Subblock-Based Constraints on Biprediction for Out-of-Boundary Conditions

Abstract

It is determined whether one of (i) a boundary of a first reference subblock of a first subblock in a first reference picture is located beyond a boundary of the first reference picture, and (ii) a boundary of a second reference subblock of a first subblock in a second reference picture is located beyond a boundary of the second reference picture. In response to (i) a boundary of a first reference subblock of a first subblock in a first reference picture is located beyond a boundary of the first reference picture, and (ii) a boundary of a second reference subblock of a first subblock in a second reference picture is located within a boundary of the second reference picture, a first subblock of a current block is reconstructed based on a uni-prediction mode such that the first subblock is reconstructed based on a second reference subblock of a second reference picture.

Description

[Technical field]

[0001] Incorporation by Reference This application claims the benefit of priority to U.S. Provisional Application No. 63 / 307,536, entitled "Sub-block based Constraint on Bi-Prediction for Out-Of-Boundary Conditions," filed on February 7, 2022, which claims the benefit of priority to U.S. Provisional Application No. 17 / 983,879, entitled "SUB-BLOCK BASED CONSTRAINT ON BI-PREDICTION FOR OUT-OF-BOUNDARY CONDITIONS," filed on November 9, 2022. The disclosures of the prior applications are incorporated herein by reference in their entireties.

[0002] This disclosure generally describes embodiments related to video coding. [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.

[0004] Uncompressed digital images and / or videos may include a sequence of pictures, each having spatial dimensions of, for example, 1920x1080 luminance samples and associated chrominance samples. The sequence of pictures may have a fixed or variable picture rate (also informally called frame rate), for example, 60 pictures per second or 60 Hz. Uncompressed images and / or videos have specific bitrate requirements. For example, 1080p60 4:2:0 video (1920x1080 luminance sample resolution at a frame rate of 60 Hz) with 8 bits per sample 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 image and / or video coding and decoding may be the reduction of redundancy in the input image and / or video signal through compression. Compression may help reduce the aforementioned bandwidth and / or storage space requirements, possibly by more than one order of magnitude. The description herein uses video encoding / decoding as an illustrative example, but the same techniques may be applied to image encoding / decoding in a similar manner without departing from the spirit of this disclosure. Both lossless and lossy compression, as well as combinations thereof, may be employed. Lossless compression refers to techniques whereby an exact copy of an original signal may be reconstructed from a compressed original signal. When using lossy compression, the reconstructed signal may not be identical to the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal useful for its intended application. For video, lossy compression is widely adopted. The amount of tolerable distortion depends on the application, e.g., a user of a particular consumer streaming application may tolerate higher distortion than a user of a television distribution application. The achievable compression ratio may reflect that higher acceptable / tolerable distortion may result in higher compression ratios.

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

[0007] Video codec techniques 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 can therefore be used as the first picture in a coded video bitstream and video session or as a still image. Samples of an intra block can undergo a transform, and the transform coefficients can be quantized before entropy coding. Intra prediction can be a technique that minimizes sample values ​​in the pre-transform domain. In some cases, the smaller the DC value after the transform and the smaller the AC coefficients, the fewer bits are required for a given quantization step size to represent the block after entropy coding.

[0008] For example, traditional intra-coding, used in MPEG-2 generation coding techniques, does not use intra-prediction. However, some newer video compression techniques include techniques that attempt to make predictions based on surrounding sample data and / or metadata obtained during encoding and / or decoding of a data block, for example. Such techniques are hereinafter 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] There may be many different forms of intra prediction. If more than one of such techniques can be used in a given video coding technique, the particular technique in use may be coded as a particular intra prediction mode that uses that particular technique. In certain cases, an intra prediction mode may have sub-modes and / or parameters that may be coded separately or included in a mode codeword that defines the prediction mode used. Which codeword is used for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency gains via intra prediction and may affect the entropy coding technique used to convert the codeword into a bitstream.

[0010] A specific mode of intra prediction was introduced in H.264, improved in H.265, and further improved in newer coding techniques such as the Joint Search Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). A predictor block can be formed using neighboring sample values ​​of already available samples. The sample values ​​of the neighboring samples are copied to the predictor block according to the direction. The reference to the direction in use can be coded in the bitstream or it can be predicted itself.

[0011] Referring to FIG. 1A, shown at the bottom right is a subset of 9 predictor directions known from the 33 possible predictor directions defined in H.265 (corresponding to the 33 angle modes of the 35 intra modes). The point (101) where the arrows converge represents the sample being predicted. The arrows represent the direction from which the sample is predicted. For example, arrow (102) indicates that sample (101) is predicted from one or more samples to the upper right at an angle of 45 degrees from the horizontal. Similarly, arrow (103) indicates that sample (101) is predicted from one or more samples to the lower 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 Y-dimensional position (e.g., row index), and its X-dimensional position (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 the block (104) in both the Y and X dimensions. Since the block is 4×4 samples in size, S44 is at the bottom right. Also shown are reference samples that follow a similar numbering scheme. The reference samples are labeled with R, their Y position (e.g., row index), and X position (column index) relative to the block (104). In both H.264 and H.265, the predicted samples are close to the block being reconstructed, and therefore negative values ​​do not need to be used.

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

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

[0015] The number of possible directions has increased as video coding techniques have developed. In H.264 (2003), nine different directions could be represented. This increased to 33 in H.265 (2013). Currently, JEM / VVC / BMS can support up to 65 directions. Experiments have been carried out to identify the most likely directions, and certain techniques of entropy coding are used to represent those likely directions with a small number of bits, accepting a certain penalty for less likely directions. Furthermore, the direction itself may be predicted from nearby directions used in neighboring, already decoded blocks.

[0016] FIG. 1B shows a schematic diagram (110) illustrating 65 intra prediction directions with JEM to illustrate the increasing number of prediction directions over time.

[0017] The mapping of intra-prediction direction bits, which represent directions in a coded video bitstream, may vary between video coding techniques. Such mappings may range, for example, from simple direct mappings to complex adaptation schemes including codewords, most probable modes, and similar techniques. However, in most cases, there may be certain directions 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, these less likely directions are represented by more bits than the more likely directions in a well-functioning video coding technique.

[0018] Image and / or video coding and decoding can be performed using inter-picture prediction with motion compensation. Motion compensation can be a lossy compression technique and can refer to a technique in which blocks of sample data from a previously reconstructed picture or part thereof (reference picture) are used to predict a newly reconstructed picture or part of a picture after being spatially shifted in a direction indicated by a motion vector (hereafter MV). In some cases, the reference picture can be the same as the picture currently being reconstructed. The MV can have two dimensions X and Y, or three dimensions, the third dimension being an indication of the reference picture in use (the latter can be indirectly a temporal dimension).

[0019] In some video compression techniques, the MV applicable to a particular area of ​​sample data can be predicted from other MVs, e.g., from MVs associated with other areas of sample data that are spatially adjacent to the area being reconstructed and that precede that MV in decoding order. Doing so can significantly reduce the amount of data required to code the MV, thereby eliminating redundancy and increasing the compression ratio. MV prediction can work effectively because, for example, when coding an input video signal derived from a camera (known as natural video), there is a statistical likelihood that areas larger than the area to which a single MV is applicable move in similar directions and therefore can be predicted using similar motion vectors, possibly derived from MVs of nearby areas. As a result, the detected MV for a given area is similar or the same as the MV predicted from the surrounding MVs, which can be represented after entropy coding with fewer bits than would be used if the MV were coded directly. In some cases, MV prediction can be an example of lossless compression of a signal (i.e., MV) derived from an original signal (i.e., a 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 offered by H.265, one that will be described with reference to Fig. 2 is a technique hereafter referred to as "spatial merging".

[0021] Referring to Figure 2, a current block (201) contains samples that have been discovered by the encoder during the motion search process to be predictable from a previous block of the same size but spatially shifted. Instead of coding its MV directly, the MV can be derived from metadata associated with one or more reference pictures, e.g., from 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 can use predictors from the same reference picture that neighboring blocks are using. Summary of the Invention [Means for solving the problem]

[0022] Aspects of the present disclosure provide a method and apparatus for video encoding / decoding. In some examples, an apparatus for video decoding includes a processing circuit.

[0023] According to one aspect of the present disclosure, a method of video decoding performed in a video decoder is provided. In the method, coded information of a plurality of sub-blocks of a current block in a current picture can be received from a coded video bitstream. A syntax element indicating a prediction mode associated with the current block in the current picture can be obtained from the coded video bitstream, and the prediction mode can be one of a uni-prediction mode and a bi-prediction mode. It can be determined that a bi-prediction mode is applied to a first sub-block of the plurality of sub-blocks, and the first sub-block is predicted based on a first reference sub-block in the first reference picture and a second reference sub-block in the second reference picture. In response to the bi-prediction mode being applied to the first sub-block of the plurality of sub-blocks, it can be determined whether (i) a boundary of the first reference sub-block is located beyond a boundary of the first reference picture, and (ii) a boundary of the second reference sub-block is located within a boundary of the second reference picture. In response to (i) a boundary of the first reference subblock being located across a boundary of the first reference picture and (ii) a boundary of the second reference subblock being located within a boundary of the second reference picture, the first subblock of the current block may be reconstructed based on a uni-prediction mode such that the first subblock is reconstructed based on a second reference subblock of the second reference picture.

[0024] The bi-prediction mode to be applied to the first sub-block may be determined based on one of: (i) signaling information included in the coded information, (ii) a non-merged inter-prediction mode applied to the current block, and (iii) a merge mode applied to the current block.

[0025] In one embodiment, it may be determined whether the boundary of the first reference sub-block is located beyond the boundary of the first reference picture by a threshold value.

[0026] The size of the first sub-block may be one of 4x4 luma samples and 8x8 luma samples based on the inter prediction mode applied to the current block.

[0027] In response to the boundary of the first reference sub-block crossing the boundary of the first reference picture and the boundary of the second reference sub-block crossing the boundary of the second reference picture, the first sub-block of the current block can be reconstructed based on the first reference sub-block in the first reference picture and the second reference sub-block in the second reference picture.

[0028] The size of the first sub-block may be equal to one of: (i) an affine sub-block size based on an affine inter prediction mode applied to the current block; (ii) a sub-block based temporal motion vector prediction (SbTMVP) sub-block size based on an SbTMVP mode applied to the current block; and (iii) a geometric partition mode (GPM) sub-block size based on a GPM mode applied to the current block.

[0029] In response to (i) a first sub-block being located within a blending area centered on a geometric partition boundary of the current block and (ii) a boundary of the first reference sub-block crossing a boundary of the first reference picture, the first sub-block can be reconstructed based on a second reference sub-block, the boundary of the second reference sub-block being located within the boundary of the second reference picture.

[0030] In response to the first sub-block being predicted by the uni-prediction mode, uni-prediction motion information of the uni-prediction mode for the first sub-block may be stored.

[0031] In response to at least one pixel of the first sub-block being predicted by the uni-prediction mode, uni-prediction motion information of the uni-prediction mode for the first sub-block may be stored.

[0032] In some embodiments, one of a decoder-side motion vector precision improvement (DMVR) mode, a bidirectional optical flow (BDOF) mode, and a bi-prediction with coding unit level weights (BCW) mode may be excluded for a first sub-block of a current block in response to at least one of a boundary of the first reference sub-block crossing a boundary of the first reference picture or a boundary of the second reference sub-block crossing a boundary of the second reference picture.

[0033] In some embodiments, DMVR may be performed on the first subblock to determine a first predictive subblock based on a first reference subblock in a first reference picture and a second predictive subblock based on a second reference subblock in a second reference picture. Bi-predictive motion information may be stored for the first subblock indicating that the first subblock is predicted based on the first predictive subblock in the first reference picture and the second predictive subblock in the second reference picture.

[0034] According to another aspect of the present disclosure, an apparatus is provided, the apparatus including a processing circuit, the processing circuit being configured to perform any of the methods for video encoding / decoding.

[0035] Aspects of the present disclosure also provide a non-transitory computer-readable medium storing instructions that, when executed by a computer for video decoding, cause the computer to perform any of the methods for video encoding / decoding.

