Video decoding method and video encoding method

Abstract

Aspects of the present disclosure provide an apparatus and method including a processing circuit that determines, based on a syntax element in a coded video bitstream, that a current block in a current picture is coded in a sub-block-based frame rate up-conversion (FRUC) mode, and determines a corresponding block of the current block based on an offset vector indicating an offset between the current block and the corresponding block in the current picture. The processing circuit determines a temporal motion vector predictor (TMVP) of a first sub-block in the corresponding block based on a sub-block in a forward reference picture and a sub-block in a backward reference picture. The sub-blocks in the forward reference picture and the backward reference picture are adapted using the sub-block-based FRUC mode. The processing circuit determines a TMVP of a sub-block in the current block based on the TMVP of a first sub-block in the corresponding block.

Description

[Technical field]

[0001] This disclosure describes embodiments generally relating to video coding. [Background technology]

[0002] The background description provided herein is intended to generally present the context of the present disclosure. The work of the presently named inventors is not expressly or impliedly admitted as prior art to the present disclosure to the extent that that work is described in this Background section, and any aspects of the description that may not otherwise qualify as prior art at the time of filing.

[0003] An uncompressed digital image and / or video 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 (commonly known as frame rate) of, 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) at 8 bits per sample requires a bandwidth approaching 1.5 Gbit / s. One hour of such video requires over 600 Gbytes of storage space.

[0004] One objective of image and / or video encoding and decoding can be the reduction of redundancy in the input image and / or video signal through compression. Compression can help reduce the above bandwidth and / or storage space requirements, in some cases by more than one order of magnitude. The description herein uses video encoding / decoding as an example, but the same techniques can be applied in a similar manner to image encoding / decoding without departing from the spirit of this disclosure. Both lossless and lossy compression, as well as combinations thereof, can be used. Lossless compression refers to techniques where an exact copy of the original signal can be reconstructed from the compressed original signal. When using lossy compression, the reconstructed signal may not be the same as the original signal, but the distortion between the original signal and the reconstructed signal is small enough to make the reconstructed signal useful for the intended application. In the case of video, lossy compression is widely used. The amount of distortion that is tolerated depends on the application, for example, 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 a higher tolerable / acceptable distortion may result in a higher compression ratio.

[0005] Video encoders and decoders can utilize techniques from a number of broad categories, including, for example, motion compensation, transform processing, quantization, and entropy coding.

[0006] 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 an intra picture. Intra pictures and their derivatives, such as independent decoder refresh pictures, can be used to reset the decoder state and therefore can be used as the first picture of 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 needed for a given quantization step size to represent the block after entropy coding.

[0007] Conventional intra-coding, e.g., as 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, e.g., surrounding sample data and / or metadata obtained during the encoding / decoding of a block of data. Such techniques are hereinafter referred to as "intra-prediction" techniques. It should be noted that, at least in some cases, intra-prediction uses reference data only from the current picture being reconstructed, and not from a reference picture.

[0008] There may be many different forms of intra prediction. If more than one such technique is available for 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 some cases, an intra prediction mode may have sub-modes and / or parameters that may be coded independently or may be included in a mode codeword, which defines the prediction mode being used. Since which codeword to use for a given mode, sub-mode, and / or parameter combination may affect the coding efficiency gains through intra prediction, entropy coding techniques may be used to convert the codewords into a bitstream.

[0009] A specific mode of intra prediction was introduced by H.264, refined in H.265, and further refined in newer coding techniques such as Joint Exploration Model (JEM), Versatile Video Coding (VVC), and Benchmark Set (BMS). A predictor block may be formed using neighboring sample values ​​of already available samples. The sample values ​​of the neighboring samples are copied into the predictor block depending on the direction. The reference of the direction in use may be coded in the bitstream or may be predicted itself.

[0010] Referring to FIG. 1A, at the bottom right, a subset of 9 known predictor directions is represented from the 33 possible predictor directions defined in H.265 (corresponding to the 33 angle modes of the 35 intra modes). The point where the arrows converge (101) corresponds to the sample being predicted. The arrows correspond to the direction in which the sample is predicted. For example, the arrow (102) indicates that the sample (101) is predicted from one or more samples to the upper right and at an angle of 45 degrees from the horizontal. Similarly, the arrow (103) indicates that the sample (101) is predicted from one or more samples to the lower left of the sample (101) and at an angle of 22.5 degrees from the horizontal.

[0011] Still referring to FIG. 1A, at the top left is depicted a square block (104) of 4×4 samples (indicated by a thick dashed line). The square block (104) contains 16 samples, each labeled with "S", its position in the Y dimension (e.g., row index), and its position in the X dimension (e.g., column index). For example, sample S21 is the second sample (from the top) in the Y dimension and the first sample (from the left) in the X dimension. Similarly, sample S44 is the fourth sample in 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 adjacent to the block being reconstructed, and therefore negative values ​​do not need to be used.

[0012] Intra-picture prediction can work by copying reference sample values ​​from neighboring samples indicated by the signaled prediction direction. For example, suppose the coded video bitstream includes signaling for this block indicating a prediction direction consistent with arrow (102), i.e., the sample is predicted from one or more prediction samples in the upper right corner at an angle of 45 degrees from the horizontal. In that case, samples S41, S32, S23, and S14 are predicted from the same reference sample R05. Then, sample S44 is predicted from reference sample R08.

[0013] In some cases, values ​​of multiple reference samples may be combined, for example through interpolation, to calculate a reference sample, particularly when the orientation is not equally divisible by 45 degrees.

[0014] The number of possible directions has increased as video coding techniques have developed. In H.264 (2003), nine different directions could be represented. That 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 in entropy coding are used to represent those likely directions with a small number of bits, while accepting a slight penalty for less likely directions. Furthermore, the direction itself can sometimes be predicted from neighboring directions used in neighboring, already decoded blocks.

[0015] FIG. 1B shows a schematic diagram (110) representing 65 intra prediction directions according to JEM to illustrate the growing number of prediction directions over time.

[0016] The mapping of intra-prediction direction bits representing directions in the coded video bitstream may vary from one video coding technique to another. Such mappings can vary, for example, from simple direction mappings, to codewords, to complex adaptation schemes including 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. Since the goal of video compression is to reduce redundancy, these less likely directions will be represented by more bits than more likely directions in a video coding technique that works well.

[0017] Image and / or video encoding / 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 used for the prediction of a newly reconstructed picture or picture portion after blocks of sample data from a previously reconstructed picture or portion thereof (reference picture) are 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 indirectly be the temporal dimension).

[0018] In some video compression techniques, the MV applicable to a particular area of ​​sample data can be predicted from other MVs, e.g., from those that pertain to other areas of sample data that are spatially adjacent to the area being reconstructed and that precede it in decoding order. Doing so can significantly reduce the amount of data required to code the MV, thereby removing redundancy and increasing compression. For example, when coding an input video signal obtained from a camera (known as natural video), MV prediction can work because there is a statistical possibility that areas larger than the area to which a single MV is applicable move in a similar direction, and therefore, in some cases, can be predicted using similar motion vectors derived from MVs of neighboring areas. As a result, the MV determined for a given area is similar or the same as the MV predicted from the surrounding MVs, and after entropy coding, can be represented with fewer bits than would be used if coding the MV 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 can be lossy, e.g., due to rounding errors when calculating a predictor from several surrounding MVs.

[0019] Various MV prediction mechanisms are described in H.265 / HEVC (ITU-T Rec. H265, “High Efficiency Video Coding”, December 2016). Among the many MV prediction mechanisms proposed by H.265, a technique hereafter called “spatial merging” is described with reference to FIG.

[0020] Referring to Figure 2, a current block (201) has samples that are found 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, for example, from the most recent reference picture (in decoding order), using the MV associated with any one of the five surrounding samples denoted as A0, A1 and B0, B1, B2 (202 to 206, respectively). In H.265, MV prediction can use predictors from the same reference picture that neighboring blocks use. Summary of the Invention

[0021] Aspects of the disclosure provide a method and apparatus for video encoding / decoding. In some examples, the apparatus for video decoding includes a processing circuit. The processing circuit decodes prediction information of a current block in a current picture from a coded video bitstream. The prediction information indicates a sub-block-based Frame-Rate Up Conversion (FRUC) (also referred to as a sub-block-based FRUC mode). The processing circuit determines a corresponding block of the current block based on an offset vector. The offset vector indicates an offset between the current block and the corresponding block in the current picture. The processing circuit determines a Temporal Motion Vector Predictor (TMVP) of a first sub-block in the corresponding block based on a sub-block in a forward reference picture of the current picture and a sub-block in a backward reference picture of the current picture. The sub-block in the forward reference picture and the sub-block in the backward reference picture are matched using the sub-block-based FRUC. The processing circuit determines a TMVP of a sub-block in the current block based on a TMVP of a first sub-block in the corresponding block.

[0022] In an example, the processing circuit determines the TMVP of a sub-block in a current block as the TMVP of the first sub-block in the corresponding block.

[0023] In the example, the processing circuitry determines the motion vector (MV) of the TMVP of a sub-block in the current block as the vector sum of the offset vector and each MV of the TMVP of the first sub-block in the corresponding block.

[0024] In the example, the offset vector is zero.

[0025] In an example, the processing circuit receives an index in a coded video bitstream and determines an offset vector from a predefined offset vector list based on the index.

[0026] In an example, the offset vector is signaled in the coded video bitstream.

[0027] In an example, in response to the TMVP of a second sub-block in the corresponding block not being determined by the sub-block-based FRUC, the processing circuit determines the TMVP of the second sub-block based on the TMVP of the first sub-block in the corresponding block.

[0028] In an example, the processing circuit determines a TMVP of a first sub-block in a corresponding block based on a motion vector between a sub-block in a forward reference picture and a sub-block in a backward reference picture, the motion vector passing through one of a center position, an upper left position, an upper right position, a lower left position, or a lower right position in the first sub-block in the corresponding block.

[0029] In the example, the Picture Order Count (POC) of the forward reference picture is smaller than the POC of the current picture, and the POC of the backward reference picture is larger than the POC of the current picture.

[0030] In the example, the subblock merging candidate list includes a subblock-based Temporal Motion Vector Prediction (SbTMVP) candidate and a FRUC-based subblock merging candidate indicating the TMVP of each subblock in the current block. The processing circuitry reconstructs the current block based on the FRUC-based subblock merging candidate in response to the subblock merging index indicating the FRUC-based subblock merging candidate.

[0031] In the example, the subblock merging candidate list includes FRUC-based subblock merging candidates that indicate the TMVP of each subblock in the current block. The subblock merging candidate list does not include a subblock-based temporal motion vector prediction (SbTMVP) candidate. In response to the subblock merging index indicating the FRUC-based subblock merging candidate, the processing circuit reconstructs the current block based on the FRUC-based subblock merging candidate.

[0032] If a FRUC-based subblock merging candidate indicating the TMVP of each subblock in the current block is available, the subblock merging candidate list includes the FRUC-based subblock merging candidate and does not include a subblock-based temporal motion vector prediction (SbTMVP) candidate. If a FRUC-based subblock merging candidate is not available, the subblock merging candidate list includes the SbTMVP candidate.

[0033] In an example, the predefined subblock size is N×N luma samples. If the width W of the current block is less than N and the height H of the current block is greater than or equal to N, the processing circuitry partitions the current block into subblocks having a subblock width of W and a subblock height of N. If H is less than N and W is greater than or equal to N, the processing circuitry partitions the current block into subblocks having a subblock width of N and a subblock height of H.

[0034] In an embodiment, the processing circuit decodes prediction information of a current block in a current picture from a coded video bitstream. The prediction information indicates sub-block-based FRUC. The processing circuit determines an initial temporal motion vector prediction (TMVP) of a first sub-block in the current block based on a sub-block in a forward reference picture of the current picture and a sub-block in a backward reference picture of the current picture. The sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted based on the sub-block-based FRUC. The processing circuit determines a TMVP of a first sub-block in the current block based on an initial TMVP and a motion vector offset (MVO) of the first sub-block in the current block.

[0035] In an example, the processing circuit determines a motion vector (MV) of the TMVP of the first subblock in the current block as a vector sum of the MVO and each of the MVs of the TMVP of the first subblock in the current block.

[0036] In an example, the processing circuit receives an index in a coded video bitstream and determines an MVO from a predefined MVO list based on the index n i .

[0037] In an example, the MVO is signaled in the coded video bitstream.

[0038] In the example, in response to the initial TMVP of a second sub-block in the current block not being determined by the sub-block-based FRUC, the processing circuit determines the initial TMVP of the second sub-block based on the initial TMVP of the first sub-block in the current block.

[0039] In an example, the subblock merging candidate list includes a subblock-based temporal motion vector prediction (SbTMVP) candidate and a FRUC-based subblock merging candidate indicating the TMVP of each subblock in the current block. In response to the subblock merging index indicating the FRUC-based subblock merging candidate, the processing circuit reconstructs the current block using the FRUC-based subblock merging candidate.

[0040] In an example, the subblock merging candidate list includes FRUC-based subblock merging candidates that indicate the TMVP of each subblock in the current block. The subblock merging candidate list does not include a subblock-based temporal motion vector prediction (SbTMVP) candidate. In response to the subblock merging index indicating the FRUC-based subblock merging candidate, the processing circuit reconstructs the current block using the FRUC-based subblock merging candidate.

[0041] In an embodiment, a coded video bitstream including a current picture is received. The current picture includes a current block, the current block including a plurality of sub-blocks. It may be determined based on a syntax element in the coded video bitstream that the current block including the plurality of sub-blocks is coded in a sub-block-based FRUC mode.

[0042] Aspects of the present disclosure also provide a non-transitory computer-readable storage medium storing instructions that, when executed by a computer for video decoding, cause the computer to perform a method for video decoding.

