal to the value of the first RPL flag and the first RPL index for the first RPL syntax structure, respectively; and the method further comprises: encoding the second RPL flag and the second RPL index for the second RPL syntax structure into the slice header when the PPS level flag is equal to a second value; The first RPL flag equal to 1 specifies that the first reference picture list of the current picture is derived based on one of the RPL syntax structures with listIdx equal to 0 in a sequence parameter set (SPS), and the first RPL flag equal to 0 specifies that the first reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 0; the second RPL flag equal to 1 specifies that the second reference picture list of the current picture is derived based on one of the RPL syntax structures in the SPS with listIdx equal to 1, and the second RPL flag equal to 0 specifies that the second reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 1; the first RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 0, that is used to derive the first reference picture list of the current picture to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 0; the second RPL index specifies an index of the RPL syntax structure, with listIdx equal to 1, used to derive the second reference picture list for the current picture, to a list of the RPL syntax structures included in the SPS and with listIdx equal to 1, and the method further comprises: encoding a first syntax element into the coded video bitstream, the first syntax element specifying a number of RPL syntax structures for the first reference picture list included in the SPS; encoding an SPS level flag into the coded video bitstream; determining, when the SPS level flag is equal to 1, that a second syntax element is not encoded into the coded video bitstream and is inferred to be equal to the first syntax element, the second syntax element specifying the number of RPL syntax structures for the second reference picture lists included in the SPS; and encoding the second syntax element into the coded video bitstream when the SPS level flag is equal to 0.

7. The method of claim 6 , wherein the PPS level flag is designated as rpl1_idx_present_flag.

8. The method of claim 6 or 7, wherein the first RPL flag is expressed as ref_pic_list_sps_flag[0] and the first RPL index is expressed as ref_pic_list_idx[0].

9. 9. The method of claim 8, wherein the second RPL flag is expressed as ref_pic_list_sps_flag[1] and the second RPL index is expressed as ref_pic_list_idx[1].

10. 10. The method of claim 6, wherein the first syntax element is expressed as num_ref_pic_lists_in_sps[0] and the second syntax element is expressed as num_ref_pic_lists_in_sps[1].

11. A decoding device comprising a processor and a memory, the processor coupled to the memory; The processor may further include instructions stored in the memory that cause the processor to: Parsing picture parameter set (PPS) level flags from the coded video bitstream; parsing a first reference picture list (RPL) flag and a first RPL index for a first RPL syntax structure from the coded video bitstream; determining, when the PPS level flag has a first value, that a second RPL flag and a second RPL index for a second RPL syntax structure are not present in a slice header of the coded video bitstream, and that the value of the second RPL flag and the second RPL index for the second RPL syntax structure are inferred to be equal to the value of the first RPL flag and the first RPL index for the first RPL syntax structure, respectively; The first RPL flag equal to 1 specifies that the first reference picture list of the current picture is derived based on one of the RPL syntax structures with listIdx equal to 0 in a sequence parameter set (SPS), and the first RPL flag equal to 0 specifies that the first reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 0; the second RPL flag equal to 1 specifies that the second reference picture list of the current picture is derived based on one of the RPL syntax structures in the SPS with listIdx equal to 1, and the second RPL flag equal to 0 specifies that the second reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 1; the first RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 0, that is used to derive the first reference picture list of the current picture to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 0; the second RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 1, that is used to derive the second reference picture list for the current picture, to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 1; The processor further comprises: parsing the second RPL flag and the second RPL index for the second RPL syntax structure from the slice header when the PPS level flag is a second value; parsing a first syntax element from the coded video bitstream, the first syntax element specifying a number of RPL syntax structures for the first reference picture list included in the SPS; parsing an SPS level flag from the coded video bitstream; determining, when the SPS level flag is equal to 1, that a second syntax element is absent from the coded video bitstream and is inferred to be equal to the first syntax element, the second syntax element specifying the number of RPL syntax structures for the second reference picture list included in the SPS; The processor further comprises: parsing the second syntax element from the coded video bitstream when the SPS level flag is equal to 0. A decoding device configured to execute the instructions.

12. 12. The decoding device of claim 11, wherein the processor is further configured to perform the method of any one of claims 2 to 5.

