Method, apparatus and program for decoding a current video block of a video bitstream

Abstract

The present disclosure generally relates to video coding / decoding, and in particular to a method and system for refining motion vector candidates. An exemplary decoding method includes: receiving a coded video bitstream; extracting from the coded video bitstream a first syntax element indicating whether a mixed reference mode is applied to a current video block; extracting from the coded video bitstream a second syntax element indicating whether motion vector difference (MVD) is jointly signaled for the current video block; refining, by a device, at least one MV predictor (MVP) in a MV candidate list based on whether the at least one MVP is symmetric in response to the first syntax element indicating that a mixed reference mode is applied to the current video block and the second syntax element indicating that MVD is jointly signaled for the current video block; and decoding, by the device, the current video block based on the MV candidate list.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is based on, and claims the benefit of priority to, U.S. Provisional Patent Application No. 63 / 281,338, filed November 19, 2021, which is incorporated herein by reference in its entirety. This application also claims the benefit of priority to, and claims the benefit of priority to, U.S. Provisional Patent Application No. 63 / 289,054, filed December 13, 2021, which is incorporated herein by reference in its entirety. This application also claims the benefit of priority to, and claims the benefit of priority to, U.S. Nonprovisional Patent Application No. 17 / 963,614, filed October 11, 2022, which is incorporated herein by reference in its entirety.

[0002] FIELD This disclosure relates generally to video coding, and more particularly, to methods and systems for providing a signaling scheme for refining motion vector candidates. [Background technology]

[0003] The discussion of the background art provided herein is intended to generally present the context of the present disclosure. The inventors' work is not admitted, expressly or impliedly, as prior art to the present disclosure to the extent that that work is described in this background section, together with aspects of the description that may not otherwise be admitted as prior art at the time of filing of this application.

[0004] Video coding and decoding may be performed using inter-picture prediction with motion compensation. Uncompressed digital video may include a sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luma samples and associated full-sampled or sub-sampled chroma samples. The sequence of pictures may have a fixed or variable picture rate (also called frame rate), for example, 60 pictures per second or 60 frames per second. Uncompressed video has specific bit rate requirements for streaming or data processing. For example, a video with a pixel resolution of 1920x1080, a frame rate of 60 frames / second, and 4:2:0 chroma subsampling with 8 bits per pixel per color channel requires a bandwidth approaching 1.5 Gbit / s. One hour of such video requires more than 600 GByte of storage space.

[0005] One objective of video coding and decoding may be the reduction of redundancy in an uncompressed input video signal through compression. Compression may help reduce the aforementioned bandwidth and / or storage space requirements, in some cases by more than one order of magnitude. Both lossless and lossy compression, as well as combinations thereof, may be employed. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal through a decoding process. Lossy compression refers to a coding / decoding process where the original video information is not fully preserved when coding and cannot be fully restored when decoding. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between the original and reconstructed signals is small enough to make the reconstructed signal useful for its intended application, even with some information loss. For video, lossy compression is widely adopted in many applications. The amount of distortion that can be tolerated depends on the application. For example, a user of a particular consumer video streaming application may tolerate higher distortion than a user of a movie or television broadcast application. The compression ratio achievable by a particular coding algorithm may be selected or adjusted to reflect different distortion tolerances. That is, in general, higher distortion tolerance allows for coding algorithms that result in higher losses and higher compression ratios.

[0006] Video encoders and decoders can utilize techniques from a number of broad categories and steps, including, for example, motion compensation, Fourier transform, quantization, and entropy coding.

[0007] Video codec technology can include a technique known as intra-coding. In intra-coding, sample values ​​are represented without reference to samples or other data from previously reconstructed reference pictures. In some video codecs, a picture is spatially subdivided into blocks of samples. If all blocks of samples are coded in intra mode, the picture can be called an intra-picture. Intra-pictures and their derived pictures, such as independent decoder refresh pictures, can be used to reset the decoder state and thus can be used as the first picture in the coded video bitstream and video session or as still images. Samples of the block after intra prediction can then be transformed to the frequency domain, and the transform coefficients so generated can be quantized before entropy coding. Intra prediction represents a technique that minimizes sample values ​​in the pre-transform domain. In some cases, the smaller the DC value after transformation and the smaller the AC coefficients, the fewer bits are needed at a given quantization step size to represent the block after entropy coding.

[0008] Conventional intra-coding, for example as known from MPEG-2 generation coding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to code / decode a block based on surrounding sample data and / or metadata that precedes in decoding order the block of data being intra-coded or intra-decoded, e.g., obtained during encoding and / or decoding of spatial neighbors. Such techniques are hereafter referred to as "intra-prediction" techniques. It should be noted that in at least some cases, intra-prediction uses reference data only from the current picture being reconstructed, and not from other reference pictures.

[0009] Intra prediction may take many different forms. If more than one of such techniques is available in a given video coding technique, the technique used may be referred to as an intra prediction mode. One or more intra prediction modes may be provided in a particular codec. In certain cases, a mode may have sub-modes and / or may be associated with various parameters, and the mode / sub-mode information and intra coding parameters of a block of video may be coded individually or collectively included in the codeword of the mode. Which codeword is used for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency gains via intra prediction, and thus may also affect the entropy coding technique used to convert the codeword into a bitstream.

[0010] Certain modes of intra prediction were introduced in H.264, improved in H.265, and further improved in newer coding techniques such as Joint Search Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). In general, in intra prediction, the predictor block may be formed using neighboring sample values ​​that become available. For example, the available values ​​of a particular neighboring sample set along a particular direction and / or line may be copied into the predictor block. The reference to the direction in use may be coded in the bitstream or may itself be predicted.

[0011] Referring to FIG. 1A, shown at the bottom right is a subset of the nine predictor directions specified in the 33 possible intra predictor directions of H.265 (corresponding to the 33 angle modes of the 35 intra modes specified in H.265). The point (101) where the arrows converge represents the sample being predicted. The arrows represent the direction from which neighboring samples are used to predict the sample at 101. For example, arrow (102) indicates that sample (101) is predicted from one or more neighboring samples to the top right at an angle of 45 degrees from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from one or more neighboring samples to the bottom left of sample (101) at an angle of 22.5 degrees from the horizontal.

[0012] 1A, at the top left is shown a square block (104) of 4×4 samples (indicated by a thick dashed line). The square block (104) contains 16 samples, each labeled with "S", its position in the Y dimension (e.g., row index), and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample (from the top) in the Y dimension and the first sample (from the left) in the X dimension. Similarly, sample S44 is the fourth sample in both the Y and X dimensions in the block (104). Since the block is 4×4 samples in size, S44 is at the bottom right. Also shown is an exemplary reference sample that follows a similar numbering scheme. The reference sample is labeled R, its Y position (e.g., row index), and X position (column index) relative to the block (104). In both H.264 and H.265, predicted samples that neighbor the block being reconstructed are used.

[0013] Intra-picture prediction of block 104 may start by copying reference sample values ​​from adjacent samples according to a signaled prediction direction. For example, assume that the coded video bitstream includes signaling for this block 104 indicating the prediction direction of the arrow (102), i.e., the sample is predicted from one or more prediction samples to the upper right and at an angle of 45 degrees from the horizontal. In such a case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Then, sample S44 is predicted from reference sample R08.

[0014] In certain cases, to calculate a reference sample, especially when the orientation is not evenly divisible by 45 degrees, the values ​​of multiple reference samples may be combined, for example by interpolation.

[0015] The number of possible directions has increased as video coding technology continues to develop. In H.264 (2003), for example, nine different directions are available for intra prediction. This increases to 33 in H.265 (2013), and JEM / VVC / BMS can support up to 65 directions at the time of this disclosure. Experimental studies have been conducted to help identify the most suitable intra prediction directions, and those most suitable directions can be encoded with a small number of bits using certain techniques of entropy coding, accepting certain bit penalties for the directions. Furthermore, the direction itself may be predicted from the neighboring directions used in the intra prediction of the decoded neighboring blocks.

[0016] FIG. 1B shows a schematic diagram (180) showing 65 intra prediction directions according to JEM to illustrate the increasing number of prediction directions in various encoding techniques that have evolved over time.

[0017] Methods for mapping bits representing intra-prediction directions in a coded video bitstream to prediction directions can vary across video coding techniques, and can range, for example, from simple direct mappings of prediction directions to intra-prediction modes to complex adaptation schemes including codewords, most probable modes, and similar techniques. In all cases, however, there may be certain directions of intra-prediction that are statistically less likely to occur in the video content than certain other directions. Because the goal of video compression is to reduce redundancy, in a well-designed video coding technique, these less likely directions may be represented with more bits than the more likely directions.

[0018] Inter-picture prediction, or inter-prediction, may be based on motion compensation. In motion compensation, sample data from a previously reconstructed picture or part thereof (reference picture) may be used to predict a newly reconstructed picture or picture part (e.g., block) after being spatially shifted in a direction indicated by a motion vector (hereinafter, MV). In some cases, the reference picture may be the same as the picture currently being reconstructed. The MV may have two dimensions X and Y, or three dimensions, with the third dimension being an indication of the reference picture in use (similar to the temporal dimension).

[0019] In some video compression techniques, a current MV applicable to a particular area of ​​sample data may be predicted from other MVs, e.g., from other MVs related to other areas of sample data that are spatially adjacent to the area being reconstructed and that precede the current MV in decoding order. Doing so may significantly reduce the overall amount of data required to code the MV by relying on the removal of redundancy in correlated MVs, thereby increasing compression efficiency. MV prediction may work effectively because, for example, when coding an input video signal derived from a camera (known as natural video), areas larger than the area to which a single MV is applicable have a statistical likelihood to move in a similar direction in the video sequence, and therefore, in some cases, can be predicted using similar motion vectors derived from MVs of neighboring areas. As a result, the actual MV of a given area is similar or identical to the MV predicted from the surrounding MVs. Such MVs may further be represented with fewer bits after entropy coding than would be used if the MVs were directly coded instead of predicted from neighboring MVs. In some cases, MV prediction may be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., sample stream). In other cases, the MV prediction itself may be non-lossy, for example due to rounding errors when computing a predictor from several surrounding MVs.

[0020] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Recommendation H.265, "High Efficiency Video Coding", December 2016). Among the many MV prediction mechanisms specified by H.265, the one described below is a technique hereafter referred to as "spatial merging".

[0021] Specifically, referring to FIG. 2, a current block (201) contains samples that are detected by the encoder during the motion search process as predictable from a spatially shifted previous block of the same size. Instead of coding its MV directly, the MV may be derived from metadata associated with one or more reference pictures, e.g., the most recent reference picture (in decoding order), using MVs associated with any one of five surrounding samples, denoted A0, A1, and B0, B1, B2 (202-206, respectively). In H.265, MV prediction may use predictors from the same reference picture that neighboring blocks are using. Summary of the Invention [Means for solving the problem]

[0022] This disclosure describes various embodiments of methods, apparatuses, and computer-readable storage media for refining motion vector candidates and improving the efficiency of entropy coding / decoding in video coding / decoding.

[0023] According to one aspect, an embodiment of the present disclosure provides a method for decoding a current video block of a video bitstream. The method includes receiving, by a device, a coded video bitstream. The device includes a memory storing instructions and a processor in communication with the memory. The method also includes extracting, by the device, a first syntax element indicating whether a mixed reference mode is applied to the current video block from the coded video bitstream, extracting, by the device, a second syntax element indicating whether motion vector differences (MVDs) are jointly signaled for the current video block from the coded video bitstream, and refining, by the device, at least one MV predictor (MVP) in an MV candidate list based on whether the at least one MVP is symmetric in response to the first syntax element indicating that the mixed reference mode is applied to the current video block and the second syntax element indicating that the MVDs are jointly signaled for the current video block, and decoding, by the device, the current video block based on the MV candidate list.

[0024] According to another aspect, an embodiment of the present disclosure provides an apparatus for decoding a current video block of a video bitstream. The apparatus includes a memory storing instructions and a processor in communication with the memory. When the processor executes the instructions, the processor is configured to cause the apparatus to perform the above-described method for video decoding and / or encoding.

[0025] In another aspect, an embodiment of the present disclosure provides a non-transitory computer-readable medium storing instructions that, when executed by a computer for video decoding and / or encoding, cause the computer to perform the above-described method for video decoding and / or encoding.

[0026] These and other aspects and their implementations are described in further detail in the drawings, specification, and claims.

[0027] Further features, nature and various advantages of the disclosed subject matter will become more apparent from the following detailed description and the accompanying drawings. [Brief description of the drawings]

[0028] [Figure 1A] FIG. 13 is a schematic diagram of an example subset of intra-prediction directional modes. [Figure 1B] FIG. 2 illustrates an exemplary intra-prediction direction. [Diagram 2] FIG. 1 is a schematic diagram of a current block and its surrounding spatial merge candidates for motion vector prediction in one example. [Diagram 3] 1 is a schematic diagram of a simplified block diagram of a communication system (300) according to an exemplary embodiment. [Figure 4] 4 is a schematic diagram of a simplified block diagram of a communication system (400) according to an exemplary embodiment. [Diagram 5] 2 is a schematic diagram of a simplified block diagram of a video decoder according to an example embodiment; [Figure 6] 1 is a schematic diagram of a simplified block diagram of a video encoder according to an example embodiment; [Figure 7] 4 is a block diagram of a video encoder according to another example embodiment. [Figure 8] 4 is a block diagram of a video decoder according to another example embodiment. [Figure 9] FIG. 2 illustrates a coding block partitioning scheme according to an exemplary embodiment of the present disclosure. [Figure 10] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 11] FIG. 13 illustrates another scheme for coding block partitioning, according to an exemplary embodiment of the present disclosure. [Figure 12]FIG. 2 illustrates an exemplary partitioning of a base block into coding blocks according to an exemplary partitioning scheme. [Figure 13] FIG. 2 illustrates an exemplary division-of-thirds scheme. [Figure 14] FIG. 2 illustrates an exemplary quadtree / binary tree coding block partitioning scheme. [Figure 15] 4A-4C are diagrams illustrating a scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure. [Figure 16] 4A-4C are diagrams illustrating another scheme for splitting a coding block into multiple transform blocks and the coding order of the transform blocks according to an exemplary embodiment of the present disclosure. [Figure 17] FIG. 13 illustrates another scheme for splitting a coding block into multiple transform blocks, according to an exemplary embodiment of the present disclosure. [Figure 18] FIG. 2 illustrates a flowchart of a method according to an exemplary embodiment of the present disclosure. [Figure 19] 1 is a schematic diagram of a computer system according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] Throughout this specification and the claims, terms may have subtle meanings that are suggested or implied in the context beyond the meaning explicitly stated. The phrases "in one embodiment" or "in some embodiments" used herein do not necessarily refer to the same embodiment, and the phrases "in another embodiment" or "in other embodiments" used herein do not necessarily refer to different embodiments. Similarly, the phrases "in one implementation" or "in some implementations" used herein do not necessarily refer to the same implementation, and the phrases "in another implementation" or "in other implementations" used herein do not necessarily refer to different implementations. For example, the claimed subject matter is intended to include all or part of the exemplary embodiments / implementations.