[0043] 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]

[0044] [Figure 1A] FIG. 2 is a schematic diagram of an example subset of intra-prediction modes. [Figure 1B] FIG. 2 is an illustration of an exemplary intra-prediction direction. [Diagram 2] An example of a current block (201) and surrounding samples is shown. [Diagram 3] FIG. 3 is a schematic diagram of an example block diagram of a communication system (300). [Figure 4] FIG. 4 is a schematic diagram of an example block diagram of a communication system (400). [Diagram 5] FIG. 2 is a schematic diagram of an exemplary block diagram of a decoder. [Figure 6] FIG. 2 is a schematic diagram of an example block diagram of an encoder. [Figure 7] 1 shows a block diagram of an exemplary encoder. [Figure 8] 1 shows a block diagram of an exemplary decoder. [Figure 9] 1 illustrates locations of spatial merge candidates according to an embodiment of the present disclosure. [Figure 10] 1 illustrates candidate pairs considered for redundancy checking of spatial merge candidates according to an embodiment of the present disclosure. [Figure 11] 13 illustrates an example motion vector scaling for temporal merging candidates. [Figure 12] 13 illustrates example candidate positions for temporal merging candidates for a current coding unit. [Figure 13] 1 illustrates an exemplary sub-block-based temporal motion vector prediction (SbTMVP) process used in SbTMVP mode. [Figure 14] 1 illustrates an exemplary sub-block-based temporal motion vector prediction (SbTMVP) process used in SbTMVP mode. [Figure 15A] 1 illustrates an exemplary SbTMVP process used in SbTMVP mode. [Figure 15B] 1 illustrates an exemplary SbTMVP process used in SbTMVP mode. [Figure 16A] Two types of motion estimation (ME) examples are given, including unidirectional ME and bidirectional ME. [Figure 16B]An example of unidirectional motion vector (MV) estimation and bidirectional MV estimation is given. [Figure 16C] An example of unidirectional motion vector (MV) estimation and bidirectional MV estimation is given. [Figure 17A] 1 illustrates a frame rate up-conversion (FRUC) based sub-block temporal motion vector prediction (TMVP) mode. [Figure 17B] 1 illustrates a frame rate up-conversion (FRUC) based sub-block temporal motion vector prediction (TMVP) mode. [Figure 17C] 1 illustrates a frame rate up-conversion (FRUC) based sub-block temporal motion vector prediction (TMVP) mode. [Figure 18A] An example of FRUC-based sub-block TMVP mode is shown. [Figure 18B] An example of FRUC-based sub-block TMVP mode is shown. [Figure 19] An example of FRUC-based sub-block TMVP mode is shown. [Figure 20] 1 shows a flowchart illustrating an encoding process according to some embodiments of the present disclosure. [Figure 21] 1 shows a flowchart illustrating a decoding process according to some embodiments of the present disclosure. [Figure 22] 1 shows a flowchart illustrating an encoding process according to some embodiments of the present disclosure. [Figure 23] 1 shows a flowchart illustrating a decoding process according to some embodiments of the present disclosure. [Figure 24] FIG. 1 is a schematic diagram of a computer system according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0045] 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) that are interconnected via the network (350). In the example of FIG. 3, the first pair of terminal devices (310) and (320) perform a one-way 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 another terminal device (320) via the network (350). The encoded video data may be transmitted in the form of one or more coded video bitstreams. The terminal device (320) may receive the coded video data from the network (350), decode the coded video data to recover the video pictures, and display the video pictures according to the recovered video data. One-way data transmission may be common, such as in media serving applications.

[0046] In another example, the communication system (300) includes a second pair of terminal devices (330) and (340) performing bidirectional transmission of coded video data, e.g., during a video conference. For the bidirectional transmission of data, in the example, each of the terminal devices (330) and (340) may code video data (e.g., a stream of video pictures captured by that terminal device) for transmission to the other of the terminal devices (330) and (340) over the network (350). Each of the terminal devices (330) and (340) may also receive coded video data transmitted by the other of the terminal devices (330) and (340), decode the coded video data to recover the video pictures, and display the video pictures on an accessible display device in accordance with the recovered video data.

[0047] In the example of FIG. 3, terminal devices (310), (320), (330), and (340) are depicted as a server, a personal computer, and a smartphone, respectively, although the principles of the present disclosure need not be so limited. Embodiments of the present disclosure find use with laptop computers, tablet computers, media players, and / or dedicated video conferencing equipment. Network (350) represents any number of networks that convey coded video data between terminal devices (310), (320), (330), and (340), including, for example, wireline and / or wireless communication networks. Communication network (350) may exchange data in circuit-switched and / or packet-switched channels. Exemplary networks include telecommunications networks, local area networks, wide area networks, and / or the Internet. For purposes of this discussion, the architecture and topology of network (350) may be irrelevant to the operation of the present disclosure, unless otherwise described below.

[0048] 4 depicts a video encoder and video decoder in a streaming environment as an example application of the disclosed subject matter. The disclosed subject matter can be similarly applicable to other video-enabled applications including, for example, video conferencing, digital TV, streaming services, storage of compressed video on digital media including CDs, DVDs, memory sticks, etc.

[0049] The streaming system may include a capture subsystem (413) that may include, for example, a video source (401), e.g., a digital camera, that generates a stream of uncompressed video pictures (402). In an example, the stream of video pictures (402) includes samples captured by the digital camera. The stream of video pictures (402) is represented by a bold line to emphasize its high data volume compared to the encoded video data (404) (or coded video bitstream), which 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 coded video bitstream (404)), is represented by a thin line to emphasize its lower data volume compared to the stream of video pictures (402), which may be stored in 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 a video decoder (410), for example in an electronic device (430). The video decoder (410) decodes an incoming copy (407) of the encoded video data and generates an outgoing 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. An example of such a standard is ITU-T Recommendation H.265.In an example, the developing video coding standard is commonly known as Versatile Video Coding (VVC), and the disclosed subject matter may be used in conjunction with VVC.

[0050] It is noted that electronic devices 420 and 430 can include other components (not shown). For example, electronic device 420 can include a video decoder (not shown), and electronic device 430 can also include a video encoder (not shown).

[0051] 5 shows an example block diagram of a video decoder (510). The video decoder (510) may be included in an electronic device (530). The electronic device (530) may include a receiver (531) (e.g., a receiving circuit). The video decoder (510) may be used in place of the video decoder (410) in the example of FIG. 4.

[0052] The receiver (531) may receive one or more coded video sequences to be decoded by the video decoder (510). In an 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 coded video data. The receiver (531) may receive the coded video data together with other data, such as coded audio data and / or auxiliary data streams, which may be forwarded to their respective use entities (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 others, it can be external to the video decoder (510) (not shown). In still others, there can be a buffer memory (not shown) external to the video decoder (510), e.g., to combat network jitter, plus another buffer memory (515) within the video decoder (510), e.g., to manipulate playback timing. When the receiver (531) is receiving data from a storage / forwarding device of sufficient bandwidth and controllability, or from an isosynchronous network, the buffer memory (515) may not be needed or may be small. For use with best-effort packet networks such as the Internet, the buffer memory (515) may be needed, and can be relatively large and advantageously adaptively sized, and may be implemented at least in part in an operating system or similar element (not shown) external to the video decoder (510).

[0053] The video decoder (510) may include a parser (520) for reconstructing symbols (521) from the coded video sequence. These 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 render device (512) (e.g., a display screen), which is not an essential part of the electronic device (530) but may be coupled to the electronic device (530) as shown in FIG. 5. The control information for the rendering device may take the form of a Supplementary 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 follow a video coding technique or standard and may follow various principles including variable length coding, Huffman coding, context-dependent or non-context-dependent arithmetic coding, 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 a group of pictures (GOP), a picture, a tile, a slice, a macroblock, a coding unit (CU), a block, a transform unit (TU), a prediction unit (PU), etc. The parser (520) may also extract quantization parameter values, motion vectors, etc. from the coded video sequence information, such as transform coefficients.

[0054] The parser (520) may perform an entropy decoding / parsing operation on the video sequence received from the buffer memory (515) to generate symbols (521).

[0055] The reconstruction of symbols (521) can have a wide variety of units depending on the type of coded video picture or portion thereof (e.g., inter and intra pictures, inter and intra blocks) and other factors. Which units are included and how may be controlled by subgroup control information parsed by the parser (520) from the coded video sequence. The flow of such subgroup control information between the parser (520) and the following units is not shown for clarity.

[0056] Beyond the functional blocks already mentioned, the video decoder (510) may be conceptually subdivided into a number of functional units, which are described below. In an actual implementation operating under commercial constraints, many of these units may interact closely with each other and may be at least partially integrated with each other. However, for purposes of describing the disclosed subject matter, the following conceptual subdivision into functional units is adequate.

[0057] The first unit is a scalar / inverse transform unit (551), which receives the quantized transform coefficients as symbols (521) from the parser (520), along with control information including what to transform to use, block size, quantization factor, quantization scaling matrix, etc. The scalar / inverse transform unit (551) can output blocks containing sample values ​​that can be input to an aggregator (555).

[0058] In some cases, the output samples of the scaler / inverse transformer (551) may relate to intra-coded blocks, which 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 may 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, 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 transformer unit (551).

[0059] In other cases, the output samples of the scalar / inverse transform unit (551) may relate to an inter-coded and potentially motion-compensated block. In such cases, the motion compensated prediction unit (553) may access the reference picture memory (557) to fetch samples used for prediction. After motion compensating the fetched samples according to the symbols (521) related to the block, the samples may be added by the aggregator (555) to the output of the scalar / inverse transform unit (551) (in this case referred to as residual samples or residual signals) to generate output sample information. The addresses in the reference picture memory (557) from which the motion compensated prediction unit (553) fetches prediction samples may be controlled by motion vectors available to the motion compensated prediction unit (553), for example in the form of symbols (521), which may have X, Y, and reference picture components. Motion compensation can also include interpolation of sample values ​​fetched from the reference picture memory (557) when sub-sample accurate motion vectors are used, as well as motion vector prediction mechanisms.

[0060] 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 that are controlled by parameters included in the coded video sequence (also called the coded video bitstream) and made available to the loop filter unit (556) as symbols (521) from the parser (520). Video compression may also be responsive to meta-information obtained during the decoding of previous portions (in decoding order) of the coded picture or coded video sequence, and may also be responsive to previously constructed loop filtered sample values.

[0061] The output of the loop filter unit (556) can be a sample stream that can be output to a render device (512) and further stored in a reference picture memory (557) for use in future inter-picture prediction.

[0062] Once a particular coded picture is fully reconstructed, it may 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) may become part of the reference picture memory (557), and any unused current picture buffer may be reallocated before beginning reconstruction of a subsequent coded picture.

[0063] The video decoder (510) may perform decoding operations according to a given video compression technique in a standard such as ITU-T Recommendation H.265. The coded video sequence may conform to the syntax prescribed by the video compression technique or standard in use, in the sense that the coded video sequence conforms to both the syntax of the video compression technique or standard and a profile documented in the video compression technique or standard. In particular, a profile may select a particular tool from all tools available in the video compression technique or standard as the only tool available for use under that profile. Also, for compliance, the complexity of the coded video sequence is required to be within the bounds 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 / second), maximum reference picture size, etc. The limits set by the level may in some cases be further limited through a Hypothetical Reference Decoder (HRD) specification and metadata for HRD buffer management signaled in the coded video sequence.

[0064] In an embodiment, the receiver (531) may receive additional (redundant) data along with the encoded video. The additional data may also be included as part of the coded video sequence. The additional data may be used by the video decoder (510) to properly decode the data and / or to more accurately reconstruct the original video data. The additional data may take the form of, for example, temporal, spatial, or signal-to-noise ratio (SNR) enhancement layers, redundant slices, redundant pictures, forward error correction codes, etc.

[0065] 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 transmitting circuit). The video encoder (603) may be used in place of the video encoder (403) of the example of FIG.

[0066] The video encoder (603) may receive video samples from a video source (601) (which is not part of the electronic device (620) in the example of FIG. 6) that may capture video images to be coded by the video encoder (603). In other examples, the video source (601) is part of the electronic device (620).

[0067] 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 can be of any suitable bit depth (e.g., 8-bit, 10-bit, 12-bit, etc.), any color space (e.g., BT.601 YCrCB, RGB, etc.), and any suitable sampling structure (e.g., YCrCb 4:2:0, YCrCb 4:4:4). In a media serving system, the video source (601) may be a storage device 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 multiple individual pictures that, when viewed in sequence, impart motion. The picture itself may be organized as a spatial array of pixels, each of which may have one or more samples depending on the sampling structure, color space, etc., in use. Those skilled in the art can easily understand the relationship between pixels and samples. The remainder of this specification focuses on samples.

[0068] According to an 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 constraints as required. Imposing 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 as described below. Coupling is not shown for clarity. Parameters set by the controller (650) may include parameters related to rate control (picture skip, quantizer, lambda value for rate-distortion optimization techniques, etc.), picture size, group-of-picture (GOP) layout, maximum motion vector search range, etc. The controller (650) may be configured with other appropriate functions related to the video encoder (603) optimized for a particular system design.

[0069] In some embodiments, the video encoder (603) is configured to operate in a coding loop. As an oversimplified description, in an example, the coding loop can include a source coder (630) (e.g., responsible for generating symbols, such as a symbol stream, based on an input picture to be coded and a reference picture) and a (local) decoder (633) embedded in the video encoder (603). The decoder (633) reconstructs the symbols to generate sample data in a similar manner that a (remote) decoder would also generate. The reconstructed sample stream (sample data) is input to a reference picture memory (634). Since the decoding of the symbol stream produces bit-exact results independent of the location of the decoder (local or remote), the content in the reference picture memory (634) is also bit-perfect between the local and remote encoders. That is, the predictive part of the encoder "sees" exactly the same sample values ​​as the decoder would "see" when using prediction during decoding. This basic principle of reference picture synchronicity (and the resulting drift when synchronicity cannot be maintained, for example due to channel errors) is also used in several related techniques.

[0070] The operation of the "local" decoder (633) can be the same as a "remote" decoder, such as the video decoder (510), already described in detail above in conjunction with Figure 5. Referring also momentarily to Figure 5, however, the entropy decoding portion of the video decoder (510), including the buffer memory (515) and the parser (520), may not be fully implemented in the local decoder (633), given that symbols are available and the encoding / decoding of the symbols into a coded video sequence by the entropy coder (645) and parser (520) can be lossless.

[0071] In embodiments, the decoder techniques, except for parsing / entropy decoding, present in the decoder are present in the same or substantially the same functional form in the corresponding encoder. Thus, the disclosed subject matter focuses on the operation of the decoder. Descriptions of the encoder techniques may be omitted, in that they are the inverse of the decoder techniques described generically. To the extent that certain details are provided below.

[0072] In operation, in some examples, 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 the 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 pictures that may be selected as predictive references for the input picture.