13. 1. An encoding device comprising a processor and a memory, The processor is coupled to the memory, and the instructions stored in the memory cause the processor to: encoding a picture parameter set (PPS) level flag into the coded video bitstream; encoding a first reference picture list (RPL) flag and a first RPL index for a first RPL syntax structure into the coded video bitstream; when the PPS level flag is equal to a first value, a second RPL flag and a second RPL index for a second RPL syntax structure are not coded into a slice header of the coded video bitstream, and the value of the second RPL flag and the second RPL index for the second RPL syntax structure are inferred to be equal to the value of the first RPL flag and the first RPL index for the first RPL syntax structure, respectively; The processor further comprises: encoding the second RPL flag and the second RPL index for the second RPL syntax structure into the slice header when the PPS level flag is equal to a second value; The first RPL flag equal to 1 specifies that the first reference picture list of the current picture is derived based on one of the RPL syntax structures with listIdx equal to 0 in a sequence parameter set (SPS), and the first RPL flag equal to 0 specifies that the first reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 0; the second RPL flag equal to 1 specifies that the second reference picture list of the current picture is derived based on one of the RPL syntax structures in the SPS with listIdx equal to 1, and the second RPL flag equal to 0 specifies that the second reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 1; the first RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 0, that is used to derive the first reference picture list of the current picture to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 0; the second RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 1, that is used to derive the second reference picture list for the current picture, to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 1; The processor further comprises: encoding a first syntax element into the coded video bitstream, the first syntax element specifying a number of RPL syntax structures for the first reference picture list included in the SPS; and encoding an SPS level flag into the coded video bitstream; determining, when the SPS level flag is equal to 1, that a second syntax element is not encoded into the coded video bitstream and is inferred to be equal to the first syntax element, the second syntax element specifying a number of RPL syntax structures for the second reference picture list included in the SPS; The processor further comprises: causing the second syntax element to be encoded into the coded video bitstream when the SPS level flag is equal to 0. A coding device configured to execute instructions.

14. 14. The encoding device of claim 13, wherein the processor is further configured to perform the method of any one of claims 7 to 10.

15. An encoder comprising processing circuitry for implementing the method according to any one of claims 6 to 10.

16. A decoder comprising processing circuitry for implementing the method according to any one of claims 1 to 5.

17. A computer program comprising a program code for performing the method of any one of claims 1 to 10 when the computer program is run on a computer or processor.

18. a parsing unit configured to parse a picture parameter set (PPS) level flag from a coded video bitstream, the parsing unit comprising: a parsing unit further configured to parse a first reference picture list (RPL) flag and a first RPL index to a first RPL syntax structure from the coded video bitstream; a determining unit configured to determine, when the PPS level flag has a first value, that a second RPL flag and a second RPL index for a second RPL syntax structure are not present in a slice header of the coded video bitstream, and that the value of the second RPL flag and the second RPL index for the second RPL syntax structure are inferred to be equal to the value of the first RPL flag and the first RPL index for the first RPL syntax structure, respectively; The first RPL flag equal to 1 specifies that the first reference picture list of the current picture is derived based on one of the RPL syntax structures with listIdx equal to 0 in a sequence parameter set (SPS), and the first RPL flag equal to 0 specifies that the first reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 0; the second RPL flag equal to 1 specifies that the second reference picture list of the current picture is derived based on one of the RPL syntax structures in the SPS with listIdx equal to 1, and the second RPL flag equal to 0 specifies that the second reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 1; the first RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 0, that is used to derive the first reference picture list of the current picture to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 0; the second RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 1, that is used to derive the second reference picture list for the current picture, to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 1; when the PPS level flag has a second value, the parsing unit is further configured to parse the second RPL flag and the second RPL index for the second RPL syntax structure from the slice header; the parsing unit is further configured to parse a first syntax element from the coded video bitstream, the first syntax element specifying a number of RPL syntax structures for the first reference picture list included in the SPS; the parsing unit is further configured to parse an SPS level flag from the coded video bitstream; When the SPS level flag is equal to 1, the determining unit is further configured to determine that a second syntax element is not present in the coded video bitstream and is inferred to be equal to the first syntax element, the second syntax element specifying a number of RPL syntax structures for the second reference picture list included in the SPS; The decoding device, wherein the parsing unit is further configured to parse the second syntax element from the coded video bitstream when the SPS level flag is equal to 0.

