Systems and methods for selecting and grouping warped samples

Abstract

Various embodiments described herein include methods and systems for encoding and decoding video. In one aspect, the method includes obtaining video data including a plurality of blocks including a first block, the video data being coded in a warp mode or a motion mode. The method further includes identifying two or more warp groups for the first block and determining a respective cost associated with each warp group of the two or more warp groups. The method also includes selecting a warp group from the two or more warp groups based on the respective costs, and encoding the first block and a syntax element indicating the warp mode or the motion mode according to the selected warp group, regardless of whether a valid motion vector is available.

Description

[Technical Field]

[0001] Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 401,477, entitled "Method and Apparatus for Warp Sample Selection and Grouping Improvements," filed August 26, 2022, and is a continuation of and claims priority to U.S. Patent Application No. 18 / 143,520, entitled "Systems and Methods for Warp Sample Selection and Grouping," filed May 4, 2023, both of which are incorporated herein by reference in their entirety.

[0002] FIELD Embodiments of the present disclosure relate generally to video encoding and decoding, including, but not limited to, systems and methods for warped sampling selection and grouping. [Background technology]

[0003] Digital video is supported by a variety of electronic devices, such as digital televisions, laptop or desktop computers, tablet computers, digital cameras, digital recording devices, digital media players, video game consoles, smartphones, video teleconferencing devices, video streaming devices, etc. The electronic devices send, receive, or communicate digital video data over communication networks and / or store the digital video data on storage devices. Because communication networks have limited bandwidth capacity and storage devices have limited memory resources, video coding may be used to compress the video data according to one or more video coding standards before the video data is communicated or stored.

[0004] Multiple video codec standards have been developed. For example, video coding standards include AOMedia Video 1 (AV1), Versatile Video Coding (VVC), Joint Exploration test Model (JEM), High-Efficiency Video Coding (HEVC / H.265), Advanced Video Coding (AVC / H.264), and Moving Picture Expert Group (MPEG) coding. Video coding generally utilizes prediction methods (e.g., inter-prediction, intra-prediction, etc.) that exploit the redundancy inherent in video data. Video coding aims to compress video data into a format that uses a lower bitrate while avoiding or minimizing degradation of video quality.

[0005] HEVC, also known as H.265, is a video compression standard designed as part of the MPEG-H project. ITU-T and ISO / IEC published the HEVC / H.265 standard in 2013 (Version 1), 2014 (Version 2), 2015 (Version 3), and 2016 (Version 4). Versatile Video Coding (VVC), also known as H.266, is a video compression standard intended as the successor to HEVC. ITU-T and ISO / IEC published the VVC / H.266 standard in 2020 (Version 1) and 2022 (Version 2). AV1 is an open video coding format designed as a replacement for HEVC. The effective version 1.0.0 of this specification, including Errata 1, was released on January 8, 2019. Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, a video stream may be encoded into a bitstream that includes compression and then sent to a decoder that can decode / decompress the video stream for viewing or further processing. Compression of the video stream may exploit spatial and temporal correlation in the video signal through spatial and / or motion-compensated prediction. Motion-compensated prediction may include inter-prediction. Inter-prediction may use one or more motion vectors to generate a block to be encoded using previously encoded and decoded pixels. A decoder that receives the encoding signal may recreate the block.

[0007] Not all motion across an image is translational. Therefore, translational motion patterns cannot accurately describe complex motions such as rotation, zoom, and shear. To overcome this drawback, a warp motion mode using an affine model can be used. However, it is important to determine when (e.g., on which blocks) warp motion is allowed and which warp samples to use for the warp model. [Means for solving the problem]

[0008] According to some embodiments, a method for encoding video is provided, the method including: (i) obtaining video data including a plurality of blocks including a first block; (ii) identifying two or more warp groups for the first block; (iii) determining a respective cost associated with each warp group of the two or more warp groups; (iv) selecting a warp group from the two or more warp groups based on the respective costs; and (v) encoding the first block according to the selected warp group.

[0009] According to some embodiments, a method for decoding video is provided, the method including: (i) obtaining, from a bitstream, video data including a plurality of blocks including a first block; (ii) identifying a selected warp group from two or more warp groups; and (iii) decoding the first block according to the selected warp group.

[0010] According to some embodiments, a computing system, such as a streaming system, a server system, a personal computer system, or other electronic device, is provided. The computing system includes control circuitry and a memory that stores one or more instruction sets. The one or more instruction sets include instructions for performing any of the methods described herein. In some embodiments, the computing system includes an encoder component and / or a decoder component.

[0011] According to some embodiments, a non-transitory computer-readable storage medium is provided that stores one or more sets of instructions for execution by a computing system, the one or more sets of instructions including instructions for performing any of the methods described herein.

[0012] Accordingly, disclosed are devices and systems having methods for encoding / decoding video, which may complement or replace conventional methods, devices, and systems for video encoding / decoding.

[0013] The features and advantages described herein are not necessarily all-inclusive, and in particular, some additional features and advantages will be apparent to those skilled in the art upon consideration of the drawings, specification, and claims provided in this disclosure. Furthermore, it should be noted that the language used herein has been chosen primarily for purposes of readability and explanation, and not necessarily to describe or limit the subject matter described herein.

[0014] In order that the present disclosure may be more fully understood, a more particular description may be made by reference to features of various embodiments, some of which are shown in the accompanying drawings. However, the accompanying drawings merely illustrate relevant features of the present disclosure and therefore should not be considered necessarily limiting, as the description may recognize other useful features as understood by those skilled in the art upon reading the present disclosure. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a block diagram illustrating an exemplary communication system according to some embodiments. [Figure 2A] FIG. 2 is a block diagram illustrating exemplary elements of an encoder component according to some embodiments. [Figure 2B] FIG. 2 is a block diagram illustrating exemplary elements of a decoder component according to some embodiments. [Figure 3] FIG. 1 is a block diagram illustrating an exemplary server system according to some embodiments. [Figure 4A] FIG. 2 illustrates an exemplary coding tree structure according to some embodiments. [Figure 4B] FIG. 2 illustrates an exemplary coding tree structure according to some embodiments. [Figure 4C] FIG. 2 illustrates an exemplary coding tree structure according to some embodiments. [Figure 4D] FIG. 2 illustrates an exemplary coding tree structure according to some embodiments. [Figure 5A]FIG. 10 illustrates MMDV search points in two reference frames according to some embodiments. [Figure 5B] 4A-4C illustrate example motion samples used to derive model parameters for a block using warped motion prediction according to some embodiments. [Figure 5C] FIG. 10 illustrates exemplary motion vectors within a block using warp motion mode in accordance with some embodiments. [Figure 5D] FIG. 1 illustrates a current block with four spatially neighboring blocks according to some embodiments. [Figure 5E] FIG. 1 illustrates a current block with 10 neighboring blocks according to some embodiments. [Figure 6A] 1 is a flow diagram illustrating an exemplary method for encoding video according to some embodiments. [Figure 6B] 1 is a flow diagram illustrating an exemplary method for decoding video according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0016] According to common practice, the various features illustrated in the drawings are not necessarily drawn to scale, and like reference numerals may be used to denote like features throughout the specification and drawings.

[0017] This disclosure describes, among other things, improvements to warp motion modes in video encoding and decoding, for example, by considering multiple warp groups and selecting the warp group that results in the lowest loss (highest accuracy) in encoding / decoding. In some cases, coding efficiency is improved by signaling (e.g., via one or more flags) whether multi-group warp mode is enabled and / or which warp group is selected. In some cases, coding efficiency is improved by deriving (e.g., using context information) the selected warp group to use during encoding / decoding.

[0018] Exemplary Systems and Devices 1 is a block diagram illustrating a communication system 100 according to some embodiments. The communication system 100 includes a source device 102 and a plurality of electronic devices 120 (e.g., electronic devices 120-1 through 120-m) communicatively coupled to one another via one or more networks. In some embodiments, the communication system 100 is a streaming system for use in video-enabled applications, such as, for example, video conferencing applications, digital TV applications, and media storage and / or distribution applications.

[0019] Source device 102 includes a video source 104 (e.g., a camera component or media storage) and an encoder component 106. In some embodiments, video source 104 is a digital camera (e.g., configured to generate an uncompressed video sample stream). Encoder component 106 generates one or more encoded video bitstreams from the video stream. The video stream from video source 104 may have a high data volume compared to encoded video bitstream 108 generated by encoder component 106. Because encoded video bitstream 108 has a lower data volume (less data) compared to the video stream from the video source, encoded video bitstream 108 requires less bandwidth for transmission and less storage space for storage compared to the video stream from video source 104. In some embodiments, source device 102 does not include encoder component 106 (e.g., configured to transmit uncompressed video data to network 110).

[0020] The one or more networks 110 represent any number of networks that convey information between the source device 102, the server system 112, and / or the electronic device 120, including, for example, wired (cabled) and / or wireless communication networks. The one or more networks 110 may exchange data over circuit-switched and / or packet-switched channels. Exemplary networks include telecommunications networks, local area networks, wide area networks, and / or the Internet.

[0021] The one or more networks 110 include a server system 112 (e.g., a distributed / cloud computing system). In some embodiments, the server system 112 is or includes a streaming server (e.g., configured to store and / or distribute video content, such as an encoded video stream from the source device 102). The server system 112 includes a coder component 114 (e.g., configured to encode and / or decode video data). In some embodiments, the coder component 114 includes an encoder component and / or a decoder component. In various embodiments, the coder component 114 is instantiated as hardware, software, or a combination thereof. In some embodiments, the coder component 114 is configured to decode the encoded video bitstream 108 and re-encode the video data using a different encoding standard and / or method to generate encoded video data 116. In some embodiments, the server system 112 is configured to generate multiple video formats and / or encodings from the encoded video bitstream 108.