[0030] Generally, technical terms may be understood at least in part from their usage in context. For example, terms such as "and", "or", or "and / or" as used herein may include various meanings that may depend at least in part on the context in which such terms are used. Typically, "or" when used to relate a list such as A, B, or C is intended to mean A, B, and C, which are used herein in an inclusive sense, as well as A, B, or C, which are used herein in an exclusive sense. In addition, the terms "one or more" or "at least one" as used herein may be used to describe any feature, structure, or characteristic in a singular sense, or may be used to describe a combination of features, structures, or characteristics in a plural sense, depending at least in part on the context. Similarly, terms such as "a", "an", or "the" may also be understood to convey a singular usage or a plural usage, depending at least in part on the context. In addition, the terms "based on" or "determined by" may be understood not to be intended to convey an exclusive set of factors, but may instead allow for the existence of additional factors not necessarily explicitly described, again depending at least in part on the context. FIG. 3 illustrates a simplified block diagram of a communication system (300) according to one embodiment of the present disclosure. The communication system (300) includes a plurality of terminal devices that can communicate with each other, for example, via a network (350). For example, the communication system (300) includes a first pair of terminal devices (310) and (320) interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) may implement unidirectional transmission of data. For example, the terminal device (310) may code video data (e.g., of a stream of video pictures captured by the terminal device (310)) for transmission to the other terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more coded video bitstreams.The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to recover the video picture, and display the video picture according to the recovered video data. The one-way data transmission may be implemented in media serving applications, etc.

[0031] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) implementing bidirectional transmission of coded video data, which may be implemented, for example, during video conferencing applications. For the bidirectional transmission of data, in one example, each of the terminal devices (330) and (340) may code video data (e.g., of a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may also receive coded video data transmitted by the other of the terminal devices (330) and (340), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device according to the recovered video data.

[0032] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) may be implemented as a server, a personal computer, and a smartphone, although application of the principles underlying the present disclosure may not be so limited. The embodiments of the present disclosure may be implemented in desktop computers, laptop computers, tablet computers, media players, wearable computers, dedicated video conferencing equipment, and the like. The network (350) represents any number or type of network that conveys coded video data between the terminal devices (310), (320), (330), and (340), including, for example, wired (wired connection) and / or wireless communication networks. The communication network (350) 9 may exchange data over circuit-switched channels, packet-switched channels, and / or other types of channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this description, the architecture and topology of the network (350) may not be important to the operation of the present disclosure unless expressly described herein.

[0033] 4 shows an arrangement of video encoders and video decoders in a video streaming environment as one example application of the disclosed subject matter. The disclosed subject matter may be equally applicable to other video applications including, for example, video conferencing, digital television broadcasting, gaming, virtual reality, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0034] A video streaming system may include a video source (401) for creating a stream of uncompressed video pictures or images (402), a video capture subsystem (413) that may include, for example, a digital camera. In one example, the stream of video pictures (402) includes samples recorded by the digital camera of the video source 401. The stream of video pictures (402), shown as a thick line to emphasize the large amount of data when compared to the encoded video data (404) (or coded video bitstream), may be processed by an electronic device (420) that includes a video encoder (403) coupled to the video source (401). The video encoder (403) may include hardware, software, or a combination thereof to enable or implement aspects of the disclosed subject matter, as described in more detail below. The encoded video data (404) (or encoded video bitstream (404)), shown with thin lines to emphasize its low amount of data compared to the stream of uncompressed video pictures (402), may be stored directly to the streaming server (405) or to a downstream video device (not shown) for future use. One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, may access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) may include, for example, a video decoder (410) within the electronic device (430). The video decoder (410) decodes the input copy of the encoded video data (407) and creates an output stream of video pictures (411) that is uncompressed and can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). The video decoder 410 may be configured to perform some or all of the various functions described in this disclosure.In some streaming systems, the encoded video data (404), (407), and (409) (e.g., video bitstreams) may be encoded according to a particular video coding / compression standard. Examples of such standards include ITU-T Recommendation H.265. In one example, a video coding standard under development is informally known as Versatile Video Coding (VVC). The disclosed subject matter may be used in the context of VVC, as well as other video coding standards.

[0035] It should be noted that the electronic devices (420) and (430) may include other components (not shown). For example, the electronic device (420) may include a video decoder (not shown), and the electronic device (430) may also include a video encoder (not shown).

[0036] 5 shows a block diagram of a video decoder (510) according to any of the following embodiments of the present disclosure. The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) of the example of FIG. 4.

[0037] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In the same or another embodiment, one coded video sequence may be decoded at a time, with the decoding of each coded video sequence being independent of the other coded video sequences. Each video sequence may be associated with multiple video frames or images. The coded video sequences may be received from a channel (501), which may be a hardware / software link to a storage device that stores the encoded video data, or a streaming source that transmits the encoded video data. The receiver (531) may receive the encoded video data along with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to respective processing circuits (not shown). The receiver (531) may separate the coded video sequences from other data. To combat network jitter, a buffer memory (515) may be disposed between the receiver (531) and the entropy decoder / parser (520) (hereinafter, "parser (520)"). In certain applications, the buffer memory (515) may be implemented as part of the video decoder (510). In other applications, the buffer memory (515) may be separate and external to the video decoder (510) (not shown). In still other applications, there may be a buffer memory (not shown) external to the video decoder (510), for example to combat network jitter, and there may be another additional buffer memory (515) internal to the video decoder (510), for example to handle playback timing. When the receiver (531) is receiving data from a storage / forwarding device with sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may be unnecessary or may be small. For use with best-effort packet networks such as the Internet, a sufficiently sized buffer memory (515) may be required, and its size may be relatively large.Such a buffer memory may be implemented with an adaptive size and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (510).

[0038] The video decoder (510) may include a parser (520) to reconstruct symbols (521) from the coded video sequence. These categories of symbols include information used to manage the operation of the video decoder (510) and potentially information for controlling a rendering device such as a display (512) (e.g., a display screen) that may or may not be an integral part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device may be in the form of a supplemental enhancement information (SEI message) or a parameter set fragment (not shown) of video usability information (VUI). The parser (520) may parse / entropy decode the coded video sequence received by the parser (520). The entropy coding of the coded video sequence may be according to a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser (520) may extract from the coded video sequence a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder based on at least one parameter corresponding to the subgroup. The subgroups may include groups of pictures (GOPs), pictures, tiles, slices, macroblocks, coding units (CUs), blocks, transform units (TUs), prediction units (PUs), etc. The parser (520) may also extract information from the coded video sequence, such as transform coefficients (e.g., Fourier transform coefficients), quantization parameter values, motion vectors, etc.

[0039] The parser (520) may perform entropy decoding / parsing operations on the video sequence received from the buffer memory (515) to produce symbols (521).

[0040] The reconstruction of the symbols (521) may involve a number of different processing or functional units, depending on the type of video picture or portion thereof being coded (inter-picture and intra-picture, inter-block and intra-block, etc.), as well as other factors. The units that are included and how they are included may be controlled by subgroup control information parsed from the coded video sequence by the parser (520). The flow of such subgroup control information between the parser (520) and the following processing or functional units is not shown for the sake of simplicity.

[0041] Besides the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into several functional units, as described below. In an actual implementation operating under commercial constraints, many of these functional units may closely interact with each other and may be, at least in part, integrated with each other. However, for the purpose of clearly describing the various functions of the disclosed subject matter, a conceptual subdivision into functional units is adopted in the following disclosure.

[0042] The first unit may include a scalar / inverse transform unit (551), which may receive quantized transform coefficients as well as control information from the parser (520) including information indicating which type of inverse transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc. The scalar / inverse transform unit (551) may output blocks including sample values ​​that may be input to an aggregator (555).

[0043] In some cases, the output samples of the scaler / inverse transform (551) may relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture, but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) may generate a block of the same size and shape as the block being reconstructed using information of surrounding blocks that have already been reconstructed and stored in the current picture buffer (558). The current picture buffer (558) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. In some implementations, the aggregator (555) may add, on a sample-by-sample basis, the prediction information generated by the intra-prediction unit (552) to the output sample information provided by the scaler / inverse transform unit (551).

[0044] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded, potentially motion-compensated block. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for inter-picture prediction. After motion compensating the fetched samples according to the symbols (521) related to the block, these samples may be added to the output of the scalar / inverse transform unit (551) by the aggregator (555) to generate output sample information (the output of unit 551 may be referred to as a residual sample or residual signal). The address in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches the prediction sample may be controlled by a motion vector, available to the motion compensated prediction unit (553) in the form of a symbol (521), which may have, for example, an X component, a Y component (shift), and a reference picture component (time). Motion compensation may also include interpolation of sample values ​​fetched from a reference picture memory (557) when sub-sample accurate motion vectors are used, and may be associated with a motion vector prediction mechanism, etc.

[0045] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in the loop filter unit (556). Video compression techniques may include in-loop filter techniques that are controlled by parameters included in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520), but may also be responsive to previously reconstructed and loop filtered sample values ​​as well as meta-information obtained during decoding of a previous portion (in decoding order) of the coded picture or coded video sequence. As described in more detail below, several types of loop filters may be included as part of the loop filter unit 556 in various orders.

[0046] The output of the loop filter unit (556) may be a sample stream that can be output to the rendering device (512) as well as stored in a reference picture memory (557) for use in future inter-picture prediction.

[0047] Once a particular coded picture is fully reconstructed, it may be used as a reference picture for future inter-picture prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified (e.g., by the parser (520)) as a reference picture, the current picture buffer (558) may become part of the reference picture memory (557), and any unused current picture buffer may be reallocated before beginning reconstruction of the next coded picture.

[0048] The video decoder (510) may perform decoding operations according to a given video compression technique adopted in a standard, such as ITU-T Recommendation H.265. The coded video sequence may conform to a syntax specified by the video compression technique or standard used in the sense that the coded video sequence adheres to both the syntax of the video compression technique or standard and to a profile documented in the video compression technique or standard. Specifically, a profile may select a particular tool from all tools available in the video compression technique or standard as the only tool that can be used under that profile. To conform to a standard, the complexity of the coded video sequence may be within a range defined by a level of the video compression technique or standard. In some cases, the level limits a maximum picture size, a maximum frame rate, a maximum reconstruction sample rate (e.g., measured in megasamples per second), a maximum reference picture size, etc. The limits set by the level may be further limited in some cases by a specification of a hypothetical reference decoder (HRD) and metadata for HRD buffer management signaled within the coded video sequence.

[0049] In some example embodiments, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0050] 6 shows a block diagram of a video encoder (603) according to an exemplary embodiment of the present disclosure. The video encoder (603) may be included in an electronic device (620). The electronic device (620) may further include a transmitter (640) (e.g., a transmission circuit). The video encoder (603) may be used in place of the video encoder (403) of the example of FIG.

[0051] The video encoder (603) may receive video samples from a video source (601) (which is not part of the electronic device (620) in the example of FIG. 6) that may capture video images to be coded by the video encoder (603). In another example, the video source (601) may be implemented as part of the electronic device (620).

[0052] The video source (601) may provide a source video sequence to be coded by the video encoder (603) in the form of a digital video sample stream that may be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, ...), any color space (e.g., BT.601 YCrCb, RGB, XYZ ...), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media serving system, the video source (601) may be a storage device capable of storing previously prepared video. In a video conferencing system, the video source (601) may be a camera that captures local image information as a video sequence. The video data may be provided as a number of individual pictures or images that give motion when viewed in sequence. The picture itself may be organized as a spatial array of pixels, each pixel may contain one or more samples depending on the sampling structure, color space, etc. being used. Those skilled in the art can easily understand the relationship between pixels and samples. The following description focuses on samples.

[0053] According to some example embodiments, the video encoder (603) may code and compress pictures of a source video sequence into a coded video sequence (643) in real time or under any other time constraint required by the application. Enforcing an appropriate coding rate constitutes one function of the controller (650). In some embodiments, the controller (650) may be operatively coupled to and control other functional units, as described below. For simplicity, couplings are not shown. Parameters set by the controller (650) may include rate control related parameters (picture skip, quantizer, lambda value for rate distortion optimization techniques, etc.), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured to have other appropriate functions associated with the video encoder (603) optimized for a particular system design.

[0054] In some example embodiments, the video encoder (603) may be configured to operate in a coding loop. As an oversimplified explanation, in one example, the coding loop may include a source coder (630) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to create sample data in a similar manner as a (remote) decoder would create them, even though the embedded decoder 633 processes the video stream coded by the source coder 630 without entropy coding (since in the video compression techniques contemplated in the disclosed subject matter, any compression between the symbols and the coded video bitstream may be lossless). The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since decoding of the symbol stream produces bit-exact results regardless of the location of the decoder (local or remote), the contents of the reference picture memory (634) are also bit-exact between the local and remote encoders. In other words, the predictive part of the encoder "sees" exactly the same sample values ​​as the reference picture samples that the decoder "sees" when using prediction during decoding. This basic principle of reference picture synchrony (and the resulting drift when synchrony cannot be maintained, e.g., due to channel errors) is used to improve coding quality.

[0055] The operation of the "local" decoder (633) may be the same as the operation of a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. Referring also briefly to Figure 5, however, because symbols are available and the encoding / decoding of symbols into a coded video sequence by the entropy coder (645) and parser (520) may be lossless, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and parser (520), may not be fully implemented in the local decoder (633) within the encoder.

[0056] At this point, it can be said that any decoder technology, except for parsing / entropy decoding, which may only exist in the decoder, may necessarily also need to exist in the corresponding encoder in substantially the same functional form. For this reason, the disclosed subject matter may focus on the decoder operation, which is similar to the decoding part of the encoder. Thus, the description of the encoder technology may be omitted, since it is the reverse of the decoder technology described in general. Only in certain areas or aspects, a more detailed description of the encoder is provided below.

[0057] In operation, in some example implementations, the source coder (630) may perform motion-compensated predictive coding, which predictively codes an input picture with reference to one or more previously coded pictures from a video sequence designated as "reference pictures." In this manner, the coding engine (632) codes color channel differences (or residuals) between pixel blocks of the input picture and pixel blocks of reference pictures that may be selected as predictive references to the input picture. The terms "residual" and its adjective form "residual" may be used interchangeably.

[0058] The local video decoder (633) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols created by the source coder (630). The operation of the coding engine (632) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may typically be a replica of the source video sequence with some errors. The local video decoder (633) may replicate the decoding process that may be performed by the video decoder on the reference pictures, such that the reconstructed reference pictures are stored in the reference picture cache (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content with reconstructed reference pictures obtained by a far-end (remote) video decoder (without transmission errors).

[0059] The predictor (635) may perform a predictive search for the coding engine (632). That is, for a new picture to be coded, the predictor (635) may search the reference picture memory (634) for sample data (as candidate reference pixel blocks) or specific metadata such as reference picture motion vectors, block shapes, etc., that may serve as suitable predictive references for the new pixels. The predictor (635) may operate on sample blocks on a pixel block by pixel block basis to find suitable predictive references. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have predictive references drawn from multiple reference pictures stored in the reference picture memory (634).

[0060] The controller (650) may manage the coding operations of the source coder (630), including, for example, setting the parameters and subgroup parameters used to encode the video data.

