WO2020056143A1 - Modifications de la construction de la liste de candidats de fusion - Google Patents

Modifications de la construction de la liste de candidats de fusion Download PDF

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Publication number
WO2020056143A1
WO2020056143A1 PCT/US2019/050820 US2019050820W WO2020056143A1 WO 2020056143 A1 WO2020056143 A1 WO 2020056143A1 US 2019050820 W US2019050820 W US 2019050820W WO 2020056143 A1 WO2020056143 A1 WO 2020056143A1
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WIPO (PCT)
Prior art keywords
merge
merge candidates
list
candidates
block
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PCT/US2019/050820
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English (en)
Inventor
Xianglin Wang
Yi-Wen Chen
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Beijing Dajia Internet Information Technology Co., Ltd.
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Application filed by Beijing Dajia Internet Information Technology Co., Ltd. filed Critical Beijing Dajia Internet Information Technology Co., Ltd.
Priority to CN201980074650.1A priority Critical patent/CN113170178A/zh
Publication of WO2020056143A1 publication Critical patent/WO2020056143A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/513—Processing of motion vectors
    • H04N19/517—Processing of motion vectors by encoding
    • H04N19/52—Processing of motion vectors by encoding by predictive encoding

Definitions

  • the present application generally relates to video data encoding and decoding, and in particular, to method and system of modifying the construction of the merge candidates list during video data encoding and decoding.
  • 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 gaming consoles, smart phones, video teleconferencing devices, video streaming devices, etc.
  • the electronic devices transmit, receive, encode, decode, and/or store digital video data by implementing video compression/decompression standards as defined by MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), High Efficiency Video Coding (HEVC), and Versatile Video Coding (VVC) standard.
  • Video compression typically includes performing spatial (intra frame) prediction and/or temporal (inter frame) prediction to reduce or remove redundancy inherent in the video data.
  • a video frame is partitioned into one or more slices, each slice having multiple video blocks, which may also be referred to as coding tree units (CTUs).
  • Each CTU may contain one coding unit (CU) or recursively split into smaller CUs until the predefined minimum CU size is reached.
  • Each CU also named leaf CU
  • Each CU contains one or multiple transform units (TUs) and each CU also contains one or multiple prediction units (PUs).
  • Each CU can be coded in either intra, inter or IBC modes.
  • Video blocks in an intra coded (I) slice of a video frame are encoded using spatial prediction with respect to reference samples in neighbor blocks within the same video frame.
  • Video blocks in an inter coded (P or B) slice of a video frame may use spatial prediction with respect to reference samples in neighbor blocks within the same video frame or temporal prediction with respect to reference samples in other previous and/or future reference video frames.
  • the process of finding the reference block may be accomplished by block matching algorithm.
  • Residual data representing pixel differences between the current block to be coded and the predictive block is referred to as a residual block or prediction errors.
  • An inter-coded block is encoded according to a motion vector that points to a reference block in a reference frame forming the predictive block, and the residual block. The process of determining the motion vector is typically referred to as motion estimation.
  • An intra coded block is encoded according to an intra prediction mode and the residual block.
  • the residual block is transformed from the pixel domain to a transform domain, e.g., frequency domain, resulting in residual transform coefficients, which may then be quantized.
  • the quantized transform coefficients initially arranged in a two-dimensional array, may be scanned to produce a one-dimensional vector of transform coefficients, and then entropy encoded into a video bitstream to achieve even more compression.
  • the encoded video bitstream is then saved in a computer-readable storage medium (e.g., flash memory) to be accessed by another electronic device with digital video capability or directly transmitted to the electronic device wired or wirelessly.
  • the electronic device then performs video decompression (which is an opposite process to the video compression described above) by, e.g., parsing the encoded video bitstream to obtain syntax elements from the bitstream and reconstructing the digital video data to its original format from the encoded video bitstream based at least in part on the syntax elements obtained from the bitstream, and renders the reconstructed digital video data on a display of the electronic device.