[0036] 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]

[0037] [Figure 1A]FIG. 2 is a schematic diagram of an example subset of intra-prediction modes. [Figure 1B] FIG. 2 is a diagram of an example intra-prediction direction. [Diagram 2] FIG. 2 is a schematic diagram of a current block and its surrounding spatial merge candidates in one example. [Diagram 3] FIG. 3 is a schematic diagram of a simplified block diagram of a communication system (300) according to one embodiment. [Figure 4] FIG. 4 is a schematic diagram of a simplified block diagram of a communication system (400) according to one embodiment. [Diagram 5] FIG. 2 is a schematic diagram of a simplified block diagram of a decoder according to one embodiment. [Figure 6] FIG. 2 is a schematic diagram of a simplified block diagram of an encoder according to one embodiment. [Figure 7] 4 shows a block diagram of an encoder according to another embodiment; [Figure 8] 4 shows a block diagram of a decoder according to another embodiment; [Figure 9] 1 illustrates exemplary locations of spatial merge candidates. [Figure 10] 1 illustrates an exemplary redundancy check of spatial merge candidates. [Figure 11] 1 illustrates a schematic diagram of an example of motion vector scaling for temporal merge candidates. [Figure 12] 13 illustrates exemplary candidate positions for temporal merge candidates. [Figure 13A] A schematic diagram of the four-parameter affine model is shown. [Figure 13B] A schematic diagram of the six-parameter affine model is shown. [Figure 14] 4 illustrates a schematic diagram of an example affine motion vector field associated with sub-blocks within a block. [Figure 15] 1 shows a schematic diagram of exemplary locations of spatial merging candidates; [Figure 16] 1 shows a schematic diagram of an example of control point motion vector inheritance. [Figure 17] 13A-13C show schematic diagrams of exemplary positions of candidates for configuring an affine merge mode; [Figure 18] 1 shows a schematic diagram of an example of prediction accuracy improvement using optical flow (PROF). [Figure 19] 1 shows a schematic diagram of exemplary spatial neighboring blocks for sub-block-based temporal motion vector prediction (SbTMVP). [Figure 20] FIG. 1 shows a schematic diagram of an exemplary SbTMVP process. [Figure 21] 1 shows a schematic diagram of an exemplary extended coding unit (CU) region for bidirectional optical flow (BDOF). [Figure 22] 1 shows a schematic diagram of an example of decoding-side motion vector refinement. [Diagram 23] 1 shows an example of geometric partition mode (GPM) partitions grouped by identical angles. [Figure 24] 1 illustrates an exemplary uni-predictive motion vector (MV) selection for the GPM. [Diagram 25] 1 shows a schematic diagram of an exemplary geometric division. [Figure 26] 1 shows an example specification of adaptive motion vector resolution (AMVR) in VVC. [Figure 27] 1 illustrates an example sub-block level bi-prediction constraint. [Figure 28] 1 shows a flowchart illustrating an example decoding process according to some embodiments of the present disclosure. [Figure 29] 1 shows a flowchart illustrating an example encoding process according to some embodiments of the present disclosure. [Diagram 30] FIG. 1 is a schematic diagram of a computer system according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] FIG. 3 illustrates an example block diagram of a communication system (300). 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) perform unidirectional transmission of data. For example, the terminal device (310) may code video data (e.g., 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 reconstruct the video pictures, and display the video pictures according to the reconstructed video data. Unidirectional data transmission may be common, such as in media serving applications.

[0039] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) for bidirectional transmission of coded video data, for example during a video conference. For bidirectional transmission of data, in one example, each of the terminal devices (330) and (340) may code video data (e.g., a stream of video pictures captured by the 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 reconstruct the video pictures, and display the video pictures on an accessible display device according to the reconstructed video data.

[0040] In the example of FIG. 3, the terminal devices (310), (320), (330), and (340) are illustrated as a server, a personal computer, and a smartphone, respectively, although the principles of the present disclosure are not so limited. The embodiments of the present disclosure apply with laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. The network (350) represents any number of networks that convey 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) may exchange data over circuit-switched and / or packet-switched channels. Representative networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this discussion, the architecture and topology of the network (350) may not be important to the operation of the present disclosure unless otherwise described herein below.

[0041] 4 illustrates a video encoder and video decoder in a streaming environment as one example of an application for the disclosed subject matter. The disclosed subject matter may be equally applicable to other video-enabled applications including, for example, video conferencing, digital television, streaming services, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0042] The streaming system may include a video source (401) that creates a stream of uncompressed video pictures (402), a capture subsystem (413) that may include, for example, a digital camera. In one example, the stream of video pictures (402) includes samples taken by a digital camera. The stream of video pictures (402) is illustrated as a thick line to emphasize its high amount of data compared to the encoded video data (404) (or coded video bitstream) and 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), illustrated as a thin line to emphasize its low amount of data compared to the stream of video pictures (402), may be stored on a streaming server (405) for future use. One or more streaming client subsystems, such as the client subsystems (406) and (408) of FIG. 4, can access the streaming server (405) to retrieve copies (407) and (409) of the encoded video data (404). The client subsystem (406) can include, for example, a video decoder (410) in an electronic device (430). The video decoder (410) decodes an input copy (407) of the encoded video data and creates an output stream (411) of video pictures that can be rendered on a display (412) (e.g., a display screen) or other rendering device (not shown). In some streaming systems, the encoded video data (404), (407), and (409) (e.g., a video bitstream) can be encoded according to a particular video coding / compression standard.Examples of those 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.

[0043] It should be noted that the electronic devices (420) and (430) may include other components (not shown). For example, the electronic device (420) may also include a video decoder (not shown), and the electronic device (430) may also include a video encoder (not shown).

[0044] 5 shows an example block diagram of a video decoder (510). The video decoder (510) can be included in an electronic device (530). The electronic device (530) can include a receiver (531) (e.g., a receiving circuit). The video decoder (510) can be used in place of the video decoder (410) in the example of FIG. 4.

[0045] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In one embodiment, one coded video sequence is received at a time, and the decoding of each coded video sequence is independent of the decoding of the other coded video sequences. 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. The receiver (531) may receive the encoded video data together with other data, e.g., coded audio data and / or auxiliary data streams, which may be forwarded to a respective usage entity (not shown). The receiver (531) may separate the coded video sequences from the other data. To combat network jitter, a buffer memory (515) may be coupled between the receiver (531) and the entropy decoder / parser (520) (hereinafter "parser (520)"). In certain applications, the buffer memory (515) is part of the video decoder (510). In other applications, the buffer memory (515) can be 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 an 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, the buffer memory (515) may be necessary and may be relatively large, may be advantageously of 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).

[0046] The video decoder (510) may include a parser (520) for reconstructing symbols (521) from the coded video sequence. The categories of symbols include information used to manage the operation of the video decoder (510) and information for controlling a rendering device such as a rendering device (512) (e.g., a display screen) that is not an integral part of the electronic device (530) but may potentially be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device(s) may be in the form of a supplemental enhancement information (SEI message) or a video usability information (VUI) parameter set fragment (not shown). The parser (520) may parse / entropy decode the received coded video sequence. The 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 dependency, 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 group. The subgroups may include Group 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, quantization parameter values, motion vectors, etc.

[0047] The parser (520) may perform an entropy decoding / parsing operation on the video sequence received from the buffer memory (515) to produce symbols (521).

[0048] The reconstruction of the symbols (521) may involve a number of different units, depending on the type of coded video picture or portion thereof (inter-picture and intra-picture, inter-block and intra-block, etc.), as well as other factors. Which units are involved and how can 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 units is not shown for the sake of simplicity.

[0049] Beyond the functional blocks already mentioned, the video decoder (510) can be conceptually subdivided into several functional units, as described below. In an actual implementation operating under commercial constraints, many of these units will interact closely with each other and may be, at least in part, integrated with each other. However, for purposes of describing the disclosed subject matter, the following conceptual subdivision into functional units is adequate:

[0050] The first unit is a scalar / inverse transform unit (551), which receives quantized transform coefficients as well as control information from the parser (520) including which transform to use, block size, quantization coefficients / parameters, quantization scaling matrices, etc. as symbol(s) (521). The scalar / inverse transform unit (551) can output blocks containing sample values ​​that can be input to an aggregator (555).

[0051] In some cases, the output samples of the scaler / inverse transform unit (551) may relate to intra-coded blocks. Intra-coded blocks are 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 can be provided by an intra-picture prediction unit (552). In some cases, the intra-picture prediction unit (552) generates a block of the same size and shape as the block being reconstructed using surrounding already reconstructed information fetched from a current picture buffer (558). The current picture buffer (558) buffers, for example, a partially reconstructed current picture and / or a fully reconstructed current picture. The aggregator (555) adds, possibly 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).

[0052] 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 motion compensate the fetched samples according to the symbols (521) relating to the block from which the samples used for prediction may be fetched, and then these samples may be added by the aggregator (555) to the output of the scalar / inverse transform unit (551) to generate output sample information (in this case referred to as residual samples or residual signals). The addresses in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches the prediction samples may be controlled by motion vectors available to the motion compensated prediction unit (553), for example in the form of symbols (521) that may have an X component, a Y component, and a reference picture component. Motion compensation may also include interpolation of sample values ​​fetched from the reference picture memory (557) when sub-sample accurate motion vectors are used, motion vector prediction mechanisms, etc.

[0053] The output samples of the aggregator (555) may be subjected to various loop filtering techniques in a loop filter unit (556). Video compression techniques may include in-loop filter techniques controlled by parameters included in the coded video sequence (also called the coded video bitstream) and provided to the loop filter unit (556) as symbols (521) from the parser (520). Video compression may also be performed in response to meta-information obtained during decoding of a coded picture or previous portion (in decoding order) of the coded video sequence, or in response to previously reconstructed and loop filtered sample values.

[0054] The output of the loop filter unit (556) may be a sample stream that can be output to a rendering device (512) or stored in a reference picture memory (557) for use in future inter-picture prediction.

[0055] Once a particular coded picture is fully reconstructed, it can be used as a reference picture for future prediction. For example, once a coded picture corresponding to a current picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by the parser (520)), the current picture buffer (558) can become part of the reference picture memory (557), and a new current picture buffer can be reallocated before beginning reconstruction of a subsequent coded picture.

[0056] The video decoder (510) may perform decoding operations according to a given video compression technique or standard, such as ITU-T Recommendation H.265. The coded video sequence may comply with the syntax specified by the video compression technique or standard being used in the sense that the coded video sequence adheres to both the syntax of the video compression technique or standard and the profile documented in the video compression technique or standard. Specifically, the profile may select certain tools as limited tools available under the profile from all tools available in the video compression technique or standard. It may also be required for compliance that the complexity of the coded video sequence is within a range defined by the level of the video compression technique or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. The limits set by the level may be further limited in some cases by the specification of a hypothetical reference decoder (HRD) and metadata for HRD buffer management signaled within the coded video sequence.

[0057] In one embodiment, 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(s). 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.

[0058] 6 shows an example block diagram of a video encoder (603). The video encoder (603) is included in an electronic device (620). The electronic device (620) includes a transmitter (640) (e.g., a transmission circuit). The video encoder (603) can be used in place of the video encoder (403) of the example of FIG.

[0059] 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 the video image(s) to be coded by the video encoder (603). In another example, the video source (601) is part of the electronic device (620).

[0060] 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 Y CrCb, RGB, ...), and any suitable sampling structure (e.g., Y CrCb 4:2:0, Y CrCb 4:4:4). In a media serving system, the video source (601) may be a storage device that stores 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 that give motion when viewed in sequence. The pictures themselves 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.

[0061] According to one embodiment, 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. Enforcing an appropriate coding rate is one function of the controller (650). In some embodiments, the controller (650) controls and is operatively coupled to other functional units described below. For simplicity, coupling is not shown. Parameters set by the controller (650) may include rate control related parameters (picture skip, quantization, lambda value for rate distortion optimization techniques, ...), picture size, Group of Pictures (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured to have other appropriate functions related to the video encoder (603) optimized for a particular system design.

[0062] In some embodiments, the video encoder (603) is configured to operate in a coding loop. As an oversimplified explanation, in one example, the coding loop can include a source coder (630) (responsible for creating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture, for example) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to create sample data in a manner similar to what a (remote) decoder would also create. The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since decoding of the symbol stream results in bit-exact results regardless of the location of the decoder (local or remote), the contents in 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 decoder would "see" when using prediction during decoding as reference picture samples. This basic principle of reference picture synchrony (and the resulting drift when synchrony cannot be maintained, eg, due to channel errors) is also used in several related techniques.

[0063] 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 the symbol-pair 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).

[0064] In one embodiment, the decoder techniques, except for parsing / entropy decoding, present in the decoder are present in the corresponding encoder in the same or substantially the same functional form. Therefore, the subject matter of the disclosure focuses on the operation of the decoder. The description of the encoder techniques can be omitted, since they are the opposite of the decoder techniques described generically. Only in certain areas will more detailed descriptions be provided below.

[0065] In some examples, during operation, 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 differences between pixel blocks of the input picture and pixel blocks of the reference picture(s) that may be selected as the predictive reference(s) to the input picture.

[0066] 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. If the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may typically be a copy 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 and store the reconstructed reference pictures in the reference picture memory (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content with the reconstructed reference pictures obtained by the far-end video decoder (without transmission errors).

[0067] The predictor (635) may perform a prediction 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 prediction references for the new picture. The predictor (635) may operate pixel block by pixel block to find a suitable prediction reference. In some cases, as determined by the search results obtained by the predictor (635), the input picture may have a prediction reference chosen from multiple reference pictures stored in the reference picture memory (634).

[0068] 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.

[0069] The output of all the aforementioned functional units may be subjected to entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by applying lossless compression to the symbols according to techniques such as Huffman coding, variable length coding, arithmetic coding, etc.

[0070] The transmitter (640) may buffer the coded video sequence(s) created by the entropy coder (645) 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 encoder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0071] The controller (650) may manage the operation of the video encoder (603). The controller (650) may assign a particular coded picture type to each coded picture during coding, which may affect the coding technique that may be applied to the respective picture. For example, pictures may often be assigned as one of the following picture types:

[0072] An intra picture (I-picture) may be a picture 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.

[0073] A predictive picture (P picture) may be a picture that can be coded and decoded using intra- or inter-prediction, which predicts sample values ​​for each block using at most one motion vector and reference index.