[0061] The output of all the aforementioned functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by lossless compression of the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0062] The transmitter (640) may buffer the coded video sequence created by the entropy coder (645) and prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0063] The controller (650) can manage the operation of the video encoder (603). During coding, the controller (650) can assign a particular coded picture type to each coded picture, which may affect the coding techniques that may be applied to the respective picture. For example, pictures may often be assigned as one of the following picture types:

[0064] An intra picture (I-picture) may be one that can be coded and decoded without using other pictures in a sequence as a source of prediction. Some video codecs allow different types of intra pictures, including, for example, independent decoder refresh ("IDR") pictures. Those skilled in the art are aware of these variations of I-pictures, as well as their respective uses and characteristics.

[0065] A predictive picture (P picture) may be a picture that can be coded and decoded using intra- or inter-prediction, which uses at most one motion vector and reference index to predict sample values ​​for each block.

[0066] A bidirectionally predicted picture (B-picture) may be a picture that can be coded and decoded using intra- or inter-prediction that uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, a multi-predicted picture may use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0067] A source picture may generally be spatially subdivided into multiple sample coding blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and coded block by block. A block may be predictively coded with reference to other (already coded) blocks as determined by the coding assignment applied to the respective picture of the block. For example, a block of an I picture may be non-predictively coded or predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). A pixel block of a P picture may be predictively coded via spatial prediction or via temporal prediction with reference to one previously coded reference picture. A block of a B picture may be predictively coded via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures. A source picture or an intermediate processed picture may be subdivided into other types of blocks for other purposes. The division of coding blocks and other types of blocks may or may not follow the same method, as described in more detail below.

[0068] The video encoder (603) may perform coding operations in accordance with a given video coding technique or standard, such as ITU-T Recommendation H.265. In its operations, the video encoder (603) may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancy in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0069] In some example embodiments, the transmitter (640) may transmit additional data along with the encoded video. The source coder (630) may include such data as part of the coded video sequence. The additional data may include temporal / spatial / SNR enhancement layers, other forms of redundant data such as redundant pictures and slices, SEI messages, VUI parameter set fragments, etc.

[0070] Video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits temporal or other correlation between pictures. For example, a particular picture being encoded / decoded, called the current picture, may be divided into blocks. If a block in the current picture is similar to a reference block in a previously coded yet buffered reference picture in the video, it may be coded by a vector, called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0071] In some exemplary embodiments, bi-prediction techniques may be used for inter-picture prediction. According to such bi-prediction techniques, two reference pictures, such as a first reference picture and a second reference picture, are used, both of which advance the current picture in the video in decoding order (but may be in the past or future, respectively, in display order). A block in the current picture may be coded by a first motion vector that points to a first reference block in the first reference picture and a second motion vector that points to a second reference block in the second reference picture. A block may be jointly predicted by a combination of the first reference block and the second reference block.

[0072] Furthermore, merge mode techniques may be used to improve coding efficiency in inter-picture prediction.

[0073] According to some exemplary embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed on a block-by-block basis. For example, a picture in a sequence of video pictures is divided into coding tree units (CTUs) for compression, and the CTUs in a picture may have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may include three parallel coding tree blocks (CTBs), i.e., one luma CTB and two chroma CTBs. Each CTU may be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels may be partitioned into one CU of 64×64 pixels, or four CUs of 32×32 pixels. Each of one or more of the 32×32 blocks may be further partitioned into four CUs of 16×16 pixels. In some exemplary embodiments, each CU may be analyzed during encoding to determine a prediction type for that CU from among various prediction types, such as an inter prediction type and an intra prediction type. A CU may be divided into one or more prediction units (PUs) according to temporal and / or spatial predictability. In general, each PU includes one luma prediction block (PB) and two chroma PBs. In one embodiment, prediction operations in coding (encoding / decoding) are performed in units of prediction blocks. The division of a CU into PUs (or PBs of different color channels) may be performed in various spatial patterns. A luma PB or a chroma PB may include a matrix of sample values ​​(e.g., luma values), such as, for example, 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0074] 7 shows a diagram of a video encoder (703) according to another exemplary embodiment of the present disclosure. The video encoder (703) is configured to receive a processed block (e.g., a predictive block) of sample values ​​in a current video picture in a sequence of video pictures and to encode the processed block into a coded picture that is part of a coded video sequence. The exemplary video encoder (703) can be used in place of the example video encoder (403) of FIG. 4.

[0075] For example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a predictive block of 8×8 samples. The video encoder (703) then determines, for example, using rate-distortion optimization (RDO), whether the processing block is best coded using intra-mode, inter-mode, or bi-predictive mode. If it is determined that the processing block is coded in intra-mode, the video encoder (703) may encode the processing block into a coded picture using intra-prediction techniques, and if it is determined that the processing block is coded in inter-mode or bi-predictive mode, the video encoder (703) may encode the processing block into a coded picture using inter-prediction techniques or bi-prediction techniques, respectively. In some exemplary embodiments, a merge mode may be used as a sub-mode of inter-picture prediction, in which a motion vector is derived from one or more motion vector predictors without the benefit of coded motion vector components outside the predictors. In some other exemplary embodiments, there may be motion vector components applicable to the current block. Thus, the video encoder (703) may include components not explicitly shown in FIG. 7, such as a mode decision module, to determine the prediction mode of a processing block.

[0076] In the example of FIG. 7, the video encoder (703) includes an inter-encoder (730), an intra-encoder (722), a residual calculator (723), a switch (726), a residual encoder (724), a general controller (721), and an entropy encoder (725) coupled to each other as shown in the exemplary arrangement of FIG.

[0077] The inter-encoder (730) is configured to receive samples of a current block (e.g., a processing block), compare the block to one or more reference blocks in a reference picture (e.g., blocks in previous and subsequent pictures in display order), generate inter-prediction information (e.g., a description of redundancy information, motion vectors, merge mode information according to inter-encoding techniques), and calculate an inter-prediction result (e.g., a predicted block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the encoded video information using a decoding unit 633 incorporated in the example encoder 620 of FIG. 6 (shown as residual decoder 728 of FIG. 7, as described in more detail below).

[0078] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), compare the block with already coded blocks in the same picture, generate transformed quantized coefficients, and possibly also generate intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). The intra encoder (722) can calculate intra prediction results (e.g., prediction blocks) based on the intra prediction information and reference blocks in the same picture.

[0079] The generic controller (721) may be configured to determine generic control data and control other components of the video encoder (703) based on the generic control data. In one example, the generic controller (721) determines a prediction mode of the block and provides a control signal to the switch (726) based on the prediction mode. For example, if the prediction mode is an intra mode, the generic controller (721) controls the switch (726) to select an intra mode result for use by the residual calculator (723) and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream, and if the prediction mode of the block is an inter mode, the generic controller (721) controls the switch (726) to select an inter prediction result for use by the residual calculator (723) and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0080] The residual calculator (723) may be configured to calculate a difference (residual data) between a received block and a prediction result for a block selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) may be configured to encode the residual data to generate transform coefficients. For example, the residual encoder (724) may be configured to transform the residual data from the spatial domain to the frequency domain to generate transform coefficients. The transform coefficients then undergo a quantization process to obtain quantized transform coefficients. In various exemplary embodiments, the video encoder (703) also includes a residual decoder (728). The residual decoder (728) is configured to perform an inverse transform and generate decoded residual data. The decoded residual data may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) may generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) may generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks may be appropriately processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures.

[0081] The entropy encoder (725) may be configured to format a bitstream to include the encoded block and to perform entropy coding. The entropy encoder (725) may be configured to include various information in the bitstream. For example, the entropy encoder (725) may be configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other suitable information in the bitstream. When coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode, the residual information may not be present.

[0082] 8 shows a diagram of an example video decoder (810) according to another embodiment of the present disclosure. The video decoder (810) is configured to receive coded pictures that are part of a coded video sequence and decode the coded pictures to generate reconstructed pictures. In one example, the video decoder (810) can be used in place of the example video decoder (410) of FIG. 4.

[0083] In the example of FIG. 8, the video decoder (810) includes an entropy decoder (871), an inter-decoder (880), a residual decoder (873), a reconstruction module (874), and an intra-decoder (872), all coupled together as shown in the exemplary arrangement of FIG. 8.

[0084] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols that represent syntax elements of which the coded picture is composed. Such symbols may include, for example, prediction information (e.g., intra- or inter-prediction information) that may identify the mode in which the block is coded (e.g., intra-mode, inter-mode, bi-prediction mode, merged submode, or another submode), certain samples or metadata used for prediction by the intra-decoder (872) or inter-decoder (880), residual information in the form of quantized transform coefficients, etc. In one example, if the prediction mode is an inter- or bi-prediction mode, the inter-prediction information is provided to the inter-decoder (880), and if the prediction type is an intra-prediction type, the intra-prediction information is provided to the intra-decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0085] The inter decoder (880) may be configured to receive the inter prediction information and generate inter prediction results based on the inter prediction information.

[0086] The intra decoder (872) may be configured to receive intra prediction information and to generate a prediction result based on the intra prediction information.

[0087] The residual decoder (873) may be configured to perform inverse quantization to extract inverse quantized transform coefficients, and process the inverse quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also utilize certain control information (to include quantizer parameters (QP)), which may be provided by the entropy decoder (871) (a data path is not shown, as this may be only a small amount of control information).

[0088] The reconstruction module (874) may be configured to combine, in the spatial domain, the residual as output by the residual decoder (873) and the prediction result (possibly as output by an inter prediction module or an intra prediction module) to form a reconstructed block that forms part of a reconstructed picture as part of the reconstructed video. It should be noted that other suitable operations, such as a deblocking operation, may also be performed to improve visual quality.

[0089] It should be noted that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using any suitable technique. In some exemplary embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more integrated circuits. In another embodiment, the video encoders (403), (603), and (603) and the video decoders (410), (510), and (810) may be implemented using one or more processors executing software instructions.

[0090] Turning to block partitioning for coding and decoding, a general partitioning may start from a base block and may follow a predefined set of rules, a specific pattern, a partitioning tree, or any partitioning structure or scheme. The partitioning may be hierarchical and recursive. After isolating or dividing the base block according to any of the exemplary partitioning procedures described below or other procedures, or combinations thereof, a final set of partitions or coding blocks may be obtained. Each of these partitions may be at one of various partitioning levels in the partitioning hierarchy and may be partitions of various shapes. Each of the partitions may be referred to as a coding block (CB). In various exemplary partitioning implementations described further below, each resulting CB may be a CB of any of the allowed sizes and partitioning levels. Such partitions are referred to as coding blocks because they may form a unit for which some basic coding / decoding decisions may be made and coding / decoding parameters may be optimized, determined, and signaled in the encoded video bitstream. The highest or deepest level in the final partition represents the depth of the coding block partitioning tree structure. The coding block may be a luma coding block or a chroma coding block. The CB tree structure for each color is sometimes called a coding block tree (CBT).

[0091] The coding blocks of all color channels may be collectively referred to as a coding unit (CU). The hierarchical structure of all color channels may be collectively referred to as a coding tree unit (CTU). The partitioning pattern or partitioning structure of various color channels within a CTU may or may not be the same.

[0092] In some implementations, the split tree scheme or structure used for the luma channel and the chroma channel may not need to be the same. In other words, the luma channel and the chroma channel may have separate coding tree structures or patterns. Furthermore, whether the luma channel and the chroma channel use the same coding partition tree structure or different coding partition tree structures, and the actual coding partition tree structure to be used may depend on whether the slice being coded is a P slice, a B slice, or an I slice. For example, for an I slice, the chroma channel and the luma channel may have separate coding partition tree structures or coding partition tree structure modes, while for a P slice or a B slice, the luma channel and the chroma channel may share the same coding partition tree scheme. When separate coding partition tree structures or modes are applied, the luma channel may be split into CBs by one coding partition tree structure, and the chroma channel may be split into chroma CBs by another coding partition tree structure.

[0093] In some exemplary implementations, a predefined partitioning pattern may be applied to the base block. As shown in FIG. 9, an exemplary four-way partitioning tree may start at a first predefined level (e.g., 64×64 block level or other size as the base block size), and the base block may be partitioned hierarchically down to a predefined lowest level (e.g., 4×4 level). For example, the base block may follow four predefined partitioning options or patterns illustrated by 902, 904, 906, and 908, and the partition designated as R is capable of recursive partitioning in that the same partitioning option illustrated in FIG. 9 may be repeated at a lower scale down to the lowest level (e.g., 4×4 level). In some implementations, additional restrictions may be added to the partitioning scheme of FIG. 9. In the implementation of FIG. 9, rectangular partitions (e.g., 1:2 / 2:1 rectangular partitions) may be allowed but not recursive, while square partitions are allowed to be recursive. Subsequent partitioning of FIG. 9 by recursion, if necessary, generates a final set of coding blocks. A coding tree depth may be further defined to indicate the division depth from a root node or root block. For example, the coding tree depth for a root node or root block of 64×64 block may be set to 0, and after the root block is further divided one time according to FIG. 9, the coding tree depth increases by 1. The maximum or deepest level from the 64×64 base block to the 4×4 minimum partition is 4 (starting from level 0) in the above scheme. Such a division scheme may be applied to one or more of the color channels. Each color channel may be independently divided according to the scheme of FIG. 9 (e.g., for each of the color channels at each hierarchical level, a division pattern or option in the predefined pattern may be determined independently). Alternatively, two or more color channels may share the same hierarchical pattern tree of FIG. 9 (e.g., for two or more color channels at each hierarchical level, the same division pattern or option in the predefined pattern may be selected).

[0094] FIG. 10 illustrates another exemplary predefined partitioning pattern that allows the recursive partitioning to form a partitioning tree. As illustrated in FIG. 10, an exemplary 10-way partitioning structure or pattern may be predefined. The root block may start from a predefined level (e.g., from a base block at a 128×128 level or a 64×64 level). The exemplary partitioning structure in FIG. 10 includes various 2:1 / 1:2 and 4:1 / 1:4 rectangular partitions. A partition type with three subpartitions, shown at 1002, 1004, 1006, and 1008 in the second column of FIG. 10, may be referred to as a “T-shaped” partition. The “T-shaped” partitions 1002, 1004, 1006, and 1008 may be referred to as a left T-shaped, an upper T-shaped, a right T-shaped, and a lower T-shaped. In some exemplary implementations, none of the rectangular partitions in FIG. 10 may be further subdivided. A coding tree depth may be further defined to indicate the partitioning depth from the root node or root block. For example, the coding tree depth for a root node or root block of a 128×128 block may be set to 0, and after the root block is further divided one time according to FIG. 10, the coding tree depth increases by 1. In some implementations, only the all-square partitions of 1010 may allow recursive division to the next level of the division tree following the pattern of FIG. 10. In other words, recursive division may not be possible for the square partitions in the T-shaped patterns 1002, 1004, 1006, and 1008. The division procedure following FIG. 10 by recursion generates a final set of coding blocks, if necessary. Such a scheme may be applied to one or more of the color channels. In some implementations, more flexibility may be added to the use of partitions less than 8×8 levels. For example, in some cases, 2×2 chroma inter prediction may be used.

[0095] In some other example implementations of coding block partitioning, a quadtree structure may be used to partition a base block or an intermediate block into quadtree partitions. Such quadtree partitioning may be applied hierarchically and recursively to any square partition. Whether a base block or intermediate block or partition is further quadtree partitioned may be adapted to various local characteristics of the base block or intermediate block / partition. The quadtree partitioning at the picture boundary may be further adapted. For example, an implicit quadtree partitioning may be implemented at the picture boundary such that a block continues to be quadtree partitioned until its size fits into the picture boundary.