  • video decompression which is an opposite process to the video compression described above
  • the present application describes implementations related to video data encoding and decoding and, more particularly, to system and method of parallel processing of video data during video encoding and decoding using history-based motion vector prediction.
  • a method of decoding video data is performed at a computing device having one or more processors and memory storing a plurality of programs to be executed by the one or more processors.
  • a computing device performs a method of decoding video data by generating a merge list, including:
  • a first group of spatial merge candidates inserting into the merge list, a first group of spatial merge candidates; appending to the merge list a second group of temporal merge candidates; in response to determining that that there exists at least two merge candidates in the merge list: appending to the merge list a third group of averaged merge candidate based on the at least two merge candidates; in response to determining that there are less than a maximum-allowed number of merge candidates in the merge list: appending, to the merge list, a fourth group of history -based motion vector prediction (HMVP) merge candidates; and receiving, from the bitstream, a merge index identifying a merge candidate in the merge list; and generating a prediction block using the identified merge candidate in the merge list.
  • HMVP history -based motion vector prediction
  • a computing device includes one or more processors, memory and a plurality of programs stored in the memory.
  • the programs when executed by the one or more processors, cause the computing device to perform operations as described above.
  • a non-transitory computer readable storage medium stores a plurality of programs for execution by a computing device having one or more processors.
  • the programs when executed by the one or more processors, cause the computing device to perform operations as described above.
  • FIG. l is a block diagram illustrating an exemplary video encoding and decoding system in accordance with some implementations of the present disclosure.
  • FIG. 2 is a block diagram illustrating an exemplary video encoder in accordance with some implementations of the present disclosure.
  • FIG. 3 is a block diagram illustrating an exemplary video decoder in accordance with some implementations of the present disclosure.
  • FIGS. 4A-4D are block diagrams illustrating how a frame is recursively quad- tree partitioned into multiple video blocks of different sizes in accordance with some implementations of the present disclosure.
  • FIG. 5A is a block diagram illustrating spatially neighboring and temporally collocated block positions of a current CU to be encoded in accordance with some implementations of the present disclosure.
  • FIG. 5B is a block diagram illustrating multi-threaded encoding of multiple rows of CTETs of a picture using wavefront parallel processing in accordance with some implementations of the present disclosure.
  • FIG. 6 is a block diagram illustrating an exemplary modified insertion order of motion information in a merge motion vector prediction candidate list in accordance with some implementations of the present disclosure.
  • FIG. 7 is a flowchart illustrating an exemplary process by which a video coder implements the techniques of constructing a merge motion vector prediction candidate list in accordance with some implementations of the present disclosure.
  • FIG. 1 is a block diagram illustrating an exemplary system 10 for encoding and decoding video blocks in parallel in accordance with some implementations of the present disclosure.
  • system 10 includes a source device 12 that generates and encodes video data to be decoded at a later time by a destination device 14.
  • Source device 12 and destination device 14 may comprise any of a wide variety of electronic devices, including desktop or laptop computers, tablet computers, smart phones, set-top boxes, digital televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like.
  • source device 12 and destination device 14 are equipped with wireless communication capabilities.
  • destination device 14 may receive the encoded video data to be decoded via a link 16.
  • Link 16 may comprise any type of communication medium or device capable of moving the encoded video data from source device 12 to destination device 14.
  • link 16 may comprise a communication medium to enable source device 12 to transmit the encoded video data directly to destination device 14 in real-time.
  • the encoded video data may be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14.
  • the communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines.
  • the communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet.
  • the communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device 12 to destination device 14.
  • the encoded video data may be transmitted from output interface 22 to a storage device 32. Subsequently, the encoded video data in storage device 32 may be accessed by destination device 14 via input interface 28.
  • Storage device 32 may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data.
  • storage device 32 may correspond to a file server or another intermediate storage device that may hold the encoded video data generated by source device 12.
  • Destination device 14 may access the stored video data from storage device 32 via streaming or downloading.
  • the file server may be any type of computer capable of storing encoded video data and transmitting the encoded video data to destination device 14.