[0073] The local video decoder (633) may decode the coded video data of pictures that may be designated as reference pictures based on the symbols generated by the source coder (630). The operation of the coding engine (632) may advantageously be a lossy process. When the coded video data may be decoded in a video decoder (not shown in FIG. 6), the reconstructed video sequence may usually be a copy of the source video sequence with some errors. The local video decoder (633) may reproduce the decoding process that may be performed by the video decoder on the reference pictures, causing the reconstructed reference pictures to be stored in the reference picture cache (634). In this way, the video encoder (603) may locally store copies of reconstructed reference pictures that have common content with the reconstructed reference pictures that would be obtained by the far-end video decoder (without transmission errors).

[0074] 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 look for certain metadata, such as reference picture motion vectors, block shapes, or sample data (as candidate reference pixel blocks) from the reference picture memory (634) that may be suitable prediction references for the new picture. The predictor (635) may operate on a sample block-by-pixel block basis 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 prediction references derived from multiple reference pictures stored in the reference picture memory (634).

[0075] 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.

[0076] The output of all the above functional units may undergo entropy coding in an entropy coder (645), which converts the symbols produced by the various functional units into a coded video sequence by applying lossless compression to the symbols according to techniques such as Huffman coding, variable length coding, or arithmetic coding.

[0077] The transmitter (640) may buffer the coded video sequence produced by the entropy coder (645) to prepare it for transmission over a communication channel (660), which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter (640) may merge the coded video data from the video coder (603) with other data to be transmitted, such as coded audio data and / or auxiliary data streams (sources not shown).

[0078] A controller (650) may manage the operation of the video encoder (603). During coding, the controller (650) may assign a particular coded picture type to each coded picture, which may affect the coding technique that may be applied to each picture. For example, pictures may often be assigned as one of the following picture types:

[0079] An Intra Picture (I-picture) may be a picture that can be coded and decoded without using any other picture in a sequence as a source of prediction. Some video codecs allow various types of Intra pictures, including, for example, Independent Decoder Refresh (IDR) pictures. Those skilled in the art are aware of such variations of I-pictures and their respective applications and characteristics.

[0080] A Predictive Picture (P-picture) may be a picture that can be coded and decoded by intra- or inter-prediction using at most one motion vector and reference index to predict sample values ​​for each block.

[0081] A Bi-directionally Predictive Picture (B-picture) may be a picture that can be coded and decoded by intra- or inter-prediction using at most two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multiple-predictive picture(s) can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0082] A source picture may generally be spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples, respectively) and coded block by block. Blocks may be predictively coded with reference to other (already coded) blocks as determined by the coding assignment applied to each picture of the block. For example, blocks of I pictures may be non-predictively coded or they may be predictively coded with reference to already coded blocks of the same picture (spatial or intra prediction). Pixel blocks of P pictures may be predictively coded by spatial prediction with reference to one previously coded reference picture or by temporal prediction. Blocks of B pictures may be predictively coded by spatial prediction with reference to one or two previously coded reference pictures or by temporal prediction.

[0083] The video encoder (603) may perform coding operations according to a given video coding technique or standard, such as ITU-T Recommendation H.265. During its operation, 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 defined by the video coding technique or standard being used.

[0084] In an 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 types of redundant data such as redundant pictures and slices, SEI messages or VUI parameter set fragments, etc.

[0085] A video may be captured as multiple source pictures (video pictures) in a time sequence. Intra-picture prediction (often abbreviated as intra-prediction) exploits spatial correlation in a given picture, while inter-picture prediction exploits correlation (temporal or other) between pictures. In an example, a particular picture being coded / decoded, called a current picture, is partitioned into blocks. If a block in the current picture is similar to a reference block in a previously coded reference picture in the video that is still buffered, then that block in the current picture may be coded by a vector called a motion vector. A motion vector points to a reference block in a reference picture, and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0086] In some embodiments, bi-prediction techniques may be used in inter-picture prediction. According to bi-prediction techniques, two reference pictures are used, e.g., a first reference picture and a second reference picture, both preceding in decoding order (but may be past and future, respectively, in display order) the current picture in the video. A block in the current picture may be coded with 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. The block is predictable by a combination of the first and second reference blocks.

[0087] Furthermore, merge mode techniques can be used in inter-picture prediction to improve coding efficiency.

[0088] According to some embodiments of the present disclosure, predictions such as inter-picture prediction and intra-picture prediction are performed in units of blocks. For example, according to the HEVC standard, pictures in a sequence of video pictures are partitioned 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 may 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 four CUs of 32×32 pixels, or 16 CUs of 16×16 pixels. In an example, each CU is analyzed to determine a prediction type for the CU, such as an inter-prediction type or an intra-prediction type. The CU is partitioned into one or more prediction units (PUs) according to temporal and / or spatial predictability. In general, each PU includes one luma prediction block (PB) and two chroma PBs. In an 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.

[0089] 7 shows an example diagram of a video encoder (703). The video encoder (703) is configured to receive a processed block of sample values ​​(e.g., a predictive block) in a current video picture included 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 an example, the video encoder (703) is used in place of the video encoder (403) of the example of FIG. 4.

[0090] In an HEVC example, the video encoder (703) receives a matrix of sample values ​​for a processing block, such as a prediction block of 8x8 samples. The video encoder (703) determines whether the processing block is best coded in intra mode, inter mode, or bi-prediction mode, for example using rate-distortion optimization. If the processing block is to be coded in intra mode, the video encoder (703) may use intra prediction techniques to encode the processing block into a coded picture, and if the processing block is to be coded in inter mode or bi-prediction mode, the video encoder (703) may use inter prediction or bi-prediction techniques, respectively, to encode the processing block into a coded picture. In certain video coding techniques, the merge mode can be an inter-picture prediction sub-mode in which motion vectors are derived from one or more motion vector predictors without benefit of coded motion vector components outside the predictors. In certain other video coding techniques, there may be motion vector components applicable to the current block. In an example, the video encoder (703) includes other components, such as a mode decision module (not shown) that determines the mode of the processing block.

[0091] 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 as shown in FIG.

[0092] 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 residual information according to an inter-coding technique, motion vectors, merge mode information), and calculate an inter-prediction result (e.g., a prediction block) based on the inter-prediction information using any suitable technique. In some examples, the reference picture is a decoded reference picture that has been decoded based on the coded video information.

[0093] The intra encoder (722) is configured to receive samples of a current block (e.g., a processing block), in some cases compare the block to previously coded blocks in the same picture, and generate transformed quantized coefficients and, in some cases, intra prediction information (e.g., intra prediction direction information according to one or more intra encoding techniques). In an example, the intra encoder (722) also calculates an intra prediction result (e.g., a prediction block) based on the intra prediction information and a reference block in the same picture.

[0094] 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 an 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, if the mode is an intra mode, the generic controller (721) controls the switch (726) to select the intra mode result for use by the residual calculator (723), and controls the entropy encoder (725) to select intra prediction information and include the intra prediction information in the bitstream. If the mode is an inter mode, the generic controller (721) controls the switch (726) to select the inter prediction result for use by the residual calculator (723), and controls the entropy encoder (725) to select inter prediction information and include the inter prediction information in the bitstream.

[0095] 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 on the residual data to encode the residual data to generate transform coefficients. In an 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 may be used by the intra-encoder (722) and the inter-encoder (730) as appropriate. For example, the inter-encoder (730) can generate decoded blocks based on the decoded residual data and the inter-prediction information, and the intra-encoder (722) can generate decoded blocks based on the decoded residual data and the intra-prediction information. The decoded blocks are appropriately processed to generate decoded pictures, which may be buffered in a memory circuit (not shown) and used as reference pictures in some examples.

[0096] 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 accordance with an appropriate standard, such as the HEVC standard. In an example, the entropy encoder (725) is configured to include general control data, selected prediction information (e.g., intra-prediction information or inter-prediction information), residual information, and other appropriate information in the bitstream. It should be noted that when coding a block in a merged sub-mode of either an inter mode or a bi-prediction mode in accordance with the disclosed subject matter, the residual information is not present.

[0097] 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 an example, the video decoder (810) is used in place of the video decoder (410) of the example of FIG. 4.

[0098] 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 as shown in FIG.

[0099] The entropy decoder (871) may be configured to reconstruct from the coded picture certain symbols representing syntax elements from which the coded picture is constructed. Such symbols may include prediction information (e.g., intra prediction information or inter prediction information) that may, for example, identify the mode in which the block is coded (e.g., intra mode, or inter mode or bi-prediction mode in merged or other submodes), the specific samples or metadata used for prediction by the intra decoder (872) or the inter decoder (880), respectively. The symbols may also include residual information, for example in the form of quantized transform coefficients. In an example, if the prediction mode is an inter or bi-prediction mode, the inter prediction information is provided to the inter decoder (880), and if the prediction type is an intra prediction type, the intra prediction information is provided to the intra decoder (872). The residual information may undergo inverse quantization and is provided to the residual decoder (873).

[0100] The inter decoder (880) is configured to receive the inter prediction information and to generate inter prediction results based on the inter prediction information.

[0101] The intra decoder (872) is configured to receive the intra prediction information and to generate a prediction result based on the intra prediction information.

[0102] The residual decoder (873) is configured to perform inverse quantization to retrieve inverse quantized transform coefficients, and process the inverse quantized transform coefficients to transform the residual from the frequency domain to the spatial domain. The residual decoder (873) may also require certain control information (to include quantization parameters (QPs)), which may be provided by the entropy decoder (871) (datapath not shown since this is only low volume control information).

[0103] The reconstruction module (874) is configured to combine the residual information output by the residual decoder (873) and the prediction result (possibly output by an inter- or intra-prediction module) in the spatial domain to form a reconstructed block. The reconstructed block may be part of a reconstructed picture, which in turn may be part of a reconstructed video. It is noted that other suitable operations, such as a deblocking operation, may be performed to improve visual quality.

[0104] It is understood that the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using any suitable technology. In some embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more integrated circuits. In other embodiments, the video encoders (403), (603), and (703) and the video decoders (410), (510), and (810) may be implemented using one or more processors executing software instructions.

[0105] Various inter prediction modes can be used in VVC. In case of inter predicted CU, the motion parameters can include MV, one or more reference picture index, reference picture list usage index, and additional information for certain coding features to be used for inter predicted sample generation. The motion parameters can be signaled explicitly or implicitly. In case of CU coded in skip mode, the CU can be associated with a PU and may have no significant residual coefficients, coded motion vector delta or MV difference (e.g. MVD), or reference picture index. Merge mode can be specified when the motion parameters of the current CU are obtained from neighboring CUs, including spatial and / or temporal candidates, and optionally additional information as introduced in VVC. Merge mode can be applied to inter predicted CUs as well as skip mode cases. In an example, an alternative to merge mode is explicit transmission of motion parameters, where MV, corresponding reference picture index and reference picture list usage flag for each reference picture list, and other information are explicitly signaled for each CU.

[0106] In an embodiment, such as VVC, the VVC Test Model (VTM) reference software supports the following motion vector prediction modes: Enhanced merge prediction, Merge Motion Vector Difference (MMVD) mode, Adaptive Motion Vector Prediction (AMVP) mode with symmetric MVD signaling, Affine motion compensation prediction, Sub-block based temporal motion vector prediction (SbTMVP), Adaptive Motion Vector Resolution (AMVR), motion field storage (1 / 16 luma sample MV storage and 8x8 motion field compression), Bi-prediction with CU-level weights (BCW), Bi-Directional Optical Flow (BDOF), Prediction Refinement using Optical Flow (PROF), Decoder side Motion Vector Refinement (DMVR), Combined Inter and Intra Prediction (CIF), and Combination Inter and Intra Prediction (CIF). It includes one or more sophisticated inter-prediction coding tools, including Continuous Inter-Prediction Prediction (CIIP), Geometric Partitioning Mode (GPM), and others.

[0107] Enhanced merge prediction can be used in some examples, such as VTM4, where the merge candidate list is constructed by including, in order, five types of candidates: spatial Motion Vector Predictor(s) (MVP) from spatially neighboring CUs, temporal MVP from co-located CUs, History-based MVP(s) (HMVP) from a First-In-First-Out (FIFO) table, pairwise average MVP, and zero MV.

[0108] The size of the merge candidate list may be signaled in the slice header. In an example, the maximum allowed size of the merge candidate list is 6 in VTM4. For each CU coded in merge mode, the index of the best merge candidate (e.g., merge index) may be coded using Truncated Unary (TU) binarization. The first bin of the merge index can be coded by context (e.g., Context-Adaptive Binary Arithmetic Coding, CABAC), and for the other bins, bypass coding can be used.

[0109] Some examples of the generation process for each category of merge candidates are given below. In an embodiment, spatial candidates are derived as follows: The derivation of spatial merge candidates in VVC can be the same as that in HEVC. In an example, up to four merge candidates are selected from candidates at the positions depicted in FIG. 9. FIG. 9 illustrates the positions of spatial merge candidates according to an embodiment of the present disclosure. With reference to FIG. 9, the derivation order is B1, A1, B0, A0, and B2. Position B2 is considered only if any CU at positions A0, B0, B1, and A1 is unavailable (e.g., because the CU belongs to another slice or another tile) or is intra-coded. After the candidate at position A1 is added, the addition of the remaining candidates undergoes a redundancy check to ensure that candidates with the same motion information are removed from the candidate list, improving coding efficiency.

[0110] To reduce computational complexity, not all possible candidate pairs are considered in the described redundancy check. Instead, only pairs connected with arrows in FIG. 10 are considered, and a candidate is added to the candidate list only if the corresponding candidates used in the redundancy check do not have the same motion information. FIG. 10 illustrates candidate pairs considered for redundancy check of spatial merge candidates according to an embodiment of the present disclosure. Referring to FIG. 10, each arrow-connected pair includes A1 and B1, A1 and A0, A1 and B2, B1 and B0, and B1 and B2. Thus, candidates at positions B1, A0, and / or b2 can be compared with the candidate at position A1, and candidates at positions B0 and B2 can be compared with the candidate at position B1.

[0111] In an embodiment, the temporal candidates are derived as follows: In an example, only one temporal merge candidate is added to the candidate list. FIG. 11 shows an example motion vector scaling for temporal merge candidates. To derive a temporal merge candidate for a current CU (1111) in a current picture (1101), a scaled MV (1121) (e.g., shown by a dashed line in FIG. 11) may be derived based on a co-located CU (1112) belonging to a co-located reference picture (1104). In an example, a co-located reference picture (also called a co-located picture) is, for example, a specific reference picture used for temporal motion vector prediction. A co-located reference picture used for temporal motion vector prediction may be indicated by a reference index in a syntax such as a high-level syntax (e.g., a picture header, a slice header).