[0022] In some embodiments, server system 112 functions as a media-enabled network element (MANE). For example, server system 112 may be configured to prune encoded video bitstream 108 to adapt potentially different bitstreams to one or more of electronic devices 120. In some embodiments, a MANE is provided separate from server system 112.

[0023] Electronic device 120-1 includes a decoder component 122 and a display 124. In some embodiments, decoder component 122 is configured to decode encoded video data 116 to generate an output video stream that can be rendered on a display or other type of rendering device. In some embodiments, one or more of electronic devices 120 does not include a display component (e.g., communicatively coupled to an external display device and / or includes media storage). In some embodiments, electronic device 120 is a streaming client. In some embodiments, electronic device 120 is configured to access server system 112 to obtain encoded video data 116.

[0024] The source device and / or the plurality of electronic devices 120 may also be referred to as “terminal devices” or “user devices.” In some embodiments, one or more of the source device 102 and / or the electronic devices 120 are instances of a server system, a personal computer, a portable device (e.g., a smartphone, tablet, or laptop), a wearable device, a videoconferencing device, and / or other types of electronic devices.

[0025] In an exemplary operation of communication system 100, source device 102 transmits encoded video bitstream 108 to server system 112. For example, source device 102 may code a stream of pictures captured by the source device. Server system 112 may receive encoded video bitstream 108 and decode and / or encode encoded video bitstream 108 using coder component 114. For example, server system 112 may apply encoding to the video data suitable for network transmission and / or storage. Server system 112 may transmit encoded video data 116 (e.g., one or more coded video bitstreams) to one or more of electronic devices 120. Each electronic device 120 may decode encoded video data 116 to recover, and optionally display, video pictures.

[0026] In some embodiments, the transmission is a unidirectional data transmission. Unidirectional data transmission may be utilized in media serving applications, etc. In some embodiments, the transmission is a bidirectional data transmission. Bidirectional data transmission may be utilized in video conferencing applications, etc. In some embodiments, the encoded video bitstream 108 and / or the encoded video data 116 are encoded and / or decoded according to any of the video coding / compression standards described herein, such as HEVC, VVC, and / or AV1.

[0027] FIG. 2A is a block diagram illustrating exemplary elements of the encoder component 106 according to some embodiments. The encoder component 106 receives a source video sequence from a video source 104. In some embodiments, the encoder component includes a receiver (e.g., transceiver) component configured to receive the source video sequence. In some embodiments, the encoder component 106 receives a video sequence from a remote video source (e.g., a video source that is a component of a device different from the encoder component 106). The video source 104 may provide the source video sequence in the form of a digital video sample stream that may be of any suitable bit depth (e.g., 8-bit, 10-bit, or 12-bit), any color space (e.g., BT.601 Y CrCb, or RGB), and any suitable sampling structure (e.g., Y CrCb 4:2:0 or Y CrCb 4:4:4). In some embodiments, the video source 104 is a storage device that stores previously captured / prepared video. In some embodiments, the video source 104 is a camera that captures local image information as a video sequence. Video data may be provided as multiple individual pictures that, when viewed sequentially, convey motion. The pictures themselves are organized as a spatial array of pixels, each of which may contain one or more samples, depending on the sampling structure, color space, etc., in use. Those skilled in the art will readily understand the relationship between pixels and samples. The following discussion focuses on samples.

[0028] The encoder component 106 is configured to code and / or compress pictures of a source video sequence into a coded video sequence 216 in real time or under other time constraints required by the application. Enforcing an appropriate coding rate is one function of the controller 204. In some embodiments, the controller 204 controls and is operatively coupled to other functional units described below. Parameters set by the controller 204 may include rate control-related parameters (e.g., picture skip, quantizer, and / or lambda value for rate-distortion optimization techniques), picture size, group of pictures (GOP) layout, maximum motion vector search range, etc. Those skilled in the art can readily identify other functions of the controller 204 that may be associated with the encoder component 106 being optimized for a particular system design.

[0029] In some embodiments, the encoder component 106 is configured to operate in a coding loop. In a simplified example, the coding loop includes a source coder 202 (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 210. The decoder 210 reconstructs the symbols to generate sample data, similar to a (remote) decoder (when the compression between the symbols and the coded video bitstream is lossless). The reconstructed sample stream (sample data) is input to a reference picture memory 208. Because decoding the symbol stream produces bit-exact results regardless of the location of the decoder (local or remote), the contents of the reference picture memory 208 are also bit-exact between the local and remote encoders. In this way, the encoder's predictor interprets the same sample values ​​as reference picture samples as the decoder interprets when using prediction during decoding. This principle of reference picture synchrony (and the resulting drift if synchrony cannot be maintained, e.g., due to channel error) is known to those skilled in the art.

[0030] The operation of decoder 210 may be the same as that of a remote decoder, such as decoder component 122, described in detail below in connection with Figure 2B. However, with brief reference to Figure 2B, because symbols are available and the encoding / decoding of the symbols into a coded video sequence by entropy coder 214 and parser 254 may be lossless, the entropy decoding portion of decoder component 122, including buffer memory 252 and parser 254, may not be fully implemented in local decoder 210.

[0031] At this point, it can be said that any decoder technology other than analysis / entropy decoding present in the decoder must also necessarily exist in the corresponding encoder in substantially the same functional form. For this reason, the subject matter of this disclosure focuses on the operation of the decoder. The description of the encoder technology can be omitted because the encoder technology is the opposite of the decoder technology, which is described generically. Only certain parts require more detailed description, which are shown below.

[0032] As part of its operation, source coder 202 may perform motion-compensated predictive coding, which predictively codes an input frame with reference to one or more previously coded frames from a video sequence designated as reference frames. In this method, coding engine 212 codes differences between pixel blocks of the input frame and pixel blocks of reference frames that may be selected as predictive references for the input frame. Controller 204 may manage the coding operations of source coder 202, including, for example, setting parameters and subgroup parameters used to encode the video data.

[0033] The decoder 210 decodes the coded video data of frames that may be designated as reference frames based on symbols created by the source coder 202. The operation of the coding engine 212 may preferably be a lossy process. When the coded video data is decoded by a video decoder (not shown in FIG. 2A ), the reconstructed video sequence may be a replica of the source video sequence with some errors. The decoder 210 may replicate the decoding process that may be performed by a remote video decoder on the reference frames and store the reconstructed reference frames in the reference picture memory 208. In this way, the encoder component 106 locally stores copies of reconstructed reference frames that have common content as the reconstructed reference frames that will be obtained by the remote video decoder (without transmission errors).

[0034] The predictor 206 may perform a predictive search for the coding engine 212. That is, for a new frame to be coded, the predictor 206 may search the reference picture memory 208 for sample data (as candidate reference pixel blocks) or for specific metadata, such as reference picture motion vectors, block shapes, etc., that can serve as suitable predictive references for the new picture. The predictor 206 may operate on sample block by pixel block to find a suitable predictive reference. In some cases, as determined by the search results obtained by the predictor 206, the input picture may have predictive references drawn from multiple reference pictures stored in the reference picture memory 208.

[0035] The outputs of all the aforementioned functional units may undergo entropy coding in entropy coder 214. Entropy coder 214 converts the symbols produced by the various functional units into a coded video sequence by losslessly compressing the symbols according to techniques known to those skilled in the art (e.g., Huffman coding, variable length coding, and / or arithmetic coding).

[0036] In some embodiments, the output of the entropy coder 214 is coupled to a transmitter. The transmitter may be configured to buffer the coded video sequence generated by the entropy coder 214 and prepare it for transmission over a communication channel 218, which may be a hardware / software link to a storage device that stores the encoded video data. The transmitter may be configured to merge the coded video data from the source coder 202 with other data to be transmitted, such as coded audio data and / or an auxiliary data stream (source not shown). In some embodiments, the transmitter may transmit additional data along with the encoded video. The source coder 202 may include such data as part of the coded video sequence. The additional data may include other forms of redundant data, such as temporal / spatial / SNR enhancement layers, redundant pictures and slices, supplemental enhancement information (SEI) messages, visual usability information (VUI) parameter set fragments, etc.

[0037] The controller 204 may manage the operation of the encoder component 106. During coding, the controller 204 may assign a specific coded picture type to each coded picture, which may affect the coding technique applied to the respective picture. For example, a picture may be assigned as an intra picture (I picture), a predicted picture (P picture), or a bidirectionally predicted picture (B picture). An intra picture may be coded and decoded without using any other frame in the 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 will recognize these variations of I pictures and their respective uses and characteristics, so they will not be repeated here. A predicted picture may be coded and decoded using intra prediction or inter prediction, which uses at most one motion vector and reference index to predict sample values ​​for each block. Bidirectionally predicted pictures can be coded and decoded using intra or inter prediction, which uses up to two motion vectors and reference indices to predict the sample values ​​of each block. Similarly, multiple predicted pictures can use more than two reference pictures and associated metadata for the reconstruction of a single block.