  • Exemplary file servers include a web server (e.g., for a website), an FTP server, network attached storage (NAS) devices, or a local disk drive.
  • Destination device 14 may access the encoded video data through any standard data connection, including a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on a file server.
  • a wireless channel e.g., a Wi-Fi connection
  • a wired connection e.g., DSL, cable modem, etc.
  • source device 12 includes a video source 18, a video encoder 20 and an output interface 22.
  • Video source 18 may include a source such as a video capture device, e.g., a video camera, a video archive containing previously captured video, a video feed interface to receive video from a video content provider, and/or a computer graphics system for generating computer graphics data as the source video, or a combination of such sources.
  • a video capture device e.g., a video camera, a video archive containing previously captured video
  • video feed interface to receive video from a video content provider
  • computer graphics system for generating computer graphics data as the source video, or a combination of such sources.
  • source device 12 and destination device 14 may form camera phones or video phones.
  • the implementations described in the present application may be applicable to video coding in general, and may be applied to wireless and/or wired applications.
  • the captured, pre-captured, or computer-generated video may be encoded by video encoder 20.
  • the encoded video data may be transmitted directly to destination device 14 via output interface 22 of source device 12.
  • the encoded video data may also (or alternatively) be stored onto storage device 32 for later access by destination device 14 or other devices, for decoding and/or playback.
  • Output interface 22 may further include a modem and/or a transmitter.
  • Destination device 14 includes an input interface 28, a video decoder 30, and a display device 34.
  • Input interface 28 may include a receiver and/or a modem and receive the encoded video data over link 16.
  • the encoded video data communicated over link 16, or provided on storage device 32 may include a variety of syntax elements generated by video encoder 20 for use by video decoder 30 in decoding the video data. Such syntax elements may be included within the encoded video data transmitted on a communication medium, stored on a storage medium, or stored a file server.
  • destination device 14 may include a display device
  • Display device 34 which can be an integrated display device and an external display device that is configured to communicate with destination device 14.
  • Display device 34 displays the decoded video data to a user, and may comprise any of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.
  • LCD liquid crystal display
  • OLED organic light emitting diode
  • Video encoder 20 and video decoder 30 may operate according to proprietary or industry standards, such as VVC, HEVC, MPEG-4, Part 10, Advanced Video Coding (AVC), or extensions of such standards. It should be understood that the present application is not limited to a specific video coding/decoding standard and may be applicable to other video coding/decoding standards. It is generally contemplated that video encoder 20 of source device 12 may be configured to encode video data according to any of these current or future standards. Similarly, it is also generally contemplated that video decoder 30 of destination device 14 may be configured to decode video data according to any of these current or future standards.
  • Video encoder 20 and video decoder 30 each may be implemented as any of a variety of suitable encoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof.
  • DSPs digital signal processors
  • ASICs application specific integrated circuits
  • FPGAs field programmable gate arrays
  • an electronic device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the video coding/decoding operations disclosed in the present disclosure.
  • Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device.
  • CDEC combined encoder/decoder
  • FIG. 2 is a block diagram illustrating an exemplary video encoder 20 in accordance with some implementations described in the present application.
  • Video encoder 20 may perform intra and inter predictive coding of video blocks within video frames. Intra predictive coding relies on spatial prediction to reduce or remove spatial redundancy in video data within a given video frame or picture. Inter predictive coding relies on temporal prediction to reduce or remove temporal redundancy in video data within adjacent video frames or pictures of a video sequence.
  • video encoder 20 includes video data memory 40, prediction processing unit 41, decoded picture buffer (DPB) 64, summer 50, transform processing unit 52, quantization unit 54, and entropy encoding unit 56.
  • Prediction processing unit 41 further includes motion estimation unit 42, motion compensation unit 44, partition unit 45, intra prediction processing unit 46, and intra block copy (BC) unit 48.
  • video encoder 20 also includes inverse quantization unit 58, inverse transform processing unit 60, and summer 62 for video block reconstruction.