[0074] A bidirectionally predicted picture (B-picture) may be a picture that can be coded and decoded using intra- or inter-prediction, which predicts sample values ​​for each block using at most two motion vectors and reference indexes. Similarly, a multi-predictive picture can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0075] A source picture is generally spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) and may be coded block by block. A block may be predictively coded with reference to other (already coded) blocks as determined by a coding assignment applied to the block's respective picture. 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.

[0076] 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.

[0077] In one embodiment, 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.

[0078] Video may be captured in a time sequence as multiple source pictures (video pictures). Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits the (temporal or other) correlation between pictures. In one example, a particular picture being encoded / decoded, called the current picture, is divided into blocks. When a block in the current picture is similar to a reference block in a previously coded and still buffered reference picture in the video, the block in the current picture may be coded by a vector called a motion vector. The motion vector points to a reference block in the reference picture and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0079] In some embodiments, bi-prediction techniques can be used in inter-picture prediction. According to bi-prediction techniques, two reference pictures, such as a first reference picture and a second reference picture, both of which precede the current picture in the video in decoding order (but may be in the past and future, respectively, in display order), are used. A block in the current picture can 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 can be predicted by a combination of the first reference block and the second reference block.

[0080] Furthermore, merge mode techniques can be used to improve coding efficiency in inter-picture prediction.

[0081] According to some 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, according to the HEVC standard, a picture in a sequence of video pictures is divided into coding tree units (CTUs) for compression, and the CTUs in a picture have the same size, such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU includes three coding tree blocks (CTBs), one luma CTB and two chroma CTBs. Each CTU can be recursively quadtree partitioned into one or more coding units (CUs). For example, a CTU of 64×64 pixels can be partitioned into one CU of 64×64 pixels, or into four CUs of 32×32 pixels, or into 16 CUs of 16×16 pixels. In one example, each CU is analyzed to determine a prediction type of the CU, such as an inter prediction type or an intra prediction type. A CU is divided into one or more prediction units (PUs) according to temporal predictability 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. Taking a luma prediction block as an example of a prediction block, the prediction block includes a matrix of pixel values ​​(e.g., luma values), such as 8×8 pixels, 16×16 pixels, 8×16 pixels, 16×8 pixels, etc.

[0082] 7 shows an example diagram of a video encoder (703). 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. In one example, the video encoder (703) is used in place of the video encoder (403) of the example of FIG. 4.

[0083] In an HEVC 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) determines whether the processing block is best coded using intra-mode, inter-mode, or bi-predictive mode, for example using rate-distortion optimization. If 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 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 certain video coding techniques, a merge mode in which a motion vector is derived from one or more motion vector predictors without the aid of an external coded motion vector component of the predictor may be an inter-picture prediction sub-mode. In certain other video coding techniques, there may be a motion vector component applicable to the current block. In one example, the video encoder (703) includes other components, such as a mode decision module (not shown), to determine the mode of the processing block.

[0084] 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 FIG. 7.

[0085] 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 a previous picture and a subsequent picture), generate inter-prediction information (e.g., a description of redundancy information, motion vectors, merge mode information according to an inter-encoding technique), 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 is decoded based on the encoded video information.

[0086] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), possibly compare the block to 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). In one example, the intra encoder (722) also calculates intra prediction results (e.g., predicted blocks) based on the intra prediction information and reference blocks in the same picture.

[0087] The generic controller (721) is 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 the mode of the block and provides a control signal to the switch (726) based on the mode. For example, when the 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 to include the intra prediction information in the bitstream, and when the mode 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 to include the inter prediction information in the bitstream.

[0088] The residual calculator (723) is configured to calculate a difference (residual data) between the received block and a prediction result selected from the intra-encoder (722) or the inter-encoder (730). The residual encoder (724) is configured to operate based on the residual data to encode the residual data to generate transform coefficients. In one example, the residual encoder (724) is 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 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 can 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 are suitably processed to generate decoded pictures, which in some examples may be buffered in a memory circuit (not shown) and used as a reference picture.

[0089] The entropy encoder (725) is configured to format a bitstream to include the encoded block. The entropy encoder (725) is configured to include various information in the bitstream according to an appropriate standard, such as the HEVC standard. In one example, the entropy encoder (725) is configured to include in the bitstream general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other appropriate information. It should be noted that, in accordance with the disclosed subject matter, no residual information is present when coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode.

[0090] 8 shows an example diagram of a video decoder (810). 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) is used in place of the video decoder (410) of the example of FIG. 4.

[0091] 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), coupled to each other as shown in FIG.

[0092] 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-mode, inter-mode, bi-predictive mode, inter-mode and bi-predictive mode of merged or other submodes, etc.) that may identify the mode in which the block is coded, as well as certain samples or metadata used for prediction by the intra-decoder (872) or the inter-decoder (880), respectively (e.g., intra-prediction and inter-prediction information, etc.). The symbols may also include, for example, residual information in the form of quantized transform coefficients, etc. In one example, if the prediction mode is an inter-mode or bi-predictive 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).

[0093] The inter decoder (880) is configured to receive the inter prediction information and to generate inter prediction results based on the inter prediction information.

[0094] The intra decoder (872) may be configured to receive intra prediction information and generate a prediction result based on the intra prediction information.

[0095] The residual decoder (873) is configured to perform inverse quantization to extract inverse quantized transform coefficients, and process the inverse quantized transform coefficients to transform the residual information from the frequency domain to the spatial domain. The residual decoder (873) may also require certain control information (to include quantization parameters (QPs)), which may be provided by the entropy decoder (871) (datapaths not shown as this may be only a small amount of control information).

[0096] The reconstruction module (874) is configured to combine, in the spatial domain, the residual information output by the residual decoder (873) and the prediction result (possibly output by the inter prediction module or the intra prediction module) to form a reconstructed block that may become part of a reconstructed picture, which may become part of a reconstructed video. It should be noted that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0097] It should be noted that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) can be implemented using any suitable technology. In one embodiment, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) can 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) can be implemented using one or more processors executing software instructions.

[0098] This disclosure includes embodiments related to MV constraints at the sub-block level to disable, i.e., prohibit, bi-prediction (e.g., bi-prediction in AMVP mode) when the MV points outside the reference picture boundary. In the case of merge mode, the merge MV from the merge candidate can also be constrained at the sub-block level for bi-prediction mode.

[0099] ITU-T VCEG (Q6 / 16) and ISO / IEC MPEG (JTC 1 / SC 29 / WG 11) published the H.265 / HEVC (High Efficiency Video Coding) standard in 2013 (version 1), 2014 (version 2), 2015 (version 3), and 2016 (version 4). In 2015, these two standardization bodies jointly formed the Joint Video Exploration Team (JVET) to explore the possibility of developing the next video coding standard beyond HEVC. In October 2017, these two standardization bodies issued a Joint Call for Proposals on Video Compression with Capability beyond HEVC (CfP). By February 15, 2018, 22 CfP responses for standard dynamic range (SDR), 12 CfP responses for high dynamic range (HDR), and 12 CfP responses for 360 video categories were submitted. In April 2018, all received CfP responses were evaluated at the 122 MPEG / 10th JVET meeting. As a result of the meeting, JVET formally started the standardization process for next-generation video coding beyond HEVC. This new standard was named Versatile Video Coding (VVC), and JVET was renamed the Joint Video Experts Team. In 2020, ITU-T VCEG (Q6 / 16) and ISO / IEC MPEG (JTC 1 / SC 29 / WG 11) published the VVC video coding standard (version 1).

[0100] In inter prediction, motion parameters are needed for each inter predicted coding unit (CU), e.g., to code the VVC features to be used for inter predicted sample generation. The motion parameters may include motion vectors, reference picture indexes, reference picture list usage indexes, and / or additional information. The motion parameters may be signaled explicitly or implicitly. If a CU is coded in skip mode, the CU may be associated with one PU, and significant residual coefficients, coded motion vector deltas, and / or reference picture indexes may not be needed. If a CU is coded in merge mode, the motion parameters of the CU may be obtained from neighboring CUs. The neighboring CUs may include spatial and temporal candidates, as well as additional schedules (or additional candidates) as introduced in VVC. The merge mode may be applied to any inter predicted CU, not just for skip mode. An alternative to the merge mode is explicit transmission of motion parameters, where the motion vectors, the corresponding reference picture indexes of each reference picture list, the reference picture list usage flag, and / or other necessary information may be explicitly signaled for each CU.

[0101] In VVC, the VVC Test Model (VTM) reference software may include several new and improved inter-predictive coding tools, which may include one or more of the following: (1) Enhanced Merge Prediction (2) Merged Motion Vector Differential (MMVD) (3) AMVP mode with symmetric MVD signaling (4) Affine motion compensation prediction (5) Sub-block-based Temporal Motion Vector Prediction (SbTMVP) (6) Adaptive Motion Vector Resolution (AMVR) (7) Motion field storage: 1 / 16 luma sample MV storage and 8x8 motion field compression (8) Bi-prediction with CU-level weights (BCW) (9) Bidirectional Optical Flow (BDOF) (10) Improved Decoder Motion Vector Accuracy (DMVR) (11) Combined Inter- and Intra-Prediction (CIIP) (12) Geometric Partitioning Mode (GPM)

[0102] The merge candidate list can be constructed by including five types of candidates, as in VTM4: The merge candidate list can be constructed in the following order: 1) Spatial MVP from spatially neighboring CUs, 2) Temporal MVP from collocated CUs; 3) History-based MVP from a FIFO table, 4) Pairwise average MVP, and 5) Zero MV.

[0103] The size of the merge list can be signaled in the slice header. The maximum allowed size of the merge list can be 6, as in VTM4. For each CU coded in merge mode, the index of the best merge candidate can be encoded, for example using truncated unary binarization. The first bin of the merge index can be coded with the context, and bypass coding can be used for the other bins.

[0104] In spatial candidate derivation, for example in VVC, the derivation of spatial merge candidates can be the same as or similar to the derivation of spatial merge candidates in HEVC. The maximum number of merge candidates (e.g., four merge candidates) can be selected, for example, from the selection located at the positions illustrated in FIG. 9. As shown in FIG. 9, the current block (901) is located at positions A, B, C, D, E, E, F, G, H, I, I, J, J, J, J, J, J, 0 , A 1 , B 0 , B 1 , and B. 2The spatial merge candidates can be derived in the order of B 1 , A 1 , B 0 , A 0 , and B. 2 Position B 2 is position A 0 , B 0 , B 1 , or A 1 Position A may only be considered if any CU (or block) in position A is not available (e.g., because the CU belongs to another slice or tile) or is intra-coded. 1 After a candidate (or block) is added, the addition of the remaining candidate (or block) may be subject to a redundancy check. The redundancy check may ensure that candidates with the same motion information are removed from the merge list so that coding efficiency is improved. To reduce computational complexity, the redundancy check may not consider all possible candidate pairs. Instead, only the candidate pairs connected by the arrows in FIG. 10 may be considered. For example, the redundancy check may be applied to five candidate pairs, such as the candidate pair A1 and B1, the candidate pair A1 and A0, etc. A candidate may be added to the merge list only if the corresponding candidate used for the redundancy check does not contain the same motion information. For example, the candidate B0 may be added to the merge list only if the corresponding candidate B1 does not contain the same motion information.

[0105] In temporal candidate derivation, only one candidate may be added to the merge list. For example, as shown in FIG. 11, in derivation of a temporal merge candidate for a current CU (1114), a scaled motion vector may be derived based on a co-located CU (1104) belonging to a co-located reference picture (1112). The reference picture list used to derive the co-located CU (1104) may be explicitly signaled in the slice header. The scaled motion vector of the temporal merge candidate may be obtained as illustrated by the dotted line (1102) in FIG. 11, which is scaled from the motion vector of the co-located CU (1104) using picture order count (POC) distances tb and td. tb may be defined as the POC difference between the reference picture (e.g., Curr_ref) (1106) of the current picture and the current picture (e.g., Curr_pic) (1108). td may be defined as the POC difference between the collocated picture's reference picture (e.g., Col_ref) (1110) and the collocated picture (e.g., Col_pic) (1112). The reference picture index of the temporal merge candidate may be set equal to 0.

[0106] The location of the temporal candidate is shown in FIG. 0 and Candidate C 1 For example, position C 0 If the CU at position C is unavailable, is intra-coded, or is outside the current row of the CTU, 1 can be used. Otherwise, position C 0 can be used to derive temporal merge candidates.

[0107] In HEVC, a translational motion model is applied to motion compensated prediction (MCP). In the real world, many types of motion may exist, such as zoom in / out, rotation, perspective motion, and other irregular motion. In VTM, etc., block-based affine transform motion compensated prediction can be applied. Figure 13A shows an affine motion field of a block (1302) described by two control point motion information (4 parameters). Figure 13B shows an affine motion field of a block (1304) described by three control point motion vectors (6 parameters).

[0108] As shown in FIG. 13A, in a four-parameter affine motion model, the motion vector at a sample position (x, y) in a block (1302) can be derived in equation (1) as follows:

number

number

[0109] As shown in FIG. 13B, in a six-parameter affine motion model, the motion vector at a sample position (x, y) within a block (1304) can be derived in equation (3) as follows:

number

number

[0110] As shown in FIG. 14, to simplify the motion compensation prediction, a block-based affine transformation prediction can be applied. To derive a motion vector for each 4×4 luma sub-block, the motion vector of the central sample (e.g., (1402)) of each sub-block (e.g., (1404)) in the current block (1400) can be calculated according to equations (1)-(4) and rounded to 1 / 16 fractional precision. Then, a motion compensation interpolation filter can be applied to generate a prediction for each sub-block using the derived motion vector. The sub-block size of the chroma components can also be set as 4×4. The MV of a 4×4 chroma sub-block can be calculated as the average of the MVs of the four corresponding 4×4 luma sub-blocks.