19. 1. A coding device comprising a coding unit, the coding unit comprising: Encoding a picture parameter set (PPS) level flag into the coded video bitstream; Encoding a first reference picture list (RPL) flag and a first RPL index for a first RPL syntax structure into the coded video bitstream. It is configured as follows: when the PPS level flag is equal to a first value, a second RPL flag and a second RPL index for a second RPL syntax structure are not coded into a slice header of the coded video bitstream, and the value of the second RPL flag and the second RPL index for the second RPL syntax structure are inferred to be equal to the value of the first RPL flag and the first RPL index for the first RPL syntax structure, respectively; the encoding unit further comprises: encoding the second RPL flag and the second RPL index for the second RPL syntax structure into the slice header when the PPS level flag is equal to a second value; It is configured as follows: The first RPL flag equal to 1 specifies that the first reference picture list of the current picture is derived based on one of the RPL syntax structures with listIdx equal to 0 in a sequence parameter set (SPS), and the first RPL flag equal to 0 specifies that the first reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 0; the second RPL flag equal to 1 specifies that the second reference picture list of the current picture is derived based on one of the RPL syntax structures in the SPS with listIdx equal to 1, and the second RPL flag equal to 0 specifies that the second reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 1; the first RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 0, that is used to derive the first reference picture list of the current picture to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 0; the second RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 1, that is used to derive the second reference picture list for the current picture, to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 1; the encoding unit further comprises: encoding a first syntax element into the coded video bitstream, the first syntax element specifying a number of RPL syntax structures for the first reference picture list included in the SPS; Encoding an SPS level flag into the coded video bitstream It is configured as follows: when the SPS level flag is equal to 1, a determining unit is configured to determine that a second syntax element is not encoded into the coded video bitstream and is inferred to be equal to the first syntax element, the second syntax element specifying a number of RPL syntax structures for the second reference picture list included in the SPS; The encoding device, wherein when the SPS level flag is equal to 0, the encoding unit is further configured to encode the second syntax element into the coded video bitstream.

20. 1. A system for processing a bitstream, comprising: a server and one or more storage devices; wherein the one or more storage devices are configured to store one or more bitstreams, the bitstreams comprising a Picture Parameter Set (PPS) level flag, a first Reference Picture List (RPL) flag, and a first RPL index for a first RPL syntax structure; when the PPS level flag has a first value, a second RPL flag and a second RPL index for a second RPL syntax structure are not present in a slice header of the coded video bitstream, and the value of the second RPL flag and the second RPL index for the second RPL syntax structure are inferred to be equal to the value of the first RPL flag and the first RPL index for the first RPL syntax structure, respectively; The first RPL flag equal to 1 specifies that the first reference picture list of the current picture is derived based on one of the RPL syntax structures with listIdx equal to 0 in a sequence parameter set (SPS), and the first RPL flag equal to 0 specifies that the first reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 0; the second RPL flag equal to 1 specifies that the second reference picture list of the current picture is derived based on one of the RPL syntax structures in the SPS with listIdx equal to 1, and the second RPL flag equal to 0 specifies that the second reference picture list of the current picture is derived based on the RPL syntax structure directly included in the slice header with listIdx equal to 1; the first RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 0, that is used to derive the first reference picture list of the current picture to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 0; the second RPL index specifies an index of the RPL syntax structure, whose listIdx is equal to 1, that is used to derive the second reference picture list for the current picture, to a list of the RPL syntax structures that are included in the SPS and whose listIdx is equal to 1; when the PPS level flag has a second value, the bitstream further comprises the second RPL flag and the second RPL index for the second RPL syntax structure; the bitstream further comprises a first syntax element and an SPS level flag, the first syntax element specifying a number of RPL syntax structures for the first reference picture list included in the SPS; When the SPS level flag is equal to 1, a second syntax element is absent from the bitstream and is inferred to be equal to the first syntax element, the second syntax element specifying the number of RPL syntax structures for the second reference picture lists included in the SPS; and when the SPS level flag is equal to 0, the bitstream further comprises the second syntax element; The system wherein the server is configured to retrieve one or more bitstreams from the one or more storage devices in response to a decoder request, and transmit the one or more bitstreams to the decoder.

Images