  • a deblocking filter (not shown) may be positioned between summer 62 and DPB 64 to filter block boundaries to remove blockiness artifacts from reconstructed video.
  • Video encoder 20 may take the form of a fixed or programmable hardware unit or may be divided among one or more of the illustrated fixed or programmable hardware units.
  • Video data memory 40 may store video data to be encoded by the components of video encoder 20.
  • the video data in video data memory 40 may be obtained, for example, from video source 18.
  • DPB 64 is a buffer that stores reference video data for use in encoding video data by video encoder 20 (e.g., in intra or inter predictive coding modes).
  • Video data memory 40 and DPB 64 may be formed by any of a variety of memory devices.
  • video data memory 40 may be on-chip with other components of video encoder 20, or off-chip relative to those components.
  • partition unit 45 within prediction processing unit 41 partitions the video data into video blocks.
  • This partitioning may also include partitioning a video frame into slices, tiles, or other larger coding units (CUs) according to a predefined splitting structures such as quad-tree structure associated with the video data.
  • the video frame may be divided into multiple video blocks (or sets of video blocks referred to as tiles).
  • Prediction processing unit 41 may select one of a plurality of possible predictive coding modes, such as one of a plurality of intra predictive coding modes or one of a plurality of inter predictive coding modes, for the current video block based on error results (e.g., coding rate and the level of distortion).
  • Prediction processing unit 41 may provide the resulting intra or inter prediction coded block to summer 50 to generate a residual block and to summer 62 to reconstruct the encoded block for use as part of a reference frame subsequently. Prediction processing unit 41 also provides syntax elements, such as motion vectors, intra-mode indicators, partition information, and other such syntax information, to entropy encoding unit 56.
  • intra prediction processing unit 46 within prediction processing unit 41 may perform intra predictive coding of the current video block relative to one or more neighbor blocks in the same frame as the current block to be coded to provide spatial prediction.
  • Motion estimation unit 42 and motion compensation unit 44 within prediction processing unit 41 perform inter predictive coding of the current video block relative to one or more predictive blocks in one or more reference frames to provide temporal prediction.
  • Video encoder 20 may perform multiple coding passes, e.g., to select an appropriate coding mode for each block of video data.
  • motion estimation unit 42 determines the inter prediction mode for a current video frame by generating a motion vector, which indicates the displacement of a prediction unit (PU) of a video block within the current video frame relative to a predictive block within a reference video frame, according to a predetermined pattern within a sequence of video frames.
  • Motion estimation performed by motion estimation unit 42, is the process of generating motion vectors, which estimate motion for video blocks.
  • a motion vector may indicate the displacement of a PU of a video block within a current video frame or picture relative to a predictive block within a reference frame (or other coded unit) relative to the current block being coded within the current frame (or other coded unit).
  • Intra BC unit 48 may determine vectors, e.g., block vectors, for intra BC coding in a manner similar to the determination of motion vectors by motion estimation unit 42 for inter prediction, or may utilize motion estimation unit 42 to determine the block vector.
  • a predictive block is a block of a reference frame that is deemed as closely matching the PU of the video block to be coded in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of square difference (SSD), or other difference metrics.
  • video encoder 20 may calculate values for sub- integer pixel positions of reference frames stored in DPB 64. For example, video encoder 20 may interpolate values of one-quarter pixel positions, one-eighth pixel positions, or other fractional pixel positions of the reference frame. Therefore, motion estimation unit 42 may perform a motion search relative to the full pixel positions and fractional pixel positions and output a motion vector with fractional pixel precision.
  • Motion estimation unit 42 calculates a motion vector for a PU of a video block in an inter prediction coded frame by comparing the position of the PU to the position of a predictive block of a reference frame selected from a first reference frame list (List 0) or a second reference frame list (List 1), each of which identifies one or more reference frames stored in DPB 64. Motion estimation unit 42 sends the calculated motion vector to motion compensation unit 44 and then to entropy encoding unit 56.