[0096] In some other example implementations, a hierarchical bisection from the base block may be used. For such a scheme, the base block or mid-level block may be divided into two partitions. The bisection may be either horizontal or vertical. For example, a horizontal bisection may divide the base block or mid-block into equal left and right partitions. Similarly, a vertical bisection may divide the base block or mid-block into equal top and bottom partitions. Such bisection may be hierarchical and recursive. It may be determined at each of the base block or mid-block whether the bisection scheme should continue and, if the scheme continues further, whether a horizontal or vertical bisection should be used. In some implementations, further division may stop at a predefined minimum partition size (in one or both dimensions). Alternatively, further division may stop once a predefined division level or depth from the base block is reached. In some implementations, the aspect ratio of the partitions may be limited. For example, the aspect ratio of the partitions may not be smaller than 1:4 (or larger than 4:1). Therefore, a vertical strip partition, having a vertical to horizontal aspect ratio of 4:1, can only be further divided vertically into an upper and lower partition, each having a vertical to horizontal aspect ratio of 2:1.

[0097] In yet some other examples, a three-way division scheme may be used to divide the base block or any intermediate blocks, as shown in FIG. 13. The ternary pattern may be implemented vertically, as shown at 1302 in FIG. 13, or horizontally, as shown at 1304 in FIG. 13. The exemplary division ratio in FIG. 13 is shown as 1:2:1 either vertically or horizontally, but other ratios may be predefined. In some implementations, two or more different ratios may be predefined. Such a three-way division scheme may be used to complement a quadtree or bipartition structure, in that such a ternary tree division can capture objects located at block centers in one contiguous partition, whereas quadtrees and bipartitions always divide along block centers, thus dividing objects into separate partitions. In some implementations, the width and height of the partitions of the exemplary ternary tree are always powers of two to avoid further transformations.

[0098] The above partitioning schemes may be combined in any manner at different partitioning levels. As an example, the quadtree and bipartitioning schemes described above may be combined to partition the base block into a quadtree-bipartition (QTBT) structure. In such a scheme, the base block or intermediate blocks / partitions may be either quadtree-partitioned or bipartitioned, if specified, according to a set of predefined conditions. A particular example is shown in FIG. 14. In the example of FIG. 14, the base block is first quadtree-partitioned into four partitions, as shown by 1402, 1404, 1406, and 1408. Each of the resulting partitions is then either quadtree-partitioned into four further partitions (such as 1408) or bipartitioned into two further partitions at the next level (e.g., either horizontally or vertically, such as 1402 or 1406, both of which are symmetric), or not partitioned (such as 1404). Bisection or quadtree partitioning may be recursively enabled for square partitions as shown by the overall exemplary partitioning pattern in 1410 and the corresponding tree structure / representation in 1420, where solid lines represent quadtree partitioning and dashed lines represent bisection. A flag may be used for each bisection node (non-leaf binary partition) to indicate whether the bisection is horizontal or vertical. For example, flag "0" may represent horizontal bisection and flag "1" may represent vertical bisection, as shown in 1420, which matches the partitioning structure in 1410. In the case of quadtree partitioning, there is no need to indicate the partition type, since quadtree partitioning always splits a block or partition both horizontally and vertically to generate four sub-blocks / partitions of equal size. In some implementations, flag "1" may represent horizontal bisection and flag "0" may represent vertical bisection.

[0099] In some example implementations of QTBT, the quadtree and bisection rule sets may be represented by the following predefined parameters and their associated corresponding functions: -CTU size: quadtree root node size (base block size) -MinQTSize: The minimum allowable quadtree leaf node size. -MaxBTSize: Maximum allowable binary tree root node size -MaxBTDepth: Maximum allowed binary tree depth -MinBTSize: The minimum allowable binary tree leaf node size. In some exemplary implementations of the QTBT partitioning structure, the CTU size may be set as 128×128 luma samples with two corresponding 64×64 blocks of chroma samples (when the exemplary chroma subsampling is considered and used), the MinQTSize may be set as 16×16, the MaxBTSize may be set as 64×64, the MinBTSize may be set as 4×4 (for both width and height), and the MaxBTDepth may be set as 4. A quadtree partition may be applied to the CTU first to generate quadtree leaf nodes. The quadtree leaf nodes may have a size from its minimum allowable size of 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If a node is 128×128, it will not be split by the binary tree first because its size exceeds MaxBTSize (i.e., 64×64). Otherwise, any node that does not exceed MaxBTSize may be split by the binary tree. In the example of FIG. 14, the base block is 128×128. The base block can only be quadtree partitioned according to a predefined set of rules. The base block has a partition depth of 0. Each of the resulting four partitions is 64×64, not exceeding MaxBTSize, and may be further quadtree or bintree partitioned at level 1. The process continues. When the bintree depth reaches MaxBTDepth (i.e., 4), no further partitions may be considered. When the width of a bintree node is equal to MinBTSize (i.e., 4), no further horizontal partitions may be considered. Similarly, when the height of a bintree node is equal to MinBTSize, no further vertical partitions may be considered.

[0100] In some example implementations, the above QTBT scheme may be configured to support flexibility for luma and chroma to have the same QTBT structure or separate QTBT structures. For example, for P slices and B slices, the luma CTB and chroma CTB in one CTU may share the same QTBT structure. However, for I slices, the luma CTB may be divided into CBs by a QTBT structure, and the chroma CTB may be divided into chroma CBs by another QTBT structure. This means that CUs may be used to refer to different color channels in an I slice, for example, an I slice may consist of a coding block of a luma component or a coding block of two chroma components, and a CU in a P slice or B slice may consist of coding blocks of all three color components.

[0101] In some other implementations, the QTBT scheme may be complemented with the ternary scheme described above. Such implementations may be referred to as a multi-type tree (MTT) structure. For example, in addition to the bisection of the node, one of the trisection patterns of FIG. 13 may be selected. In some implementations, only square nodes may undergo trisection. An additional flag may be used to indicate whether the trisection is horizontal or vertical.

[0102] The design of two-level or multi-level trees, such as the QTBT implementation and the QTBT implementation complemented by trisection, may be motivated primarily by reduced complexity. In theory, the complexity of traversing a tree is T D where T represents the number of split types and D is the depth of the tree. Trade-offs may be made by using multitypes (T) while reducing the depth (D).

[0103] In some implementations, the CB may be further divided. For example, the CB may be further divided into multiple prediction blocks (PBs) for the purpose of intra-frame prediction or inter-frame prediction during the coding and decoding processes. In other words, the CB may be further divided into different sub-partitions, where individual prediction decisions / configurations may be made. In parallel, the CB may be further divided into multiple transform blocks (TBs) for the purpose of describing the level at which the transformation or inverse transformation of the video data is performed. The division scheme of the CB into PBs and TBs may be the same or different. For example, each division scheme may be implemented using a unique procedure based on, for example, various characteristics of the video data. The division scheme of the PBs and TBs may be independent in some exemplary implementations. The division schemes and boundaries of the PBs and TBs may be correlated in some other exemplary implementations. In some implementations, for example, the TBs may be divided after the PB division, and in particular, each PB may then be further divided into one or more TBs after being determined following the division of the coding block. For example, in some implementations, the PB may be divided into one, two, four, or other number of TBs.

[0104] In some implementations, the luma and chroma channels may be processed differently to split the base blocks into coding blocks and further into predictive and / or transform blocks. For example, in some implementations, splitting of coding blocks into predictive and / or transform blocks may be allowed for the luma channel, but such splitting of coding blocks into predictive and / or transform blocks may not be allowed for the chroma channels. In such implementations, the transform and / or prediction of luma blocks may thus be performed only at the coding block level. In another example, the minimum transform block size of the luma and chroma channels may be different, e.g., the coding blocks of the luma channel may be allowed to be split into smaller transform and / or predictive blocks than the chroma channels. In yet another example, the maximum depth of the splitting of coding blocks into transform and / or predictive blocks may be different between the luma and chroma channels, e.g., the coding blocks of the luma channel may be allowed to be split into deeper transform and / or predictive blocks than the chroma channels. As a specific example, a luma coding block may be divided into transform blocks of multiple sizes that can be represented by a recursive partitioning down by up to two levels, and transform block shapes such as square, 2:1 / 1:2, and 4:1 / 1:4, as well as transform block sizes from 4×4 to 64×64 may be allowed. However, for chroma blocks, only the largest possible transform block designated for the luma block may be allowed.

[0105] In some example implementations for partitioning a coding block into PBs, the depth, shape, and / or other characteristics of the PB partition may depend on whether the PB is intra-coded or inter-coded.

[0106] The division of the coding block (or prediction block) into transform blocks may be performed in various exemplary manners, including but not limited to quadtree division and predefined pattern division, recursively or non-recursively, further considering transform blocks at the boundaries of the coding block or prediction block. In general, the resulting transform blocks may be at different division levels, may not be the same size, and may not need to be square in shape (e.g., they may be rectangular with some allowed size and aspect ratio). Further examples are described in more detail below in connection with Figures 15, 16, and 17.

[0107] However, in some other implementations, the CB obtained via any of the above partitioning schemes may be used as a basic or minimum coding block for prediction and / or transformation. In other words, no further partitioning is performed for the purpose of performing inter-prediction / intra-prediction and / or for the purpose of transformation. For example, the CB obtained from the above QTBT scheme may be used as a unit for performing prediction as it is. Specifically, such a QTBT structure removes the concept of multiple partition types, i.e., removes the separation of CU, PU, ​​and TU, and supports more flexibility on CU / CB partition shapes as described above. In such a QTBT block structure, the CU / CB can have either a square or rectangular shape. The leaf nodes of such a QTBT are used as units for prediction and transformation processing without further partitioning. This means that the CU, PU, ​​and TU have the same block size in such an exemplary QTBT coding block structure.

[0108] The various CB division schemes described above, as well as further division of the CB into PB and / or TB (including no PB / TB division), may be combined in any manner. The following specific implementations are provided as non-limiting examples.

[0109] Specific exemplary implementations of the division of coding blocks and transform blocks are described below. In such exemplary implementations, base blocks may be divided into coding blocks using recursive quadtree division or predefined division patterns described above (such as the division patterns of Figures 9 and 10). At each level, whether to continue further quadtree division of a particular partition may be determined by local video data characteristics. The resulting CBs may be at various quadtree division levels and of various sizes. The decision of whether to code a picture area using inter-picture (temporal) prediction or intra-picture (spatial) prediction may be made at the CB level (or at the CU level for all three color channels). Each CB may be further divided into one, two, four, or other number of PBs according to a predefined PB division type. Within one PB, the same prediction process may be applied, and related information may be transmitted to the decoder on a PB basis. After obtaining the residual blocks by applying the prediction process based on the PB division type, the CBs may be divided into TBs according to another quadtree structure similar to the coding tree for CBs. In this particular implementation, the CB or TB may not be limited to a square. Furthermore, in this particular example, the PB may be square or rectangular in inter prediction, and only square in intra prediction. The coding block may be divided, for example, into four square TBs. Each TB may be further divided recursively (using quadtree partitioning) into smaller TBs called residual quadtrees (RQTs).

[0110] Another exemplary implementation for splitting a base block into CB, PB, and / or TB is further described below. For example, rather than using multiple partition unit types such as the types shown in FIG. 9 or FIG. 10, a quadtree with nested multi-type trees using bipartition and tripartition segmentation structures (e.g., QTBT or QTBT with tripartition described above) may be used. Separation of CB, PB, and TB (i.e., splitting CB into PB and / or TB, and splitting PB into TB) may be abandoned except when necessary for CBs with sizes too large for the maximum transform length, when such CBs require further splitting. This exemplary splitting scheme may be designed to support further flexibility on CB splitting shapes, such that prediction and transformation can both be performed at the CB level without further splitting. In such coding tree structures, the CBs can have either square or rectangular shapes. Specifically, the coding tree block (CTB) may first be split by a quadtree structure. The quadtree leaf nodes may then be further split by a nested multi-type tree structure. An example of a nested multi-type tree structure using bisection or trisection is shown in Figure 11. Specifically, the example multi-type tree structure of Figure 11 includes four split types called vertical bisection (SPLIT_BT_VER) (1102), horizontal bisection (SPLIT_BT_HOR) (1104), vertical trisection (SPLIT_TT_VER) (1106), and horizontal trisection (SPLIT_TT_HOR) (1108). Then, CB corresponds to a leaf of the multi-type tree. In this example implementation, as long as CB is not too large for the maximum transform length, this segmentation is used for both prediction and transform processing without further splitting. This means that in most cases, CB, PB, and TB have the same block size in a quadtree with a nested multi-type tree coding block structure. An exception occurs when the maximum supported transform length is smaller than the width or height of the color components of CB.In some implementations, in addition to bisection or trisection, the nested pattern of FIG. 11 may further include a quadtree division.

[0111] One specific example of a quadtree with nested multi-type tree coding block structure of block partitioning (including quadtree partitioning, bisection, and trisection options) for one base block is shown in FIG. 12. More specifically, FIG. 12 shows that a base block 1200 is quadtree partitioned into four square partitions 1202, 1204, 1206, and 1208. A decision to further use the multi-type tree structure and quadtree of FIG. 11 for further partitioning is made for each of the quadtree partitioned partitions. In the example of FIG. 12, partition 1204 is not further partitioned. Partition 1202 and partition 1208 each adopt another quadtree partitioning. In partition 1202, the second level quadtree partitioned top left, top right, bottom left, and bottom right partitions adopt third level partitioning of quadtree, horizontal bisection 1104 of FIG. 11, non-split, and horizontal trisection 1108 of FIG. 11, respectively. Partition 1208 adopts another quadtree partitioning, and the second level quadtree partitioned top-left, top-right, bottom-left, and bottom-right partitions adopt the third level partitioning of vertical trisection 1106, unsplit, unsplit, and horizontal bisection 1104 of FIG. 11, respectively. Two of the subpartitions of the top-left partition of the third level of 1208 are further split according to horizontal bisection 1104 and horizontal trisection 1108 of FIG. 11, respectively. Partition 1206 adopts the second level partitioning pattern into two partitions following vertical bisection 1102 of FIG. 11, and the two partitions are further split at the third level according to horizontal trisection 1108 and vertical bisection 1102 of FIG. 11, respectively. A fourth level partitioning is further applied to one of them according to horizontal bisection 1104 of FIG. 11.

[0112] In the above specific example, the maximum luma transform size may be 64×64, and the maximum supported chroma transform size may be different from the luma, e.g., 32×32. Even if the above example CB of FIG. 12 is not generally further divided into smaller PBs and / or TBs, when the width or height of a luma coding block or a chroma coding block is larger than the maximum transform width or maximum transform height, the luma coding block or the chroma coding block may be automatically divided in the horizontal and / or vertical directions to satisfy the transform size constraints in that direction.