[0111] In affine merge prediction, an affine merge (AF_MERGE) mode may be applied for CUs with both width and height equal to or greater than 8. The CPMV of the current CU may be generated based on the motion information of spatially neighboring CUs. Up to five CPMVP candidates may be applied to affine merge prediction, and an index may be signaled to indicate which of the five CPMVP candidates may be used for the current CU. In affine merge prediction, the following three types of CPMV candidates may be used to form an affine merge candidate list: (1) inherited affine merge candidates extrapolated from the CPMV of neighboring CUs, (2) constructed affine merge candidates with CPMVP derived using the translation MV of neighboring CUs, and (3) zero MV.

[0112] In VTM3, up to two inherited affine candidates can be applied. The two inherited affine candidates can be derived from the affine motion models of the neighboring blocks. For example, one inherited affine candidate can be derived from the left neighboring CU, and the other inherited affine candidate can be derived from the upper neighboring CU. An exemplary candidate block can be shown in FIG. 15. As shown in FIG. 15, for the left predictor (or the left inherited affine candidate), the scanning order can be A0→A1, and for the upper predictor (or the upper inherited affine candidate), the scanning order can be B0→B1→B2. Thus, only the first available inherited candidate from each side can be selected. No pruning check may be performed between the two inherited candidates. Once the neighboring affine CU is identified, the control point motion vector of the neighboring affine CU can be used to derive a CPMVP candidate in the affine merge list of the current CU. As shown in FIG. 16, if a neighboring block A to the lower left of the current block (1604) is coded in affine mode, the motion vector v 2 , v 3 , and v 4 When block A is coded using a four-parameter affine model, two CPMVs of the current CU (1604) are obtained by multiplying v 2 and v 3 When block A is coded using a six-parameter affine model, the three CPMVs of the current CU (1602) can be calculated according to v 2 , v 3 , and v 4 It can be calculated according to:

[0113] The constructed affine candidate of the current block may be a candidate constructed by combining the neighborhood translation motion information of each control point of the current block. The motion information of the control points may be derived from the specified spatial and temporal neighborhoods, which may be shown in FIG. 17. As shown in FIG. 17, the CPMV k(k=1, 2, 3, 4) represents the kth control point of the current block (1702). CPMV 1 In this case, B2 block → B3 block → A2 block can be checked, and the MV of the first available block can be used. 2 In this case, B1 block → B0 block can be checked. CPMV 3 In this case, A1 block → A0 block can be checked. CPM 4 If not available, TMVP uses CPMV 4 It can be used as.

[0114] After the MVs of the four control points are obtained, an affine merge candidate can be constructed for the current block (1702) based on the motion information of the four control points. For example, an affine merge candidate can be constructed based on a combination of the MVs of the four control points in the following order: {CPMV 1 ,CPMV 2 ,CPMV 3}, {CPMV 1 ,CPMV 2 ,CPMV 4}, {CPMV 1 ,CPMV 3 ,CPMV 4}, {CPMV 2 ,CPMV 3 ,CPMV 4}, {CPMV 1 ,CPMV 2}, {CPMV 1 ,CPMV 3}.

[0115] A combination of three CPMVs can constitute a six-parameter affine merge candidate, and a combination of two CPMVs can constitute a four-parameter affine merge candidate. To avoid the motion scaling process, if the reference indexes of the control points are different, the associated combination of control point MVs can be discarded.

[0116] After the inheritance and composition affine merge candidates have been checked, a zero MV may be inserted at the end of the merge list if the list is not already full.

[0117] In affine AMVP prediction, the affine AMVP mode can be applied for CUs with both width and height of 16 or more. A CU-level affine flag can be signaled in the bitstream to indicate whether the affine AMVP mode is used, and then another flag can be signaled to indicate whether 4-parameter affine or 6-parameter affine is applied. In affine AMVP prediction, the difference between the CPMV of the current CU and the predictor of the CPMVP of the current CU can be signaled in the bitstream. The size of the affine AMVP candidate list can be 2, and the affine AMVP candidate list can be generated by using 4 types of CPMV candidates in the following order: (1) Inherited affine AMVP candidates extrapolated from the CPMVs of neighboring CUs, (2) A constructed affine AMVP candidate with CPMVP derived using the translational MVs of nearby CUs; (3) Translational MV from nearby CUs, and (40 Zero MV.

[0118] The check order of the inherited affine AMVP candidates may be the same as the check order of the inherited affine merge candidates. To determine the AVMP candidates, only affine CUs with the same reference picture as the current block may be considered. The pruning process may not be applied when the inherited affine motion predictor is inserted into the candidate list.

[0119] The constructed AMVP candidates can be derived from the specified spatial neighborhood. As shown in FIG. 17, the same check order as in the affine merge candidate construction can be applied. In addition, the reference picture indexes of the neighboring blocks can also be checked. The first block in the check order can be inter-coded and have the same reference picture as the current CU (1702). If the current CU (1702) is coded in 4-parameter affine mode and mv 0 and MV 1 If both of the CPMVs are available, one configured AMVP candidate can be determined. The configured AMVP candidate can be further added to the affine AMVP list. If the current CU (1702) is coded in a 6-parameter affine mode and all three CPMVs are available, the configured AMVP candidate can be added as a candidate in the affine AMVP list. Otherwise, the configured AMVP candidate can be set as unavailable.

[0120] If there are still less than two candidates in the affine AMVP list after the inherited affine AMVP candidates and the constructed AMVP candidates have been checked, mv 0 , mv 1 and mv 2 can be added in order. mv 0 , mv 1 and mv 2 can serve as a translation MV to predict all control point MVs of the current CU (e.g., (1702)), if available. Finally, if the affine AMVP is not yet full, a zero MV can be used to fill the affine AMVP list.

[0121] Sub-block-based affine motion compensation can save memory access bandwidth and reduce computational complexity compared to pixel-based motion compensation at the expense of a prediction accuracy penalty. To achieve finer granularity of motion compensation, prediction accuracy improvement using optical flow (PROF) can be used to correct sub-block-based affine motion compensation prediction without increasing memory access bandwidth for motion compensation. In VVC, after sub-block-based affine motion compensation is performed, the accuracy of luma prediction samples can be improved by adding the difference derived by the optical flow equation. PROF can be described in four steps as follows:

[0122] Step (1): Sub-block-based affine motion compensation may be performed to generate a sub-block prediction I(i,j).

[0123] Step (2): Spatial gradient of subblock prediction g x (i,j) and g y (i,j) can be calculated at each sample position using a 3-tap filter [-1,0,1]. The gradient calculation can be the same as the gradient calculation in BDOF. For example, the spatial gradient g x (i,j) and g y (i,j) can be calculated based on equations (5) and (6), respectively. g x (i,j)=(I(i+1,j)>>shift1)-(I(i-1,j)>>shift1) Equation (5) g y (i,j)=(I(i,j+1)>>shift1)-(I(i,j-1)>>shift1) Equation (6) As shown in equations (5) and (6), shift1 can be used to control the accuracy of the gradient. A sub-block (e.g., 4×4) prediction can be extended by one sample on each side for gradient calculation. To avoid additional memory bandwidth and additional interpolation calculations, the extended samples on the extended boundary can be copied from the nearest integer pixel location in the reference picture.

[0124] Step (3): The luma prediction refinement can be calculated by the optical flow equation as shown in Equation (7). ΔI(i,j)=g x (i,j)*Δv x (i,j)+g y (i,j)*Δv y (i,j) Equation (7) where Δv(i,j) is the sum of the sample MV calculated for sample position (i,j), denoted as v(i,j), and the MV of the sub-block to which sample (i,j) belongs, v SB MV(i,j) may be a difference between the subblock MV represented by v(i,j) and the current block MV represented by v(i,j). FIG. 14 shows an example illustration of a difference between a sample MV and a subblock MV. As shown in FIG. 18, a subblock (1802) may be included in a current block (1800), and a sample (1804) may be included in the subblock (1802). The sample (1804) may include a sample motion vector v(i,j) corresponding to a reference pixel (1806). The subblock (1802) may include a subblock motion vector v(i,j). SB The sub-block motion vector v SB Based on, the sample (1804) may correspond to the reference pixel (1808). The difference between the sample MV and the sub-block MV, represented by Δv(i,j), may be indicated by the difference between the reference pixel (1806) and the reference pixel (1808). Δv(i,j) may be quantized with a precision of 1 / 32 luma sample units.

[0125] Since the affine model parameters and sample positions relative to the subblock center may not change from one subblock to another, Δv(i,j) can be calculated for a first subblock (e.g., (1802)) and reused for other subblocks (e.g., (1810)) in the same CU (e.g., (1800)). dx(i,j) is calculated from the sample position (i,j) to the subblock center (x SB ,y SB ), and dy(i,j) be the vertical offset, Δv(x,y) can be derived by equations (8) and (9) as follows:

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[0126] To maintain accuracy, the center of the subblock (x SB ,y SB ) is ((W SB -1) / 2, (H SB -1) / 2), where W SB and H SB are the width and height of the sub-block, respectively.

[0127] Once Δv(x,y) is obtained, the parameters of the affine model can be obtained. For example, in the case of a four-parameter affine model, the parameters of the affine model can be shown in Equation (10).

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[0128] Step (4): Finally, the luma prediction improvement ΔI(i,j) may be added to the sub-block prediction I(i,j). The final prediction I′ may be generated as shown in equation (12). I'(i,j)=I(i,j)+ΔI(i,j) Equation (12)

[0129] PROF may not be applied for an affine coded CU in two cases: (1) when all control points MV are the same, indicating that the CU has only translational motion, and (2) when the affine motion parameters are larger than a specified limit because sub-block-based affine MC has been dropped to CU-based MC to avoid large memory access bandwidth requirements.

[0130] Sub-block-based temporal motion vector prediction (SbTMVP) may be supported in related coding standards such as VVC. Similar to TMVP in HEVC, SbTMVP may use motion fields in co-located pictures of the current picture to improve the motion vector prediction (e.g., merge mode) of CUs in the current picture. Co-located pictures used by TMVP may also be used for SbTMVP. SbTMVP may differ from TMVP in the following aspects: (1) TMVP predicts behavior at the CU level, while SbTMVP predicts behavior at the sub-CU level. (2) TMVP fetches a temporal motion vector from a co-located block in a co-located picture (e.g., the co-located block can be a bottom-right block or a center block with respect to the current CU). SbTMVP applies a motion shift before fetching temporal motion information from the co-located picture, and the motion shift can be obtained from a motion vector from one of the spatial neighboring blocks of the current CU.

[0131] An exemplary spatial neighborhood block applied to SbTMVP can be shown in FIG. 19. As shown in FIG. 19, SbTMVP can predict the motion vector of a sub-CU (not shown) in a current CU (1902) in two steps. In the first step, the spatial neighborhood A1 (1904) in FIG. 19 can be examined. If A1 (1904) has a motion vector that uses a collocated picture of the current picture as a reference picture, the motion vector of A1 (1904) can be selected as the motion shift (or displacement vector) of SbTMVP to find the corresponding sub-block in the collocated picture for each sub-block of the current CU. If no such motion vector is identified, the motion shift can be set to (0,0).

[0132] In the second step, the motion shift identified in the first step may be applied (e.g., added to the coordinates of the current CU) to obtain sub-CU level motion information (e.g., sub-CU level motion vector and reference index) from the collocated picture. As shown in FIG. 20, a current CU (2004) may be included in a current picture (2002). The current CU (2004) may include multiple sub-CUs (or sub-blocks), such as a sub-CU (2006). A neighboring block A1 (2008) may be located on the lower left side of the current CU (2004). In the example of FIG. 20, a motion shift (or DV) (2010) may be set as the motion vector of the neighboring block A1 (2008). According to the DV (2010), a reference block A1' (2018) of the neighboring block A1 (2008) may be determined. A reference block (2014) adjacent to the reference block A1' (2018) can be determined as a reference block of the current block (2004). For each sub-CU (e.g., (2006)) in the current block (2004), the motion information of the corresponding block (or corresponding sub-CU) (e.g., (2016)) in the reference block (2014) in the collocated picture (2012) of the current picture (1702) can be used to derive the motion information of the respective sub-CU. Each sub-block (e.g., (2016)) in the reference block (2014) can be the smallest motion grid covering the central sample of the sub-block. After the motion information of the collocated sub-CU (e.g., (2016)) is identified, the motion information can be converted to the motion vector and reference index of the current sub-CU (e.g., (2006)). The motion information can be converted into a motion vector and reference index for the current sub-CU in a manner similar to the TMVP process of HEVC, and temporal motion scaling can be applied to align the temporal motion vector of the reference picture to the temporal motion vector of the current CU.