  • Motion compensation performed by motion compensation unit 44, may involve fetching or generating the predictive block based on the motion vector determined by motion estimation unit 42.
  • motion compensation unit 44 may locate a predictive block to which the motion vector points in one of the reference frame lists, retrieve the predictive block from DPB 64, and forward the predictive block to summer 50.
  • Summer 50 then forms a residual video block of pixel difference values by subtracting pixel values of the predictive block provided by motion compensation unit 44 from the pixel values of the current video block being coded.
  • the pixel difference values forming the residual vide block may include luma or chroma difference components or both.
  • Motion compensation unit 44 may also generate syntax elements associated with the video blocks of a video frame for use by video decoder 30 in decoding the video blocks of the video frame.
  • the syntax elements may include, for example, syntax elements defining the motion vector used to identify the predictive block, any flags indicating the prediction mode, or any other syntax information described herein. Note that motion estimation unit 42 and motion compensation unit 44 may be highly integrated, but are illustrated separately for conceptual purposes.
  • intra BC unit 48 may generate vectors and fetch predictive blocks in a manner similar to that described above in connection with motion estimation unit 42 and motion compensation unit 44, but with the predictive blocks being in the same frame as the current block being coded and with the vectors being referred to as block vectors as opposed to motion vectors.
  • intra BC unit 48 may determine an intra-prediction mode to use to encode a current block.
  • intra BC unit 48 may encode a current block using various intra-prediction modes, e.g., during separate encoding passes, and test their performance through rate-distortion analysis. Next, intra BC unit 48 may select, among the various tested intra-prediction modes, an appropriate intra- prediction mode to use and generate an intra-mode indicator accordingly.
  • intra BC unit 48 may calculate rate-distortion values using a rate-distortion analysis for the various tested intra-prediction modes, and select the intra-prediction mode having the best rate- distortion characteristics among the tested modes as the appropriate intra-prediction mode to use.
  • Rate-distortion analysis generally determines an amount of distortion (or error) between an encoded block and an original, unencoded block that was encoded to produce the encoded block, as well as a bitrate (i.e., a number of bits) used to produce the encoded block.
  • Intra BC unit 48 may calculate ratios from the distortions and rates for the various encoded blocks to determine which intra-prediction mode exhibits the best rate-distortion value for the block.
  • intra BC unit 48 may use motion estimation unit 42 and motion compensation unit 44, in whole or in part, to perform such functions for Intra BC prediction according to the implementations described herein.
  • a predictive block may be a block that is deemed as closely matching the block to be coded, in terms of pixel difference, which may be determined by sum of absolute difference (SAD), sum of squared difference (SSD), or other difference metrics, and identification of the predictive block may include calculation of values for sub-integer pixel positions.
  • video encoder 20 may form a residual video block by subtracting pixel values of the predictive block from the pixel values of the current video block being coded, forming pixel difference values.
  • the pixel difference values forming the residual video block may include both luma and chroma component differences.
  • Intra prediction processing unit 46 may intra-predict a current video block, as an alternative to the inter-prediction performed by motion estimation unit 42 and motion compensation unit 44, or the intra block copy prediction performed by intra BC unit 48, as described above.
  • intra prediction processing unit 46 may determine an intra prediction mode to use to encode a current block. To do so, intra prediction processing unit 46 may encode a current block using various intra prediction modes, e.g., during separate encoding passes, and intra prediction processing unit 46 (or a mode select unit, in some examples) may select an appropriate intra prediction mode to use from the tested intra prediction modes.
  • Intra prediction processing unit 46 may provide information indicative of the selected intra-prediction mode for the block to entropy encoding unit 56. Entropy encoding unit 56 may encode the information indicating the selected intra-prediction mode in the bitstream.
  • summer 50 forms a residual video block by subtracting the predictive block from the current video block.
  • the residual video data in the residual block may be included in one or more transform units (TUs) and is provided to transform processing unit 52.
  • Transform processing unit 52 transforms the residual video data into residual transform coefficients using a transform, such as a discrete cosine transform (DCT) or a conceptually similar transform.