[0038] A source picture may generally be spatially subdivided into multiple sample blocks (e.g., blocks of 4x4, 8x8, 4x8, or 16x16 samples each) 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 the block's respective picture. For example, blocks of an I-picture may be nonpredictively coded or predictively coded with reference to already coded blocks of the same picture (spatial prediction or intra-prediction). Pixel blocks of a P-picture may be nonpredictively coded via spatial prediction or via temporal prediction with reference to one previously coded reference picture. Pixel blocks of a B-picture may be nonpredictively coded via spatial prediction or via temporal prediction with reference to one or two previously coded reference pictures.

[0039] Video may be captured in time sequence as multiple source pictures (video pictures). Intra-picture prediction (often abbreviated as intra-prediction) uses spatial correlation within a given picture, while inter-picture prediction uses correlation (temporal or other) between pictures. In one example, a particular picture being encoded / decoded, called the current picture, is divided into blocks. When a block in the current picture is similar to a reference block in a previously coded and still buffered reference picture in the video, the block in the current picture may be coded by a vector called a motion vector. The motion vector points to a reference block in the reference picture and may have a third dimension that identifies the reference picture if multiple reference pictures are used.

[0040] Encoder component 106 may perform coding operations according to a predetermined video coding technique or standard, such as any of those described herein. In doing so, encoder component 106 may perform various compression operations, including predictive coding operations that exploit temporal and spatial redundancies in the input video sequence. Thus, the coded video data may conform to a syntax specified by the video coding technique or standard being used.

[0041] 2B is a block diagram illustrating exemplary elements of the decoder component 122 according to some embodiments. The decoder component 122 of FIG. 2B is coupled to the channel 218 and the display 124. In some embodiments, the decoder component 122 includes a transmitter coupled to the loop filter unit 256 and configured to transmit data to the display 124 (e.g., via a wired or wireless connection).

[0042] In some embodiments, decoder component 122 includes a receiver coupled to channel 218 and configured to receive data from channel 218 (e.g., via a wired or wireless connection). The receiver may be configured to receive one or more coded video sequences to be decoded by decoder component 122. In some embodiments, the decoding of each coded video sequence is independent of the other coded video sequences. Each coded video sequence may be received from channel 218, which may be a hardware / software link to a storage device that stores the encoded video data. The receiver receives the encoded video data along with other data, e.g., coded audio data and / or auxiliary data streams, which may be forwarded to their respective using entities (not shown). The receiver may separate the coded video sequence from the other data. In some embodiments, the receiver receives additional (redundant) data along with the encoded video. The additional data may be included as part of the coded video sequence. The additional data may be used by decoder component 122 to decode the data and / or to more accurately reconstruct the original video data. The additional data may be in the form of, for example, a temporal layer, a spatial layer, or an SNR enhancement layer, redundant slices, redundant pictures, forward error correction codes, etc.

[0043] According to some embodiments, the decoder component 122 includes a buffer memory 252, a parser 254 (sometimes referred to as an entropy decoder), a scaler / inverse transform unit 258, an intra-picture prediction unit 262, a motion compensation prediction unit 260, an aggregator 268, a loop filter unit 256, a reference picture memory 266, and a current picture memory 264. In some embodiments, the decoder component 122 is implemented as an integrated circuit, a series of integrated circuits, and / or other electronic circuitry. In some embodiments, the decoder component 122 is implemented at least partially in software.

[0044] Buffer memory 252 is coupled between channel 218 and parser 254 (e.g., to combat network jitter). In some embodiments, buffer memory 252 is separate from decoder component 122. In some embodiments, a separate buffer memory is provided between the output of channel 218 and decoder component 122. In some embodiments, in addition to buffer memory 252 within decoder component 122 (e.g., configured to handle playout timing), a separate buffer memory is provided external to decoder component 122 (e.g., to combat network jitter). When receiving data from a storage / forwarding device with sufficient bandwidth and controllability or from an isosynchronous network, buffer memory 252 may be unnecessary or may be small. For use in a best-effort packet network such as the Internet, buffer memory 252 may be required, and may be relatively large, advantageously adaptively sized, and at least partially implemented in an operating system or similar element (not shown) external to decoder component 122.

[0045] The parser 254 is configured to reconstruct symbols 270 from the coded video sequence. The symbols may include, for example, information used to manage the operation of the decoder component 122 and / or information for controlling a rendering device such as the display 124. The control information for the rendering device may be in the form of, for example, a supplemental enhancement information (SEI) message or a video usability information (VUI) parameter set fragment (not shown). The parser 254 parses (entropy decodes) the coded video sequence. The coding of the coded video sequence may follow a video coding technique or standard and may follow principles well known to those skilled in the art, including variable length coding, Huffman coding, arithmetic coding with or without context sensitivity, etc. The parser 254 may extract a set of subgroup parameters for at least one of the subgroups of pixels in the video decoder from the coded video sequence based on at least one parameter corresponding to the group. The subgroup 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. Parser 254 may also extract information from the coded video sequence, such as transform coefficients, quantization parameter values, motion vectors, etc.

[0046] The reconstruction of symbols 270 may involve several different units, depending on the type of video picture or portion thereof being coded (inter-picture and intra-picture, inter-block and intra-block, etc.), as well as other factors. Which units are involved and how they are involved may be controlled by subgroup control information parsed from the coded video sequence by parser 254. The flow of such subgroup control information between parser 254 and the following units is not depicted for convenience of explanation.

[0047] In addition to the functional blocks already mentioned, the decoder component 122 can be conceptually subdivided into several functional units, as described below. In an actual implementation operating under commercial constraints, many of these units will interact closely with each other and may be at least partially integrated with each other. However, for purposes of describing the disclosed subject matter, the conceptual division into the following functional units will be maintained.

[0048] The scaler / inverse transform unit 258 receives the quantized transform coefficients as well as control information (e.g., which transform to use, block size, quantization coefficients, and / or quantization scaling matrices) as symbols 270 from the parser 254. The scaler / inverse transform unit 258 may output blocks containing sample values ​​that may be input to an aggregator 268.

[0049] In some cases, the output samples of the scaler / inverse transform unit 258 relate to intra-coded blocks, i.e., blocks that do not use prediction information from a previously reconstructed picture but can use prediction information from a previously reconstructed portion of the current picture. Such prediction information may be provided by the intra-picture prediction unit 262. The intra-picture prediction unit 262 may generate blocks of the same size and shape as the block being reconstructed using surrounding already reconstructed information fetched from the current (partially reconstructed) picture from the current picture memory 264. The aggregator 268 may add, on a sample-by-sample basis, the prediction information generated by the intra-picture prediction unit 262 to the output sample information provided by the scaler / inverse transform unit 258.

[0050] In other cases, the output samples of the scalar / inverse transform unit 258 relate to an inter-coded, potentially motion-compensated, block. In such cases, the motion-compensated prediction unit 260 may access the reference picture memory 266 to fetch samples used for prediction. After motion-compensating the fetched samples according to symbols 270 associated with the block, these samples may be added by the aggregator 268 to the output of the scalar / inverse transform unit 258 to generate output sample information (in this case, referred to as residual samples or a residual signal). The addresses in the reference picture memory 266 from which the motion-compensated prediction unit 260 fetches the prediction samples may be controlled by motion vectors. The motion vectors may be available to the motion-compensated prediction unit 260 in the form of symbols 270, which may have, for example, X, Y, and reference picture components. Motion compensation may also include interpolation of fetched sample values ​​from the reference picture memory 266 when sub-sample accurate motion vectors are used, motion vector prediction mechanisms, and the like.

[0051] The output samples of aggregator 268 may be subjected to various loop filtering techniques in loop filter unit 256. Video compression techniques may include in-loop filter techniques controlled by parameters included in the coded video bitstream and made available to loop filter unit 256 as symbols 270 from parser 254, but may also be responsive to meta-information obtained during decoding of a coded picture or previous portion (in decoding order) of the coded video sequence, or to previously reconstructed and loop-filtered sample values.

[0052] The output of the loop filter unit 256 may be a sample stream that can be output to a rendering device such as the display 124, and also stored in a reference picture memory 266 for use in future inter-picture prediction.

[0053] Once fully reconstructed, a particular coded picture can be used as a reference picture for future prediction. Once a coded picture is fully reconstructed and the coded picture is identified as a reference picture (e.g., by parser 254), the current reference picture can become part of reference picture memory 266, and a new current picture memory can be reallocated before starting reconstruction of the next coded picture.

[0054] Decoder component 122 may perform decoding operations according to a predetermined video compression technology, which may be documented in a standard, such as any of the standards described herein. The coded video sequence may conform to the syntax specified by the video compression technology or standard being used, in the sense of adhering to the syntax of the video compression technology or standard as specified in the video compression technology document or standard, specifically the profile document therein. To comply with some video compression technologies or standards, the complexity of the coded video sequence may also be within a range specified by the level of the video compression technology or standard. In some cases, the level limits the maximum picture size, maximum frame rate, maximum reconstruction sample rate (e.g., measured in megasamples per second), maximum reference picture size, etc. The limits set by the level may, in some cases, be further limited by a hypothetical reference decoder (HRD) specification and HRD buffer management metadata signaled in the coded video sequence.

[0055] 3 is a block diagram illustrating a server system 112 according to some embodiments. The server system 112 includes a control circuit 302, one or more network interfaces 304, a memory 314, a user interface 306, and one or more communication buses 312 for interconnecting these components. In some embodiments, the control circuit 302 includes one or more processors (e.g., a CPU, a GPU, and / or a DPU). In some embodiments, the control circuit includes one or more field programmable gate arrays (FPGAs), hardware accelerators, and / or one or more integrated circuits (e.g., application specific integrated circuits).