[0133] In BCW, a bi-predictive signal such as HEVC can be generated by averaging two prediction signals obtained from two different reference pictures and / or using two different motion vectors. In VVC, the bi-predictive mode can be extended beyond simple averaging to allow weighted averaging of two prediction signals. In one example, the weighted averaging of two prediction signals can be shown in Equation (13). P bi-pred =((8-w)*P 0 +w*P 1 +4)>>3 Formula (13) where w can be a weight and P 0 can be the first predictor, P 1 can be the second predictor. In weighted average bi-prediction, several weights, such as five weights, may be allowed, e.g., w∈{-2,3,4,5,10}. For each bi-predictive CU, the weight w can be determined in one of two ways: (1) for non-merged CUs, the weight index can be signaled after the motion vector differential, or (2) for merged CUs, the weight index can be inferred from neighboring blocks based on the merge candidate index. In one example, the BCW is applied only to CUs with 256 or more luma samples (e.g., CU width × CU height is 256 or more). For low-latency pictures, all five weights can be used. For non-low-latency pictures, a smaller number of weights, such as only three weights (e.g., w∈{3,4,5}), can be used.

[0134] In the encoder, a fast search algorithm can be applied to find the weight index without significantly increasing the encoder complexity. An exemplary fast search algorithm can be summarized as follows: (1) When combined with AMVR, unequal weights may only be conditionally checked for 1-pel and 4-pel motion vector precision if the current picture is a low-latency picture. (2) When combined with affine, affine ME is performed for unequal weights only if the affine mode is selected as the current best mode. (3) When two reference pictures in bi-prediction are the same, unequal weights can only be checked conditionally. (4) Depending on the POC distance between the current picture and the reference picture of the current picture, the coding quantization parameter (QP), and the temporal level, unequal weights may not be explored when certain conditions are met.

[0135] The BCW weight index may be coded using one context-coded bin followed by a bypass-coded bin. The first context-coded bin may indicate whether equal weights are used. If unequal weights are used, an additional bin may be signaled using bypass coding to indicate which unequal weights are used.

[0136] Weighted prediction (WP) may be processed at the picture level and may be a coding tool supported by video standards such as H.264 / AVC and HEVC standards to efficiently code video content with fading. Support for WP may also be added to the VVC standard. WP may allow weighting parameters (e.g., weights and offsets) to be signaled for each reference picture in each of the reference picture lists L0 and L1. In that case, the weight(s) and offset(s) of the corresponding reference picture(s) may be applied during motion compensation. WP and BCW may be designed for different types of video content. To avoid interactions between WP and BCW that may complicate VVC decoder design, when a CU uses WP, the BCW weight index may not be signaled and w may be inferred to be 4 (e.g., equal weights are applied). For merge CU, the weight index may be inferred from neighboring blocks based on merge candidate indexes. The merge CU may be obtained based on one of a normal merge mode and an inheritance affine merge mode. For the configured affine merge mode, the affine motion information can be configured based on up to three blocks of motion information. The BCW index of a CU that uses the configured affine merge mode can simply be set equal to the BCW index of the first control point MV.

[0137] In some examples, CIIP and BCW may not be jointly applied to a CU, such as in VVC. If a CU is coded in CIIP mode, the BCW index of the current CU may be set to 2, for example, equal weights.

[0138] Bidirectional Optical Flow (BDOF) in VVC was previously called BIO in JEM. Compared to the JEM version, BDOF in VVC can be a simpler version that requires fewer computations, especially in terms of the number of multiplications and the size of the multipliers.

[0139] BDOF may be used to improve the accuracy of a bi-predictive signal of a CU at a 4×4 sub-block level. BDOF may be applied to a CU if the CU satisfies the following conditions: (1) The CU is coded using a “true” bi-prediction mode, i.e., one of the two reference pictures is before the current picture in display order, and the other is after the current picture in display order; (2) The distances (e.g., POC differences) from the two reference pictures to the current picture are the same; (3) both reference pictures are short-term reference pictures; (4) the CU is not coded using affine mode or SbTMVP merge mode; (5) The CU has more than 64 luma samples. (6) Both the CU height and the CU width are equal to or greater than 8 luma samples; (7) The BCW weight index indicates equal weights; (8) Weight position (WP) is not enabled for the current CU; (9) CIIP mode is not used for the current CU.

[0140] BDOF may be applied only to the luma component. As the name BDOF suggests, the BDOF mode may be based on the optical flow concept, which assumes that the object motion is smooth. For each 4×4 sub-block, the motion refinement (v x ,v y) can be calculated by minimizing the difference between the L0 predicted samples and the L1 predicted samples. Then, the motion refinement can be used to adjust the bi-predictive sample values ​​in the 4×4 sub-block. BDOF can include steps such as:

[0141] First, the horizontal and vertical gradients of the two predicted signals from reference list L0 and reference list L1

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[0142] Next, the gradient S 1 , S 2 , S 3 , S 5 , and S 6 The autocorrelation and cross-correlation of can be calculated according to equations (16) to (20) as follows: S 1 =Σ (i,j)∈Ω Abs(ψ x (i,j)) Equation (16) S 2 =Σ (i,j)∈Ω ψ x(i,j) Sign(ψ y (i,j)) Equation (17) S 3 =Σ (i,j)∈Ω θ(i,j)·Sign(ψ x (i,j)) Equation (18) S 5 =Σ (i,j)∈Ω Abs(ψ y (i,j)) Equation (19) S 6 =Σ (i,j)∈Ω θ(i,j)·Sign(ψ y (i,j)) Equation (20) In the formula, ψ x (i,j), ψ y (i,j) and θ(i,j) can be provided by equations (21) to (23), respectively.

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[0143] Next, the motion accuracy improvement (v x ,v x ) can be derived using the cross-correlation and auto-correlation terms using equations (24) and (25) below.

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[0144] Finally, the BDOF samples of the CU can be calculated by adjusting the bi-predictive samples in equation (27) as follows: pred BDOF (x,y)=(I (0) (x,y)+I (1) (x,y)+b(x,y)+ο offset )>>shift) Equation (27) The values ​​can be selected such that the multipliers in the BDOF process do not exceed 15 bits and the maximum bit width of the intermediate parameters in the BDOF process can be kept within 32 bits.

[0145] To derive the gradient value, we select some predicted samples I in list k (k=0, 1) outside the current CU boundary. (k)(i,j) needs to be generated. As illustrated in FIG. 21, BDOF in VVC can use an extended one row / column (2102) around the boundary (2106) of the CU (2104). To control the computational complexity of generating out-of-bounds predicted samples, predicted samples in the extended region (e.g., the unshaded region in FIG. 21) can be generated by directly taking reference samples of nearby integer positions without interpolation (e.g., using a floor() operation on the coordinates), and a normal 8-tap motion compensation interpolation filter can be used to generate predicted samples in the CU (e.g., the shaded region in FIG. 21). These extended sample values ​​can be used only in gradient calculation. In the remaining steps of the BDOF process, if samples and gradient values ​​outside the CU boundary are needed, those samples and gradient values ​​can be padded (e.g., repeated) from the nearest neighbors of those samples and gradient values.

[0146] If the width and / or height of a CU is greater than 16 luma samples, the CU may be divided into sub-blocks with width and / or height equal to 16 luma samples, and the sub-block boundaries may be treated as CU boundaries in the BDOF process. The maximum unit size of the BDOF process may be limited to 16×16. For each sub-block, the BDOF process may be skipped. If the sum of absolute differences (SAD) between the initial L0 predicted sample and the initial L1 predicted sample is less than a threshold, the BDOF process may not be applied to the sub-block. The threshold may be set equal to (8*W*K(H>>1), where W may indicate the width of the sub-block and H may indicate the height of the sub-block. To avoid further complexity of the SAD calculation, the SAD between the initial L0 predicted sample and the initial L1 predicted sample calculated in the DMVR process may be reused in the BBOF process.

[0147] If BCW is enabled for the current block, i.e., if the BCW weight index indicates unequal weights, bidirectional optical flow may be disabled. Similarly, if WP is enabled for the current block, i.e., if the luma weight flag (e.g., luma_weight_lx_flag) is 1 for either of the two reference pictures, BDOF may also be disabled. If the CU is coded in symmetric MVD mode or CIIP mode, BDOF may also be disabled.

[0148] To improve the accuracy of the MV in the merge mode, such as in VVC, a bilateral matching (BM) based decoder-side motion vector refinement can be applied. In bi-predictive operation, the refinement MV can be searched around the initial MV in the reference picture list L0 and the reference picture list L1. The BM method can calculate the distortion between two candidate blocks in the reference picture list L0 and the reference picture list L1.

[0149] Figure 22 shows an example schematic diagram of BM-based decoder-side motion vector refinement. As shown in Figure 22, a current picture (2202) may include a current block (2208). The current picture may include a reference picture list L0 (2204) and a reference picture list L1 (2206). The current block (2208) may include an initial reference block (2212) in the reference picture list L0 (2204) with an initial motion vector MV0 and an initial reference block (2214) in the reference picture list L1 (2206) with an initial motion vector MV1. A search process may be performed around an initial MV0 in the reference picture list L0 (2204) and an initial MV1 in the reference picture list L1 (2206). For example, a first candidate reference block (2210) may be identified in the reference picture list L0 (2204), and a first candidate reference block (2216) may be identified in the reference picture list L1 (2206). The SAD between the candidate reference blocks (e.g., (2210) and (2216)) based on each MV candidate (e.g., MV0' and MV1') around the initial MV (e.g., MV0 and MV1) may be calculated. The MV candidate with the lowest SAD may become the refinement MV and may be used to generate a bi-predictive signal for predicting the current block (2208).

[0150] The application of DMVR may be restricted and may only be applied to CUs that are mode and feature coded, such as in VVC, as follows: (1) CU-level merge mode with bi-predictive MVs, (2) one reference picture is in the past with respect to the current picture and another reference picture is in the future; (3) The distance (e.g., POC difference) from the two reference pictures to the current picture is the same; (4) both reference pictures are short-term reference pictures; (5) The CU has more than 64 luma samples. (6) Both the CU height and the CU width are equal to or greater than 8 luma samples; (7) The BCW weight index indicates equal weights; (8)WP is not enabled for the current block, (9) CIIP mode is not used for the current block.

[0151] The improved MVs derived by the DMVR process are used to generate inter-prediction samples and can be used in temporal motion vector prediction for future picture coding, while the original MVs are used in the deblocking process and can be used in spatial motion vector prediction for future CU coding.

[0152] In DVMR, the search points can surround the initial MV, and the MV offset can follow the MV difference mirroring rule. In other words, any point checked by DMVR, represented by a candidate MV pair (MV0, MV1), can follow the MV difference mirroring rule shown in Equation (28) and Equation (29). MV0'=MV0+MV_offset Equation (28) MV1'=MV1-MV_offset formula (29) where MV_offset may represent a refinement offset between the initial MV and the refinement MV in one of the reference pictures. The refinement search range may be two integer luma samples from the initial MV. The search may include an integer sample offset search stage and a fractional sample refinement stage.

[0153] For example, a full search of 25 points may be applied to the integer sample offset search. The SAD of the initial MV pair may be calculated first. If the SAD of the initial MV pair is less than a threshold, the integer sample stage of the DMVR may be terminated. Otherwise, the SAD of the remaining 24 points may be calculated and checked in a scan order, such as a raster scan order. The point with the smallest SAD may be selected as the output of the integer sample offset search stage. In order to reduce the uncertainty penalty of the DMVR accuracy improvement, the original MV in the DMVR process may have a priority to be selected. The SAD between the reference blocks referenced by the initial MV candidates may be reduced by ¼ of the SAD value.

[0154] The integer sample search may be followed by a fractional sample refinement. To reduce computational complexity, the fractional sample refinement may be derived by using a parametric error surface equation instead of an additional search with SAD comparison. The fractional sample refinement may be conditionally invoked based on the output of the integer sample search stage. If the integer sample search stage is terminated at the center with the smallest SAD in either the first iteration search or the second iteration search, the fractional sample refinement may be further applied.

[0155] In the parametric error surface based sub-pixel offset estimation, the central position cost and the costs at the four neighboring positions from the center can be used to fit a 2D parabolic error surface equation based on Equation (30). E(x,y)=A(xx min ) 2 +B(yy min ) 2 +C formula (30) In the formula, (x min ,y min ) may correspond to the decimal position with the smallest cost, and C may correspond to the smallest cost value. By solving equation (30) using the cost values ​​of the five search points, (x min ,ymin ) can be calculated in equations (31) and (32). x min =(E(-1,0)-E(1,0)) / (2(E(-1,0)+E(1,0)-2E(0,0))) Equation (31) y min =(E(0,-1)-E(0,1)) / (2((E(0,-1)+E(0,1)-2E(0,0))) Equation (32) x min and y min The value of x can be automatically constrained to be between -8 and 8 since all cost values ​​are positive and the minimum value is E(0,0). min and y min The value constraint of can accommodate half-pel (or pixel) offsets with 1 / 16-pel MV precision in VVC. min ,y min ) can be added to the integer distance refinement MV to obtain a subpixel accurate refinement delta MV.