  • DCT discrete cosine transform
  • Transform processing unit 52 may send the resulting transform coefficients to quantization unit 54.
  • Quantization unit 54 quantizes the transform coefficients to further reduce bit rate. The quantization process may also reduce the bit depth associated with some or all of the coefficients. The degree of quantization may be modified by adjusting a quantization parameter.
  • quantization unit 54 may then perform a scan of a matrix including the quantized transform coefficients.
  • entropy encoding unit 56 may perform the scan.
  • entropy encoding unit 56 entropy encodes the quantized transform coefficients into a video bitstream using, e.g., context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CAB AC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique.
  • CAVLC context adaptive variable length coding
  • CAB AC context adaptive binary arithmetic coding
  • SBAC syntax-based context-adaptive binary arithmetic coding
  • PIPE probability interval partitioning entropy
  • the encoded bitstream may then be transmitted to video decoder 30, or archived in storage device 32 for later transmission to or retrieval by video decoder 30.
  • Entropy encoding unit 56 may also entropy encode the motion vectors and the other syntax elements for the current video frame being coded.
  • Inverse quantization unit 58 and inverse transform processing unit 60 apply inverse quantization and inverse transformation, respectively, to reconstruct the residual video block in the pixel domain for generating a reference block for prediction of other video blocks.
  • motion compensation unit 44 may generate a motion compensated predictive block from one or more reference blocks of the frames stored in DPB 64. Motion compensation unit 44 may also apply one or more interpolation filters to the predictive block to calculate sub-integer pixel values for use in motion estimation.
  • Summer 62 adds the reconstructed residual block to the motion compensated predictive block produced by motion compensation unit 44 to produce a reference block for storage in DPB 64.
  • the reference block may then be used by intra BC unit 48, motion estimation unit 42 and motion compensation unit 44 as a predictive block to inter predict another video block in a subsequent video frame.
  • FIG. 3 is a block diagram illustrating an exemplary video decoder 30 in accordance with some implementations of the present application.
  • Video decoder 30 includes video data memory 79, entropy decoding unit 80, prediction processing unit 81, inverse quantization unit 86, inverse transform processing unit 88, summer 90, and DPB 92.
  • Prediction processing unit 81 further includes motion compensation unit 82, intra prediction processing unit 84, and intra BC unit 85.
  • Video decoder 30 may perform a decoding process generally reciprocal to the encoding process described above with respect to video encoder 20 in connection with FIG. 2.
  • motion compensation unit 82 may generate prediction data based on motion vectors received from entropy decoding unit 80
  • intra- prediction unit 84 may generate prediction data based on intra-prediction mode indicators received from entropy decoding unit 80.
  • a unit of video decoder 30 may be tasked to perform the implementations of the present application. Also, in some examples, the implementations of the present disclosure may be divided among one or more of the units of video decoder 30.
  • intra BC unit 85 may perform the implementations of the present application, alone, or in combination with other units of video decoder 30, such as motion compensation unit 82, intra prediction processing unit 84, and entropy decoding unit 80.
  • video decoder 30 may not include intra BC unit 85 and the functionality of intra BC unit 85 may be performed by other components of prediction processing unit 81, such as motion compensation unit 82.
  • Video data memory 79 may store video data, such as an encoded video bitstream, to be decoded by the other components of video decoder 30.
  • the video data stored in video data memory 79 may be obtained, for example, from storage device 32, from a local video source, such as a camera, via wired or wireless network communication of video data, or by accessing physical data storage media (e.g., a flash drive or hard disk).
  • Video data memory 79 may include a coded picture buffer (CPB) that stores encoded video data from an encoded video bitstream.
  • Decoded picture buffer (DPB) 92 of video decoder 30 stores reference video data for use in decoding video data by video decoder 30 (e.g., in intra or inter predictive coding modes).
  • Video data memory 79 and DPB 92 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magneto-resistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices.