[0056] The network interface 304 may be configured to interface with one or more communication networks (e.g., wireless, wired, and / or optical networks). The communication networks may be local, wide-area, metropolitan, vehicular and industrial, real-time, delay-tolerant, etc. Examples of communication networks include local area networks such as Ethernet, cellular networks including WLAN, GSM, 3G, 4G, 5G, LTE, etc., television wired or wireless wide-area digital networks including cable, satellite, and terrestrial television, vehicular and industrial networks including CANBus, etc. Such communications may be unidirectional, receive only (e.g., broadcast television), unidirectional transmit only (e.g., CANbus to a specific CANbus device), or bidirectional (e.g., to another computer system using a local or wide-area digital network). Such communications may include communications to one or more cloud computing networks.

[0057] The user interface 306 includes one or more output devices 308 and / or one or more input devices 310. The input devices 310 may include one or more of a keyboard, a mouse, a trackpad, a touchscreen, a data glove, a joystick, a microphone, a scanner, a camera, etc. The output devices 308 may include one or more of an audio output device (e.g., a speaker), a visual output device (e.g., a display or monitor), etc.

[0058] Memory 314 may include high-speed random-access memory (such as DRAM, SRAM, DDR RAM, and / or other random-access solid-state memory devices) and / or non-volatile memory (such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, and / or other non-volatile solid-state storage devices). Memory 314 optionally includes one or more storage devices located remotely from control circuitry 302. Memory 314, or a non-volatile solid-state memory device within memory 314, comprises a non-transitory computer-readable storage medium. In some embodiments, memory 314, or the non-transitory computer-readable storage medium of memory 314, stores the following programs, modules, instructions, and data structures, or a subset or superset thereof: • an operating system 316 that handles various basic system services and includes procedures for performing hardware-dependent tasks; • a network communications module 318 used to connect the server system 112 to other computing devices via one or more network interfaces 304 (e.g., via wired and / or wireless connections); A coding module 320 for performing various functions related to encoding and / or decoding of data, such as video data. In some embodiments, the coding module 320 is an instance of the coder component 114. The coding module 320 may include, but is not limited to, one or more of the following: a decoding module 322 for performing various functions relating to decoding of the encoded data, such as those described above with respect to the decoder component 122; and an encoding module 340 for performing various functions relating to encoding data, such as those described above with respect to the encoder component 106; and A picture memory 352 that stores pictures and picture data and is used, for example, with the coding module 320. In some embodiments, the picture memory 352 includes one or more of the reference picture memory 208, the buffer memory 252, the current picture memory 264, and the reference picture memory 266.

[0059] In some embodiments, the decoding module 322 includes a parsing module 324 (e.g., configured to perform the various functions described above with respect to the parser 254), a transform module 326 (e.g., configured to perform the various functions described above with respect to the scaler / inverse transform unit 258), a prediction module 328 (e.g., configured to perform the various functions described above with respect to the motion compensation prediction unit 260 and / or the intra-picture prediction unit 262), and a filter module 330 (e.g., configured to perform the various functions described above with respect to the loop filter unit 256).

[0060] In some embodiments, the encoding module 340 includes a code module 342 (e.g., configured to perform various functions described above with respect to the source coder 202, the coding engine 212, and / or the entropy coder 214) and a prediction module 344 (e.g., configured to perform various functions described above with respect to the predictor 206). In some embodiments, the decoding module 322 and / or the encoding module 340 include a subset of the modules shown in FIG. 3. For example, a shared prediction module is used by both the decoding module 322 and the encoding module 340.

[0061] Each of the above-identified modules stored in memory 314 corresponds to an instruction set for performing the functions described herein. The above-identified modules (e.g., instruction sets) need not be implemented as separate software programs, procedures, or modules; thus, various subsets of these modules may be combined or otherwise rearranged in various embodiments. For example, coding module 320 optionally does not include separate decoding and encoding modules, but rather uses the same set of modules to perform both sets of functionality. In some embodiments, memory 314 stores a subset of the above-identified modules and data structures. In some embodiments, memory 314 stores additional modules and data structures not described above, such as an audio processing module.

[0062] In some embodiments, the server system 112 includes a web or Hypertext Transfer Protocol (HTTP) server, a File Transfer Protocol (FTP) server, and web pages and applications implemented using Common Gateway Interface (CGI) scripts, the PHP Hypertext Preprocessor (PHP), Active Server Pages (ASP), Hypertext Markup Language (HTML), Extensible Markup Language (XML), Java, JavaScript, Asynchronous JavaScript and XML (AJAX), XHP, Javelin, Wireless Universal Resource Files (WURFL), and the like.

[0063] While FIG. 3 illustrates a server system 112 according to some embodiments, FIG. 3 is not intended as a structural schematic of the embodiments described herein, but rather as a functional description of various features that may be present in one or more server systems. In practice, and as will be recognized by those skilled in the art, items shown separately may be combined and some items may be separated. For example, some items shown separately in FIG. 3 may be implemented on a single server, and single items may be implemented by one or more servers. The actual number of servers used to implement server system 112 and how functionality is allocated among them will vary from implementation to implementation and, optionally, depend in part, on the amount of data traffic the server system handles during peak and average usage periods.

[0064] Example Coding Approach 4A-4D show exemplary coding tree structures according to some embodiments. As shown in the first coding tree structure (400) in FIG. 4A, some coding techniques (e.g., VP9) use a 4-way partition tree from a 64x64 level down to a 4x4 level, with some additional restrictions on 8x8 blocks. Note that in FIG. 4A, the partition designated as R refers to recursion, in that the same partition tree is repeated at a lower scale until a minimum of a 4x4 level is reached.

[0065] As shown in the second coding tree structure (402) of FIG. 4B, some coding techniques (e.g., AV1) extend the partition tree to a 10-way structure, increasing the maximum size (e.g., called a superblock in VP9 / AV1 parlance) from 128x128. The second coding tree structure includes a 4:1 / 1:4 rectangular partition not found in the first coding tree structure. The partition type with three subpartitions in the second row of FIG. 4B is called a T-type partition. The rectangular partitions in this tree structure cannot be further subdivided. In addition to the coding block size, a coding tree depth can be defined to indicate the division depth from the root node. Specifically, the coding tree depth of the root node, e.g., 128x128, is set to 0, and after the tree block is further divided, the coding tree depth increases by 1.

[0066] Rather than enforcing a fixed transform unit size as in VP9, ​​AV1 allows luma coding blocks to be divided into transform units of multiple sizes that can be represented by recursive partitions down by up to two levels. To incorporate AV1's expanded coding block partitions, square, 2:1 / 1:2, and 4:1 / 1:4 transform sizes are supported, ranging from 4x4 to 64x64. For chroma blocks, only the largest possible transform units are allowed.

[0067] As an example, to adapt to various local characteristics, such as in HEVC, CTUs may be divided into CUs by using a quadtree structure represented as a coding tree. The decision of whether to use inter-picture (temporal) prediction or intra-picture (spatial) prediction to code a picture area is made at the CU level. Each CU can be further divided into one, two, or four PUs depending on the PU partition type. The same prediction process is applied within one PU, and related information is transmitted to the decoder on a PU-by-PU basis. After obtaining residual blocks by applying a prediction process based on the PU partition type, the CU can be divided into TUs according to another quadtree structure, such as the CU's coding tree. One important feature of the HEVC structure is its multiple partition concepts, including CUs, PUs, and TUs. In HEVC, CUs or TUs can only be square in shape, while PUs can be square or rectangular in shape for inter-predicted blocks. In HEVC, one coding block may be further divided into four square sub-blocks, and a transform is performed on each sub-block (TU). Each TU can be further divided recursively (using quadtree partitioning) into smaller TUs called residual quadtrees (RQTs). At picture boundaries, such as in HEVC, implicit quadtree partitioning can be employed so that blocks maintain the quadtree partitioning until their size fits the picture boundary.

[0068] A quaternary tree with nested multitype trees using binary and ternary split segment structures such as VVC can replace the concept of multiple partition unit types, eliminating the separation of CU, PU, ​​and TU concepts except when necessary for CUs with sizes too large for the maximum transform length, and supporting high flexibility in CU partition shapes. In the coding tree structure, CUs can have either square or rectangular shapes. ACTUs are first partitioned using a quaternary tree (also called a quad-tree) structure. Leaf nodes of the quaternary tree can then be further split using a multitype tree structure. As shown in the third coding tree structure (404) in FIG. 4C, the multitype tree structure includes four split types. For example, the multitype tree structure includes a vertical binary split (SPLIT_BT_VER), a horizontal binary split (SPLIT_BT_HOR), a vertical ternary split (SPLIT_TT_VER), and a horizontal ternary split (SPLIT_TT_HOR). The leaf nodes of the multitype tree are called CUs, and this segmentation is used for prediction and transform processing without further division, unless the CU is too large for the maximum transform length. This means that in most cases, CUs, PUs, and TUs have the same block size in a quadtree with a nested multitype tree coding block structure. An exception occurs when the supported maximum transform length is smaller than the width or height of the color components of the CU. An example of block partitioning for one CTU (406) is shown in Figure 4D, which shows an exemplary quadtree with a nested multitype tree coding block structure.

[0069] The maximum supported luma transform size is 64x64, as in VVC, and the maximum supported chroma transform size may be 32x32. If the width or height of the CB is larger than the maximum transform width or height, the CB is automatically split horizontally and / or vertically to meet the transform size limit in that direction.