[0156] In VVC and the like, bilinear interpolation and sample padding can be applied. The resolution of the MV can be, for example, 1 / 16 luma samples. The fractional position samples can be interpolated using an 8-tap interpolation filter. In DMVR, the search point can surround the MV of the initial fractional pel with integer sample offsets, and thus the fractional position samples need to be interpolated for the DMVR search process. To reduce the computational complexity, a bilinear interpolation filter can be used to generate fractional samples for the search process in DMVR. In another important effect, by using a bilinear filter with a search range of 2 samples, DVMR does not access more reference samples compared to the normal motion compensation process. After the precision-enhanced MV is obtained using the DMVR search process, a normal 8-tap interpolation filter can be applied to generate the final prediction. Due to the lack of access to more reference samples compared to the normal MC process, samples that may not be needed for the interpolation process based on the original MV but may be needed for the interpolation process based on the precision-enhanced MV can be padded from the available samples.

[0157] If the width and / or height of a CU is greater than 16 luma samples, the CU may be further divided into sub-blocks having widths and / or heights equal to 16 luma samples. The maximum unit size of the DMVR search process may be limited to 16×16.

[0158] GPM can be applied for inter prediction. Geometric partition mode can be signaled using a CU-level flag as a type of merge mode. Other merge modes can include normal merge mode, MMVD mode, CIIP mode, and sub-block merge mode. In one example, w×h=2 m ×2 n64 partitions can be supported by the geometric partition mode of a CU of size m, where m, n ∈ {3...6}, excluding 8x64 and 64x8.

[0159] When GPM is used, the CU can be divided into two parts by a geometrically arranged straight line (or dividing line). The position of the dividing line can be mathematically derived from the angle and offset parameters of a particular partition (e.g., one of 64 partitions). Figure 23 shows an example GPM division grouped by the same angle. As illustrated in Figure 23, the 64 supported GPM partitions can be provided in 24 groups (e.g., group (2302)). The partitions in each group can have the same angle index and different offset indexes in the range of {0...3}.

[0160] Each part of the geometric partition in a CU can be inter-predicted using the respective motion. Uni-prediction can be enabled for each partition (or each part) in a CU. Thus, each part of the geometric partition can have one motion vector and one reference index. As with traditional bi-prediction, uni-prediction motion constraints can be applied to ensure that only two motion-compensated predictions are required for each CU. The uni-prediction motion of each partition can be derived, for example, using the process described in Figure 24.

[0161] If a geometric partition mode is applied to the current CU, a geometric partition index and two merge indexes may be further signaled. The partition index may indicate the partition mode of the geometric partition, and each merge index may be associated with a respective partition. The maximum GPM candidate size may be explicitly signaled in the SPS to specify the syntax binarization of the GPM merge index. After each part (or partition) of the geometric partition is predicted, the sample values ​​along the geometric partition edge may be adjusted using a blending process with adaptive weights, such as the adaptive weights shown in Equations (37) to (39). The prediction signal of the current CU may further undergo a transformation process and a quantization process, similar to other prediction modes (e.g., inter prediction mode). Finally, the motion field of the current CU predicted using the geometric partition mode may be stored.

[0162] The uni-predictive candidate list can be directly derived from the merge candidate list constructed according to the extended merge prediction process. Let n be denoted as the index of the uni-predictive motion in the geometric uni-predictive candidate list. The LX motion vector of the nth extended merge candidate with X equal to the parity of n can be used as the nth uni-predictive motion vector of the geometric partition mode. The motion vector (or uni-predictive motion vector) can be marked with "x" in FIG. 24. As shown in FIG. 24, if the merge index n is even, such as 0, 2, 4, etc., the MV from the L0 reference list can be applied. If the merge index n is odd, such as 1, 3, etc., the MV from the L1 reference list can be applied. If the corresponding LX motion vector of the nth extended merge candidate does not exist, the L(1-X) motion vector of the same candidate can be used as the uni-predictive motion vector of the geometric partition mode. For example, when n=0, if the L0 motion vector is not available, the L1 motion vector can be applied to the 0th merge candidate.

[0163] After each portion of the geometric partition of the CU is predicted using the corresponding motion, blending can be applied to the two predicted signals to derive samples around the geometric partition edge. The blending weights for each position of the CU can be derived based on the distance between the respective position and the partition edge.

[0164] The distance from the position (x, y) to the partition edge can be derived in equations (33) to (36) as follows: d(x,y)=(2x+1-w)cos(φ i )+(2y+1-h)sin(φ i )-ρ j Formula (33) ρ j =ρ x,j cos(φ i )+ρ y,j sin(φ i ) Formula (34)

number

number

number

[0165] A first MV (or MV1) from a first part of the geometric partition, a second MV (or MV2) from a second part of the geometric partition, and a combined MV of MV1 and MV2 can be stored in a motion field of a CU coded in geometric partition mode.

[0166] The stored motion vector type (or sType) for each position in the motion field can be determined in equation (40) as follows: sType=abs(motionIdx)<32?2:(motionIdx≦0?(1-partIdx):partIdx) Formula (40) where motionIdx may be equal to d(4x+2,4y+2). The part index partIdx may depend on the angle index i.

[0167] If sType is equal to 0 or 1, then MV1 or MV2 can be stored in the corresponding motion field, otherwise if sType is equal to 2, then a combined MV from MV1 and MV2 can be stored. The combined MV can be generated using a process as follows: 1) If MV1 and MV2 are from different reference picture lists (eg, one from L0 and the other from L1), then MV1 and MV2 are simply combined to form a bi-predictive motion vector. 2) Otherwise, if MV1 and MV2 are from the same list, then only uni-predictive motion MV2 is stored.

[0168] In related video coding standards such as HEVC and AVC / H.264, a fixed motion vector resolution of quarter luma samples may be applied. However, to achieve overall rate-distortion optimality, an optimal trade-off between displacement vector rate and prediction error rate must be selected. The motion vector resolution may be selected at the coding block level, such as in VVC, to trade-off bit rate vs. fidelity (or accuracy) for signaling motion parameters. For example, the motion vector resolution may be selected by the AMVR mode. The AMVR mode may be signaled at the coding block level, for example, if at least one component of the MVD is not equal to 0. The motion vector predictor may be rounded to a given resolution such that the resulting motion vector may be guaranteed to fall into a grid of the given resolution. For each given resolution, a corresponding AmvrShift value may be defined in Table 1. The resolution of the motion vector differential (or MVD) may be specified with a left shift operation of only the AmvrShift value, which may be shown in FIG. 26. A given motion vector differential is represented as MvdL0 and MvdL1 in AMVP mode, and MvdCpL0 and MvdCpL1 in affine AMVP mode, and can be modified when AMVR mode is enabled.

[0169] [Table 1]

[0170] Related coding standards such as VVC allow motion vectors pointing outside the frame boundary for both uni-prediction and bi-prediction. However, if at least one MV crosses the frame boundary, a good inter-predictor may not be obtained for bi-prediction.

[0171] In this disclosure, an MV constraint for inter bi-prediction may be applied. The MV constraint may be applied at a sub-block level in one example. The sub-block-based bi-prediction constraint generally refers to a prediction constraint in a bi-prediction mode applicable at a sub-block level. Whether a sub-block of a current block is predicted by one of a uni-prediction mode and a bi-prediction mode may be determined based on the sub-block-based bi-prediction constraint. The bi-prediction mode may indicate that a sub-block of a current block is predicted based on a first reference sub-block in a first reference picture and a second sub-block in a second reference picture. The uni-prediction mode may indicate that a sub-block of a current block is predicted based on one of a first reference sub-block and a second reference sub-block. According to the subblock-based bi-prediction constraint, in one embodiment, when the boundary of the first reference subblock of the subblock in the first reference picture is located beyond the boundary of the first reference picture and the boundary of the second reference subblock of the subblock in the second reference picture is located within the boundary of the second reference picture, the subblock of the current block can be reconstructed based on the uni-prediction mode such that the subblock is reconstructed based on the second reference subblock of the second reference picture. In one embodiment, when the boundary of the first reference subblock of the subblock in the first reference picture is located beyond the boundary of the first reference picture and the boundary of the second reference subblock of the subblock in the second reference picture is located beyond the boundary of the second reference picture, the subblock of the current block can still be reconstructed based on the bi-prediction mode such that the subblock is reconstructed based on the first reference subblock of the first reference picture and the second reference subblock of the second reference picture.

[0172] In one embodiment, a subblock-based bi-prediction constraint can be applied for inter bi-prediction, such as at the subblock level. In one embodiment, the subblocks can have a predefined subblock size N×N. In one example, the subblock size can be 8×8 luma samples. In one example, the subblock size can be 4×4 luma samples.

[0173] In one embodiment, for each N×N subblock in a coding block with inter bi-predictive MVs, if one MV of the reference list points outside the boundary of the reference picture by more than a threshold of M pixels (or if a reference block of a reference picture pointed to by the MV exceeds the boundary of the reference picture by a threshold of M pixels), the subblock may be changed to uni-predictive mode using only MVs in the reference list that do not point beyond the out-of-bounds threshold on the corresponding reference picture (or using only another reference block of another reference picture pointed to by another MV that does not exceed the boundary of another reference picture by a threshold of M pixels). For example, if a first motion vector of an inter bi-predictive MV in a first reference list points outside the boundary of the first reference picture by more than a threshold of M pixels and a second motion vector of an inter bi-predictive MV in a second reference list points within the boundary of the second reference picture or outside the boundary of the second reference picture by less than a threshold of M pixels, the subblock may be changed to uni-predictive mode. Thus, the second MV of the inter bi-predictive MV on the second reference picture of the second reference list can be applied for the uni-predictive mode.

[0174] For example, as indicated in FIG. 27, a shaded reference sub-block (e.g., (2714)) in a reference block (2704) indicated by MV0 may be located beyond the boundary (2712) of a reference picture (2702) from reference list L0 by a threshold M, and a reference sub-block (e.g., (2716)) in a reference block (2710) indicated by MV1 may be located within a reference picture (2710) from reference list L1. Thus, a shaded sub-block (e.g., (2718)) in a current block (2706) corresponding to a shaded reference sub-block in a reference block (2704) may use uni-prediction with MV1 for motion compensation. Thus, a shaded sub-block (e.g., (2718)) in a current block (2706) may be predicted based on a corresponding sub-block (e.g., (2716)) in a reference picture (2710). Other subblocks, such as non-shaded subblocks (e.g., (2720)) of the current block (2706) can still use bi-prediction with both MV0 and MV1 on reference lists L0 and L1, respectively. For example, subblock (2720) can be predicted based on subblock (2722) in reference block (2704) and subblock (2724) in reference block (2710).

[0175] In one example, the threshold M may be equal to 0. In this case, a motion vector (e.g., MV0) that points to any location outside the boundary of a reference picture (e.g., (2704)) (or the reference block pointed to by the motion vector is beyond any location outside the boundary of the reference picture) may be considered to be outside the boundary of the reference picture and needs to be constrained. For example, as shown in Figure 27, if the boundary (2726) of a sub-block (2714) is beyond the boundary (2712) of the reference picture (2702), then the sub-block (2714) may be constrained and the sub-block (2718) may be predicted based on the sub-block (2716).

[0176] In one example, the threshold M can be equal to 0.5 (or 0.5 luma samples). In this case, a motion vector that points to any position outside the boundary of the reference picture by more than 0.5 luma samples (or a reference block pointed to by the motion vector is beyond any position outside the boundary of the reference picture by more than 0.5 luma samples) can be considered to be outside the boundary of the reference picture and needs to be constrained. For example, as shown in Figure 27, if the boundary (2726) of the sub-block (2714) is beyond the boundary (2712) of the reference picture (2702) by more than 0.5 luma samples, the sub-block (2714) can be constrained and the sub-block (2718) can be predicted based on the sub-block (2716).

[0177] In one embodiment, for an N×N sub-block in a coding block with inter bi-predictive MV, if the inter bi-predictive motion vectors in both reference lists point to a reference block beyond the boundary of the respective reference picture by a threshold of M pixels, the sub-block may be unconstrained and still use normal bi-predictive mode. For example, as shown in Figure 27, if the sub-block (2716) is also located beyond the boundary of the reference picture (2710), the sub-block (2718) may still use normal bi-predictive mode and be predicted based on the reference sub-block (2714) and the reference sub-block (2716).

[0178] Sub-block-based bi-prediction constraints may be applied to coding blocks associated with one or more particular prediction modes. In one embodiment, sub-block-based bi-prediction constraints may be applied to coding blocks having an inter-prediction mode, such as an affine inter-prediction mode.

[0179] In one example, when a sub-block-based bi-prediction constraint is applied to a coding block having an affine mode, the sub-block size used for the bi-prediction constraint may be the same as the affine sub-block size, such as 4x4 luma samples in VVC, regardless of the predefined sub-block size of NxN.

[0180] In one embodiment, a sub-block based bi-prediction constraint may be applied for coding blocks having a temporal motion vector prediction mode such as SbTMVP mode.

[0181] In one example, when a sub-block-based bi-prediction constraint is applied to a coding block having SbTMVP mode, the sub-block size used for the bi-prediction constraint can be the same as the SbTMVP sub-block size, such as 8x8 luma samples in VVC, regardless of the predefined sub-block size of NxN.

[0182] In one embodiment, a sub-block-based bi-predictive constraint may be applied to a bi-predictive blending area of ​​GPM or triangulation mode (TPM). When the constraint is applied, whether a blending process is applied to the GPM / TPM bi-predictive blending area may be determined based on the constraint. The blending area may include samples centered on the partition boundaries of two partitions of GPM or TPM.