[0112] The reference picture list used to derive the co-located CU (1112) may be explicitly signaled in the slice header. The scaled MV (1121) of the temporal merge candidate may be obtained, as indicated by the dashed line in FIG. 11. The scaled MV (1121) may be scaled from the MV of the co-located CU (1112) using Picture Order Count (POC) distances tb and td. The POC distance tb may be defined to be the POC distance between the current reference picture (1102) of the current picture (1101) and the current picture (1101). The POC distance td may be defined to be the POC distance between the co-located reference picture (1104) of the co-located picture (1103) and the co-located picture (1103). The reference picture index of the temporal merge candidate may be set to zero.

[0113] FIG. 12 shows exemplary candidate positions (e.g., C0 and C1) of a temporal merge candidate of a current CU. The position of the temporal merge candidate can be selected between candidate positions C0 and C1. Candidate position C0 is located at the bottom right corner of the current CU's colocated CU (1210). Candidate position C1 is located at the center of the current CU's colocated CU (1210). If the CU at candidate position C0 is unavailable, intra-coded, or outside the current row of the CTU, candidate position C1 is used to derive the temporal merge candidate. Otherwise, for example, if the CU at candidate position C0 is available, not intra-coded, and within the current row of the CTU, candidate position C0 is used to derive the temporal merge candidate.

[0114] Merge with Motion Vector Difference (MMVD) mode can be used for skip mode or merge mode depending on the motion vector representation method. Merge candidates such as those used in VVC can be reused in MMVD mode. Candidates can be selected among the merge candidates as starting points (e.g., MV predictor (MVP)) and can be further extended by MMVD mode. MMVD mode can provide a new motion vector representation with simplified signaling. The motion vector representation method includes starting points and MV difference (MVD). In an example, the MVD is indicated by the magnitude of the MVD (or motion magnitude) and the direction of the MVD (e.g., motion direction).

[0115] MMVD mode can use, for example, a merge candidate list as used in VVC. In an embodiment, only candidates that are of the default merge type (e.g., MRG_TYPE_DEFAULT_N) are considered for MMVD mode. The starting point can be indicated or defined by a base candidate index (IDX). The base candidate index can indicate the best candidate among the candidates (e.g., base candidates) in the merge candidate list. Table 1 shows an example relationship between the base candidate index and the corresponding starting point. A base candidate index that is 0, 1, 2, or 3 indicates that the corresponding starting point is the first MVP, the second MVP, the third MVP, or the fourth MVP. In an example, when the number of base candidates is equal to 1, the base candidate IDX is not signaled. [Table 1]

[0116] The distance index may indicate motion magnitude information of the MVD, such as the magnitude of the MVD. For example, the distance index indicates a distance (e.g., a predefined distance) from a starting point (e.g., the MVD indicated by the base candidate index). In an example, the distance is one of a number of predefined distances as shown in Table 2. Table 2 shows an example relationship between the distance index and the corresponding distance (in units of samples or pixels). 1 pel in Table 2 is 1 sample or 1 pixel. For example, a distance index of 1 indicates that the distance is 1 / 2 pel or 1 / 2 sample. [Table 2]

[0117] The direction index can represent the direction of the MVD relative to the starting point. The direction index can represent one of multiple directions, such as the four directions shown in Table 3. For example, a direction index of 00 indicates that the direction of the MVD is along the positive x-axis. [Table 3]

[0118] The MMVD flag may be signaled after sending the skip and merge flag. If the skip and merge flag is true, the MMVD flag may be parsed. In an example, if the MMVD flag is equal to 1, the MMVD syntax (e.g., including the distance index and / or the direction index) may be parsed. If the MMVD flag is not equal to 1, the AFFINE flag may be parsed. If the AFFINE flag is equal to 1, the AFFINE mode is used to code the current block. If the AFFINE flag is not equal to 1, the skip / merge index may be parsed for the skip / merge mode, e.g., as used in VTM.

[0119] 13 and 14 show an example of a search process in MMVD mode. By performing a search process, indices including a base candidate index, a direction index, and / or a distance index may be determined for a current block (1300) in a current picture (or called a current frame) (1301).

[0120] A first motion vector (MV) (1311) and a second MV (1321) belonging to a first merging candidate are shown. The first merging candidate may be a merging candidate in a merging candidate list constructed for the current block (1300). The first MV (1311) and the second MV (1321) may be associated with two reference pictures (1302) and (1303) in the reference picture lists L0 and L1, respectively. Accordingly, two starting points (1411) and (1421) in Figures 13 and 14 may be determined at the reference pictures (1302) and (1303), respectively.

[0121] In an example, based on the starting points (1411) and (1421), multiple predefined points (e.g., 1-12 shown in FIG. 14) extending vertically (represented as +Y or -y) or horizontally (represented as +X and -X) from the starting points (1411) and (1421) in the reference pictures (1302) and (1303) may be evaluated. In one example, a pair of points that mirror each other with respect to the respective starting points (1411) or (1412), such as the pair of points (1414) and (1424) or the pair of points (1415) and (1425), may be used to determine a pair of MVs (1314) and (1324) or a pair of MVs (1315) and (1325) that may form a candidate MV predictor (MVP) for the current block (1300). MVP candidates determined based on predefined points surrounding the starting point (1411) and / or (1412) may be evaluated. Referring to FIG. 13, the MVD (1312) between the first MV (1311) and MV (1314) has a magnitude of 1S. The MVD (1322) between the second MV (1321) and MV (1324) has a magnitude of 1S. Similarly, the MVD between the first MV (1311) and MV (1315) has a magnitude of 2S. The MVD between the second MV (1321) and MV (1325) has a magnitude of 2S.

[0122] In addition to the first merge candidate, other available or valid merge candidates in the merge candidate list of the current block (1300) may be evaluated as well. In one example, in case of a uni-predicted merge candidate, only one prediction direction associated with one of the two reference picture lists is evaluated.

[0123] In an example, based on the evaluation, a best MVP candidate can be determined. Accordingly, corresponding to the best MVP candidate, a best merge candidate can be selected from the merge list, and the motion direction and motion distance can also be determined. For example, based on the selected merge candidate and Table 1, a base candidate index can be determined. Based on the selected MVP, such as the one corresponding to the predefined point (1415) (or (1425)), the direction and distance (e.g., 2S) of the point (1415) relative to the start point (1411) can be determined. According to Tables 2 and 3, the direction index and distance index can be determined accordingly.

[0124] As described above, two indexes, such as a distance index and a direction index, can be used to indicate the MVD in the MMVD mode. Alternatively, a single index may be used to indicate the MVD in the MMVD mode, for example, using a table that pairs a single index with the MVD.

[0125] To improve coding efficiency and reduce MV transmission overhead, sub-block level MV refinement may be applied to extend CU-level temporal motion vector prediction (TMVP). In an example, sub-block-based TMVP (SbTMVP) mode allows for inheriting motion information at the sub-block level from a co-located reference picture. As mentioned above, the co-located reference picture may be indicated by a reference index in a syntax such as a high-level syntax (e.g., a picture header, a slice header).

[0126] Each sub-block of a current CU (large-sized current CU) in a current picture may have its own motion information without explicitly transmitting the block partition structure or its own motion information. In SbTMVP mode, the motion information of each sub-block may be obtained, for example, in three steps, as follows: In the first step, a Displacement Vector (DV) of the current CU may be derived. The DV may indicate a block in a collocated reference picture, for example, the DV points from a current block in a current picture to a block in a collocated reference picture. Thus, the block indicated by the DV is considered to be collocated with the current block and is called the co-located block of the current block. In the second step, the availability of an SbTMVP candidate may be confirmed, and a central motion (e.g., the central motion of the current CU) may be derived. In the third step, sub-block motion information may be derived from the corresponding sub-block in the collocated block using the DV. The three steps may be combined into one or two steps, and / or the order of the three steps may be adjusted.

[0127] Unlike TMVP candidate derivation, which derives temporal MVs from co-located blocks in a reference frame or picture, in SbTMVP, a DV (e.g., a DV derived from the MV of the current CU's left neighboring CU) may be applied to find a corresponding sub-block in the co-located picture for each sub-block in the current CU in the current picture. If the corresponding sub-block is not inter-coded, the motion information of the current sub-block may be set to be the motion of the center of the co-located block.

[0128] The SbTMVP mode may be supported by various video coding standards, including, for example, VVC. Similar to the TMVP mode, for example, in HEVC, in the SbTMVP mode, the motion fields (also called motion information fields or MV fields) in the co-located picture can be used to improve the MV prediction and merging mode of the CU in the current picture. In an example, the SbTMVP mode differs from the TMVP mode in the following aspects: (i) the TMVP mode predicts the motion information at the CU level, while the SbTMVP mode predicts the motion information at the sub-CU level; (ii) the TMVP mode fetches the temporal MV from a co-located block in the co-located picture (e.g., the co-located block is the bottom-right or center block with respect to the current CU), while the SbTMVP mode can apply a motion shift before fetching the temporal motion information from the co-located picture. In an example, the motion shift used in SbTMVP is obtained from the MV of one of the spatially neighboring blocks of the current CU.

[0129] Figures 15A and 15B show an exemplary SbTMVP process used in the SbTMVP mode. The SbTMVP process can predict the MV of a sub-CU (e.g., sub-block) in a current CU (e.g., current block) (1501) in a current picture (1511), for example, in two steps. In a first step, a spatial neighbor (e.g., A1) of the current block (1501) in Figures 15A and 15B is tested. If the spatial neighbor (e.g., A1) has a MV (1521) that uses a co-located picture (1512) as a reference picture for the spatial neighbor (e.g., A1), then the MV (1521) can be selected to be the motion shift (or DV) to be applied to the current block (1501). If no such MV (e.g., an MV that uses a co-located picture (1512) as a reference picture) is identified, then the motion shift or DV can be set to be a zero MV (e.g., (0,0)). In some examples, MVs of further spatial neighbors, such as A0, B0, b1, etc., are checked if no such MVs are identified for spatial neighbor A1.

[0130] In a second step, the motion shift or DV (1521) identified in the first step may be applied to the current block (1501) to obtain sub-CU level motion information (e.g., including MV and reference index) from the co-located picture (1512) (e.g., the DV (1521) is added to the coordinates of the current block). In the example shown in FIG. 15B, the motion shift or DV (1521) is set to be the MV of the spatial neighbor A1 (e.g., block A1) of the current block (1501). For each sub-CU or sub-block (1531) in the current block (1501), the motion information of the corresponding co-located block (1591) in the co-located picture (1512) (e.g., the motion information of the smallest motion grid covering the central sample of the co-located block (1591)) may be used to derive the motion information of the sub-CU or sub-block (1531). After the motion information of the co-located sub-CU (1532) in the co-located block (1591) is identified, the motion information of the co-located sub-CU (1532) can be converted to motion information (e.g., MV and one or more reference indexes) of the current sub-CU (1531) using a scaling method, for example in a manner similar to the TMVP process used in HEVC, where temporal motion scaling is applied to align pictures of the temporal MV to the reference pictures of the current CU.

[0131] The motion field of the current block (1501) derived based on the DV (1521) may include motion information of each sub-block (1531) in the current block (1501), such as an MV and one or more associated reference indexes. The motion field of the current block (1501) may also be referred to as an SbTMVP candidate and corresponds to the DV (1521).

[0132] 15B shows an example of a motion field or SbTMVP candidate of a current block (1501). The motion information of a bi-predicted sub-block (1531(1)) includes a first MV and a first index indicating a first reference picture in reference picture list 0 (L0), a second MV and a second index indicating a second reference picture in reference picture list 1 (L1). In the example, the motion information of a uni-predicted sub-block (1531(2)) includes an MV and an index indicating a reference picture in L0 or L1.

[0133] In an example, the DV (1521) is applied to the center position of the current block (1501) to find the displaced center position in the co-located picture (1512). If the block containing the displaced center position is not inter-coded, the SbTMVP candidate is considered unavailable. Otherwise, if the block containing the displaced center position (e.g., the co-located block (1591)) is inter-coded, the motion information of the center position of the current block (1501), referred to as the center motion of the current block (1501), may be derived from the motion information of the block containing the displaced center position in the co-located picture (1512). In an example, a scaling process may be used to derive the center motion of the current block (1501) from the motion information of the block containing the displaced center position in the co-located picture (1512). When SbTMVP candidates are available, the DV (1521) may be applied to find a corresponding sub-block (1532) in the co-located picture (1512) for each sub-block (1531) of the current block (1501). The motion information of the corresponding sub-block (1532) may be used to derive motion information for the sub-block (1531) in the current block (1501), for example, in the same manner used to derive the central motion of the current block (1501). In an example, if the corresponding sub-block (1532) is not inter-coded, the motion information of the current sub-block (1531) is set to be the central motion of the current block (1501).

[0134] In some examples, for example in VVC, a composite sub-block-based merge list including SbTMVP candidates and affine merge mode is used in signaling the sub-block-based merge mode. The SbTMVP mode can be enabled or disabled by a sequence parameter set (SPS) flag. When the SbTMVP mode is enabled, the SbTMVP candidate (or SbTMVP predictor) can be added as the first entry of a sub-block-based merge list including sub-block-based merge candidates, followed by affine merge candidates. The size of the sub-block-based merge list can be signaled in the SPS. In an example, the maximum allowed size of the sub-block-based merge list is 5 in VVC. In an example, multiple SbTMVP candidates are included in the sub-block-based merge list.

[0135] In some examples, for example in VVC, the sub-CU size used in SbTMVP mode is fixed to be 8×8, for example used in affine merge mode. In examples, SbTMVP mode is only applicable to CUs whose width and height are both 8 or more. The sub-block size (e.g., 8×8) may be configurable to other sizes, such as 4×4 in the ECM software model used for searching beyond VVC. In examples, multiple collocated pictures, such as two collocated frames, are utilized to provide temporal motion information for TMVP and / or SbTMVP in AMVP mode.

[0136] In a related technique, a frame rate up-conversion (FRUC) process can be used in a display to generate a high frame rate video based on a low frame rate video. The FRUC process can be used to generate interpolated pictures or frames based on other pictures (e.g., forward and backward reference pictures) by using any suitable method, such as picture repetition, picture averaging, motion compensation, and / or the like.