[0070] In VTM7, the coding tree scheme supports the ability for luma and chroma to have separate block tree structures. In some cases, for P slices and B slices, the luma CTB and chroma CTB in one CTU share the same coding tree structure. However, for I slices, luma and chroma can have separate block tree structures. When the separate block tree mode is applied, the luma CTB is divided into CUs by one coding tree structure, and the chroma CTB is divided into chroma CUs by another coding tree structure. This means that a CU in an I slice contains or consists of a coding block for the luma component or coding blocks for two chroma components, and a CU in a P slice or B slice can always contain or consist of coding blocks for all three color components unless the video is monochrome.

[0071] To support extended coding block partitions, multiple transform sizes (ranging from 4 points to 64 points in each dimension) and transform shapes (square, rectangular with width / height ratios of 2:1 / 1:2, and 4:1 / 1:4) are utilized for AV1, etc.

[0072] In merge mode, implicitly derived motion information can be directly used to generate the prediction sample for the current CU. A merge mode with motion vector difference (MMVD) is introduced to VVC. The MMVD flag is signaled immediately after sending the skip or merge flag and can specify whether the MMVD mode is used for the CU. In MMVD, after a merge candidate is selected, it can be further refined by the signaled MVD information. The MVD information may include a merge candidate flag, an index specifying the motion magnitude, and an index indicating the motion direction. In merge mode, one of the first two merge candidate flags in the merge list can be used as the MV base. The merge candidate flag can be signaled to specify which flag is used.

[0073] The distance index specifies the magnitude of the motion and indicates a predefined offset from the starting point. Figure 5A shows MMDV search points in two reference frames according to some embodiments. As shown in Figure 5A, the offset may be added to either the horizontal or vertical component of the starting MV. The relationship between the distance index and the predefined offset is shown in Table 1 below.

[0074] [Table 1]

[0075] The direction index represents the direction of the MVD relative to the starting point. The direction index may represent one of four directions shown in Table 2 below. The meaning of the MVD code may differ according to the information of the starting MV. If the starting MV is a uni-predictive MV or a bi-predictive MV where both lists point to the same side of the current picture (e.g., the POCs of the two references are both greater than the POC of the current picture, or both less than the POC of the current picture), the code in Table 2 specifies the sign of the MV offset added to the starting MV. If the starting MV is a bi-predictive MV where two MVs point to different sides of the current picture (e.g., the POC of one reference is greater than the POC of the current picture, and the POC of the other reference is less than the POC of the current picture), and the difference of the POC in list 0 (L0) is greater than the difference of the POC in list 1 (L1), the code in Table 2 specifies the sign of the MV offset added to the MV component of L0 of the starting MV, and the sign of the MV of L1 has an opposite value. If the POC difference in L1 is greater than L0, the sign in Table 2 specifies the sign of the MV offset added to the MV component of L1 of the starting MV, and the sign of the MV of L0 has the opposite value.

[0076] In some embodiments, the MVD is scaled according to the difference in each direction of the POC. For example, if the difference in the POC in both lists is the same, no scaling is required. If the difference in the POC in L0 is greater than the difference in the POC of L1, the MVD of L1 is scaled. If the POC difference of L1 is greater than L0, the MVD of L0 is scaled as well. If the starting MV is uni-predicted, the MVD is added to the available MV.

[0077] [Table 2]

[0078] As an example, in VVC, in addition to the normal unidirectional prediction and bidirectional prediction mode MVD signaling, a symmetric MVD mode of bidirectional MVD signaling may be applied. In the symmetric MVD mode, motion information including both L0 and L1 reference picture indexes and the MVD of L1 may be derived (but not signaled).

[0079] The decoding process for the symmetric MVD mode may be as follows: First, at the slice level, the variables BiDirPredFlag, RefIdxSymL0, and RefIdxSymL1 are derived. For example, if mvd_l1_zero_flag is 1, set BiDirPredFlag equal to 0. If the nearest reference picture in L0 and the nearest reference picture in L1 form a forward-backward pair of reference pictures or a backward-forward pair of reference pictures, BiDirPredFlag is set to 1, and both the reference pictures in L0 and L1 are short-term reference pictures. Otherwise, BiDirPredFlag is set to 0. Second, at the CU level, if a CU is bi-predictively coded and BiDirPredFlag is equal to 1, a symmetric mode flag indicating whether symmetric mode is used is explicitly signaled. If the symmetric mode flag is true (equal to 1), only mvp_l0_flag, mvp_l1_flag, and MVD0 are explicitly signaled. The L0 and L1 reference indices are set equal to a pair of reference pictures, respectively. Finally, MVD1 is set equal to (-MVD0).

[0080] In some embodiments, for each coded block in an interframe, if the mode of the current block is an inter-coded mode rather than a skip mode, a separate flag is signaled to indicate whether a single reference mode or a mixed reference mode is used for the current block. In the single reference mode, a predictive block may be generated by one motion vector. In the mixed reference mode, a predictive block is generated by a weighted average of two predictive blocks derived from two motion vectors. The modes that can be signaled in the single reference case are detailed in Table 3 below.

[0081] [Table 3]

[0082] The modes that can be signaled in case of mixed references are detailed in Table 4 below.

[0083] [Table 4]

[0084] Some standards, such as AV1, allow for 1 / 8-pixel motion vector accuracy (or precision). To signal motion vector differentials within reference frame list 0 (L0) or list 1 (L1), syntax may be used as follows: For example, the syntax mv_joint indicates which components of the motion vector differential are non-zero. A syntax mv_joint value of 0 indicates the absence of non-zero MVD along either the horizontal or vertical direction; a value of 1 indicates the presence of non-zero MVD along only the horizontal direction; a value of 2 indicates the presence of non-zero MVD along only the vertical direction; and a value of 3 indicates the presence of non-zero MVD along both the horizontal and vertical directions. The syntax mv_sign indicates whether the motion vector differential is positive or negative. The syntax mv_class indicates the class of the motion vector differential. As shown in Table 5 below, a higher class means a larger magnitude of the motion vector differential. The syntax mv_bit indicates the integer part of the offset between the motion vector differential and the start of the magnitude of each MV class. The syntax mv_fr indicates the first two fractional bits of the motion vector differential. The syntax mv_hp indicates the third fractional bit of the motion vector differential.

[0085] [Table 5]

[0086] For NEW_NEARMV and NEAR_NEWMV modes (shown in Table 4), the precision of the MVD depends on the associated class and the magnitude of the MVD. For example, fractional MVDs are only allowed if the magnitude of the MVD is one pixel or less. Then, only one MVD value is allowed if the associated MV class value is MV_CLASS_1 or greater, and the MVD value for each MV class is derived as 4, 8, 16, 32, or 64 for MV class 1 (MV_CLASS_1), MV class 2 (MV_CLASS_2), MV class 3 (MV_CLASS_3), MV class 4 (MV_CLASS_4), or MV class 5 (MV_CLASS_5). The allowed MVD values ​​for each MV class are shown in Table 6 below.

[0087] [Table 6]

[0088] In some embodiments, one context is used to signal mv_joint or mv_class if the current block is coded using NEW_NEARMV or NEAR_NEWMV mode, and another context is used to signal mv_joint or mv_class if the current block is not coded using NEW_NEARMV or NEAR_NEWMV mode.

[0089] An inter-coding mode, i.e., JOINT_NEWMV, may be applied to indicate whether the MVDs of two reference lists are jointly signaled. When the inter-prediction mode is equivalent to the JOINT_NEWMV mode, the MVDs of reference L0 and reference L1 are jointly signaled. Therefore, only one MVD, called joint_mvd, may be signaled and transmitted to the decoder, and the ΔMVs of reference L0 and reference L1 may be derived from joint_mvd. The JOINT_NEWMV mode is signaled together with the NEAR_NEARMV, NEAR_NEWMV, NEW_NEARMV, NEW_NEWMV, and GLOBAL_GLOBALMV modes.

[0090] When JOINT_NEWMV mode is signaled and the picture order count (POC) distances between two reference frames and the current frame are different, the MVD for reference L0 or reference L1 is scaled based on the POC distance. For example, the distance between reference frame L0 and the current frame is denoted as td0, and the distance between reference frame L1 and the current frame is denoted as td1. If td0 is equal to or greater than td1, joint_mvd is used directly for reference L0, and the mvd for reference L1 is derived from joint_mvd based on the following equation (1):

number

number

[0091] An inter-coded mode, i.e., AMVDMV, may be added to the single-reference example. When the AMVDMV mode is selected, it indicates that adaptive MVD resolution (AMVD) is applied to the signal MVD. A flag, e.g., amvd_flag, may be added in the JOINT_NEWMV mode to indicate whether AMVD is applied to the joint MVD coding mode. When adaptive MVD resolution is applied to the joint MVD coding mode (referred to as joint AMVD coding), the MVDs of two reference frames are signaled together, and the accuracy of the MVD is implicitly determined by the size of the MVD. The MVDs of two (or more) reference frames are signaled together, and MVD coding is applied.

[0092] AMVR, first proposed in CWG-C012, supports a total of seven MV precisions (8, 4, 2, 1, 1 / 2, 1 / 4, 1 / 8). For each prediction block, the AVM encoder explores all supported precision values ​​and signals the highest precision to the decoder. To reduce encoder runtime, two precision sets are supported. Each precision set contains four default precisions. The precision set is adaptively selected at the frame level based on the frame's maximum precision value. Similar to AV1, the maximum precision is signaled in the frame header. Table 7 summarizes the supported precision values ​​based on the frame-level maximum precision.