[0113] In the specific example of the division of the base block into CBs above, as described above, the coding tree scheme can support the ability for luma and chroma to have separate block tree structures. For example, for P slices and B slices, the luma CTB and chroma CTB in one CTU can share the same coding tree structure. For I slices, for example, luma and chroma may have separate coding block tree structures. When separate block tree structures are applied, the luma CTB may be divided into luma CBs by one coding tree structure, and the chroma CTB is divided into chroma CBs by another coding tree structure. This means that a CU in an I slice may be composed of a coding block of a luma component or a coding block of two chroma components, and a CU in a P slice or B slice is always composed of coding blocks of all three color components unless the video is monochrome.

[0114] When a coding block is further divided into multiple transform blocks, the transform blocks therein may be ordered in the bitstream according to various orders or scanning schemes. Exemplary implementations for dividing a coding block or a predictive block into transform blocks and the coding order of the transform blocks are described in further detail below. In some exemplary implementations, as described above, the transform division can support transform blocks of multiple shapes, e.g., 1:1 (square), 1:2 / 2:1, and 1:4 / 4:1, with transform block sizes ranging from, e.g., 4×4 to 64×64. In some implementations, if the coding block is smaller than or equal to 64×64, the transform block division may be applied only to the luma component, such that for chroma blocks, the transform block size is identical to the coding block size. Otherwise, if the width or height of the coding block is greater than 64, both the luma coding block and the chroma coding block may be implicitly divided into multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32), respectively, of transform blocks.

[0115] In some example implementations of transform block partitioning, for both intra-coded and inter-coded blocks, a coding block may be further partitioned into multiple transform blocks with a partition depth up to a predefined number of levels (e.g., two levels). The partition depth and size of the transform block may be related. For some example implementations, the mapping from the transform size of the current depth to the transform size of the next depth is shown below in Table 1.

[0116] [Table 1]

[0117] Based on the example mapping in Table 1, for a 1:1 square block, the next level transform split can create four 1:1 square sub-transform blocks. The transform split may stop at, for example, 4×4. Thus, a transform size of the current depth of 4×4 corresponds to the same size of 4×4 of the next depth. In the example of Table 1, for a 1:2 / 2:1 non-square block, the next level transform split can create two 1:1 square sub-transform blocks, while for a 1:4 / 4:1 non-square block, the next level transform split can create two 1:2 / 2:1 sub-transform blocks.

[0118] In some example implementations, further restrictions may be applied on transform block partitioning for the luma components of intra-coded blocks. For example, for each level of transform partitioning, all sub-transform blocks may be restricted to have equal size. For example, for a 32×16 coding block, level 1 transform partitioning creates two 16×16 sub-transform blocks, and level 2 transform partitioning creates eight 8×8 sub-transform blocks. In other words, to keep the transform units equal in size, a second level partitioning must be applied to all first level sub-blocks. An example of transform block partitioning for an intra-coded square block according to Table 1 is shown in FIG. 15 with the coding order indicated by the arrows. Specifically, 1502 shows a square coding block. The first level partitioning according to Table 1 into four equal-sized transform blocks is shown in 1504 with the coding order indicated by the arrows. The second level partitioning of all first level equal-sized blocks according to Table 1 into 16 equal-sized transform blocks is shown in 1506 with the coding order indicated by the arrows.

[0119] In some example implementations, the above restrictions on intra-coding may not apply to the luma components of an inter-coded block. For example, after the first level of transform splitting, any one of the sub-transform blocks may be further split independently at another level. Thus, the resulting transform blocks may or may not be blocks of the same size. An example splitting of an inter-coded block into transform blocks according to their coding order is shown in FIG. 16. In the example of FIG. 16, an inter-coded block 1602 is split into transform blocks at two levels according to Table 1. At the first level, the inter-coded block is split into four transform blocks of equal size. Then, only one of the four transform blocks (but not all of them) is further split into four sub-transform blocks, resulting in a total of seven transform blocks with two different sizes, as shown by 1604. An example coding order of these seven transform blocks is shown by arrows at 1604 in FIG. 16.

[0120] In some example implementations, for chroma components, some further restrictions on the transform blocks may be applied: for example, for chroma components, the transform block size may be as large as the coding block size, but cannot be smaller than a predefined size, e.g., 8×8.

[0121] In some other example implementations, for coding blocks with either width (W) or height (H) greater than 64, both luma coding blocks and chroma coding blocks may be implicitly divided into multiples of min(W,64)×min(H,64) and min(W,32)×min(H,32) transform units, respectively, where in this disclosure, “min(a,b)” can return the smaller value between a and b.

[0122] FIG. 17 further illustrates another alternative exemplary scheme for splitting a coding block or a predictive block into transform blocks. As illustrated in FIG. 17, instead of using recursive transform partitioning, a set of predefined partition types may be applied to a coding block according to the transform type of the coding block. In the particular example illustrated in FIG. 17, one of six exemplary partition types may be applied to split the coding block into various numbers of transform blocks. Such a scheme for generating transform block partitions may be applied to either a coding block or a predictive block.

[0123] More specifically, the partitioning scheme of FIG. 17 provides up to six exemplary partitioning types for any given transform type (transform type refers to the type of primary transform, such as, for example, ADST). In this scheme, every coding block or predictive block may be assigned a transform partitioning type, for example, based on a rate-distortion cost. In one example, the transform partitioning type assigned to a coding block or predictive block may be determined based on the transform type of the coding block or predictive block. As shown by the six transform partitioning types illustrated in FIG. 17, a particular transform partitioning type may correspond to the partitioning size and pattern of the transform block. The correspondence between various transform types and various transform partitioning types may be predefined. An example is shown below in which capitalized labels indicate transform partitioning types that may be assigned to a coding block or predictive block based on a rate-distortion cost.

[0124] ·PARTITION_NONE: Allocate the transformation size equal to the block size.

[0125] ·PARTITION_SPLIT: Allocates a transformation size of 1 / 2 the block size in width and 1 / 2 the block size in height.

[0126] ·PARTITION_HORZ: Allocates a transformation size with width equal to the block size and height equal to 1 / 2 the block size.

[0127] ·PARTITION_VERT: Allocates a transformation size with a width half the block size and a height equal to the block size.

[0128] ·PARTITION_HORZ4: Allocates a transformation size with width equal to the block size and height equal to 1 / 4 of the block size.

[0129] ·PARTITION_VERT4: Allocates a transformation size with a width of 1 / 4 of the block size and a height equal to the block size.

[0130] In the above example, the transform split types shown in Figure 17 include uniform transform sizes for all split transform blocks. This is not a limitation but merely an example. In some other implementations, mixed transform block sizes may be used for the split transform blocks in a particular split type (or pattern).

[0131] The PBs (or CBs, also called PBs if not further divided into predictive blocks) obtained from any of the above partitioning schemes can become individual blocks for coding via either intra-prediction or inter-prediction. For inter-prediction on the current PB, a residual between the current block and the predictive block can be generated, coded, and included in the coded bitstream.

[0132] Inter prediction may be performed, for example, in single reference mode or mixed reference mode. In some implementations, a skip flag may be included in the bitstream of the current block first (or at a higher level) to indicate whether the current block is inter-coded and not skipped. If the current block is inter-coded, another flag may be further included in the bitstream as a signal indicating whether a single reference mode or a mixed reference mode is used for predicting the current block. In the case of a single reference mode, one reference block may be used to generate a prediction block of the current block. In the case of a mixed reference mode, two or more reference blocks may be used to generate a prediction block, for example, by weighted averaging. A mixed reference mode may be referred to as a multiple reference mode, a two-reference mode, or a multiple reference mode. One or more reference blocks may be identified using one or more reference frame indexes and further using a corresponding one or more motion vectors indicating a shift between the reference block and the current block, for example, in positions in horizontal and vertical pixels. For example, the inter-predicted block of the current block may be generated from a single reference block identified by one motion vector in a reference frame as the predictive block in a single reference mode, while in the case of a mixed reference mode, the predictive block may be generated by a weighted average of two reference blocks in two reference frames indicated by two reference frame indexes and two corresponding motion vectors. The motion vectors may be coded and included in the bitstream in various ways.

[0133] In some implementations, an encoding or decoding system may maintain a decoded picture buffer (DPB). Some images / pictures may be maintained in the DPB waiting to be displayed (in the decoding system), and some images / pictures in the DPB may be used as reference frames to enable inter prediction (in the decoding system or encoding system). In some implementations, reference frames in the DPB may be tagged as either short-term or long-term references for the current image being encoded or decoded. For example, short-term reference frames may include frames used for inter prediction of blocks in the current frame or a predefined number (e.g., two) of subsequent video frames closest to the current frame in decoding order. Long-term reference frames may include frames in the DPB that can be used to predict image blocks in frames beyond a predefined number of frames from the current frame in decoding order. Information regarding such tags for short-term and long-term reference frames may be referred to as a reference picture set (RPS) and may be added to the header of each frame in the encoded bitstream. Each frame in the encoded video stream can be identified by a Picture Order Counter (POC), which is numbered according to the playback sequence, either in an absolute manner or in relation to a group of pictures starting with an I-frame, for example.

[0134] In some example implementations, one or more reference picture lists including identification of short-term and long-term reference frames for inter prediction may be formed based on information in the RPS. For example, a single picture reference list may be formed for unidirectional inter prediction, denoted as L0 reference (or reference list 0), and two picture reference lists may be formed for bidirectional inter prediction, denoted as L0 (or reference list 0) and L1 (or reference list 1) for each of the two prediction directions. The reference frames included in the L0 and L1 lists may be ordered in various predetermined manners. The lengths of the L0 and L1 lists may be signaled in the video bitstream. The unidirectional inter prediction may be either a single reference mode or a mixed reference mode, where multiple references for generating a prediction block by weighted averaging in the mixed prediction mode are on the same side of the block to be predicted. The bidirectional inter prediction may be only a mixed mode, in that the bidirectional inter prediction includes at least two reference blocks.

[0135] In some implementations, a merge mode (MM) for inter prediction may be implemented. In general, for a merge mode, one or more of the motion vectors in single reference prediction or mixed reference prediction of the current PB may be derived from other motion vectors, rather than being calculated and signaled independently. For example, in an encoding system, a current motion vector of a current PB may be represented by a difference between the current motion vector and one or more other already encoded motion vectors (referred to as reference motion vectors). Such a difference of the motion vector, rather than the entire current motion vector, may be encoded and included in the bitstream and linked to the reference motion vector. Correspondingly, in a decoding system, a motion vector corresponding to the current PB may be derived based on the decoded motion vector difference and the decoded reference motion vector linked therewith. As a specific form of the general merge mode (MM) inter prediction, such inter prediction based on the motion vector difference may be referred to as a merge mode with motion vector difference (MMVD). Thus, the general MM or the MMVD in particular may be implemented to exploit the correlation between the motion vectors associated with different PBs to improve coding efficiency. For example, adjacent PBs may have similar motion vectors and therefore the MVD may be small and can be coded efficiently. In another example, motion vectors may be correlated temporally (between frames) for similarly positioned / located blocks in space.

[0136] In some example implementations, an MM flag may be included in the bitstream during the encoding process to indicate whether the current PB is in merge mode. Additionally or alternatively, an MMVD flag may be included and signaled in the bitstream during the encoding process to indicate whether the current PB is in MMVD mode. MM and / or MMVD flags or indicators may be provided at the PB level, CB level, CU level, CTB level, CTU level, slice level, picture level, etc. In a particular example, both an MM flag and an MMVD flag may be included for the current CU, and the MMVD flag may be signaled immediately after the skip flag and the MM flag to specify whether the MMVD mode is used for the current CU.

[0137] In some example implementations of MMVD, a list of reference motion vector (RMV) or MV predictor candidates for motion vector prediction may be formed for a predicted block. The list of RMV candidates may include a predetermined number (e.g., two) of MV predictor candidate blocks whose motion vectors may be used to predict the current motion vector. The RMV candidate blocks may include blocks selected from adjacent blocks and / or temporal blocks in the same frame (e.g., blocks that are co-located in the ongoing or subsequent frames of the current frame). These options represent blocks that are in a spatial or temporal position relative to the current block that are likely to have a similar or identical motion vector to the current block. The size of the list of MV predictor candidates may be predetermined. For example, the list may include two or more candidates. To be on the list of RMV candidates, a candidate block may, for example, need to have the same reference frame (or frames) as the current block, must exist (e.g., if the current block is near an edge of a frame, a boundary check needs to be performed), must already be encoded during the encoding process, and / or must already be decoded during the decoding process. In some implementations, the list of merge candidates may be filled first with spatially adjacent blocks (scanned in a certain predefined order) if available and satisfy the above conditions, and then with temporal blocks if space is still available in the list. The adjacent RMV candidate blocks may be selected, for example, from the blocks to the left and above the current block. The list of RMV predictor candidates may be dynamically formed at various levels (sequence, picture, frame, slice, superblock, etc.) as a dynamic reference list (DRL). The DRL may be signaled in the bitstream.

[0138] In some implementations, the actual MV predictor candidate used as the reference motion vector for predicting the motion vector of the current block may be signaled. When the RMV candidate list includes two candidates, a one-bit flag called a merge candidate flag may be used to indicate the selection of the reference merge candidate. For the current block being predicted in a mixed mode, each of the multiple motion vectors predicted using the MV predictor may be associated with a reference motion vector from the merge candidate list. The encoder can determine which RMV candidate more closely predicts the current coding block and signal the selection as an index to the DRL.

[0139] In some exemplary implementations of MMVD, after an RMV candidate is selected and used as a base motion vector predictor for a motion vector to be predicted, a motion vector difference (MVD or delta MV representing the difference between the motion vector to be predicted and the reference candidate motion vector) may be calculated in the encoding system. Such an MVD may include information representing the magnitude of the MV difference and the direction of the MV difference, both of which may be signaled in the bitstream. The magnitude of the motion difference and the direction of the motion difference may be signaled in various ways.

[0140] In some exemplary implementations of MMVD, a distance index may be used to specify motion vector difference magnitude information and indicate one of a set of predefined offsets representing a predefined motion vector difference from a starting point (reference motion vector). Then, the MV offset according to the signaled index may be added to either the horizontal or vertical component of the starting (reference) motion vector. Whether the horizontal or vertical component of the reference motion vector should be offset may be determined by the direction information of the MVD. An exemplary predefined relationship between the distance index and the predefined offset is specified in Table 2.

[0141] [Table 2]

[0142] In some exemplary implementations of MMVD, a direction index may be further signaled and used to represent the direction of the MVD relative to the reference motion vector. In some implementations, the direction may be limited to either the horizontal or vertical direction. An exemplary 2-bit direction index is shown in Table 3. In the example of Table 3, the interpretation of the MVD may change according to the information of the start / reference MV. For example, if the start / reference MV corresponds to a single-prediction block or a bi-prediction block with both reference frame lists pointing to the same side of the current picture (i.e., the POCs of the two reference pictures are both greater than the POC of the current picture or both less than the POC of the current picture), the code in Table 3 may specify the sign (direction) of the MV offset added to the start / reference MV. If the start / reference MV corresponds to a bi-predictive block with two reference pictures on different sides of the current picture (i.e., the POC of one reference picture is larger than that of the current picture and the POC of the other reference picture is smaller than that of the current picture) and the difference between the reference POC in picture reference list 0 and the current frame is larger than the difference between the reference POC in picture reference list 1 and the current frame, the codes in Table 3 may specify the sign of the MV offset added to the reference MV corresponding to the reference picture in picture reference list 0, and the sign of the offset of the MV corresponding to the reference picture in picture reference list 1 may have the opposite value (opposite sign of the offset). Otherwise, if the difference between the reference POC in picture reference list 1 and the current frame is larger than the difference between the reference POC in picture reference list 0 and the current frame, the codes in Table 3 may specify that the sign of the MV offset added to the reference MV associated with picture reference list 1 and the sign of the offset to the reference MV associated with picture reference list 0 have opposite values.