[0137] In an example, a FRUC process with motion compensation is used to determine an interpolated picture (or an interpolated frame), and may be referred to as motion-compensated FRUC (MC-FRUC). In MC-FRUC, object motion may be used to generate an interpolated frame. MC-FRUC may include two steps: Motion Estimation (ME) and Motion-Compensated Interpolation (MCI). Motion estimation may track the motion trajectory between a forward reference picture and a backward reference picture. Motion Vectors (MVs) may be generated in ME. Interpolated pictures may be generated based on the MVs in MCI.

[0138] Similar to video coding, Block-Matching Motion Estimation (BM-ME) can be used in MC-FRUC. In MC-FRUC, an image is divided into blocks, and the motion or movement (e.g., motion trajectory) of each block can be estimated according to ME between forward and backward reference pictures.

[0139] FIG. 16A shows an example in which two types of MEs, including one-way ME (also called unilateral ME) and two-way ME (also called bilateral ME), may be used in BM-ME. In FIG. 16A, a first reference picture (e.g., forward reference picture) (1602) and a second reference picture (e.g., backward reference picture) (1603) may be used in motion estimation. One-way ME may be used to determine the MV (1621) of a block (1613) in a second reference picture (1603) by searching for a block (1612) in the first reference picture (1602) that matches the block (1613) in the second reference picture (1603). A block (1611) along a motion trajectory (e.g., translation from block (1613) to block (1612)) may be found in a picture (e.g., an interpolated picture) (1601).

[0140] Bidirectional ME may be used to determine MVs (1631)-(1632) passing through a block (1611) in a picture (1601) using temporal symmetry between a block (1612) in a first reference picture (1602) and a block (1613) in a second reference picture (1603). In bilateral ME, blocks (1612)-(1613) are adapted.

[0141] FIG. 16B shows examples of unidirectional MV estimation and bidirectional MV estimation. In unidirectional MV estimation, the second reference picture (1603) may be divided into blocks (e.g., non-overlapping blocks) including the block (1613). A search range (1642) around an initial block in the first reference picture (1602) may be determined. Each block in the search range (1642) in the first reference picture (1602) may be compared to the block (1613). The difference between the block (1613) and each block in the search range (1642) may be determined based on any suitable method, such as Sum of Absolute Difference (SAD), Sum of Absolute Translated Differences (SATD), Sum of Squared Errors (SSE), mean removed SAD / SATD / SSE, variance, partial SAD, partial SSE, partial SATD, etc. The block (1612) that has the smallest difference (e.g., the smallest SAD) from the block (1613) in the second reference picture (1603) may be selected, and the MV (1621) associated with blocks (1612)-(1613) may be determined.

[0142] In an example, MV (1621) indicates motion (e.g., translation or motion trajectory) between blocks (1612) and (1613). The MV of block (1611) can be estimated based on the MV (1621) that points to block (1611). In an example, an MV predictor (e.g., a temporal MV predictor or TMVP) (1622) of block (1611) is determined based on the MV (1621). For example, the MV (1621) can be temporally scaled to determine the TMVP of block (1611). If a first POC difference between picture (1601) and the forward reference picture (1602) is equal to a second POC difference between picture (1601) and the backward reference picture (1603), then the TMVP (1622) is one-half the MV (1621). Similarly, other TMVPs of blocks in the picture (1601) can be determined, and thus a first MV field of the picture (1601), indicating motion information (e.g., TMVP) of blocks in the picture (1601), can be determined using unidirectional MV estimation.

[0143] The second MV field of the picture (1601) may be determined similarly as described above, starting from a block in the forward reference picture (1602) and looking for a corresponding matching block in the backward reference picture (1603).

[0144] In some examples, the MV field of the picture (1601) is determined based on a first MV field of the picture (1601) and a second MV field of the picture (1601).

[0145] In an example of bidirectional MV estimation, two unidirectional MV estimates may be used. The first unidirectional MV estimate is described above in FIG. 16B, where a block (1612) is determined from a block (1613) and an MV (1621) is determined based on blocks (1612)-(1613). After the block (1612) is determined, the second unidirectional MV estimate shown in FIG. 16C may start from the block (1612) to search for a corresponding block (1618) in a search range (1643) in a backward reference picture (1603) that matches the block (1612) using the unidirectional MV estimation described in FIG. 16B. In an example, the corresponding block (1618) in the backward reference picture (1603) is the block (1613). In another example, the corresponding block (1618) in the backward reference picture (1603) is different from the block (1613), for example as shown in FIG. 16C. MV (1623) may be determined based on blocks (1612) and (1618). Similarly, in the example, TMVP, which is an estimate for the MV of block (1611), may be determined based on MVs (1621) and (1623).

[0146] In another example of bidirectional MV estimation, for a block (1611) in picture (1601), a search of a search range (1652) in a forward reference picture (1602) and a search range (1653) in a backward reference picture (1603) may be performed to determine a MV (1631)-(1632) through the block (1611) in picture (1601). For example, the blocks in the search range (1652) are compared to the blocks in the search range (1653). As described for unidirectional MV estimation, the difference between the blocks in the search range (1652) and the blocks in the search range (1653) is determined. The block (1612)-(1613) with the smallest difference (e.g., having the smallest SAD) may be selected, and the MV (1631)-(1632) may be determined. In the example, the MV (1631) is the opposite of the MV (1632). In the example, MV(1631) is not the opposite of MV(1632). The TMVP of block (1611) may be determined based on MV(1631)-(1632). In the example, MV(1631) refers to block (1613) from block (1611), and MV(1632) refers to block (1612) from block (1611), so the TMVP of block (1611) is determined from MV(1631)-(1632) without temporal scaling.

[0147] The motion information of the current picture (e.g., MVs of blocks of the current picture) may be determined (e.g., derived) using the FRUC mode, rather than being signaled. In the FRUC mode, the motion information of the current picture, such as the motion information (e.g., MVs) of blocks in the current picture, may be determined based on motion estimation that tracks a motion trajectory between reference blocks in two respective reference pictures, as described in FIG. 16B and FIG. 16C. For example, in the FRUC mode, the motion information of a block (e.g., (1611)) in the current picture (e.g., (1601)) is determined based on motion estimation that tracks a motion trajectory between reference blocks (e.g., (1612)-(1613)) in two respective reference pictures (e.g., (1602)-(1603)).

[0148] In some embodiments, e.g., in VVC and ECM, the SbTMVP mode may use DVs derived only from the MVs of the current CU's neighboring CUs, so the motion information (inherited motion information) of the SbTMVP mode may not be valid, e.g., due to weak relationships in the spatial domain between the current CU and the neighboring CUs.

[0149] This application describes embodiments related to the derivation of SbTMVP by using FRUC.

[0150] According to an embodiment of the present disclosure, the blocks or sub-blocks in the two pictures can be used to determine motion information of the first sub-block in the current block when the current block in the current picture is coded with inter prediction using a sub-block-based mode. In an example, the two pictures are forward reference pictures (or forward reference frames) or backward reference pictures (or backward reference frames) of the current picture. In an example, the picture order count (POC) of one of the two pictures (e.g., the forward reference picture) is smaller than the POC of the current picture, and the POC of the other of the two pictures (e.g., the backward reference picture) is larger than the POC of the current picture. According to an embodiment of the present disclosure, the motion information of the first sub-block can be determined using sub-block-based FRUC, for example, implemented using the unidirectional MV estimation and / or bidirectional MV estimation described above.

[0151] 17A-17C illustrate sub-block-based FRUC or a sub-block-based FRUC mode. A current block (1704) is in a current picture (1701). The current block (1704) may include multiple sub-blocks, such as (1711)-(1714). The sub-blocks (1711)-(1714) may have any suitable width N and any suitable height M, such as N×M. N and M may be positive integers. In an example, one of N and M is 1 and the other of N and M is greater than 1. The widths N and heights M of the sub-blocks (1711)-(1714) may be the same or different.

[0152] 17A-17C, a corresponding block (1706) of a current block (1704) may be determined based on a first offset vector (e.g., a first motion vector offset (MVO)) (1705), where the first offset vector (1705) may indicate an offset between the current block (1704) and the corresponding block (1706). In an example, the first offset vector (1705) is signaled for the current block (1704) and parsed to indicate a location of the corresponding block (1706) within the current picture (1701). The corresponding block (1706) is within the current picture (1701). The corresponding block (1706) may include sub-blocks (1721)-(1724), which correspond to sub-blocks (1711)-(1714), respectively.

[0153] The motion information of a sub-block (e.g., (1721)) in a corresponding block (1706) may be estimated or predicted based on a sub-block (e.g., (1741)) in a forward reference picture (1702) of a current picture (1701) and a corresponding sub-block (e.g., (1731)) in a corresponding backward reference picture (1703) of the current picture (1701) using any suitable FRUC process, such as unidirectional MV estimation (e.g., as described in FIG. 16B) or bidirectional MV estimation (e.g., as described in FIG. 16B and FIG. 16C). In an example, an additional unidirectional MV estimation and / or an additional bidirectional MV estimation is performed based on an additional forward reference picture and / or an additional backward reference picture. In some examples, the motion information of a sub-block (e.g., (1721)) is determined based on the respective motion information obtained from the unidirectional MV estimation and / or the bidirectional MV estimation. Motion information for other sub-blocks (eg, (1722)-(1724)) within the corresponding block (1706) may be determined using the FRUC process in a similar manner.

[0154] In general, multiple sub-blocks in the forward reference picture (1702) and the backward reference picture (1703) may be used to determine (e.g., estimate) motion information for each sub-block in the corresponding block (1706). In an example, more than two sub-blocks in the forward reference picture (1702) and the backward reference picture (1703) are used. Referring again to Figures 16B and 16C, when two unidirectional MV estimates are used as bidirectional MV estimates, three blocks (1612), (1613), and (1618) can be used, where blocks (1612) and (1613) are used to determine the MV and blocks (1613) and (1618) are used to determine the other MV.

[0155] In the example shown in FIG. 17A, one-way MV estimation (e.g., similar to that described in FIG. 16B) may be used to determine a TMVP (e.g., CorTMVP) (1751)-(1754) for each sub-block (1721)-(1724) in a corresponding block (1706). The TMVP (1751)-(1754) associated with the corresponding block (1706) may be referred to as CorTMVP. The TMVP (1751)-(1754) may be a predictor of, or an estimate for, the motion information (e.g., MV) of each of the sub-blocks (1721)-(1724). In the example, the TMVP (1751)-(1754) of each subblock (1721)-(1724) is determined based on the subblocks (1731)-(1734) in the backward reference picture (1703) and the corresponding subblocks (1741)-(1744) in the forward reference picture (1702), respectively. In some examples, other subblocks in the backward reference picture (1703) and the forward reference picture (1702) are used to determine the TMVPs (1751)-(1754).

[0156] In the example, multiple one-way MV estimates may be used to determine the TMVPs (1751)-(1754) of each of the sub-blocks (1721)-(1724) within a corresponding block (1706).

[0157] In an example, bidirectional MV estimation (e.g., as described in Figures 16B and 16C) can be used to determine the TMVPs (7151)-(1754) of each sub-block (1721)-(1724) within a corresponding block (1706).

[0158] The TMVPs (1751)-(1754) of the respective sub-blocks (1721)-(1724) in the corresponding block (1706) can be derived as described above. In Figure 17A, for illustrative purposes, the TMVPs (1751)-(1754) are represented by arrows pointing from the sub-blocks (1731)-(1734) in the backward reference picture (1703) to the sub-blocks (1741)-(1744) in the forward reference picture (1702).

[0159] The TMVPs (1751)-(1754) of each of the sub-blocks (1721)-(1724) may include MVs for unidirectional prediction. FIG. 17B shows an example of the TMVPs (1751)-(1754) of each of the sub-blocks (1721)-(1724) in the corresponding block (1706) (e.g., the size and direction of the TMVPs (1751)-(1754) are shown). The TMVPs (1751)-(1754) of each of the sub-blocks (1721)-(1724) may include (i) CorTMVs associated with the forward reference picture (1702). L0 (xi,yi) or CorTMV L0,i (e.g., MV), or (ii) a CorTMV associated with a backward reference picture (1703). L1 (xi,yi) or CorTMVL 1,i (e.g., MV). Coordinates (xi, yi) may indicate the i-th sub-block in the corresponding block (1706) at position (xi, yi). The parameter i may be an integer, e.g., 0, 1, 2, or 3, each of which refers to a sub-block (1721)-(1724) in the corresponding block (1706).

[0160] In the example, unidirectional MV estimation starts from a subblock in the backward reference picture (1703) to look for a match (e.g., subblock (1741)) in the forward reference picture (1702), thus determining the TMVP (1751). The TMVP (1751) is the MV (e.g., CorTMV) associated with the backward reference picture (1703). L1,0 ) can be regarded as

[0161] In some instances, CorTMV L0,i CorTMVL relates to the first reference picture list 0 (L0) 1,i relates to the second reference picture list (L1).

[0162] In the example, the TMVPs (1751) to (1754) of each of the subblocks (1721) to (1724) may include MVs for bi-prediction, as shown in FIG. 17C. The TMVPs (1751) to (1754) of each of the subblocks (1721) to (1724) may include MVs for bi-prediction, as shown in FIG. L0,i and (ii) CorTMV. L1,i It can be expressed using:

[0163] The TMVPs of the sub-blocks (1711)-(1714) in the current block (1704) may be determined based on the TMVPs of the sub-blocks (1721)-(1724) in the corresponding block (1706), respectively. The TMVPs of the sub-blocks (1711)-(1714) in the current block (1704) may be determined based on the MV offsets and the sub-blocks (1721)-(1724) in the corresponding block (1706), respectively. In the example, the TMVPs of the sub-blocks (1711)-(1714) in the current block (1704) may be determined by the vector sum of the first offset vector (MVO1) and the TMVPs of the sub-blocks (1721)-(1724) in the corresponding block (1706), as shown in Equation 1.

number

[0164] The motion field of the current block (1704) can include motion information of the sub-blocks (1711) to (1714). In the case of single prediction, the TMVP of the sub-blocks (1711) to (1714) can include four vectors (e.g., SbTMV L0,i and SbTMV L1,i , where i is a number from 0 to 3 corresponding to the sub-blocks (1711) to (1714). ) and can indicate the motion information of the sub-blocks (1711) to (1714). In the case of bi-prediction, the TMVP of the sub-blocks (1711) to (1714) can include eight vectors (e.g., SbTMV L0,i and SbTMV L1,i , where i is a value from 0 to 3 corresponding to the sub-blocks (1711) to (1714).) It is possible to indicate the motion information of the sub-blocks (1711) to (1714).