[0093] [Table 7]

[0094] In the AV1-like AOM Video Model (AVM), a frame-level flag exists to indicate whether the MV of a frame contains sub-pixel precision. AMVR is valid only if the value of the cur_frame_force_integer_mv flag is 0. In AMVR, if the block precision is less than the maximum precision, the motion model and interpolation filter are not signaled. If the block precision is less than the maximum precision, the motion mode is inferred as translational motion and the interpolation filter is inferred as a regular interpolation filter. Similarly, if the block precision is either 4 or 8 pixels, the inter-intra mode is not signaled and is inferred as 0.

[0095] Motion compensation usually assumes a translation motion model between the reference block and the target block, while warping motion uses an affine motion model, which can be expressed by the following equation (3):

number

[0096] In global warp motion compensation, for each inter reference frame, global motion information is signaled, which includes a global motion type and some motion parameters. The global motion types and the number of associated parameters are listed in Table 8.

[0097] [Table 8]

[0098] After signaling the reference frame index, if global motion is selected, the global motion type and parameters associated with the given reference frame are used for the current coding block.

[0099] In local warp motion compensation, local warp motion is allowed for inter-coding blocks if the following conditions are met: First, the current block must use single-reference prediction. The width or height of the coding block must be equal to or greater than 8. Finally, at least one of the adjacent neighboring blocks must use the same reference frame as the current block.

[0100] When local warp motion is used for the current block, the affine model parameters are estimated by minimizing the mean square of the difference between the reference and the modeled mapping based on the MVs of the current block and its adjacent neighboring blocks. To estimate the parameters of the local warp motion, if the neighboring blocks use the same reference frame as the current block, a mapping sample pair is obtained, consisting of a central sample in the neighboring block and a corresponding sample in the reference frame. Then, three additional samples are created by shifting the central position by 1 / 4 sample in one or both dimensions. These additional samples may also be considered as mapping sample pairs to ensure the stability of the model parameter estimation process.

[0101] The MVs of neighboring blocks used to derive motion parameters are called motion samples. Motion samples are selected from neighboring blocks that use the same reference frame as the current block. Note that warped motion prediction mode is only valid for blocks that use a single reference frame.

[0102] 5B shows an example motion sample used to derive model parameters for a block using local warp motion prediction according to some embodiments. As shown in FIG. 5B, the motion vectors of neighboring blocks B0, B1, and B2 are denoted as MV0, MV1, and MV2, respectively. A current block is predicted using uni-prediction with reference frame Ref0. For example, neighboring block B0 is predicted using mixed prediction with reference frames Ref0 and Ref1, neighboring block B1 is predicted using uni-prediction with reference frame Ref0, and neighboring block B2 is predicted using mixed prediction with reference frames Ref0 and Ref2. The motion vector MV0 of B0 is Ref0 , B1 MV1 Ref0 and B2 MV2 Ref0 may be used as the motion sample for deriving the affine motion parameters of the current block.

[0103] In local warp motion, samples and motion vectors of neighboring blocks can be collected in a stack to calculate a warp model using a regression / least squared error method. For example, in AV1 and AVM, a group of sample positions pointed to by the MV in the reference picture and its reference position is collected. For example, up to eight pairs of positions are stored in the stack for the regression / least squared error warp model calculation.

[0104] In warp motion mode, the motion of neighboring blocks is smoothly extended into the current block, with the ability to modify the warp parameters. This allows for complex warp motions spanning multiple blocks while minimizing blocking artifacts. To achieve this, for example, warp motion mode constructs a new warp model based on two constraints: the per-pixel motion vectors generated by the new warp model must be contiguous with the per-pixel motion vectors in neighboring blocks, and the pixel at the center of the current block must have a per-pixel motion vector that matches the signaled motion vector for the block as a whole. Figure 5C illustrates motion vectors within a block using warp extension mode according to some embodiments. For example, if a neighboring block to the left of the current block is warped, as shown in Figure 5C, a warp model that matches the motion vectors shown in Figure 5C is used.

[0105] The two constraints for constructing a new warp model imply specific equations involving the warp parameters of the neighboring blocks and the current block. These equations can then be solved to calculate the warp model of the current block. For example, if (A,...,F) represents the neighboring warp models and (A',...,F') represents the new warp model, the first constraint is, at each point along the common edge, as follows:

number

[0106] The second constraint specifies that the motion vector at the center of the block must be equal to the signaled one. This provides two additional equations, resulting in a system of six equations in six variables with a unique solution. These equations may be solved efficiently in both software and hardware. The solution may be solved using basic addition, subtraction, multiplication, and division by powers of two. Therefore, this mode is less complex than the least-squares-based local warp mode.

[0107] Note that there may be multiple neighboring blocks to extend from. Therefore, a method is needed to select which block to extend from. This problem arises in motion vector prediction as well. Specifically, there are several possible motion vectors from nearby blocks, one of which should be selected as the base. The solution for this can be extended to address the need. This is done by tracking the source of each motion vector prediction. Then, the warped motion mode is enabled only if the selected motion vector prediction is obtained directly from a neighboring block. That block is then used as a single "neighboring block" in the remainder of the algorithm. Note that the neighboring warp model may be fine as is without requiring further modification.

[0108] As used herein, the term "block" may be interpreted as a prediction block, a coding block, or a coding unit (CU). Spatially, neighboring blocks may be scanned as shown in FIG. 5D. If a neighboring block has the same reference picture as the current block (e.g., if the neighboring block is composite, one of the reference pictures is the same as the reference picture of the current block), the center position of this neighboring block and the center position of its reference block, indicated by the MV of this neighboring block, are collected. The scan order may be defined as shown in FIG. 5D. Specifically, (1) scan the neighboring blocks in the upper row, (2) scan the neighboring blocks in the left column, (3) scan the upper-left block, and (4) scan the upper-right block. In some embodiments, the neighboring blocks shown in FIG. 5D correspond to a single warp group.

[0109] In some embodiments, multiple warp groupings are considered for use in generating the warp model. For example, instead of using one set of neighboring blocks to derive the warp model, multiple groups of spatially and / or temporally neighboring blocks and MVs are collected / evaluated, and one of these groups is used to generate the warp model.

[0110] FIG. 5E illustrates a current block having multiple spatially and / or temporally neighboring blocks, according to some embodiments. In the example of FIG. 5E, blocks marked with "S" indicate spatially neighboring blocks, blocks marked with "T" indicate temporally neighboring blocks, and blocks marked with "S / T" indicate spatially and / or temporally neighboring blocks. In some embodiments, multiple warp groups are identified / constructed using the neighboring blocks illustrated in FIG. 5E. As an example, a first warp group may correspond to the neighboring blocks illustrated in FIG. 5D. In this example, a second warp group may correspond to the spatially / temporally neighboring blocks surrounding corners P1, P3, and P4 in FIG. 5E. A third warp group may correspond to the spatially / temporally neighboring blocks surrounding corners P2, P3, and P4. For example, for the block marked with "S / T" in FIG. 5E, spatial neighbors are scanned first, and if not available, temporal neighbors are scanned. In some embodiments, for the temporal neighborhood, the block size is assumed to be 8x8.

[0111] In AV1 and AOM designs, there is a warp mode / motion mode analysis dependency. That is, the decoder needs to first collect neighboring blocks and MVs, and if there are no valid MVs, the warp mode is not signaled or implied. The problem is that the analysis process is delayed because neighboring block MVs need to be constructed first. Furthermore, constructing all warp groups at the decoder side increases the decoding complexity.

[0112] 6A is a flow diagram illustrating a method 600 for encoding video according to some embodiments. Method 600 may be implemented in a computing system (e.g., server system 112, source device 102, or electronic device 120) having control circuitry and memory storing instructions for execution by the control circuitry. In some embodiments, method 600 is performed by executing instructions stored in memory (e.g., memory 314) of the computing system.

[0113] The system obtains video data including a plurality of blocks, including a first block (602). In some embodiments, the first block is coded in a warp mode or a motion mode. The system identifies two or more warp groups for the first block (604). The system determines a respective cost associated with each warp group of the two or more warp groups (606). The system selects a warp group from the two or more warp groups based on the respective costs (608). The system encodes the first block according to the selected warp group (610). In some embodiments, encoding the first block includes encoding the first block and a syntax element indicating a warp mode or a motion mode according to the selected warp group, regardless of whether a valid motion vector is available. In some embodiments, the system encodes the first block according to the selected warp group according to (e.g., in response to) a determination that a valid motion vector is not available for deriving a warp model (e.g., a valid motion vector is not available for deriving a warp model).

[0114] In some embodiments, the dependency between MVs of neighboring blocks and warp mode / motion mode syntax element parsing is removed (e.g., to reduce pipeline delays of parsing warp mode / motion mode syntax elements). In some embodiments, if there are no valid MVs for warp model derivation while parsing / signaling a syntax element of a warp mode / motion mode syntax element, the warp mode / motion mode syntax element is parsed / signaled. In one example, if there are no valid neighboring block MVs, syntax element 0 is signaled at the encoder and parsed at the decoder.