[0143] [Table 3]

[0144] In some example implementations, the MVD may be scaled according to the difference in POC in each direction. If the difference in POC in both lists is the same, no scaling is required. Otherwise, if the difference in POC in reference list 0 is greater than that of reference list 1, the MVD of reference list 1 is scaled. If the POC difference of reference list 1 is greater than list 0, the MVD of list 0 may be scaled as well. If the starting MV is uni-predicted, the MVD is added to the available or reference MV.

[0145] In some example implementations of MVD coding and signaling for bidirectional composite prediction, in addition to or instead of coding and signaling two MVDs separately, symmetric MVD coding may be implemented such that only one MVD needs to be signaled and the other MVD can be derived from the signaled MVD. In such implementations, motion information including reference picture indexes of both list 0 and list 1 is signaled. However, for example, only the MVD associated with reference list 0 is signaled, and the MVD associated with reference list 1 is not signaled and is derived. Specifically, at the slice level, a flag called "mvd_l1_0_flag" may be included in the bitstream to indicate whether reference list 1 is not signaled in the bitstream. If this flag is 1, indicating that reference list 1 is equal to 0 (and thus not signaled), a bidirectional prediction flag called "BiDirPredFlag" may be set to 0, which means there is no bidirectional prediction. Otherwise, if mvd_l1_0_flag is 0, BiDirPredFlag may be set to 1 if the closest reference picture in list 0 and the closest reference picture in list 1 form a forward and backward pair of reference pictures or a backward and forward pair of reference pictures, and both reference pictures in list 0 and list 1 are short-term reference pictures. Otherwise, BiDirPredFlag is set to 0. A BiDirPredFlag of 1 may indicate that a symmetric mode flag is additionally signaled in the bitstream. A decoder may extract the symmetric mode flag from the bitstream if BiDirPredFlag is 1. The symmetric mode flag may be signaled, for example, at the CU level (if necessary) to indicate whether a symmetric MVD coding mode is used for the corresponding CU.When the symmetric mode flag is 1, it indicates the use of a symmetric MVD coding mode, indicating that only the reference picture indexes of both list 0 and list 1 (called "mvp_l0_flag" and "mvp_l1_flag") are signaled by the MVD associated with list 0 (called "MVD0"), and the other motion vector difference "MVD1" should be derived rather than signaled. For example, MVD1 may be derived as -MVD0. Thus, in the exemplary symmetric MVD mode, only one MVD is signaled. In some other exemplary implementations for MV prediction, a harmonic scheme may be used to implement a general merged mode MMVD, as well as some other types of MV prediction, for both single reference mode MV prediction and mixed reference mode MV prediction. Various syntax elements may be used to signal how the MV of the current block is predicted.

[0146] For example, for a single reference mode, the following MV prediction modes may be signaled:

[0147] NEARMV-Use one of the motion vector predictors (MVPs) in the list indicated by the DRL (Dynamic Reference List) index directly without MVD.

[0148] NEWMV--Use one of the motion vector predictors (MVP) in the list signaled by the DRL index as a reference and apply the delta to the MVP (eg, use MVD).

[0149] GLOBALMV - Use motion vectors based on frame-level global motion parameters.

[0150] Similarly, for a mixed reference inter prediction mode that uses two reference frames corresponding to the two MVs to be predicted, the following MV prediction modes may be signaled:

[0151] NEAR_NEARMV - For each of the two MVs to predict, use one of the motion vector predictors (MVPs) in the list signaled by the DRL index without the MVD.

[0152] NEAR_NEWMV - To predict the first of two motion vectors, one of the motion vector predictors (MVPs) in the list signaled by the DRL index without MVD is used as a reference MV, and to predict the second of two motion vectors, one of the motion vector predictors (MVPs) in the list signaled by the DRL index is used as a reference MV together with the additionally signaled delta MV (MVD).

[0153] NEW_NEARMV - Use one of the motion vector predictors (MVP) in the list signaled by the DRL index without MVD as a reference MV to predict the second of two motion vectors, and use one of the motion vector predictors (MVP) in the list signaled by the DRL index as a reference MV together with the additionally signaled delta MV (MVD) to predict the first of two motion vectors.

[0154] NEW_NEWMV - Use one of the motion vector predictors (MVPs) in the list signaled by the DRL index as a reference MV and use it together with the additionally signaled delta MV to predict for each of the two MVs.

[0155] GLOBAL_GLOBALMV - Use MV from each reference based on frame-level global motion parameters.

[0156] Thus, the term "NEAR" above refers to MV prediction using a reference MV without MVD as a general merge mode, whereas the term "NEW" refers to MV prediction using a reference MV and including offsetting it with the signaled MVD as in the MMVD mode. In the case of mixed inter prediction, both the reference-based motion vector and the above motion vector delta may generally be different or independent between the two references, even though they may be correlated and such correlation may be exploited to reduce the amount of information required to signal the two motion vector deltas. In such a situation, joint signaling of the two MVDs may be implemented and indicated in the bitstream.

[0157] The dynamic reference list (DRL) discussed above may be used to hold a set of indexed motion vectors that are dynamically maintained and considered as candidate motion vector predictors.

[0158] In some exemplary implementations, a predefined resolution of the MVD may be allowed. For example, a motion vector accuracy (or precision) of 1 / 8 pixels may be allowed. The above-mentioned MVDs in various MV prediction modes may be constructed and signaled in various ways. In some implementations, various syntax elements may be used to signal the above-mentioned motion vector difference in reference frame list 0 or list 1.

[0159] For example, a syntax element called "mv_joint" can specify which components of the motion vector difference associated with it are non-zero. In the case of MVD, this is signaled for all non-zero components together. For example, mv_joint has the following values: 0 can indicate no non-zero MVD along either the horizontal or vertical direction, 1 can be shown that there is non-zero MVD only along the horizontal direction, 2 can be shown that there is non-zero MVD only along the vertical direction, 3 can be shown to have non-zero MVD along both the horizontal and vertical directions.

[0160] If the "mv_joint" syntax element for MVD signals that there are no non-zero MVD components, no further MVD information may be signaled. However, if the "mv_joint" syntax signals that there are one or two non-zero components, additional syntax elements may be further signaled for each of the non-zero MVD components, as described below.

[0161] For example, a syntax element called "mv_sign" may be used to further specify whether the corresponding motion vector difference component is positive or negative.

[0162] In another example, a syntax element called "mv_class" may be used to specify a class of motion vector difference between a predefined set of classes of corresponding non-zero MVD components. The predefined classes of motion vector difference may be used, for example, to separate a continuous magnitude space of motion vector differences into non-overlapping ranges, each range corresponding to an MVD class. Thus, the signaled MVD class indicates the magnitude range of the corresponding MVD component. In the example implementation shown in Table 4 below, higher classes correspond to motion vector differences with a larger magnitude range. In Table 4, the symbol (n,m) is used to represent a range of motion vector differences greater than n pixels and less than or equal to m pixels.

[0163] [Table 4]

[0164] In some other examples, a syntax element called "mv_bit" may be further used to specify the integer portion of the offset between a non-zero motion vector difference component and the magnitude of the start of the correspondingly signaled MV class magnitude range. Thus, mv_bit may indicate the magnitude or amplitude of the MVD. The number of bits required for "my_bit" to signal the full range of each MVD class may vary depending on the MV class. For example, MV_CLASS 0 and MV_CLASS 1 in the implementation of Table 4 may require only a single bit to indicate an integer pixel offset of 1 or 2 from a starting MVD of 0, and each higher MV_CLASS in the example implementation of Table 4 may require progressively one more bit for "mv_bit" than the previous MV_CLASS.

[0165] In some other examples, a syntax element called "mv_fr" may be further used to specify the first two fractional bits of the motion vector difference of the corresponding non-zero MVD component, and a syntax element called "mv_hp" may be used to specify the third fractional bit (high resolution bit) of the motion vector difference of the corresponding non-zero MVD component. The two bits of "mv_fr" essentially provide a 1 / 4 pixel MVD resolution, while the "mv_hp" bits may further provide a 1 / 8 pixel resolution. In some other implementations, two or more "mv_hp" bits may be used to provide an MVD pixel resolution finer than 1 / 8 pixel. In some example implementations, additional flags may be signaled at one or more of various levels to indicate whether an MVD resolution of 1 / 8 pixel or finer is supported. If an MVD resolution does not apply to a particular coding unit, the above syntax elements for the corresponding unsupported MVD resolution may not be signaled.

[0166] In some example implementations above, the fractional resolution may be independent of the MVD of different classes. In other words, a predefined number of "mv_fr" and "mv_hp" bits may be used to signal fractional MVD of non-zero MVD components regardless of the magnitude of the motion vector difference to provide similar options for motion vector resolution.

[0167] However, in some other exemplary implementations, the resolution of the motion vector difference in various MVD magnitude classes can be differentiated. Specifically, a high-resolution MVD for a large MVD magnitude of a higher MVD class may not provide a statistically significant improvement in compression efficiency. Therefore, the MVD can be coded at a reduced resolution (integer pixel resolution or fractional pixel resolution) for a larger MVD magnitude range corresponding to a higher MVD magnitude class. Similarly, the MVD can be coded at a reduced resolution (integer pixel resolution or fractional pixel resolution) for a generally larger MVD value. Such MVD class-dependent or MVD magnitude-dependent MVD resolution may generally be referred to as adaptive MVD resolution, magnitude-dependent adaptive MVD resolution, or magnitude-dependent MVD resolution. The term "resolution" may further be referred to as "pixel resolution". The adaptive MVD resolution may be implemented in various ways as described by the following exemplary implementations to achieve better compression efficiency overall. In particular, the reduction in the number of signaling bits by aiming for a less accurate MVD may be greater than the additional bits required to code the inter-prediction residual as a result of such a less accurate MVD, due to the statistical observation that non-adaptively processing the MVD resolution of a large-scale or high-class MVD at a similar level as a low-scale or low-class MVD cannot significantly increase the inter-prediction residual coding efficiency of a block with a large-scale or high-class MVD. In other words, using a higher MVD resolution for a large-scale or high-class MVD may not result in more coding gain than using a lower MVD resolution.

[0168] In some typical example implementations, the pixel resolution or precision of the MVD may or may not decrease with increasing MVD class. Reducing the pixel resolution of the MVD corresponds to a coarser MVD (or a larger step from one MVD level to the next). In some implementations, the correspondence between MVD pixel resolution and MVD class may be specified, predefined, or preconfigured, and thus does not need to be signaled in the encoded bitstream.

[0169] In some example implementations, each of the MV classes in Table 3 may be associated with a different MVD pixel resolution.

[0170] In some example implementations, each MVD class may be associated with a single allowed resolution. In some other implementations, one or more MVD classes may be associated with two or more optional MVD pixel resolutions. Thus, a signal in the bitstream of a current MVD component having such an MVD class may be followed by additional signaling to indicate the optional pixel resolution selected for the current MVD component.

[0171] In some example implementations, the adaptively allowed MVD pixel resolutions may include, but are not limited to, (in descending order of resolution) 1 / 64pel (pixels), 1 / 32pel, 1 / 16pel, 1 / 8pel, 1-4pel, 1 / 2pel, 1pel, 2pel, 4pel.... Thus, each ascending MVD class may be associated with one of these MVD pixel resolutions in non-ascending order. In some implementations, an MVD class may be associated with two or more of the above resolutions, where the higher resolution may be less than or equal to the lower resolution of the preceding MVD class. For example, if MV_CLASS_3 in Table 4 is associated with optional 1pel and 2pel resolutions, then the highest resolution to which MV_CLASS_4 in Table 4 may be associated would be 2pel. In some other implementations, the highest allowed resolution of an MV class may be higher than the lowest allowed resolution of the preceding (lower) MV class. However, the average of allowed resolutions for ascending MV classes may only be in non-ascending order.

[0172] In some implementations, if fractional pixel resolution higher than 1 / 8 pel is allowed, the "mv_fr" and "mv_hp" signaling may be extended to accommodate a total of more than 3 fractional bits.

[0173] In some example implementations, fractional pixel resolution may be allowed only for MVD classes equal to or less than the threshold MVD class. For example, fractional pixel resolution may be allowed only for MVD-CLASS 0 and not for all other MV classes in Table 4. Similarly, fractional pixel resolution may be allowed only for MVD classes equal to or less than any one of the other MV classes in Table 4. For other MVD classes above the threshold MVD class, only integer pixel resolution of the MVD is allowed. In this manner, fractional resolution signaling, such as one or more of the "mv-fr" and / or "mv-hp" bits, does not need to be signaled for MVDs signaled in MVD classes equal to or greater than the threshold MVD class. For MVD classes with resolution less than one pixel, the number of bits of "mv-bit" signaling may be further reduced. For example, for MV_CLASS_5 in Table 4, the range of MVD pixel offsets is (32,64], and therefore 5 bits are required to signal the entire range at 1 pel resolution. However, if MV_CLASS_5 is associated with a 2 pel MVD resolution (a lower resolution than 1 pel resolution), then 4 bits instead of 5 bits may be required for "mv-bit", and neither "mv-fr" nor "mv-hp" need to be signaled following the signaling of "mv_class" as MV-CLASS_5.

[0174] In some example implementations, fractional pixel resolution may be allowed only for MVDs with integer values ​​less than a threshold integer pixel value. For example, fractional pixel resolution may be allowed only for MVDs smaller than 5 pixels. Corresponding to this example, fractional resolution may be allowed for MV_CLASS_0 and MV_CLASS_1 in Table 4, and not allowed for all other MV classes. In another example, fractional pixel resolution may be allowed only for MVDs smaller than 7 pixels. Corresponding to this example, fractional resolution may be allowed for MV_CLASS_0 and MV_CLASS_1 in Table 4 (having a range less than 5 pixels), and not allowed for MV_CLASS_3 and above (having a range greater than 5 pixels). For MVDs belonging to MV_CLASS_2, whose pixel range encompasses 5 pixels, fractional pixel resolution of the MVD may or may not be allowed depending on the "mv-bit" value. If the "m-bit" value is signaled as 1 or 2 (such that the integer part of the signaled MVD, calculated as the start of the pixel range of MV_CLASS_2 with offset 1 or 2 as indicated by "m-bit", is 5 or 6), fractional pixel resolution may be allowed. Otherwise, if the "mv-bit" value is signaled as 3 or 4 (such that the integer part of the signaled MVD is 7 or 8), fractional pixel resolution may not be allowed.