[0165] A FRUC-based sub-block merging candidate, also referred to as a FRUC-based sub-block TMVP candidate (e.g., a FRUC-based SbTMVP candidate), may indicate a motion field of a current block (1704) including, for example, the TMVPs of sub-blocks (1711) to (1714). The sub-block-based FRUC described in Figures 17A to 17C may also be referred to as a FRUC-based sub-block TMVP mode or a FRUC-based SbTMVP mode.

[0166] As described above in Figures 15A-15B and 17A-17C, the FRUC-based sub-block TMVP candidates (e.g., as shown in Figures 17A-17C) are determined to be different from the SbTMVP candidates as shown in Figures 15A-15B. The FRUC-based sub-block TMVP modes as shown in Figures 17A-17C are different from the SbTMVP modes as shown in Figures 15A-15B. The SbTMVP modes as shown in Figures 15A-15B may also be referred to as normal SbTMVP modes to distinguish them from the FRUC-based sub-block TMVP modes.

[0167] Figure 18A shows another example of a sub-block based FRUC mode, such as a FRUC-based sub-block TMVP mode, which is a variation from the FRUC-based sub-block TMVP mode shown in Figure 17A. The current picture (1701), current block (1704) including sub-blocks (1711)-(1714), corresponding block (1706) including sub-blocks (1721)-(1724), forward reference picture (1702) and sub-blocks (1741)-(1744), backward reference picture (1703) and sub-blocks (1731)-(1734), and first offset vector (1705) shown in Figure 18A are described in Figure 17A.

[0168] The TMVPs (1751)-(1754) of each of the sub-blocks (1721)-(1724) in the corresponding block (1706) may be determined using any suitable FRUC process (e.g., any suitable FRUC process, such as one-way MV estimation or two-way MV estimation) described in FIGS. 16B-16C and 17A-17C. In the example shown in FIGS. 18A and 18B, the TMVPs (1851)-(1854) of the sub-blocks (1711)-(1714) in the current block (1704) are respectively calculated by multiplying the TMVPs (e.g., CorTMV L0,i and / or CorTMV L1,i , where i is 0 to 3. ) is determined as (1751) to (1754).

number

[0169] SbTMV L0,i and SbTMV L1,i CorTMV L0,i and CorTMV L1,iThe TMVPs (1751) to (1754) of the subblocks (1721) to (1724) can each include an MV for one-way prediction, as shown in FIG. 18B. In FIG. 18B, the TMVPs (1751) to (1754) can include CorTMV L0,i or CorTMV L1,i where i ranges from 0 to 3. TMVP(1851)-(1854) in the current block are the same as TMVP(1751)-(1754), respectively.

[0170] FIG. 18B shows a FRUC-based sub-block TMVP candidate (eg, a FRUC-based SbTMVP candidate) that shows the motion field of the current block (1704), including, for example, TMVPs (1861)-(1864) of sub-blocks (1711)-(1714).

[0171] In some examples, the TMVPs (1751) to (1754) of each of the sub-blocks (1721) to (1724) may include MVs for bi-prediction. L0,i or CorTMV L1,i where i ranges from 0 to 3. TMVP(1851)-(1854) in the current block are the same as TMVP(1751)-(1754), respectively.

[0172] Figure 19 shows another example of a sub-block-based FRUC mode, such as a FRUC-based sub-block TMVP mode, which is a variation from the FRUC-based sub-block TMVP mode shown in Figures 17A-17C and 18A-18B. The current picture (1701), current block (1704) including sub-blocks (1711)-(1714), forward reference picture (1702) and sub-blocks (1741)-(1744), and backward reference picture (1703) and sub-blocks (1731)-(1734) shown in Figure 19 are described in Figure 17A.

[0173] The initial TMVP (e.g., CurTMV) (1951)-(1954) of each of the sub-blocks (1711)-(1714) in the current block (1704) may be determined using any suitable FRUC process, such as one-way MV estimation and / or two-way MV estimation described in Figures 16B-16C and 17A-17C. The initial TMVP (e.g., CurTMV) (1951)-(1954) may be determined using the CurTMV L0,i and / or CurTMV L1,i where i is from 0 to 3. In an example, a second offset vector (or second MVO) may be added to the initial TMVP (e.g., CurTMV) (1951)-(1954) to determine a TMVP (e.g., SbTMVP) for each sub-block (1711)-(1714) in the current block (1704) using Equation 3.

number

[0174] In an example, a second MVO is signaled and parsed. The second MVO may be the same as or different from the first MVO used in Figures 17A-7C and 18A-18B.

[0175] The offset vector (e.g., the first offset vector or the second offset vector) may be determined as follows: In one embodiment, the offset vector is a zero vector. The offset vector (which is (0,0)) does not need to be signaled in the bitstream.

[0176] In an embodiment, the offset vector may be determined as an offset vector in a predefined offset vector list. An index may be signaled to indicate which offset vector is selected from the predefined offset vector list. In an example, the offset vector may be signaled using a method similar to that used in the MMVD to signal the MVD, as described with reference to Tables 2 and 3. In an example, a single index is signaled to indicate the magnitude and direction of the offset vector. In an example, a distance index and a direction index are signaled to indicate the magnitude and direction of the offset vector. The offset vector may be determined based on one or more indexes.

[0177] In an embodiment, the offset vector is signaled for the current block in the bitstream. For example, (i) the magnitude and direction of the offset vector, or (ii) the x and y components of the offset vector may be signaled in the syntax for the current block.

[0178] The TMVP of the first sub-block (e.g., (1721)) in the corresponding block (1706) may be determined as follows: In an embodiment, the TMVP of the first sub-block (e.g., CorTMV L0,i and / or CorTMV L1,i) is unavailable, e.g., the TMVP of the first subblock cannot be derived by subblock-based FRUC. In an example, the TMVP of the first subblock in the corresponding block (1706) is not determined using subblock-based FRUC. When the TMVP of the first subblock in the corresponding block (1706) is unavailable, the TMVP of the first subblock in the corresponding block (1706) may be generated by one or more TMVPs of adjacent subblocks, such as a weighted average of the one or more TMVPs of the adjacent subblocks. Referring to FIG. 17C, when the TMVP of subblock (1721) cannot be generated by the FRUC process, the TMVP of subblock (1721) may be generated based on the TMVPs of subblocks (1722), (1723) and / or (1724).

[0179] If one or more TMVPs of adjacent subblocks are unavailable, a zero MV (eg, (0,0)) may be set as the TMVP of the first subblock of the corresponding block (1706).

[0180] Different positions of the subblocks in the corresponding block (1706) may be used to derive the TMVP of each subblock using the FRUC process. In an embodiment, a center position of each subblock in the corresponding block (1706) is used to derive the TMVP of each subblock using the FRUC process. For example, the TMVP of a first subblock in the corresponding block (1706) may be determined based on a MV passing through a center position in the first subblock. In an example, the subblock is a 4×4 unit, and thus the center position of the 4×4 unit may be (1,1), (1,2), (2,1), or (2,2). In an example, the subblock is an 8×8 unit, and thus the center position of the 8×8 unit may be (3,3), (3,4), (4,3), or (4,4).

[0181] In an embodiment, one of the top-left, top-right, bottom-left, or bottom-right positions of each sub-block in the corresponding block (1706) is used to derive the TMVP of each sub-block using the FRUC process. For example, the TMVP of a first sub-block in the corresponding block (1706) may be determined based on a MV that passes through one of the top-left, bottom-right, bottom-left, or bottom-right positions in the first sub-block.

[0182] The above description relating to the derivation of the TMVP of a first sub-block (e.g., (1721)) in a corresponding block (1706) is applicable to deriving the initial TMVP of a sub-block (e.g., (1711)) in a current block (1704) in FIG. 19.

[0183] The FRUC-based SbTMVP mode may be inferred as true or false based on the POC of the reference pictures and the current picture (1701). In an embodiment, the FRUC-based SbTMVP mode is inferred as false when the POC (e.g., in display order) of the reference pictures (e.g., all reference pictures) in L0 and I1 is less than the POC of the current picture (1701). In an embodiment, the FRUC-based SbTMVP mode is inferred as false when the POC of the reference pictures (e.g., all reference pictures) in L0 and I1 is greater than the POC of the current picture (1701).

[0184] In the example, the POC of the forward reference picture (1702) is smaller than the POC of the current picture (1701), the POC of the backward reference picture (1703) is larger than the POC of the current picture (1701), and the FRUC-based SbTMVP mode is applied to determine the TMVP of sub-blocks (1711) to (1714) of the current block (1704), as described in Figures 17A to 17C, Figures 18A to 18B, and Figure 19.

[0185] The FRUC-based sub-block TMVP candidates of the current block (1704), for example as shown in Figures 17B-17C and 18B, may be signaled in any suitable manner.

[0186] In an embodiment, a FRUC-based sub-block TMVP candidate may be signaled as a sub-block-based candidate used in a sub-block-based mode (e.g., sub-block-based merge / skip mode). A sub-block candidate list (e.g., sub-block merge / skip list) may be configured for the current block (1704). In an example, multiple sub-block-based modes (e.g., SbTMVP mode, FRUC-based sub-block TMVP mode, and / or affine mode) share a sub-block candidate list. The sub-block candidate list (e.g., sub-block merge / skip list) of the current block (1704) may include sub-block candidates (e.g., sub-block merge candidates) such as FRUC-based sub-block TMVP candidates, SbTMVP candidates used in SbTMVP mode (also referred to as normal SbTMVP mode), and the like. In an example, the sub-block candidate list of the current block (1704) may include affine candidates such as affine merge candidates used in affine merge mode. In an example, the affine merge candidates include affine inherited candidates and / or affine constructed candidates used in the affine merge / skip mode.

[0187] FRUC-based sub-block TMVP mode and SbTMVP mode (e.g., normal SbTMVP mode) may be applicable to the current block (1704). The sub-block candidate list may include FRUC-based sub-block TMVP candidates and SbTMVP candidates. An index is signaled at the CU level to indicate which candidate should be applied to the current block (1704). If the index indicates that the FRUC-based sub-block TMVP candidate should be used, the current block (1704) is coded using the FRUC-based sub-block TMVP mode, and the TMVP of the sub-blocks (1711)-(1714) of the current block (1704) is determined using the FRUC-based sub-block TMVP candidate, as described in Figures 17A-17C, 18A-18B, and 19.

[0188] In an embodiment, the FRUC-based sub-block TMVP mode replaces the SbTMVP mode (the normal SbTMVP mode used in VVC, as described in FIGS. 15A-15B), and the SbTMVP mode is not allowed for the current block (1704). For example, the sub-block candidate list (e.g., sub-block merge / skip list) of the current block (1704) includes FRUC-based sub-block TMVP candidates and does not include SbTMVP candidates.

[0189] In an embodiment, the FRUC-based sub-block TMVP mode can be used instead of the SbTMVP mode (the normal SbTMVP mode used in VVC, as described in FIGS. 15A-15B) when the FRUC-based sub-block TMVP mode is available. The SbTMVP mode (the normal SbTMVP mode used in VVC, as described in FIGS. 15A-15B) can be applied only when the FRUC-based sub-block TMVP mode is unavailable for the current block (1704).

[0190] In an embodiment, whether to enable FRUC-based sub-block TMVP mode may be signaled at a level higher than the block level, such as the slice level, the tile level, the tile group level, the picture level, or the sequence level.

[0191] In an example, the subblock size of the subblocks used in the FRUC-based sub-block TMVP mode (e.g., subblocks (1711)-(1714) and subblocks (1721)-(1724)) may be a predefined subblock size of N×M luma samples. N and M can be any suitable positive integers. A picture (e.g., forward reference picture (1702)) or a block (e.g., current block (1704)) may be partitioned into subblocks having a subblock size of N×M luma samples.

[0192] In an example, N and M are the same. A block (e.g., the current block (1704)) may be partitioned into sub-blocks having a sub-block size of N×N luma samples. When the block width W or block height H is smaller than N, a FRUC-based sub-block TMVP mode may be applied to the block, and then the block may be partitioned as follows: The corresponding sub-block width or sub-block height may be set to the block width W or block height H that is smaller than N. If W is smaller than N and H is equal to or greater than N, the block (e.g., the current block (1704)) may be partitioned into sub-blocks having a sub-block width of W and a sub-block height of N. If H is smaller than N and W is equal to or greater than N, the block (e.g., the current block (1704)) may be partitioned into sub-blocks having a sub-block width of N and a sub-block height of H.

[0193] In an embodiment, when the block width or block height is smaller than N, the FRUC-based sub-block TMVP mode may not be applied to the block.

[0194] Motion information of a block in a current picture (e.g., MVs of sub-blocks in the block) may be determined (e.g., derived) using a sub-block-based FRUC mode, rather than being signaled. In the sub-block-based FRUC mode, motion information (e.g., MVs) of sub-blocks in a block may be determined based on motion estimation that tracks a motion trajectory between reference sub-blocks in two respective reference pictures, as described in Figures 17A-17C, 18A-18B, and 19. For example, in the sub-block-based FRUC mode, motion information of a sub-block (e.g., (1711)) in a block (e.g., (1704)) in a current picture (e.g., (1701)) is determined based on motion estimation that tracks a motion trajectory between reference blocks (e.g., (1741) and (1731)) in two respective reference pictures (e.g., (1702)-(1703)).

[0195] FIG. 20 shows a flow chart describing an encoding process (2000) according to an embodiment of the present disclosure. The process (2000) may be used in a video encoder. The process (2000) may be performed by an apparatus for video coding, which may include a processing circuit. In various embodiments, the process (2000) is performed by a processing circuit, such as a processing circuit in a terminal device (310), (320), (330), or (340), a processing circuit performing the functions of a video encoder (e.g., (403), (603), (703)), etc. In some embodiments, the process (2000) is implemented in software instructions, such that the processing circuit performs the process (2000) when the processing circuit executes the software instructions. The process starts at (S2001) and proceeds to (S2010).