[0183] In one example, when a sub-block based bi-prediction constraint is applied to a coding block having a GPM mode, the sub-block size used for the bi-prediction constraint may be the same as the GPM sub-block size, such as 4x4 luma samples in VVC, regardless of the predefined sub-block size of NxN.

[0184] If a sub-block in the GPM is constrained, bi-predictive blending may not be applied for the sub-block and only uni-prediction with non-out-of-bounds reference sample positions can be used as prediction for the sub-block.

[0185] In one embodiment, if a subblock is subject to a subblock-based bi-predictive constraint and is changed to uni-predictive mode, uni-predictive motion information for the uni-predictive mode may be stored for that subblock.

[0186] In one example, uni-predictive motion estimation may be stored for each 4x4 sub-block of a bi-predictive coding unit when at least one pixel in the 4x4 sub-block is constrained to a uni-predictive mode.

[0187] In one embodiment, if a sub-block is subject to a bi-prediction constraint and is changed to uni-prediction mode, one or more bi-prediction related coding tools may be disabled for that sub-block.

[0188] In one example, DMVR may be disabled for constrained sub-blocks, which means that only the original (or initial) MV (e.g., MV1 that does not cross reference picture boundaries) of the DMVR on a valid reference list (e.g., reference list L1) can be used as the uni-predictive MV for motion compensation. The original uni-predictive MV can also be used for MV storage of the sub-block. Thus, DMVR may not be performed, and the original MV of the DMVR that does not cross reference picture boundaries can be applied to predict the sub-blocks of the current block.

[0189] In one example, DMVR can be disabled for constrained sub-blocks, which means that only the original MVs of the DMVRs on the valid reference list can be used as uni-predictive MVs for motion compensation. However, in one example, the bi-predictive MVs obtained based on the DMVR can be used for MV storage of the sub-blocks. Thus, the sub-blocks of the current block can be predicted based on one of the original MVs that does not cross the boundary of the reference picture. DMVR can be further performed to generate two final MVs by improving the accuracy of the original MV. The final MVs can be stored for the sub-blocks.

[0190] In one example, the BDOF tool can be disabled for a constrained sub-block, and only the original MV for the BDOF process on the valid reference list (e.g., MV1 that does not cross the reference picture boundary) can be used as the uni-predictive MV for motion compensation of the sub-block.

[0191] In one example, the BCW tool may be disabled for constrained sub-blocks that are changed from bi-predictive to uni-predictive.

[0192] In one example, when weighted bi-prediction is applied, the constrained sub-blocks may only use weighted uni-prediction obtained from a valid reference picture (e.g., (2708)). For example, as shown in Figure 27, sub-block (2718) may only use weighted uni-prediction based on sub-block (2716).

[0193] In one embodiment, the sub-block-based bi-prediction constraint may only be applied for non-merged inter-prediction modes, such as AMVP and affine modes.

[0194] In one embodiment, the sub-block-based bi-prediction constraint may be applied to either merged or non-merged inter-prediction modes.

[0195] In one embodiment, signaling information, such as an on / off flag, may be signaled in the bitstream to indicate whether a sub-block-based bi-prediction constraint is applied or not. The flag, i.e., the signaling information, may be signaled at a level higher than the coding block level, such as at the sequence level, picture level, slice level, tile level, tile group level, etc.

[0196] FIG. 28 shows a flow chart illustrating an example decoding process (2800) according to some embodiments of the present disclosure. FIG. 29 shows a flow chart illustrating an example encoding process (2900) according to some embodiments of the present disclosure. The proposed processes may be used separately or combined in any order. Furthermore, each of the processes (or embodiments), the encoder, and the decoder may be implemented by processing circuitry (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium.

[0197] The operations of the processes (e.g., (2800) and (2900)) may be combined or arranged in any quantity or order as desired. In embodiments, two or more of the operations of the processes (e.g., (2800) and (2900)) may be performed in parallel.

[0198] The processes (e.g., (2800) and (2900)) can be used in the reconstruction and / or encoding of a block to generate a prediction block for the block being reconstructed. In various embodiments, the processes (e.g., (2800) and (2900)) are performed by processing circuitry, such as the processing circuitry of terminal devices (310), (320), (330), and (340), processing circuitry performing the functions of a video encoder (403), processing circuitry performing the functions of a video decoder (410), processing circuitry performing the functions of a video decoder (510), processing circuitry performing the functions of a video encoder (603), etc. In some embodiments, the processes (e.g., (2800) and (2900)) are implemented with software instructions, such that the processing circuitry performs the processes (e.g., (2800) and (2900)) when the processing circuitry executes the software instructions.

[0199] As shown in Figure 28, the process (2800) may start at (S2801) and proceed to (S2810), where coded information for a number of sub-blocks of a current block in a current picture is received from a coded video bitstream.

[0200] At (S2820), a syntax element indicating a prediction mode associated with a current block in a current picture is obtained from a coded video bitstream, the prediction mode being one of a uni-prediction mode and a bi-prediction mode.

[0201] At (S2830), it is determined that a bi-prediction mode is applied to a first sub-block of the multiple sub-blocks, and the first sub-block is predicted based on a first reference sub-block in the first reference picture and a second reference sub-block in the second reference picture.

[0202] At (S2840), in response to a bi-predictive mode being applied to a first sub-block of the plurality of sub-blocks, it is determined whether (i) a boundary of the first reference sub-block is located beyond a boundary of the first reference picture, and (ii) a boundary of the second reference sub-block is located within a boundary of the second reference picture.

[0203] At (S2850), in response to (i) a boundary of the first reference subblock being located across a boundary of the first reference picture and (ii) a boundary of the second reference subblock being located within a boundary of the second reference picture, a first subblock of the current block is reconstructed based on a uni-prediction mode such that the first subblock is reconstructed based on a second reference subblock of the second reference picture.

[0204] The bi-prediction mode to be applied to the first sub-block is determined based on one of: (i) signaling information included in the coded information; (ii) a non-merge inter-prediction mode applied to the current block; and (iii) a merge mode applied to the current block.

[0205] In one embodiment, it is determined whether the boundary of the first reference sub-block is located beyond the boundary of the first reference picture by a threshold amount.

[0206] The size of the first sub-block is one of 4x4 luma samples and 8x8 luma samples based on the inter prediction mode applied to the current block.

[0207] In response to a boundary of the first reference sub-block crossing a boundary of the first reference picture and a boundary of the second reference sub-block crossing a boundary of the second reference picture, a first sub-block of the current block is reconstructed based on the first reference sub-block in the first reference picture and the second reference sub-block in the second reference picture.

[0208] The size of the first sub-block is equal to one of: (i) an affine sub-block size based on the affine inter prediction mode applied to the current block, (ii) an SbTMVP sub-block size based on the SbTMVP mode applied to the current block, and (iii) a GPM sub-block size based on the GPM mode applied to the current block.

[0209] In response to (i) the first sub-block being located within a blending area centered on a geometric partition boundary of the current block, and (ii) the boundary of the first reference sub-block crossing the boundary of the first reference picture, the first sub-block is reconstructed based on a second reference sub-block, the boundary of the second reference sub-block being located within the boundary of the second reference picture.

[0210] In response to the first sub-block being predicted by the uni-prediction mode, uni-prediction motion information for the uni-prediction mode is stored for the first sub-block.

[0211] In response to at least one pixel of the first sub-block being predicted by the uni-prediction mode, uni-prediction motion information of the uni-prediction mode is stored for the first sub-block.

[0212] In some embodiments, one of the DMVR mode, the BDOF mode, and the BCW mode is excluded for the first sub-block of the current block in response to at least one of a boundary of the first reference sub-block crossing a boundary of the first reference picture or a boundary of the second reference sub-block crossing a boundary of the second reference picture.

[0213] In some embodiments, DMVR is performed on the first subblock to determine a first predictive subblock based on a first reference subblock in a first reference picture and a second predictive subblock based on a second reference subblock in a second reference picture. Bi-predictive motion information is stored for the first subblock, indicating that the first subblock is predicted based on the first predictive subblock in the first reference picture and the second predictive subblock in the second reference picture.

[0214] After (S2840), the process proceeds to (S2899) and ends.

[0215] Process (2800) may be adapted as appropriate. Step(s) of process (2800) may be modified and / or omitted. Additional step(s) may be added. Any suitable order of performance may be used.

[0216] As shown in Figure 29, the process (2900) can start at (S2901) and proceed to (S2910). At (S2910), it is determined whether a sub-block-based bi-prediction constraint is applied to a first sub-block of a plurality of sub-blocks of a current block in a current picture. The sub-block-based bi-prediction constraint indicates whether the first sub-block is predicted by one of a uni-prediction mode and a bi-prediction mode.

[0217] At (S2920), in response to a subblock-based bi-prediction constraint being applied to a first subblock of the plurality of subblocks, it is determined whether one of (i) a boundary of a first reference subblock of the first subblock in the first reference picture is located across a boundary of the first reference picture, and (ii) a boundary of a second reference subblock of the first subblock in the second reference picture is located across a boundary of the second reference picture.

[0218] At (S2930), in response to (i) a boundary of a first reference sub-block of a first sub-block in a first reference picture crossing a boundary of the first reference picture, and (ii) a boundary of a second reference sub-block of a first sub-block in a second reference picture being located within a boundary of the second reference picture, a predicted sample of the first sub-block of the current block is generated based on a uni-prediction mode such that the first sub-block is reconstructed based on the second reference sub-block of the second reference picture.

[0219] The process then proceeds to (S2999) and ends.

[0220] The process (2900) may be adapted as appropriate. Step(s) of the process (2900) may be modified and / or omitted. Additional step(s) may be added. Any suitable order of performance may be used.

[0221] The techniques described above can be implemented as computer software using computer readable instructions and physically stored on one or more computer readable media. For example, Figure 30 illustrates a computer system (3000) suitable for implementing certain embodiments of the disclosed subject matter.

[0222] Computer software can be coded using any suitable machine code or computer language that can be subjected to mechanisms such as assembly, compilation, linking, etc. to produce code containing instructions that can be executed directly, or via interpretation, microcode execution, etc., by one or more computer central processing units (CPUs), graphics processing units (GPUs), etc.

[0223] The instructions may be executed on various types of computers or computer components including, for example, personal computers, tablet computers, servers, smartphones, gaming consoles, Internet of Things devices, and the like.

[0224] The components illustrated in Figure 30 for the computer system (3000) 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 relating to any one or combination of components illustrated in the exemplary embodiment of the computer system (3000).

[0225] The computer system (3000) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more human users, for example, via tactile input (keystrokes, swipes, data glove movements, etc.), audio input (voice, clapping, etc.), visual input (gestures, etc.), olfactory input (not shown). Human interface devices may also be used to capture certain media not necessarily directly associated with conscious human input, such as audio (voice, music, ambient sounds, etc.), images (scanned images, photographic images still images captured from a camera, etc.), and video (two-dimensional video, three-dimensional video including stereoscopic video, etc.).

[0226] The input human interface devices may include one or more (only one of each shown) of a keyboard (3001), a mouse (3002), a trackpad (3003), a touch screen (3010), a data glove (not shown), a joystick (3005), a microphone (3006), a scanner (3007), and a camera (3008).

[0227] The computer system (3000) 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, by 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 (3010), data gloves (not shown), or joystick (3005), although there may also be haptic feedback devices that do not function as input devices), audio output devices (speakers (3009), headphones (not shown), etc.), visual output devices (e.g., screens (3010), including CRT screens, LCD screens, plasma screens, OLED screens, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown), each with or without touch screen input capability, each with or without haptic feedback capability, some of which may be capable of outputting output in more than three dimensions by means of two-dimensional visual output or stereoscopic output, etc.), and printers (not shown).

[0228] The computer system (3000) may also include human accessible storage devices and their associated media, such as optical media, including CD / DVD ROM / RW (3020) with CD / DVD or similar media (3021), thumb drives (3022), removable hard drives or solid state drives (3023), legacy magnetic media such as tapes and floppy disks (not shown), and dedicated ROM / ASIC / PLD based devices such as security dongles (not shown).

[0229] Those skilled in the art will 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.

[0230] The computer system (3000) may also include an interface (3054) to one or more communication networks (3055). 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, cellular networks including WLAN, GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide area digital networks including cable, satellite and terrestrial television, vehicular and industrial including CANBus, etc. Certain networks generally require an external network interface adapter connected to a particular general purpose data port or peripheral bus (3049) (e.g., a USB port of the computer system (3000)), while other networks are generally integrated into the core of the computer system (3000) by connecting to a system bus (e.g., an Ethernet interface to a PC computer system, a cellular network interface to a smartphone computer system), as described below. Using any of these networks, the computer system (3000) can communicate with other entities. Such communications can be one-way receive only (e.g., television broadcast), one-way transmit only (e.g., CANbus to a particular CANbus device), or two-way to other computer systems using, for example, local or wide area digital networks. Specific protocols and protocol stacks can be used in each of these networks and network interfaces, as described above.

[0231] The aforementioned human interface devices, human accessible storage devices, and network interfaces may be attached to the core (3040) of the computer system (3000).