[0175] In some other implementations, only a single MVD value may be allowed for MV classes equal to or greater than the threshold MV class. For example, such a threshold MV class may be MV_CLASS 2. Thus, MV_CLASS_2 and above may only be allowed to have a single MVD value and no fractional pixel resolution. The single allowed MVD value for these MV classes may be predefined. In some examples, the single allowed value may be the upper limit of the range for each of these MV classes in Table 4. For example, MV_CLASS_2 through MV_CLASS_10 may be equal to or greater than the threshold class of MV_CLASS 2, and the single allowed MVD values ​​for these classes may be predefined as 8, 16, 32, 64, 128, 256, 512, 1024, and 2048, respectively. In some other examples, the single allowed value may be the median of the range for each of these MV classes in Table 4. For example, MV_CLASS_2 through MV_CLASS_10 may be above the class threshold, and the single allowed MVD values ​​for these classes may be predefined as 3, 6, 12, 24, 48, 96, 192, 384, 768, and 1536, respectively. Any other value within the range may also be defined as the single allowed resolution for the respective MVD class.

[0176] In the above implementation, if the signaled "mv_class" is equal to or greater than a predefined MVD class threshold, then the "mv_class" signaling alone is sufficient to determine the MVD value. The magnitude and direction of the MVD are then determined using "mv_class" and "mv_sign".

[0177] Therefore, when an MVD is signaled for just one reference frame (either from reference frame list 0 or list 1, but not both), or for two reference frames together, the accuracy (or resolution) of the MVD may depend on the class of the associated motion vector difference in Table 3 and / or the magnitude of the MVD.

[0178] In some other implementations, the pixel resolution or precision of the MVD may or may not decrease with increasing MVD magnitude. For example, the pixel resolution may depend on the integer part of the MVD magnitude. In some implementations, fractional pixel resolution may only be allowed for MVD magnitudes below an amplitude threshold. For a decoder, the integer part of the MVD magnitude may first be extracted from the bitstream. The pixel resolution may then be determined, and a determination may then be made as to whether any fractional MVD is present in the bitstream and needs to be parsed (e.g., if fractional pixel resolution is not allowed for the integer magnitude of a particular extracted MVD, the bitstream requiring extraction may not include fractional MVD bits). The above exemplary implementations for MVD class-dependent adaptive MVD pixel resolution apply to MVD magnitude-dependent adaptive MVD pixel resolution. In a particular example, MVD classes above or encompassing a magnitude threshold may be allowed to have only one predefined value.

[0179] In some implementations, a dynamic motion vector lookup scheme may be used, in which motion vector candidates are obtained from spatial and temporal neighborhoods and can be ranked for efficient entropy coding.

[0180] In some implementations, the motion vector candidate list may include a list of motion vector candidates. The motion vector candidates may refer to candidates for a motion vector predictor for a current block (or a current frame). When the motion vector candidates in the motion vector candidate list are in a particular order (e.g., based on their context, statistical probability of being selected, etc.), the motion vector predictor for the current block may be signaled for efficient entropy coding. In a non-limiting example, if a motion vector candidate with a higher statistical probability of being selected is placed in an early part of the motion vector candidate list, one or more smaller indices for signaling the motion vector candidate may be signaled, and the efficiency of entropy coding is improved.

[0181] In some implementations, a spatial motion vector predictor (MVP) may be identified by utilizing spatial neighboring blocks, including adjacent spatial neighboring blocks that are direct neighbors above and to the left of the current block, as well as non-adjacent spatial neighboring blocks that are close to, but not directly adjacent to, the current block.

[0182] In some implementations, in addition to spatially neighboring blocks, an MV predictor, known as a temporal MV predictor, may also be derived using collocated blocks of a reference picture. To generate a temporal MV predictor, the MVs of the reference frames are stored along with the reference indexes associated with the respective reference frames.

[0183] In some implementations, the orientation of the reference frame may be determined by whether the reference frame is before the current frame in display order or after the current frame in display order.

[0184] In some implementations, when the current block is intra-coded in a mixed reference mode, two reference frames may be used. If the POC of both reference frames for one motion vector pair is greater or smaller than the POC of the current frame, the orientations of the two reference frames may be considered to be the same. Otherwise, if the POC of one reference frame is greater than the POC of the current frame and the POC of the other reference frame is smaller than the POC of the current frame, the orientations of the two reference frames may be considered to be different.

[0185] In some implementations, two MVPs (or a pair of MVPs) may be symmetric if all of the following conditions are met: one MVP points to (or corresponds to) one reference frame before the current frame in display order, and the other MVP points to (or corresponds to) another reference frame after the current frame in display order; the magnitudes of the two MVPs are proportional to the POC difference between their corresponding reference frames and the current frame; and the signs of the two MVPs are opposite in this MVP pair.

[0186] In some implementations, two MVPs (or a pair of MVPs) may be asymmetric (or asymmetric) if any one or more of the following conditions are not met: one motion vector points to one reference frame before the current frame in display order and the other motion vector points to another reference frame after the current frame in display order; the magnitudes of the two MVPs are proportional to the POC difference between their corresponding reference frames and the current frame; and / or the signs of the motion vectors are opposite in this MVP pair.

[0187] In some implementations, a pair of MVPs may be called a symmetric MVP if the following conditions are met: one motion vector points to one reference frame before the current frame in display order, and the other motion vector points to another reference frame after the current frame in display order; the magnitudes of the two MVPs are proportional to the POC difference between their corresponding reference frames and the current frame; and the signs of the motion vectors are opposite in this MVP pair.

[0188] In some implementations, if motion vector difference (MVD) is signaled for multiple reference frames together, it can be assumed that the motion vector predictor (MVP) of the current block in the multiple reference frames is also symmetric. In some situations, this assumption can have some challenges / issues because the MVP of the current block may not be symmetric.

[0189] This disclosure describes various embodiments for refining motion vector candidates to address at least one of the above challenges / problems and / or improve entropy coding efficiency.

[0190] FIG. 18 illustrates a flowchart 1800 of an exemplary method according to the principles underlying the above implementations for refining motion vector candidates. An example decoding method flow may start at 1801 and may include some or all of the following steps: receiving a coded video bitstream at S1810, extracting from the coded video bitstream a first syntax element indicating whether a mixed reference mode applies to a current video block at S1820, extracting from the coded video bitstream a second syntax element indicating whether motion vector differences (MVDs) are signaled together for the current video block at S1830, refining at least one MV predictor (MVP) in an MV candidate list based on whether the at least one MVP is symmetric in response to the first syntax element indicating a mixed reference mode applies to the current video block and the second syntax element indicating MVDs are signaled together for the current video block at S1840, and / or decoding the current video block based on the MV candidate list at S1850. The example method stops at S1899.

[0191] In some implementations, S1840 may include refining at least one MVP in the MV candidate list based on symmetry of at least one MV predictor (MVP) in response to a first syntax element indicating that a mixed reference mode applies to the current video block and a second syntax element indicating that an MVD is jointly signaled for the current video block. The symmetry of an MVP may refer to whether the MVP is symmetric with respect to another MVP in the MV candidate list.

[0192] In some implementations, at least one MVP in the MV candidate list includes an MVP pair, and / or refining at least one MVP in the MV candidate list includes refining the MVP pair in the MV candidate list based on whether the MVP pair is symmetric or asymmetric.

[0193] In a non-limiting example, when the current block is coded as a mixed reference mode and MVD is signaled jointly for multiple reference frames (e.g., reference list 0 and reference list 1), the motion vector candidates in the list may be refined based on whether the MVPs in the motion vector candidate list are symmetric.

[0194] In some implementations, refining the MVP pair in the MV candidate list includes, in response to the MVP pair being symmetric, moving the MVP pair before all asymmetric MVPs in the MV candidate list.

[0195] In some implementations, refining the MVP pair in the MV candidate list includes, in response to the MVP pair being symmetric, moving the MVP pair to the top of the MV candidate list.

[0196] In a non-rimming example, if MVDs are signaled together for multiple reference frames, then symmetric MVPs in the motion vector candidate list may be placed before asymmetric MVPs in the motion vector candidate list.

[0197] In some implementations, refining an MVP pair in the MV candidate list includes moving the MVP pair to the top of the MV candidate list in response to the MVP pair being symmetric with equal picture order count (POC) distances between two reference frames and the current frame.

[0198] In a non-limiting example, when MVDs are signaled together for multiple reference frames, a symmetric MVP that has equal POC differences between the two reference frames and the current frame may be placed in the motion vector candidate list before other MVPs.

[0199] In some implementations, refining the MVP pair in the MV candidate list includes refining the MVP pair to be a symmetric MVP pair in response to the MVP pair being asymmetric. In a non-limiting example, if MVDs are signaled together for multiple reference frames and two MVPs (MVP pairs) in the motion vector candidate list are not symmetric, the two MVPs may be refined (or adjusted) as symmetric MVPs.

[0200] In some implementations, the MVP pair includes a first MVP and a second MVP, and the MVP pair is asymmetric. The first MVP has a first POC distance between a first reference frame corresponding to the first MVP and the current frame, and the second MVP has a second POC distance between a second reference frame corresponding to the second MVP and the current frame, and / or the first POC distance is greater than the second POC distance. Refining the MVP pair to be a symmetric MVP pair includes projecting the first MVP to the second reference frame to obtain the projected MVP, and replacing the second MVP with the projected MVP. In a non-limiting example, one MVP with a larger POC difference between its corresponding reference frame and the current frame is kept unchanged, and this MVP is projected to the reference frame to which the other MVP points. After this projection process, the projected MVP is used to replace the other MVP, resulting in a pair of symmetric MVPs being obtained.

[0201] In some implementations, the MVP pair includes a first MVP and a second MVP, and the MVP pair is asymmetric. The first MVP has a first POC distance between a first reference frame corresponding to the first MVP and the current frame, and / or the second MVP has a second POC distance between a second reference frame corresponding to the second MVP and the current frame, and / or the first POC distance is greater than the second POC distance. Refining the MVP pair to be a symmetric MVP pair includes projecting the first MVP to the second reference frame to obtain the projected MVP, and adding the projected MVP to the MV candidate list.

[0202] In some implementations, adding the projected MVP to the MV candidate list includes adding the projected MVP to the end of the MV candidate list.

[0203] In a non-limiting example, one MVP with a larger POC difference between the corresponding reference frame and the current frame is kept unchanged, and this MVP is projected to the reference frame to which the other MVP points. After this projection process, the projected MVP is added to the motion vector candidate list as a new MVP candidate. In some implementations, the projected MVP is added to the end of the motion vector candidate list, and / or the MVP and the projected MVP as a new symmetric MVP pair may be moved to the top of the motion vector candidate list according to some implementations described above.

[0204] In some implementations, the MVP pair includes a first MVP and a second MVP, and the MVP pair is asymmetric. Refining the MVP pair in the MV candidate list includes replacing the second MVP of the MVP pair with an MVP that is symmetric with respect to the first MVP of the MVP pair in response to the MVP pair being asymmetric with equal POC distances between the two reference frames and the current frame.

[0205] In some implementations, the first MVP of the MVP pair remains unchanged in the MV candidate list.

[0206] In some implementations, the MVP pair includes a first MVP and a second MVP, and the MVP pair is asymmetric. Refining the MVP pair in the MV candidate list includes adding an MVP that is symmetric with respect to the first MVP of the MVP pair to the MV candidate list in response to the MVP pair being asymmetric with equal POC distances between the two reference frames and the current frame.

[0207] In a non-limiting example, if MVDs are signaled together for multiple reference frames and the POC difference between the two reference frames and the current frame is equal for an MVP pair in the motion vector candidate list and the MVP pair is not symmetric, the MVP pair may be refined (or adjusted) to become symmetric by keeping the first MVP of the MVP pair unchanged and making the second MVP of the MVP pair symmetric with respect to the first MVP.

[0208] In various implementations of the present disclosure, the "first" MVP of an MVP pair may refer to the MVP placed early in the MVP pair, for example in the case of MVP pair ({MVP1, MVP2}), where the first MVP of the MVP pair may refer to MVP1 and the second MVP of the MVP pair may refer to MVP2; in another example, when the MVP pair is in the MV candidate list, the first MVP of the MVP pair may be the MVP placed at the head of the other MVP of the MVP pair (i.e., the second MVP) in the MV candidate list.

[0209] In some implementations, refining an MVP pair in the MV candidate list includes replacing the MVP pair with a symmetric MVP pair based on averaging the MVP pair in response to the MVP pair being asymmetric with equal POC distances between the two reference frames and the current frame.

[0210] In some implementations, the step of refining the MVP pairs in the MV candidate list includes a step of adding a symmetric MVP pair based on averaging the MVP pairs to the MV candidate list in response to the MVP pair being asymmetric with equal POC distances between the two reference frames and the current frame.

[0211] In a non-example, if MVDs are signaled together for multiple reference frames and the POC difference between the two reference frames and the current frame is equal for two MVPs (or MVP pairs) in the motion vector candidate list and this MVP pair is not symmetric, this MVP pair may be refined (or adjusted) as a symmetric MVP pair derived by averaging the two MVPs projected onto each of the reference frames.

[0212] In some implementations, when MVDs are signaled together for multiple reference frames and one MVP in the motion vector candidate list is not symmetric, one refined MVD is generated based on this MVP pair, which is subtracted by this refined MVD before being added to the joint MVD in the bitstream. In non-rimming examples, the refined MVD is calculated based on the MVP and / or POC difference values ​​between the corresponding reference frames and the current frame.

[0213] In some implementations, the MV can be derived based on the MVP and the MVD, for example, MV=MVP+MVD.

[0214] In the embodiments and implementations of the present disclosure, any steps and / or operations may be combined or arranged in any quantity or order, as desired. Two or more of the steps and / or operations may be performed in parallel. The embodiments and implementations of the present disclosure may be used separately or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored in a non-transitory computer-readable medium. The embodiments of the present disclosure may be applied to a luma block or a chroma block. The term block may be interpreted as a prediction block, a coding block, or a coding unit, i.e., a CU. The term block here may also be used to refer to a transform block. In the following items, when referring to a block size, it may refer to either the width or height of the block, or the maximum value of the width and height, or the minimum value of the width and height, or the size of the area (width*height), or the aspect ratio of the block (width:height, or height:width).

[0215] The techniques described above may be implemented as computer software using computer-readable instructions and physically stored on one or more computer-readable media. For example, FIG. 19 illustrates a computer system (1900) suitable for implementing certain embodiments of the disclosed subject matter.

[0216] Computer software can be coded using any suitable machine code or computer language that is amenable to mechanisms such as assembly, compilation, linking, etc. to create code that includes instructions that can be executed by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc. directly, or via interpretation, microcode execution, etc.

[0217] The instructions may be executed on various types of computers or computer components including, for example, personal computers, tablet computers, servers, smart phones, gaming consoles, Internet of Things devices, and the like.

[0218] 19 for the computer system (1900) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components illustrated in the exemplary embodiment of the computer system (1900).

[0219] The computer system (1900) may include certain human interface input devices. Such human interface input devices may respond to input by one or more human users, for example, via tactile input (such as keystrokes, swipes, data glove movements), audio input (such as voice, clapping), visual input (such as gestures), or olfactory input (not depicted). Human interface devices may also be used to capture certain media not necessarily directly associated with conscious human input, such as audio (such as voice, music, ambient sounds), images (such as scanned images, photographic images obtained from still image cameras), and video (such as two-dimensional video, three-dimensional video including stereoscopic video, etc.).

[0220] The input human interface devices may include one or more of a keyboard (1901), a mouse (1902), a trackpad (1903), a touch screen (1910), a data glove (not shown), a joystick (1905), a microphone (1906), a scanner (1907), and a camera (1908) (only one of each is depicted).