[0196] At (S2010), a corresponding block of the current block in the current picture may be determined based on an offset vector. The offset vector indicates an offset between the current block and the corresponding block in the current picture. The current block is to be coded based on sub-block-based frame rate up-conversion (FRUC) (also referred to as a sub-block-based FRUC mode). The current block includes multiple sub-blocks.

[0197] In the example, the offset vector is the zero vector.

[0198] At (S2020), a temporal motion vector predictor (TMVP) of a first sub-block in a corresponding block may be determined based on a sub-block in a forward reference picture of a current picture and a sub-block in a backward reference picture of the current picture. The sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted using sub-block-based FRUC.

[0199] In an example, when the TMVP of a second subblock in a corresponding block is not determined by subblock-based FRUC, the TMVP of the second subblock is determined based on the TMVP of a first subblock in the corresponding block. The second subblock is adjacent to the first subblock. The TMVP of the second subblock in the corresponding block can be used to determine the second subblock in the current block.

[0200] In an example, the TMVP of the first sub-block in the corresponding block is determined based on a motion vector (MV) between the sub-block in the forward reference picture and the sub-block in the backward reference picture, where the MV passes through one of a center position, a top-left position, a top-right position, a bottom-left position, or a bottom-right position of the first sub-block in the corresponding block.

[0201] In the example, the Picture Order Count (POC) of the forward reference picture is smaller than the POC of the current picture, and the POC of the backward reference picture is larger than the POC of the current picture.

[0202] At (S2030), the TMVP of a sub-block in the current block may be determined based on the TMVP of a first sub-block in the corresponding block.

[0203] In the example, the TMVP of a sub-block in a current block is determined as the TMVP of the first sub-block in the corresponding block.

[0204] In the example, the motion vector (MV) of the TMVP of a subblock in the current block is determined as the vector sum of the offset vector and each MV of the TMVP of the first subblock in the corresponding block.

[0205] In (2040), the sub-blocks in the current block may be coded based on the TMVP of the sub-blocks in the current block.

[0206] In an example, an index is encoded into the bitstream to point to an offset vector within a predefined offset vector list.

[0207] In an example, the offset vector is signaled in the encoded bitstream.

[0208] The process (2000) then proceeds to (S2099) and ends.

[0209] The process (2000) may be adapted to various scenarios as appropriate, and the steps of the process (2000) may be adjusted accordingly. One or more of the steps of the process (2000) may be adapted, omitted, repeated, and / or combined. Any suitable order may be used to implement the process (2000). Additional steps may be added.

[0210] In an embodiment, the subblock merging candidate list includes subblock-based temporal motion vector prediction (SbTMVP) candidates and FRUC-based subblock merging candidates indicating the TMVP of each subblock in the current block. The current block may be coded based on the FRUC-based subblock merging candidates, and subblock merging indexes indicating the FRUC-based subblock merging candidates may be coded and included in the bitstream.

[0211] In an embodiment, the sub-block merging candidate list includes FRUC-based sub-block merging candidates that indicate the TMVP of each sub-block in the current block. The sub-block merging candidate list does not include SbTMVP candidates. The current block can be encoded based on the FRUC-based sub-block merging candidates.

[0212] If a FRUC-based subblock merging candidate indicating the TMVP of each subblock in the current block is available, the subblock merging candidate list includes the FRUC-based subblock merging candidate and does not include the subblock-based temporal motion vector prediction (SbTMVP) candidate. If a FRUC-based subblock merging candidate is not available, the subblock merging candidate list includes the SbTMVP candidate.

[0213] The predefined subblock size is N×N luma samples. If the width W of the current block is less than N and the height H of the current block is greater than or equal to N, the current block is partitioned into subblocks with a subblock width of W and a subblock height of N. If H is less than N and W is greater than or equal to N, the current block is partitioned into subblocks with a subblock width of N and a subblock height of H.

[0214] FIG. 21 shows a flow chart describing a decoding process (2100) according to an embodiment of the present disclosure. The process (2100) may be used in a video decoder. The process (2100) may be performed by an apparatus for video coding, which may include a receiving circuit and a processing circuit. In various embodiments, the process (2100) is performed by a processing circuit in the terminal devices (310), (320), (330), and (340), a processing circuit performing the function of the video encoder (403), a processing circuit performing the function of the video decoder (410), a processing circuit performing the function of the video decoder (510), a processing circuit performing the function of the video encoder (603), etc. In some embodiments, the process (2100) is implemented in software instructions, such that the processing circuit performs the process (2100) when the processing circuit executes the software instructions. The process starts at (S2101) and proceeds to (S2110).

[0215] At (S2110), it may be determined based on syntax elements in a coded video bitstream that a current block including multiple sub-blocks is coded in a sub-block-based frame rate up-conversion (FRUC) mode (also referred to as sub-block-based FRUC). In an example, the coded video bitstream includes a current picture that includes the current block.

[0216] At (S2120), a corresponding block of the current block may be determined based on the offset vector, which indicates an offset between the current block and the corresponding block in the current picture.

[0217] In the example, the offset vector is the zero vector.

[0218] In an example, an index is received in a coded video bitstream, and an offset vector is determined from a predefined offset vector list based on the index.

[0219] In an example, the offset vector is signaled within the coded video bitstream.

[0220] At (S2130), a temporal motion vector predictor (TMVP) of a first sub-block in a corresponding block may be determined based on a sub-block in a forward reference picture of a current picture and a sub-block in a backward reference picture of a current picture. The sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted using sub-block-based FRUC.

[0221] In an example, the TMVP of a second subblock in a corresponding block is determined based on the TMVP of a first subblock in the corresponding block when the TMVP of the second subblock is not determined by subblock-based FRUC. The second subblock is adjacent to the first subblock. The TMVP of the second subblock in the corresponding block can be used to determine the second subblock in the current block.

[0222] In an example, the TMVP of the second sub-block in the corresponding block is determined based on a motion vector (MV) between the sub-block in the forward reference picture and the sub-block in the backward reference picture, where the MV passes through one of a center position, a top-left position, a top-right position, a bottom-left position, or a bottom-right position of the first sub-block in the corresponding block.

[0223] In the example, the Picture Order Count (POC) of the forward reference picture is smaller than the POC of the current picture, and the POC of the backward reference picture is larger than the POC of the current picture.

[0224] At (S2140), the TMVP of a sub-block in the current block may be determined based on the TMVP of a first sub-block in the corresponding block.

[0225] In the example, the TMVP of a sub-block in a current block is determined as the TMVP of the first sub-block in the corresponding block.

[0226] In the example, the motion vector (MV) of the TMVP of a sub-block in the current block is determined as the vector sum of the offset vector and each MV of the TMVP of the first sub-block in the corresponding block.

[0227] The process (2100) proceeds to (S2199) and ends.

[0228] The process 2100 can be adapted to various scenarios as appropriate, and the steps of the process 2100 can be adjusted accordingly. One or more of the steps of the process 2100 can be adapted, omitted, repeated, and / or combined. Any suitable order can be used to implement the process 2100. Additional steps can be added.

[0229] In an embodiment, the subblock merging candidate list includes a subblock-based temporal motion vector prediction (SbTMVP) candidate and a FRUC-based subblock merging candidate that indicates the TMVP of each subblock in the current block. The current block may be reconstructed based on the FRUC-based subblock merging candidate if the subblock merging index indicates the FRUC-based subblock merging candidate.

[0230] In an embodiment, the subblock merging candidate list includes a FRUC-based subblock merging candidate that indicates the TMVP of each subblock in the current block. The subblock merging candidate list does not include an SbTMVP candidate. The current block may be reconstructed based on the FRUC-based subblock merging candidate if the subblock merging index indicates the FRUC-based subblock merging candidate.

[0231] If a FRUC-based subblock merging candidate that indicates the TMVP of each subblock in the current block is available, the subblock merging candidate list includes the FRUC-based subblock merging candidate and does not include a subblock-based temporal motion vector prediction (SbTMVP) candidate. If a FRUC-based subblock merging candidate is available, the subblock merging candidate list includes the SbTMVP candidate.

[0232] The predefined subblock size is N×N luma samples. If the width W of the current block is less than N and the height H of the current block is greater than or equal to N, the current block is partitioned into subblocks with a subblock width of W and a subblock height of N. If H is less than N and W is greater than or equal to N, the current block is partitioned into subblocks with a subblock width of N and a subblock height of H.

[0233] FIG. 22 shows a flow chart describing an encoding process (2200) according to an embodiment of the present disclosure. The process (2200) may be used in a video encoder. The process (2200) may be performed by an apparatus for video coding, which may include a processing circuit. In various embodiments, the process (2300) is performed by a processing circuit, such as a processing circuit in a terminal device (310), (320), (330), or (340), a processing circuit that performs the functions of a video encoder (e.g., (403), (603), (703)), etc. In some embodiments, the process (2200) is implemented in software instructions, such that the processing circuit performs the process (2200) when the processing circuit executes the software instructions. The process starts at (S2201) and proceeds to (S2210).

[0234] At (S2210), an initial temporal motion vector predictor (TMVP) of a first sub-block in a current block in a current picture may be determined based on a sub-block in a forward reference picture of the current block and a sub-block in a backward reference picture of the current block. The sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted based on sub-block-based frame rate up-conversion (FRUC).

[0235] At (S2220), the TMVP of the first sub-block in the current block may be determined based on the initial TMVP and a motion vector offset (MVO) of the first sub-block in the current block.

[0236] In an example, the first sub-block in the current block may be encoded based on the TMVP of the first sub-block in the current block.

[0237] The process (2200) then proceeds to (S2299) and ends.

[0238] Process 2300 can be adapted to various scenarios as appropriate, and the steps of process 2200 can be adjusted accordingly. One or more of the steps of process 2200 can be adapted, omitted, repeated, and / or combined. Any suitable order can be used to implement process 2200. Additional steps can be added.

[0239] FIG. 23 shows a flow chart describing a decoding process (2300) according to an embodiment of the present disclosure. The process (2300) may be used in a video decoder. The process (2300) may be performed by an apparatus for video coding, which may include a receiving circuit and a processing circuit. In various embodiments, the process (2300) is performed by a processing circuit in the terminal devices (310), (320), (330), and (340), a processing circuit performing the function of the video encoder (403), a processing circuit performing the function of the video decoder (410), a processing circuit performing the function of the video decoder (510), a processing circuit performing the function of the video encoder (603), etc. In some embodiments, the process (2300) is implemented by software instructions, such that the processing circuit performs the process (2300) when the processing circuit executes the software instructions. The process starts at (S2301) and proceeds to (S2310).

[0240] At (S2310), it may be determined based on syntax elements in the coded video bitstream that a current block including multiple sub-blocks is coded in a sub-block-based frame rate up-conversion (FRUC) mode (or sub-block-based FRUC).

[0241] In an example, the coded video bitstream includes a current picture, which includes a current block.

[0242] At (S2320), an initial temporal motion vector predictor (TMVP) of a sub-block of the current block may be determined based on a sub-block in a forward reference picture of the current picture and a sub-block in a backward reference picture of the current picture. The sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted using sub-block-based FRUC.

[0243] At (S2330), the TMVP of the first sub-block in the current block may be determined based on the initial TMVP and a motion vector offset (MVO) of the first sub-block in the current block.

[0244] In the example, the motion vector (MV) of the TMVP of the first subblock in the current block is determined as the vector sum of the MVO and each MV of the TMVP of the first subblock in the current block.

[0245] In an example, an index is received in a coded video bitstream, and an MVO is determined from a predefined MVO list based on the index.

[0246] In an example, the MVO is signaled within the coded video bitstream.

[0247] The process (2300) proceeds to (S2399) and ends.

[0248] The process 2300 can be adapted to various scenarios as appropriate, and the steps of the process 2300 can be adjusted accordingly. One or more of the steps of the process 2300 can be adapted, omitted, repeated, and / or combined. Any suitable order can be used to implement the process 2300. Additional steps can be added.

[0249] The embodiments of the present disclosure may be used separately or combined in any order. Furthermore, each of the methods (or embodiments), the encoder, and the decoder may be implemented by a processing circuit (e.g., one or more processors or one or more integrated circuits). In one example, the one or more processors execute a program stored on a non-transitory computer-readable medium.

[0250] It can be implemented as computer software using computer readable instructions and physically stored on one or more computer readable media. For example, Figure 24 illustrates a computer system (2400) suitable for implementing certain embodiments of the disclosed subject matter.

[0251] The computer software may be coded in any suitable machine code or computer language that may be subject to mechanisms such as assembly, compilation, linking, etc. to generate code including instructions that may be executed by one or more central processing units (CPUs), graphics processing units (GPUs), etc., directly or through interpretation, microcode execution, etc.

[0252] The instructions may be executable by various types of computers or components thereof, including, for example, personal computers, tablet computers, servers, smartphones, gaming consoles, devices for the Internet of Things, and the like.

[0253] 24 for computer system (2400) are exemplary in nature and are not intended to suggest any limitation as to the scope of use or functionality of the computer software implementing the embodiments of the present disclosure. The arrangement of components should not be interpreted as having any dependency or requirement regarding any one or combination of components described in the exemplary embodiment of computer system (2400).

[0254] The computer system (2400) may include certain human interface input devices. Such human interface input devices may be responsive to input by one or more users through, for example, tactile input (e.g., keyboard, swipes, dataglove movements), audio input (e.g., voice, clapping), visual input (e.g., gestures), and olfactory input (not shown). The human interface devices may also be used to capture certain media that are not necessarily directly related to conscious human input, such as audio (e.g., speech, music, ambient sounds), images (e.g., scanned images, photographic images obtained from a still camera), and video (e.g., two-dimensional video, three-dimensional video including stereoscopic video).

[0255] The input human interface devices may include one or more of a keyboard (2401), a mouse (2402), a trackpad (2403), a touch screen (2410), a data glove (not shown), a joystick (2405), a microphone (2406), a scanner (2407), and a camera (2408) (only one of each is shown).

[0256] The computer system 2400 may also include certain human interface output devices that may stimulate one or more of the user's senses through, for example, tactile output, sound, light, and smell / taste. Such human interface output devices may include haptic output devices (e.g., haptic feedback via a touch screen (2410), data gloves (not shown), or joystick (2405), although there may also be haptic feedback devices that do not function as input devices), audio output devices (e.g., speakers (2409), headphones (not shown)), visual output devices (e.g., screens (2410) including CRT screens, LCD screens, plasma screens, OLED screens, each with or without touch screen input capability, each with or without haptic feedback capability, some of which are capable of outputting two-dimensional visual output or output in more than three dimensions by means of stereoscopic output, virtual reality glasses (not shown), holographic displays, and smoke tanks (not shown)), and printers (not shown).