[0232] The cores (3040) may include one or more central processing units (CPUs) (3041), graphics processing units (GPUs) (3042), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (3043), hardware accelerators for specific tasks (3044), graphics adapters (3050), etc. These devices may be connected via a system bus (3048) along with read only memory (ROM) (3045), random access memory (3046), internal mass storage such as internal non-user accessible hard drives, SSDs, etc. (3047). In some computer systems, the system bus (3048) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripheral devices may be attached directly to the core's system bus (3048) or via a peripheral bus (3049). In one example, a screen (3010) may be connected to the graphics adapter (3050). Peripheral bus architectures include PCI, USB, and the like.

[0233] The CPU (3041), GPU (3042), FPGA (3043), and accelerator (3044) can combine to execute certain instructions that may constitute the aforementioned computer code. The computer code can be stored in ROM (3045) or RAM (3046). Persistent data can be stored, for example, in internal mass storage (3047), while temporary data can also be stored in RAM (3046). Rapid storage and retrieval in any of the memory devices can be made possible by the use of cache memory, which can be closely associated with one or more of the CPU (3041), GPU (3042), mass storage (3047), ROM (3045), RAM (3046), etc.

[0234] The computer-readable medium can bear computer code for performing various computer-implemented operations. The medium and computer code can be those specially designed and constructed for the purposes of the present disclosure, or they can be of the available kind well known to those skilled in the computer software arts.

[0235] By way of example and not limitation, the computer system (3000) having the architecture, and in particular the core (3040), may provide functionality as a result of a processor (or processors) (including CPUs, GPUs, FPGAs, accelerators, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media may be user-accessible mass storage as introduced above, as well as media associated with the particular storage of the core (3040) that is non-transitory in nature, such as mass storage (3047) internal to the core or ROM (3045). Software implementing various embodiments of the present disclosure may be stored in such devices and executed by the core (3040). The computer-readable media may include one or more memory devices or chips, depending on the particular need. The software can cause the core (3040), and in particular the processors therein (including CPUs, GPUs, FPGAs, etc.), to execute certain processes or certain portions of certain processes described herein, including defining data structures stored in RAM (3046) and modifying such data structures according to processes defined by the software. Additionally or alternatively, the computer system can provide functionality as a result of logic hardwired or otherwise embodied in circuitry (e.g., accelerators (3044)) that can operate to execute certain processes or certain portions of certain processes described herein in place of or in conjunction with software. References to software can encompass logic, and vice versa, where appropriate. References to computer-readable media can 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 appropriate combination of hardware and software.

[0236] 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 CU: coding unit

[0237] While this disclosure describes several exemplary embodiments, there exist modifications, substitutions, and various alternative equivalents, which 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 this disclosure and are therefore within the spirit and scope of this disclosure. [Explanation of symbols]

[0238] 101 sample, 102 arrow, 103 arrow, 104 square block, 110 schematic diagram, 201 current block, 300 communication system, 310 terminal device, 320 terminal device, 330 terminal device, 340 terminal device, 350 network, 400 communication system, 401 video source, 402 stream of video pictures, 403 video encoder, 404 encoded video data, 405 streaming server, 406 client subsystem, 407 copy of encoded video data, 408 client subsystem, 409 copy of encoded video data, 410 video decoder, 411 stream of video pictures, 412 display, 413 capture subsystem, 420 electronic device, 501 channel, 510 video decoder, 512 rendering device, 515 buffer memory, 520 parser, 521 symbol, 530 electronic device, 531 receiver, 551 scaler / inverse transform 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 source, 603 video encoder, 620 electronic device, 630 source coder, 632 coding engine, 633 decoder, 634 reference picture memory, 635 predictor, 640 transmitter, 643 coded video sequence, 645 entropy coder, 650 controller, 660 communication channel, 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 inter encoder, 810 video decoder, 871 entropy decoder, 872 Intra decoder, 873, residual decoder, 874, reconstruction module, 880, inter decoder, 901, current block, 902, neighboring block, 903, neighboring block, 904, neighboring block, 905, neighboring block, 906, neighboring block, 1102scaled motion vector of temporal merge candidate, 1104 collocated CU, 1106 reference picture of current picture, 1108 current picture, 1110 reference picture of collocated picture, 1112 collocated picture, 1302 block, 1304 block, 1400 current block, 1402 motion vector of central sample, 1404 subblock, 1602 CU, 1604 current block, 1702 current block, 1800 current block, 1802 subblock, 1804 sample, 1806 reference pixel, 1808 reference pixel, 1810 subblock, 1902 current CU, 1904 spatial neighborhood A1, 2002 current picture, 2004 current CU, 2006 subCU, 2008 neighborhood block A1, 2010 motion shift (or DV), 2012 collocated picture, 2014 Reference block, 2016 Corresponding block (or corresponding sub-CU), 2018 Reference block A1', 2102 Extended row / column, 2104 CU, 2106 CU boundary, 2202 Current picture, 2204 Reference picture list L0, 2206 Reference picture list L1, 2208 Current block, 2210 First candidate reference block, 2212 Initial reference block, 2214 Initial reference block, 2216 First candidate reference block, 2302 Group, 2500 CU, 2502 Geometric partition edge, 2504 First part, 2506 Second part, 2702 Reference picture from reference list L0, 2704 Reference block, 2706 Current block, 2708 Reference picture, 2710 Reference block, 2712 Boundary, 2714 Reference sub-block, 2716 Reference sub-block, 2718 Shaded sub-block, 2720 Unshaded sub-block, 2722 Sub-block, 2724 Sub-block, 2726 Boundary, 2800 Decoding process, 2900 Encoding process, 3000 Computer system, 3001 Keyboard, 3002 Mouse, 3003 Trackpad, 3005 Joystick, 3006 Microphone, 3007 Scanner, 3008 Camera, 3009 Speaker, 3010 Touch screen, 3020 CD / DVD ROM / RW, 3021CD / DVD or similar medium, 3022 thumb drive, 3023 removable hard drive or solid state drive, 3040 computer system core, 3041 central processing unit (CPU), 3042 graphics processing unit (GPU), 3043 field programmable gate area (FPGA), 3044 hardware accelerator, 3045 read only memory (ROM), 3046 random access memory, 3047 internal mass storage, 3048 system bus, 3049 peripheral bus, 3050 graphics adapter, 3054 interface, 3055 communication network

Claims

1. A method of decoding performed in a decoder, said method comprising the steps of: receiving coded information for a plurality of sub-blocks of a current block in a current picture from a coded video bitstream; obtaining from the coded video bitstream a syntax element indicating a prediction mode associated with the current block in the current picture, the prediction mode being one of a uni-prediction mode and a bi-prediction mode; determining that the bi-prediction mode is applied to a first sub-block of the plurality of sub-blocks, the first sub-block being predicted based on a first reference sub-block in a first reference picture and a second reference sub-block in a second reference picture; In response to the bi-predictive mode being applied to the first sub-block of the plurality of sub-blocks, determining whether (i) a boundary of the first reference sub-block lies beyond a boundary of the first reference picture, and (ii) a boundary of the second reference sub-block lies within a boundary of the second reference picture; and in response to (i) the boundary of the first reference sub-block being located beyond the boundary of the first reference picture, and (ii) the boundary of the second reference sub-block being located within the boundary of the second reference picture, reconstructing the first sub-block of the current block based on the uni-prediction mode such that the first sub-block is reconstructed based on the second reference sub-block of the second reference picture.

2. The step of determining that the bi-predictive mode is to be applied to the first sub-block further comprises:

2. The method of claim 1, further comprising: determining that the bi-prediction mode is to be applied to the first sub-block based on one of: (i) signaling information included in the coded information; (ii) a non-merged inter-prediction mode applied to the current block; and (iii) a merge mode applied to the current block.

3. The step of determining whether (i) the boundary of the first reference sub-block lies beyond the boundary of the first reference picture, and (ii) the boundary of the second reference sub-block lies within the boundary of the second reference picture, comprises: The method of claim 1 , comprising determining whether the boundary of the first reference sub-block is located beyond the boundary of the first reference picture by a threshold.

4. The method of claim 1 , wherein a size of the first sub-block is one of 4×4 luma samples and 8×8 luma samples based on an inter prediction mode applied to the current block.

5. in response to the boundary of the first reference sub-block crossing the boundary of the first reference picture and the boundary of the second reference sub-block crossing the boundary of the second reference picture, reconstructing the first sub-block of the current block based on the first reference sub-block in the first reference picture and the second reference sub-block in the second reference picture. The method of claim 1, further comprising:

6. The size of the first sub-block is an affine sub-block size based on an affine inter prediction mode applied to the current block; a sub-block size based on a sub-block-based temporal motion vector prediction (SbTMVP) mode applied to the current block; and The method of claim 1 , wherein the sub-block size is equal to one of a geometric partition mode (GPM) sub-block size based on a GPM mode applied to the current block.

7. (i) the first sub-block is located within a blending area centered on a geometric partition boundary of the current block, and (ii) in response to the boundary of the first reference sub-block exceeding the boundary of the first reference picture, reconstructing the first sub-block based on the second reference sub-block, the boundary of which is located within the boundary of the second reference picture. The method of claim 1, further comprising:

8. storing uni-predictive motion information of the uni-predictive mode for the first sub-block in response to the first sub-block being predicted by the uni-predictive mode. The method of claim 1, further comprising:

9. storing uni-predictive motion information of the uni-predictive mode for the first sub-block in response to at least one pixel of the first sub-block being predicted by the uni-predictive mode. The method of claim 1, further comprising:

10. in response to at least one of the boundary of the first reference sub-block exceeding the boundary of the first reference picture or the boundary of the second reference sub-block exceeding the boundary of the second reference picture, exclude one of a decoder-side motion vector refinement (DMVR) mode, a bi-directional optical flow (BDOF) mode, and a bi-prediction with coding unit level weights (BCW) mode for the first sub-block of the current block. The method of claim 1, further comprising:

11. performing a decoder-side motion vector refinement (DMVR) on the first sub-block to determine a first predicted sub-block based on the first reference sub-block in the first reference picture and a second predicted sub-block based on the second reference sub-block in the second reference picture; storing, for the first sub-block, bi-predictive motion information indicating that the first sub-block is predicted based on the first predictive sub-block in the first reference picture and the second predictive sub-block in the second reference picture; The method of claim 1, further comprising:

12. receiving coded information for a plurality of sub-blocks of a current block in a current picture from a coded video bitstream; obtaining from the coded video bitstream a syntax element indicating a prediction mode associated with the current block in the current picture, the prediction mode being one of a uni-prediction mode and a bi-prediction mode; determining that the bi-prediction mode is applied to a first sub-block of the plurality of sub-blocks, the first sub-block being predicted based on a first reference sub-block in a first reference picture and a second reference sub-block in a second reference picture; in response to the bi-predictive mode being applied to the first sub-block of the plurality of sub-blocks, determining whether (i) a boundary of the first reference sub-block lies beyond a boundary of the first reference picture, and (ii) a boundary of the second reference sub-block lies within a boundary of the second reference picture; and (ii) in response to the boundary of the first reference sub-block being located beyond the boundary of the first reference picture, and (iii) the boundary of the second reference sub-block being located within the boundary of the second reference picture, reconstructing the first sub-block of the current block based on the uni-prediction mode such that the first sub-block is reconstructed based on the second reference sub-block of the second reference picture. A processing circuit configured as follows:

13. An apparatus comprising:

13. The processing circuitry includes:

13. The apparatus of claim 12, further configured to determine which bi-prediction mode is applied to the first sub-block based on one of: (i) signaling information included in the coded information; (ii) a non-merged inter-prediction mode applied to the current block; and (iii) a merge mode applied to the current block.

14. The processing circuitry includes: The apparatus of claim 12 , configured to determine whether the boundary of the first reference sub-block is located beyond the boundary of the first reference picture by a threshold.

15. The apparatus of claim 12 , wherein a size of the first sub-block is one of 4×4 luma samples and 8×8 luma samples based on an inter prediction mode applied to the current block.

16. The processing circuitry includes:

13. The apparatus of claim 12, further comprising: in response to the boundary of the first reference subblock crossing the boundary of the first reference picture and the boundary of the second reference subblock crossing the boundary of the second reference picture, reconstructing the first subblock of the current block based on the first reference subblock in the first reference picture and the second reference subblock in the second reference picture.

17. The size of the first sub-block is an affine sub-block size based on an affine inter prediction mode applied to the current block; a sub-block size based on a sub-block-based temporal motion vector prediction (SbTMVP) mode applied to the current block; and The apparatus of claim 12 , wherein the sub-block size is equal to one of a geometric partition mode (GPM) sub-block size based on a GPM mode applied to the current block.

18. The processing circuitry includes:

13. The apparatus of claim 12, further comprising: in response to (i) the first sub-block being located within a blending area centered on a geometric partition boundary of the current block, and (ii) the boundary of the first reference sub-block exceeding the boundary of the first reference picture, configured to reconstruct the first sub-block based on the second reference sub-block, the boundary of which is located within the boundary of the second reference picture.

19. The processing circuitry includes:

13. The apparatus of claim 12, further configured to: store uni-predictive motion information of the uni-predictive mode for the first sub-block in response to the first sub-block being predicted by the uni-predictive mode.

20. The processing circuitry includes:

13. The apparatus of claim 12, further configured to: store uni-predictive motion information of the uni-predictive mode for the first sub-block in response to at least one pixel of the first sub-block being predicted by the uni-predictive mode.

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