[0221] The computer system (1900) may also include certain human interface output devices. Such human interface output devices may stimulate one or more of the human user's senses, for example, via haptic output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (1910), data gloves (not shown), or joystick (1905), although there may be haptic feedback devices that do not function as input devices), audio output devices (such as speakers (1909), headphones (not depicted)), visual output devices (such as screens (1910), including CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch screen input capability, each with or without haptic feedback capability, some of which may be capable of outputting two-dimensional visual output or three- or more-dimensional output via means such as stereographic output, virtual reality glasses (not depicted), holographic displays, and smoke tanks (not depicted)), and printers (not depicted).

[0222] The computer system (1900) may also include human accessible storage devices and their associated media, such as optical media, including CD / DVD ROM / RW (1920) with CD / DVD or similar media (1921), thumb drives (1922), removable hard drives or solid state drives (1923), legacy magnetic media such as tapes and floppy disks (not depicted), and specialized ROM / ASIC / PLD based devices (not depicted) such as security dongles.

[0223] Those skilled in the art should also understand that the term "computer-readable medium" as used in connection with the subject matter of this disclosure does not encompass transmission media, carrier waves, or other transitory signals.

[0224] The computer system (1900) may also include an interface (1954) to one or more communication networks (1955). The networks may be, for example, wireless, wired, optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LAN, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable television, satellite television, and terrestrial broadcast television, vehicular and industrial including CAN bus, etc. Certain networks typically require an external network interface adapter attached to a particular general-purpose data port (e.g., a USB port of the computer system (1900)) or peripheral bus (1949), while other networks are typically integrated into the core of the computer system (1900) by attachment to a system bus as described below (e.g., an Ethernet interface to a PC computer system, or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (1900) can communicate with other entities. Such communications may be unidirectional, receive only (e.g., broadcast television), unidirectional transmit only (e.g., CANbus to a particular CANbus device), or bidirectional, for example, to other computer systems using local or wide area digital networks. Specific protocols and protocol stacks may be used with each of these networks and network interfaces, as described above.

[0225] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to the core (1940) of the computer system (1900).

[0226] The cores (1940) may include one or more central processing units (CPUs) (1941), graphics processing units (GPUs) (1942), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (1943), hardware accelerators for specific tasks (1944), graphics adapters (1950), and the like. These devices may be connected via a system bus (1948), along with read only memory (ROM) (1945), random access memory (1946), internal mass storage (1947) such as an internal hard drive or SSD that is not accessible to the user. In some computer systems, the system bus (1948) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, and the like. Peripheral devices may be attached directly to the core's system bus (1948) or via a peripheral bus (1949). In one example, a screen (1910) may be connected to the graphics adapter (1950). Architectures for peripheral buses include PCI, USB, etc.

[0227] The CPU (1941), GPU (1942), FPGA (1943), and accelerator (1944) may combine to execute certain instructions that may constitute the aforementioned computer code. That computer code may be stored in ROM (1945) or RAM (1946). Persistent data may be stored, for example, in internal mass storage (1947), while transitory data may also be stored in RAM (1946). Rapid storage and retrieval from any of the memory devices may be enabled using cache memories that may be closely associated with one or more of the CPU (1941), GPU (1942), mass storage (1947), ROM (1945), RAM (1946), etc.

[0228] The computer-readable medium can bear computer code for performing various computer-implemented operations. The medium and computer code may be those specially designed and constructed for the purposes of the present disclosure, or they may be of the available kind well known to those skilled in the computer software arts.

[0229] As a non-limiting example, a computer system (1900) having an architecture, specifically a core (1940), can provide functionality as a result of a processor (including a CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be the user-accessible mass storage introduced above, as well as media associated with a particular storage of the core (1940) of a non-transitory nature, such as the core internal mass storage (1947) or ROM (1945). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (1940). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (1940), specifically the processor therein (including a CPU, GPU, FPGA, etc.) to perform a particular process or a particular portion of a particular process described herein, including defining data structures stored in RAM (1946) and modifying such data structures according to a process defined by the software. Additionally or alternatively, a computer system may provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerator (1944)), which may operate in place of or in conjunction with software to perform particular processes or particular portions of particular processes described herein. References to software may encompass logic, and vice versa, where appropriate. References to computer-readable media may encompass circuitry (such as integrated circuits (ICs)) that stores software for execution, circuitry that embodies logic for execution, or both, where appropriate. The present disclosure encompasses any suitable combination of hardware and software.

[0230] While this disclosure describes several exemplary embodiments, there are alterations, permutations, and various substitute equivalents that fall within the scope of this disclosure. Thus, it will be appreciated that those skilled in the art can devise numerous systems and methods that, although not explicitly shown or described herein, embody the principles of the present disclosure and are therefore within the spirit and scope of the present disclosure. Appendix A: Acronyms JEM: Joint Exploration Model VVC: Versatile Video Coding BMS: Benchmark Set MV: Motion Vector HEVC: High Efficiency Video Coding SEI: Supplemental Extended Information VUI: Video Usability Information GOP: Group of Pictures TU: conversion unit PU: Prediction Unit CTU: Coding Tree Unit CTB: coding tree block PB: Predicted block HRD: Hypothetical Reference Decoder SNR: Signal to Noise Ratio CPU: Central Processing Unit GPU: Graphics Processing Unit CRT: cathode ray tube LCD: Liquid crystal display OLED: Organic Light Emitting Diode CD:Compact Disc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random Access Memory ASIC: Application Specific Integrated Circuit PLD: Programmable Logic Device LAN: Local Area Network GSM: Global System for Mobile Communications LTE: Long Term Evolution CANBus: Controller Area Network Bus USB: Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: Field Programmable Gate Area SSD: Solid State Drive IC: Integrated Circuit HDR: High Dynamic Range SDR: Standard Dynamic Range JVET: Joint Video Exploration Team MPM: Most Probable Mode WAIP: Wide-angle Intra Prediction CU: coding unit PU: Prediction Unit TU: conversion unit CTU: Coding Tree Unit PDPC: Position-dependent prediction combination ISP: Intra Subpartition SPS: Sequence Parameter Settings PPS: Picture Parameter Set APS: Adaptive Parameter Set VPS:Video Parameter Set DPS: Decoding Parameter Set ALF: Adaptive Loop Filter SAO: Sample Adaptive Offset CC-ALF: Cross-component adaptive loop filter CDEF: Constrained Directional Enhancement Filter CCSO: Cross component sample offset LSO: Local Sample Offset LR: Loop recovery filter AV1:AOMedia Video 1 AV2:AOMedia Video 2 MVD: Motion Vector Difference CfL: Chroma from Luma SDT: Semi-disjoint tree SDP: Semi-separate split SST: Semi-separated tree SB: Super Block IBC (or IntraBC): Intrablock copy CDF: Cumulative density function SCC: Screen Content Coding GBI: Generalized Biprediction BCW: Bi-prediction with CU-level weights CIIP: Combined Intra-Inter Prediction POC: Picture Order Count RPS: Reference Picture Set DPB: Decoded Picture Buffer MMVD: Merge mode with motion vector difference MV: Motion Vector MVP: Motion Vector Predictor [Explanation of symbols]

[0231] 101 Samples 102 Arrow 103 Arrow 104 Square Block 180 Schematic diagram showing intra prediction direction 201 Current Block 202 Sample 203 Sample 204 Sample 205 Samples 206 Samples 300 Communication Systems 310 Terminal Devices 320 Terminal Devices 330 Terminal Devices 340 Terminal Devices 350 Communication Network 400 Communication Systems 401 Video Source 402 Stream of uncompressed video pictures 403 Video Encoder 404 Encoded video data 405 Streaming Server 406 Client Subsystem 407 Input copy of encoded video data / Encoded video data 408 Client Subsystem 409 Copy encoded video data / Encoded video data 410 Video Decoder 411 Video Picture Output Stream 412 Display 413 Video Capture Subsystem 420 Electronic Devices 430 Electronic Devices 501 Channel 510 Video Decoder 512 Display / Rendering Device 515 Buffer Memory 520 Entropy Decoder / Parser 521 Symbols 530 Electronic Devices 531 Receiver 551 Scaler / Descaler Unit 552 Intra-picture prediction unit 553 Motion Compensation Prediction Unit 555 Aggregator 556 Loop Filter Unit 557 Reference Picture Memory 558 Current Picture Buffer 601 Video Sources 603 Video Encoder 620 Electronic Devices / Encoders 630 Source Coder 632 Coding Engine 633 Local Video Decoder / Decoding Unit 634 Reference Picture Memory / Reference Picture Cache 635 Predictors 640 Transmitter 643 coded video sequence 645 Entropy Coder 650 Controller 660 Communication Channels 703 Video Encoder 721 General-purpose controller 722 Intra Encoder 723 Residual Calculator 724 Residual Encoder 725 Entropy Encoder 726 Switch 728 Residual Decoder 730 InterEncoder 810 Video Decoder 871 Entropy Decoder 872 Intra Decoder 873 Residual Decoder 874 Reconstruction Module 880 Interdecoder 902 Predefined split options or patterns 904 Predefined split options or patterns 906 Predefined split options or patterns 908 Predefined split options or patterns 1002 "T-shaped" partition / T-shaped pattern 1004 "T-shaped" partition / T-shaped pattern 1006 "T-shaped" partition / T-shaped pattern 1008 "T-shaped" partition / T-shaped pattern 1010 Square Partition 1102 Vertical bisection 1104 Horizontal bisection 1106 Vertical third division 1108 Horizontal third division 1200 Base Block 1202 Square Partition 1204 Square Partition 1206 Square Partition 1208 Square Partition 1302 Ternary Pattern 1304 Ternary Pattern 1402 Partition 1404 Partition 1406 Partition 1408 Partition 1410 Split pattern / split structure 1420 Tree Structure / Representation 1502 Square coding block 1504 First Level Split 1506 Second Level Split 1602 Inter-coded Blocks 1604 Conversion Block 1800 Flowchart 1900 Computer Systems 1901 Keyboard 1902 Mouse 1903 Trackpad 1905 Joystick 1906 Microphone 1907 Scanner 1908 Camera 1909 Speaker 1910 Touch Screen 1920 CD / DVD ROM / RW 1921 Medium 1922 Thumb Drive 1923 Removable Hard Drive or Solid State Drive 1940 Core 1941 Central Processing Unit (CPU) 1942 Graphics Processing Unit (GPU) 1943 Field Programmable Gate Area (FPGA) 1944 Hardware Accelerator 1945 Read-Only Memory (ROM) 1946 Random Access Memory (RAM) 1947 Core Internal Mass Storage 1948 System Bus 1949 Peripheral Bus 1950 Graphics Adapter 1954 Interface 1955 Communication Network

Claims

1. 1. A method for decoding a current video block of a video bitstream, comprising: receiving a coded video bitstream by a device comprising a memory storing instructions and a processor in communication with the memory; extracting, by the device, from the coded video bitstream, a first syntax element that indicates whether a mixed reference mode applies to a current video block; extracting, by the device, from the coded video bitstream, a second syntax element that indicates whether a motion vector difference (MVD) is jointly signaled for the current video block; In response to the first syntax element indicating that the mixed reference mode applies to the current video block and the second syntax element indicating that the MVD is jointly signaled for the current video block, refining, by the device, at least one MV predictor (MVP) in an MV candidate list based on whether the MVP is symmetric; decoding, by the device, the current video block based on the MV candidate list; A method comprising:

2. the at least one MVP in the MV candidate list comprises an MVP pair; The step of refining the at least one MVP in the MV candidate list comprises: refining the MVP pairs in the MV candidate list based on whether the MVP pairs are symmetric or asymmetric; Including, The method of claim 1.

3. The step of refining the MVP pairs in the MV candidate list comprises: responsive to the MVP pair being symmetric, moving the MVP pair ahead of all asymmetric MVPs in the MV candidate list. The method of claim 2 , comprising:

4. The step of refining the MVP pairs in the MV candidate list comprises: in response to the MVP pair being symmetric, moving the MVP pair to the top of the MV candidate list. The method of claim 2 , comprising:

5. The step of refining the MVP pairs in the MV candidate list comprises: moving the MVP pair to the top of the MV candidate list in response to the MVP pair being symmetric with equal picture order count (POC) distances between two reference frames and the current frame; The method of claim 2 , comprising:

6. The step of refining the MVP pairs in the MV candidate list comprises: responsive to the MVP pair being asymmetric, refining the MVP pair to become a symmetric MVP pair; The method of claim 2 , comprising:

7. the MVP pair includes a first MVP and a second MVP; the first MVP has a first POC distance between a first reference frame corresponding to the first MVP and a current frame; the second MVP has a second POC distance between a second reference frame corresponding to the second MVP and the current frame; the first POC distance is greater than the second POC distance; The step of refining the MVP pair to become the symmetric MVP pair comprises: projecting the first MVP onto the second reference frame to obtain a projected MVP; replacing the second MVP with the projected MVP; Including, The method of claim 6.

8. the MVP pair includes a first MVP and a second MVP; the first MVP has a first POC distance between a first reference frame corresponding to the first MVP and a current frame; the second MVP has a second POC distance between a second reference frame corresponding to the second MVP and the current frame; the first POC distance is greater than the second POC distance; The step of refining the MVP pair to become the symmetric MVP pair comprises: projecting the first MVP onto the second reference frame to obtain a projected MVP; adding the projected MVP to the MV candidate list; Including, The method of claim 6.

9. The step of adding the projected MVP to the MV candidate list comprises: adding the projected MVP to the end of the MV candidate list. The method of claim 8, comprising:

10. the MVP pair includes a first MVP and a second MVP; The step of refining the MVP pairs in the MV candidate list comprises: responsive to the MVP pair being asymmetric with equal POC distances between two reference frames and a current frame, replacing the second MVP of the MVP pair with an MVP that is symmetric with respect to the first MVP of the MVP pair; Including, The method of claim 2.

11. The first MVP of the MVP pair remains unchanged in the MV candidate list. The method of claim 10.

12. the MVP pair includes a first MVP and a second MVP; The step of refining the MVP pairs in the MV candidate list comprises: adding an MVP that is symmetric with respect to the first MVP of the MVP pair to the MV candidate list in response to the MVP pair being asymmetric with equal POC distances between two reference frames and the current frame; Including, The method of claim 2.

13. The step of refining the MVP pairs in the MV candidate list comprises: responsive to the MVP pair being asymmetric with equal POC distances between two reference frames and the current frame, replacing the MVP pair with a symmetric MVP pair based on averaging the MVP pair; The method of claim 2 , comprising:

14. The step of refining the MVP pairs in the MV candidate list comprises: adding a symmetric MVP pair based on averaging the MVP pair to the MV candidate list in response to the MVP pair being asymmetric with equal POC distances between two reference frames and the current frame; The method of claim 2 , comprising:

15. 1. An apparatus for decoding a current video block of a video bitstream, comprising: a memory for storing instructions; a processor in communication with the memory, the processor configured, when executing the instructions, to cause the apparatus to perform the method of any one of claims 1 to 14; An apparatus comprising:

16. A program comprising instructions, which when executed by a processor, are configured to cause the processor to perform a method according to any one of claims 1 to 14.

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