[0257] The computer system (2400) may also include human accessible storage devices and their associated media, such as CD / DVD ROM / RW (2420) with CD / DVD or similar media (2421), thumb drives (2422), removable hard disks or solid state drives (2423), legacy magnetic media, such as tapes and floppy disks (not shown), dedicated ROM / ASIC / PLD based devices, such as security dongles (not shown), and the like.

[0258] Those skilled in the art will also understand that the term "computer-readable medium" as used in connection with the presently disclosed subject matter does not include transmission media, carrier waves, or other transitory signals.

[0259] The computer system (2400) may also include interfaces to one or more communication networks. The networks may be, for example, wireless, wireline, optical. The networks may further be local, wide area, metropolitan, vehicular and industrial, real-time, delay tolerant, etc. Examples of networks include local area networks such as Ethernet, wireless LANs, cellular networks including GSM, 3G, 4G, 5G, LTE, etc., TV wireline or wireless wide area digital networks including cable TV, satellite TV, and terrestrial broadcast TV, vehicular and factory networks including CAN bus, etc. Certain networks generally require an external network interface adapter attached to a particular general purpose digital port or peripheral bus (2449) (e.g., a USB port of the computer system (2400)). Others are generally built into the core of the computer system (2400) by attachment to a system bus as described below (e.g., an Ethernet network to a PC computer system, or a cellular network interface to a smartphone computer system). Using any of these networks, the computer system (2400) may communicate with other entities. Such communications may be one-way receive-only (e.g., broadcast TV) or one-way transmit-only (e.g., a CAN bus to a specific CAN bus device), or may be two-way, for example, to other computer systems using local or wide area digital networks. Specific protocols or protocol stacks may be used with each of the networks and network interfaces as described above.

[0260] The above-mentioned human interface devices, human accessible storage devices, and network interfaces may be attached to a core (2440) of the computer system (2400).

[0261] The cores (2440) may include one or more central processing units (CPUs) (2441), graphics processing units (GPUs) (2442), dedicated programmable processing units in the form of field programmable gate areas (FPGAs) (2443), hardware accelerators (2444) for specific tasks, etc. These devices may be connected through a system bus (2448), along with read only memory (ROM) (2445), random access memory (RAM) (2446), internal mass storage devices such as internal non-user accessible hard drives, SSDs, etc. (2447). In some computer systems, the system bus (2448) may be accessible in the form of one or more physical plugs to allow expansion with additional CPUs, GPUs, etc. Peripherals may be attached directly to the core's system bus (2448) or through a peripheral bus (2449). In an example, a screen (2410) may be connected to a graphics adapter (2450). Architectures for peripheral buses include PCI and USB.

[0262] The CPU (2441), GPU (2442), FPGA (2443), and accelerator (2444) can execute certain instructions that may combine to constitute the above computer code. The computer code may be stored in a ROM (2445) or a RAM (2446). Temporary data may also be stored in the RAM (2446), while persistent data may be stored, for example, in an internal mass storage device (2447). Rapid storage and retrieval from any of the memory devices may be made possible by the use of a cache memory. A cache memory may be closely associated with one or more of the CPU (2441), GPU (2442), mass storage device (2447), ROM (2445), RAM (2446), etc.

[0263] 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 kind well known and available to those of ordinary skill in the computer software arts.

[0264] By way of example, and not by way of limitation, the architecture, specifically the computer system (2400) having the core (2440), can provide functionality as a result of a processor (including CPU, GPU, FPGA, accelerator, etc.) executing software embodied in one or more tangible computer-readable media. Such computer-readable media can be media associated with the user-accessible mass storage devices introduced above, in addition to specific storage of the core (2440) that is non-transitory in nature, such as the core's internal mass storage (2447) or ROM (2445). Software implementing various embodiments of the present disclosure can be stored in such devices and executed by the core (2440). The computer-readable media can include one or more memory devices or chips, depending on the particular needs. The software can cause the core (2440), 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 (2446) 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 implemented by hardware or otherwise embodied in circuitry (e.g., accelerators (2444)) that can operate in place of or in conjunction with software to execute certain processes or certain portions of certain processes described herein. References to software can encompass logic, where appropriate, and vice versa. References to computer-readable media can encompass circuitry (e.g., integrated circuits (ICs)) storing software for execution, circuitry embodying logic for execution, or both, where appropriate. The present disclosure encompasses any appropriate combination of hardware and software.

[0265] Appendix A: Acronyms JEM: Joint Exploration Model VVC:Versatile Video Coding BMS:benchmark set MV:Motion Vector HEVC:High Efficiency Video Coding SEI:Supplementary Enhancement Information VUI:Video Usability Information GOP:Group of Picture(s) TU:Transform Unit(s) PU:Prediction Unit(s) CTU:Coding Tree Unit(s) CTB:Coding Tree Block(s) PB:Prediction Block(s) HRD:Hypothetical Reference Decoder SNR:Signal Noise Ratio CPU:Central Processing Unit(s) GPU:Graphics Processing Unit(s) 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(s) SSD: Solid-State Drive IC: Integrated Circuit CU: Coding Unit JVET:Joint Video Exploration Team AMVR:Adaptive Motion Vector Resolution POC: Picture Order Count SbTMVP:Subblock-based temporal motion vector prediction

[0266] While this disclosure has described several exemplary embodiments, there are alterations, permutations, and various substitute equivalents that are within the scope of this disclosure. Thus, it will be apparent to those skilled in the art that numerous systems and methods will be contemplated that embody the principles of the present disclosure and are therefore within its spirit and scope, even if not explicitly shown or described herein.

[0267] [Incorporated by reference] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 320028, entitled "TEMPORAL BASED SUBBLOCK TYPE MOTION VECTOR PREDICTOR," filed March 15, 2022, which claims the benefit of priority to U.S. Provisional Patent Application No. 17 / 984,131, entitled "TEMPORAL BASED SUBBLOCK TYPE MOTION VECTOR PREDICTOR," filed November 9, 2022. The entire disclosures of these prior applications are incorporated herein by reference in their entirety.

Claims

1. 1. A method of video decoding performed by a decoder, comprising: receiving a coded video bitstream including a current picture, the current picture including a current block, the current block including a plurality of sub-blocks; determining, based on a syntax element in the coded video bitstream, that the current block including the plurality of sub-blocks is coded in a sub-block-based frame rate up-conversion (FRUC) mode; determining a corresponding block of the current block based on an offset vector, the offset vector indicating an offset between the current block and the corresponding block in the current picture; determining a temporal motion vector predictor (TMVP) of a first sub-block in the corresponding block based on a sub-block in a forward reference picture of the current picture and a sub-block in a backward reference picture of the current picture, where the sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted using the sub-block-based FRUC mode; determining a TMVP of a sub-block among the plurality of sub-blocks in the current block based on the TMVP of the first sub-block in the corresponding block; The method according to claim 1,

2. The step of determining a TMVP of a sub-block among the plurality of sub-blocks in the current block includes: determining a TMVP of a sub-block among the plurality of sub-blocks in the current block as a TMVP of the first sub-block in the corresponding block; The method of claim 1.

3. The step of determining a TMVP of a sub-block among the plurality of sub-blocks in the current block includes: determining a motion vector (MV) of a TMVP of a sub-block among the plurality of sub-blocks in the current block as a vector sum of the offset vector and each MV of a TMVP of the first sub-block in the corresponding block; The method of claim 1.

4. the offset vector is zero; The method of claim 1.

5. receiving an index within the coded video bitstream; determining the offset vector from a predefined list of offset vectors based on the index; The method of claim 1 further comprising:

6. the offset vector is signaled in the coded video bitstream. The method of claim 1.

7. In response to a TMVP of a second sub-block in the corresponding block not being determined by the sub-block based FRUC mode, determining a TMVP of the second sub-block based on a TMVP of the first sub-block in the corresponding block; The second sub-block is adjacent to the first sub-block. The method of claim 1.

8. The step of determining the TMVP of the first sub-block in the corresponding block comprises: determining a TMVP of the first sub-block in the corresponding block based on a motion vector between a sub-block in the forward reference picture and a sub-block in the backward reference picture; the motion vector passes through one of a center position, a top-left position, a top-right position, a bottom-left position, or a bottom-right position in the first sub-block in the corresponding block; The method of claim 1.

9. a picture order count (POC) of the forward reference picture is smaller than a POC of the current picture, and a POC of the backward reference picture is larger than a POC of the current picture; The method of claim 1.

10. the sub-block merging candidate list includes sub-block-based temporal motion vector prediction (SbTMVP) candidates and FRUC-based sub-block merging candidates indicating the TMVPs of each sub-block in the current block; In response to a sub-block merging index indicating the FRUC-based sub-block merging candidate, the method includes reconstructing the current block based on the FRUC-based sub-block merging candidate. The method of claim 1.

11. a sub-block merging candidate list includes FRUC-based sub-block merging candidates indicating a TMVP of each sub-block among the plurality of sub-blocks in the current block, and the sub-block merging candidate list does not include a sub-block-based temporal motion vector prediction (SbTMVP) candidate; In response to a sub-block merging index indicating the FRUC-based sub-block merging candidate, the method includes reconstructing the current block based on the FRUC-based sub-block merging candidate. The method of claim 1.

12. in response to FRUC-based sub-block merging candidates being available that indicate a TMVP of each sub-block in the current block, a sub-block merging candidate list includes the FRUC-based sub-block merging candidates and does not include a sub-block-based temporal motion vector prediction (SbTMVP) candidate; in response to the FRUC-based sub-block merging candidate being unavailable, the sub-block merging candidate list includes the SbTMVP candidate; The method of claim 1.

13. The predefined sub-block size is N×N luma samples; In response to a width W of the current block being less than N and a height H of the current block being greater than or equal to N, the method further comprises partitioning the current block into sub-blocks having a sub-block width of W and a sub-block height of N; In response to H being less than N and W being greater than or equal to N, the method further comprises partitioning the current block into sub-blocks having a sub-block width of N and a sub-block height of H. The method of claim 1.

14. 1. A method of video decoding performed by a decoder, comprising: receiving a coded video bitstream including a current picture, the current picture including a current block, the current block including a plurality of sub-blocks; determining, based on a syntax element in the coded video bitstream, that the current block including the plurality of sub-blocks is coded in a sub-block-based frame rate up-conversion (FRUC) mode; determining an initial temporal motion vector predictor (TMVP) of a first sub-block among the plurality of sub-blocks in the current block based on a sub-block in a forward reference picture of the current picture and a sub-block in a backward reference picture of the current picture, where the sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted using the sub-block-based FRUC mode; determining a TMVP of the first sub-block among the plurality of sub-blocks in the current block based on an initial TMVP and a motion vector offset (MVO) of the first sub-block among the plurality of sub-blocks in the current block; The method according to claim 1,

15. The step of determining the TMVP of the first sub-block among the plurality of sub-blocks in the current block includes: determining a motion vector (MV) of the TMVP of the first sub-block among the plurality of sub-blocks in the current block as a vector sum of the MVO and each MV of the TMVP of the first sub-block among the plurality of sub-blocks in the current block; The method of claim 14.

16. receiving an index within the coded video bitstream; determining the MVO from a predefined MVO list based on the index; The method of claim 14 further comprising:

17. the MVO is signaled in the coded video bitstream; The method of claim 14.

18. In response to an initial TMVP of a second sub-block among the plurality of sub-blocks in the current block not being determined by the sub-block-based FRUC mode, determining an initial TMVP of the second sub-block based on the initial TMVP of the first sub-block among the plurality of sub-blocks in the current block; The second sub-block is adjacent to the first sub-block. The method of claim 14.

19. the sub-block merging candidate list includes sub-block-based temporal motion vector prediction (SbTMVP) candidates and FRUC-based sub-block merging candidates indicating the TMVP of each sub-block among the plurality of sub-blocks in the current block; In response to a sub-block merging index indicating the FRUC-based sub-block merging candidate, the method includes reconstructing the current block using the FRUC-based sub-block merging candidate. The method of claim 14.

20. a sub-block merging candidate list includes FRUC-based sub-block merging candidates indicating a TMVP of each sub-block among the plurality of sub-blocks in the current block, and the sub-block merging candidate list does not include a sub-block-based temporal motion vector prediction (SbTMVP) candidate; In response to a sub-block merging index indicating the FRUC-based sub-block merging candidate, the method includes reconstructing the current block using the FRUC-based sub-block merging candidate. The method of claim 14.

21. 1. A method of video encoding performed by an encoder, comprising: encoding a video bitstream to generate a coded video bitstream including a current picture, the current picture including a current block, the current block including a plurality of sub-blocks; determining, based on a syntax element in the coded video bitstream, that the current block including the plurality of sub-blocks is coded in a sub-block-based frame rate up-conversion (FRUC) mode; determining a corresponding block of the current block based on an offset vector, the offset vector indicating an offset between the current block and the corresponding block in the current picture; determining a temporal motion vector predictor (TMVP) of a first sub-block in the corresponding block based on a sub-block in a forward reference picture of the current picture and a sub-block in a backward reference picture of the current picture, where the sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted using the sub-block-based FRUC mode; determining a TMVP of a sub-block among the plurality of sub-blocks in the current block based on the TMVP of the first sub-block in the corresponding block; The method according to claim 1,

22. 1. A method of video encoding performed by an encoder, comprising: encoding a video bitstream to generate a coded video bitstream including a current picture, the current picture including a current block, the current block including a plurality of sub-blocks; determining, based on a syntax element in the coded video bitstream, that the current block including the plurality of sub-blocks is coded in a sub-block-based frame rate up-conversion (FRUC) mode; determining an initial temporal motion vector predictor (TMVP) of a first sub-block among the plurality of sub-blocks in the current block based on a sub-block in a forward reference picture of the current picture and a sub-block in a backward reference picture of the current picture, where the sub-block in the forward reference picture and the sub-block in the backward reference picture are adapted using the sub-block-based FRUC mode; determining a TMVP of the first sub-block among the plurality of sub-blocks in the current block based on an initial TMVP and a motion vector offset (MVO) of the first sub-block among the plurality of sub-blocks in the current block; The method according to claim 1,

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