[0115] In some embodiments, a fixed order of warp groups is constructed at the encoder side. In some embodiments, the fixed order of warp groups includes a first group of spatially neighboring blocks (e.g., as shown in FIG. 5D ). In some embodiments, the fixed order of warp groups includes a second group of spatially / temporally neighboring blocks surrounding the current block (e.g., blocks at corners P1, P3, and P4 of FIG. 5E are scanned). In some embodiments, the fixed order of warp groups includes a third group of spatially / temporally neighboring blocks surrounding the current block (e.g., blocks at corners P2, P3, and P4 of FIG. 5E are scanned). In some embodiments, the fixed order of warp groups includes a fourth group of spatially / temporally neighboring blocks surrounding the current block (e.g., blocks 1 and 4 of FIG. 5D ).

[0116] In some embodiments, while constructing warp groups (as described above), temporally neighboring blocks and corresponding MVs (e.g., marked as "T" in FIG. 5E) are not considered.

[0117] In some embodiments, a flag is signaled in the high-level syntax (e.g., SPS, PPS, PH, etc.) to indicate whether a multi-group warp model direction is used. For example, if the flag is true (or false), multiple groups are collected as described above, and one of the groups is used to derive the warp model. If the flag is false (or true), only one fixed group (e.g., the current design) is collected and used to derive the warp model.

[0118] In some embodiments, the number of groups is signaled in a high-level syntax, the groups are constructed accordingly at the encoder side, and the group indexes are parsed accordingly at the decoder side.

[0119] 6B is a flow diagram illustrating a method 650 of decoding video according to some embodiments. Method 650 may be implemented in a computing system (e.g., server system 112, source device 102, or electronic device 120) having control circuitry and memory storing instructions for execution by the control circuitry. In some embodiments, method 650 is implemented by executing instructions stored in memory (e.g., memory 314) of the computing system.

[0120] The system obtains video data including a plurality of blocks including a first block (652). The system identifies a selected warp group from two or more warp groups (654). The system decodes the first block according to the selected warp group (656).

[0121] In some embodiments, a first group is constructed in the decoder component, and if there are no valid MVs in this group, the warp mode is not signaled and is implied as non-warped. Otherwise, if there are valid MVs in this group, the warp mode is analyzed, and if the mode uses warping, the warp group index is further analyzed. If the warp group index is not equal to 0, a corresponding group is further constructed in the decoder component. In this way, in the worst case, a maximum of two groups need to be constructed in the decoder component.

[0122] In some embodiments, the dependency on the first group (described in the previous paragraph) is removed, and fixed-order groups are constructed at the encoder side (e.g., as described above with reference to method 600). In some embodiments, at the decoder component, the warp mode / motion mode syntax elements are parsed, a warp mode is selected, and a warp group index is parsed. Depending on the warp group index, a corresponding group is constructed at the decoder component. In this way, in the worst case, at most one group needs to be constructed at the decoder component.

[0123] In some embodiments, the order of the groups is derived implicitly using coded information, such as the availability of motion information from certain spatially / temporally neighboring blocks. In some embodiments, the order of the groups is signaled, for example, in a high-level syntax or at the block level. For example, an index of a selected group is signaled from a set of predefined orders of groups.

[0124] 6A and 6B depict some logical stages in a particular order, stages that are not order-dependent may be reordered, and other stages may be combined or separated. Some reordering or other groupings not specifically mentioned will be apparent to those skilled in the art, and thus the reordering and groupings presented herein are not exhaustive. Furthermore, it should be recognized that the various stages may be implemented in hardware, firmware, software, or any combination thereof.

[0125] Reference will now be made to some exemplary embodiments.

[0126] (A1) In one aspect, some embodiments include a method of video encoding (e.g., method 600). In some embodiments, the method is implemented in a computing system (e.g., server system 112) having memory and control circuitry. In some embodiments, the method is implemented in a coding module (e.g., coding module 320). In some embodiments, the method is implemented in an entropy coder (e.g., entropy coder 214). The method includes: (i) obtaining video data including a plurality of blocks including a first block; (ii) identifying two or more warp groups for the first block; (iii) determining a respective cost associated with each warp group of the two or more warp groups; (iv) selecting a warp group from the two or more warp groups based on the respective costs; and (v) encoding the first block according to the selected warp group. For example, the two or more warp groups include a group corresponding to neighboring blocks shown in FIG. 5D and a group corresponding to neighboring blocks shown in FIG. 5E. In some embodiments, determining the respective costs includes determining a coding loss corresponding to using a warp model derived from the warp group (e.g., a warp group with the lowest coding loss is selected). In some embodiments, the first block is coded in a warp mode or a motion mode. In some embodiments, encoding the first block includes encoding the first block and a syntax element indicating the warp mode or the motion mode according to the selected warp group, regardless of whether a valid motion vector is available.

[0127] (A2) In some embodiments of A1, encoding the first block in accordance with the selected warp group includes generating a warp model for the first block using the selected warp group.

[0128] (A3) In some embodiments of A2, generating the warp model includes: (i) scanning spatial neighboring blocks of the first block; (ii) generating the warp model based on the motion vectors of the spatial neighboring blocks according to a determination that the spatial neighboring blocks are available; and (iii) generating the warp model based on the motion vectors of the temporal neighboring blocks according to a determination that the spatial neighboring blocks are unavailable; (a) scanning temporal neighboring blocks of the first block, where the temporal neighboring blocks have positions corresponding to the spatial neighboring blocks; and (b) generating the warp model based on the motion vectors of the temporal neighboring blocks. For example, the selected warp group includes one or more neighboring blocks represented as spatial, one or more neighboring blocks represented as time, and / or one or more neighboring blocks represented as space / time. In this example, if the spatial neighboring blocks of the block represented as space / time are unavailable, the temporal neighboring blocks are scanned / used.

[0129] (A4) In some embodiments of any of A1-A3, a first warp group of the two or more warp groups includes a first set of spatially neighboring blocks of the first block. For example, the first set of spatially neighboring blocks are neighboring blocks to the left and / or above the first block.

[0130] (A5) In some embodiments of A4, a second warp group of the two or more warp groups includes a second set of spatially neighboring blocks of the first block, the second set being different from the first set. For example, the second set includes one or more spatial neighbors not included in the first set. In some embodiments, the first spatial neighbors are included in each of the first set and the second set, and the second spatial neighbors are included in only one of the first set and the second set.

[0131] (A6) In some embodiments of A4 or A5, a second warp group of the two or more warp groups includes one or more spatially neighboring blocks of the first block and one or more temporally neighboring blocks of the first block. In some embodiments, each warp group of the two or more warp groups does not include any temporally neighboring blocks.

[0132] (A7) In some embodiments of any of A1-A6, the two or more warp groups include four different warp groups.

[0133] (A8) In some embodiments of any of A1-A7, each warp group of the two or more warp groups has a respective scan order. In some embodiments, the respective scan orders are different from each other.

[0134] (A9) In some embodiments of any of A1-A8, the method further includes signaling the selected warp group. For example, the selected warp group is explicitly signaled with a bit or a flag. In some embodiments, the two or more warp groups have a predetermined order, and an index of the selected warp group is signaled. As another example, the selected warp group is signaled implicitly (e.g., using coded information such as the availability of motion information from certain spatial / temporal neighboring blocks).

[0135] (A10) In some embodiments of A9, the selected warp group is signaled in a high-level syntax, for example, a selected warp group flag is set in a sequence parameter set (SPS), a picture parameter set (PPS), or a picture header (PH) to signal the selected warp group.

[0136] (A11) In some embodiments of any of A1-A10, the method further includes determining whether multi-group warp mode is enabled, and two or more warp groups for the first block are identified in accordance with a determination that multi-group warp mode is enabled. In some embodiments, the method includes canceling identifying the two or more warp groups in accordance with a determination that multi-group warp mode is disabled.

[0137] (A12) In some embodiments of A11, the multi-group warp mode is signaled in a high-level syntax, for example, a multi-group warp mode flag is set in a sequence parameter set (SPS), a picture parameter set (PPS), or a picture header (PH) to signal the selected warp group.

[0138] (A13) In some embodiments of A11 or A12, the method further includes, in accordance with determining that the multi-group warp mode is disabled, encoding the first block in accordance with a default warp group.

[0139] (A14) In some embodiments of any of A1-A13, the method further includes identifying a number of warp groups for determining the associated cost, wherein two or more warp groups are identified according to the number of identified warp groups. In some embodiments, the number of warp groups is signaled in high-level syntax. In some embodiments, the encoder identifies / constructs only N warp groups, where N is signaled in high-level syntax. As an example, the maximum number of warp groups may be 4, 6, 8, or 10. In some embodiments, only a subset of the maximum number of warp groups is considered (e.g., based on a flag in the high-level syntax). For example, if N is in the range of 2 to 10, warp groups 1-N may be considered. In some embodiments, a select subset of warp groups may be considered (e.g., warp groups 1-4 may be considered, or warp groups 5-9 may be considered). In some embodiments, the warp groups to be considered are signaled (eg, by signaling a starting warp group number, an ending warp group number, and / or the range of warp groups to be considered).

[0140] (B1) In another aspect, some embodiments include a method of video decoding (e.g., method 650). In some embodiments, the method is implemented in a computing system (e.g., server system 112) having memory and control circuitry. In some embodiments, the method is implemented in a coding module (e.g., coding module 320). In some embodiments, the method is implemented in a parser (e.g., parser 254). The method includes (i) obtaining, from a bitstream, video data including a plurality of blocks including a first block; (ii) identifying a selected warp group from two or more warp groups; and (iii) decoding the first block according to the selected warp group. In some embodiments, the first block is designated to be coded in a warp mode or a motion mode. In some embodiments, the method includes decoding a syntax element indicating the warp mode or the motion mode, regardless of whether a valid motion vector is available.

[0141] (B2) In some embodiments of B1, decoding the first block in accordance with the selected warp group includes generating a warp model for the first block using the selected warp group.

[0142] (B3) In some embodiments of B1 or B2, the method further includes identifying a first warp group of the two or more warp groups, wherein the selected warp group is identified according to a determination that the first warp group includes a valid motion vector. For example, the selected warp group may be the first warp group or another warp group of the two or more warp groups.

[0143] (B4) In some embodiments of B3, the method further includes: ceasing to signal the warp mode of the first block in accordance with a determination that the first warp group does not include a valid motion vector.

[0144] (B5) In some embodiments of any of B1-B4, the selected warp group is identified based on a warp group index from the bitstream. In some embodiments, the warp group index is signaled in a high-level syntax (e.g., SPS, PPS, or PH). In some embodiments, the warp group index is signaled at the block level. For example, an index of the selected group from a predefined ordered set of groups is signaled.

[0145] (B6) In some embodiments of any of B1-B5, the selected warp group is identified based on an order of two or more warp groups, the order being determined based on context information, for example, the context information including the availability of motion information from certain spatial / temporal neighboring blocks.

[0146] (B7) In some embodiments of any of B1-B6, the method further includes identifying a number of warp groups for determining an associated cost, wherein the two or more warp groups are identified according to the number of identified warp groups. In some embodiments, the number of warp groups is signaled in high-level syntax.

[0147] (B8) In some embodiments of any of B1 to B7, the method further includes determining whether multi-group warp mode is enabled, and the selected group is identified from the two or more warp groups in accordance with determining that multi-group warp mode is enabled. In some embodiments, the method includes canceling identifying the two or more warp groups in accordance with determining that multi-group warp mode is disabled. For example, when multi-group warp mode is disabled, a default warp group is used.

[0148] (B9) In some embodiments of any of B1-B8, the bitstream corresponds to video encoded according to any of A1-A14.

[0149] The methods described herein may be used separately or combined in any order. Each method may be performed by a processing circuit (e.g., one or more processors or one or more integrated circuits). In some embodiments, the processing circuit executes a program stored on a non-transitory computer-readable medium.

[0150] In another aspect, some embodiments include a computing system (e.g., server system 112) including control circuitry (e.g., control circuitry 302) and a memory (e.g., memory 314) coupled to the control circuitry, the memory storing one or more instruction sets configured to be executed by the control circuitry, the one or more instruction sets including instructions for performing any of the methods described herein (e.g., A1-A14 and B1-B9 above).

[0151] In yet another aspect, some embodiments include a non-transitory computer-readable storage medium storing one or more instruction sets for execution by control circuitry of a computing system, the one or more instruction sets including instructions for performing any of the methods described herein (e.g., A1-A14 and B1-B9 above).

[0152] It will also be understood that although terms such as "first," "second," etc. are used herein to describe various elements, these elements are not to be limited by these terms. These terms are used only to distinguish one element from another.

[0153] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the claims. As used in describing the embodiments and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. The term "and / or," as used herein, will also be understood to refer to and include any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms "comprises" and / or "comprising," as used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0154] As used herein, the term "if" can be interpreted to mean "when" or "upon" or "in response to determining" or "in accordance with a determination" or "in response to detecting" a stated precondition is true, depending on the context. Similarly, the phrase "if it is determined that [the stated precondition is true]" or "if [the stated precondition is true]" or "when [the stated precondition is true]" can be interpreted to mean "upon determining" or "in response to determining" or "in accordance with a determination" or "upon detecting" or "in response to detecting" a stated precondition is true, depending on the context.

[0155] The foregoing description has been described with reference to specific embodiments for purposes of explanation. However, the exemplary description above is not intended to be exhaustive or to limit the scope of the claims to the precise form disclosed. Many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described to best explain the principles of operation and practical application, thereby enabling others skilled in the art to utilize them. [Explanation of symbols]

[0156] 100 Communication Systems 102 Source Devices 104 Video Sources 106 Encoder Components 108 encoded video bitstream 110 Network 112 Server System 114 Coda Constituents 116 encoded video data 120 Electronic Devices 120-1 Electronic Devices 120-m Electronic Devices 122 Decoder Components 124 display 202 Source Coder 204 Controller 206 Predictors 208 Reference Picture Memory 210 (local) decoder 212 Coding Engine 214 Entropy Coder 216 coded video sequences 218 channels 252 buffer memory 254 Parser 256 Loop Filter Unit 258 Scaler / Descaler Unit 260 Motion Compensation Prediction Unit 262 Intra-picture Prediction Unit 264 Current Picture Memory 266 Reference Picture Memory 268 Aggregators 270 symbols 302 Control circuit 304 Network Interface 306 User Interface 308 Output Devices 310 Input Devices 312 communication bus 314 memory 316 Operating Systems 318 Network Communication Module 320 Coding Module 322 Decoding Module 324 Analysis Module 326 Conversion Module 328 Prediction Module 330 Filter Module 340 Encoding Module 342 Code Module 344 Prediction Module 352 Picture Memory 400 First coding tree structure 402 Second Coding Tree Structure 404 Coding Tree Structure 406 CTU

Claims

1. 1. A method of video coding implemented in a computing system having a memory and one or more processors, the method comprising: obtaining video data including a plurality of blocks including a first block, the first block being coded in a warp mode or a motion mode; identifying two or more warp groups for the first block; determining a respective cost associated with each warp group of the two or more warp groups; selecting a warp group from the two or more warp groups based on the respective costs; encoding the first block and a syntax element indicating the warp mode or the motion mode according to the selected warp group, regardless of whether a valid motion vector is available.

2. 2. The method of claim 1 , wherein encoding the first block in accordance with the selected warp group comprises generating a warp model for the first block using the selected warp group.

3. generating the warped model comprises: scanning blocks spatially adjacent to the first block; generating the warp model based on motion vectors of the spatially neighboring blocks according to the determination that the spatially neighboring blocks are available; In accordance with a determination that the spatially neighboring block is unavailable, scanning temporal neighboring blocks of the first block, the temporal neighboring blocks having positions corresponding to the spatial neighboring blocks; and generating the warp model based on motion vectors of the temporally neighboring blocks.

4. The method of claim 1 , wherein a first warp group of the two or more warp groups includes a first set of spatially neighboring blocks of the first block.

5. 5. The method of claim 4, wherein a second warp group of the two or more warp groups includes a second set of blocks spatially neighboring the first block, the second set being different from the first set.

6. 5. The method of claim 4, wherein a second warp group of the two or more warp groups includes one or more spatially neighboring blocks of the first block and one or more temporally neighboring blocks of the first block.

7. The method of claim 1 , wherein the two or more warp groups include four different warp groups.

8. The method of claim 1 , wherein each warp group of the two or more warp groups has a respective scan order.

9. The method of claim 1 , further comprising the step of signaling the selected warp group.

10. The method of claim 9 , wherein the selected warp group is signaled in a high-level syntax.

11. 2. The method of claim 1, further comprising: determining whether a multi-group warp mode is enabled; and wherein the two or more warp groups of the first block are identified according to a determination that the multi-group warp mode is enabled.

12. The method of claim 11 , wherein the multi-group warp mode is signaled in a high-level syntax.

13. The method of claim 11 , further comprising: encoding the first block according to a default warp group according to determining that the multi-group warp mode is disabled.

14. The method of claim 1 , further comprising: identifying a number of warp groups for determining an associated cost, wherein the two or more warp groups are identified according to a number of identified warp groups.

15. a control circuit; Memory and one or more sets of instructions stored in the memory and configured for execution by the control circuitry, the one or more sets of instructions comprising: obtaining video data including a plurality of blocks including a first block, the first block being coded in a warp mode or a motion mode; identifying two or more warp groups for the first block; determining a respective cost associated with each warp group of the two or more warp groups; selecting a warp group from the two or more warp groups based on the respective costs; one or more sets of instructions including instructions for encoding the first block and a syntax element indicating the warp mode or the motion mode according to the selected warp group, regardless of whether a valid motion vector is available; and A computing system comprising:

16. 16. The computing system of claim 15, wherein encoding the first block in accordance with the selected warp group comprises generating a warp model for the first block using the selected warp group.

17. generating the warped model, scanning blocks spatially adjacent to the first block; generating the warp model based on motion vectors of the spatially neighboring blocks according to a determination that the spatially neighboring blocks are available; In accordance with a determination that the spatially neighboring block is unavailable, scanning temporal neighboring blocks of the first block, the temporal neighboring blocks having positions corresponding to the spatial neighboring blocks; and generating the warp model based on motion vectors of the temporally neighboring blocks.

18. 16. The computing system of claim 15, wherein each warp group of the two or more warp groups has a respective scan order.

19. 1. A non-transitory computer-readable storage medium storing one or more sets of instructions configured for execution by a computing device having control circuitry and memory, the one or more sets of instructions comprising: obtaining video data including a plurality of blocks including a first block, the first block being coded in a warp mode or a motion mode; identifying two or more warp groups for the first block; determining a respective cost associated with each warp group of the two or more warp groups; selecting a warp group from the two or more warp groups based on the respective costs; A non-transitory computer-readable storage medium comprising instructions for encoding the first block and a syntax element indicating the warp mode or the motion mode according to the selected warp group, regardless of whether a valid motion vector is available.

20. 20. The non-transitory computer-readable storage medium of claim 19, wherein each warp group of the two or more warp groups has a respective scan order.

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