  • DRAM dynamic random access memory
  • SDRAM synchronous DRAM
  • MRAM magneto-resistive RAM
  • RRAM resistive RAM
  • video data memory 79 and DPB 92 are depicted as two distinct components of video decoder 30 in FIG. 3. But it will be apparent to one skilled in the art that video data memory 79 and DPB 92 may be provided by the same memory device or separate memory devices.
  • video data memory 79 may be on-chip with other components of video decoder 30, or off-chip relative to those components.
  • video decoder 30 receives an encoded video bitstream that represents video blocks of an encoded video frame and associated syntax elements.
  • Video decoder 30 may receive the syntax elements at the video frame level and/or the video block level.
  • Entropy decoding unit 80 of video decoder 30 entropy decodes the bitstream to generate quantized coefficients, motion vectors or intra-prediction mode indicators, and other syntax elements. Entropy decoding unit 80 then forwards the motion vectors and other syntax elements to prediction processing unit 81.
  • intra prediction processing unit 84 of prediction processing unit 81 may generate prediction data for a video block of the current video frame based on a signaled intra prediction mode and reference data from previously decoded blocks of the current frame.
  • motion compensation unit 82 of prediction processing unit 81 produces one or more predictive blocks for a video block of the current video frame based on the motion vectors and other syntax elements received from entropy decoding unit 80.
  • Each of the predictive blocks may be produced from a reference frame within one of the reference frame lists.
  • Video decoder 30 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference frames stored in DPB 92.
  • intra BC unit 85 of prediction processing unit 81 produces predictive blocks for the current video block based on block vectors and other syntax elements received from entropy decoding unit 80.
  • the predictive blocks may be within a reconstructed region of the same picture as the current video block defined by video encoder 20.
  • Motion compensation unit 82 and/or intra BC unit 85 determines prediction information for a video block of the current video frame by parsing the motion vectors and other syntax elements, and then uses the prediction information to produce the predictive blocks for the current video block being decoded. For example, motion compensation unit 82 uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code video blocks of the video frame, an inter prediction frame type (e.g., B or P), construction information for one or more of the reference frame lists for the frame, motion vectors for each inter predictive encoded video block of the frame, inter prediction status for each inter predictive coded video block of the frame, and other information to decode the video blocks in the current video frame.
  • a prediction mode e.g., intra or inter prediction
  • an inter prediction frame type e.g., B or P
  • intra BC unit 85 may use some of the received syntax elements, e.g., a flag, to determine that the current video block was predicted using the intra BC mode, construction information of which video blocks of the frame are within the reconstructed region and should be stored in DPB 92, block vectors for each intra BC predicted video block of the frame, intra BC prediction status for each intra BC predicted video block of the frame, and other information to decode the video blocks in the current video frame.
  • a flag e.g., a flag
  • Motion compensation unit 82 may also perform interpolation using the interpolation filters as used by video encoder 20 during encoding of the video blocks to calculate interpolated values for sub-integer pixels of reference blocks. In this case, motion compensation unit 82 may determine the interpolation filters used by video encoder 20 from the received syntax elements and use the interpolation filters to produce predictive blocks.
  • Inverse quantization unit 86 inverse quantizes the quantized transform coefficients provided in the bitstream and entropy decoded by entropy decoding unit 80 using the same quantization parameter calculated by video encoder 20 for each video block in the video frame to determine a degree of quantization.
  • Inverse transform processing unit 88 applies an inverse transform, e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process, to the transform coefficients in order to reconstruct the residual blocks in the pixel domain.
  • an inverse transform e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process
  • summer 90 reconstructs decoded video block for the current video block by summing the residual block from inverse transform processing unit 88 and a corresponding predictive block generated by motion compensation unit 82 and intra BC unit 85.
  • An in-loop filter (not pictured) may be positioned between summer 90 and DPB 92 to further process the decoded video block.
  • the decoded video blocks in a given frame are then stored in DPB 92, which stores reference frames used for subsequent motion compensation of next video blocks.
  • DPB 92 or a memory device separate from DPB 92, may also store decoded video for later presentation on a display device, such as display device 34 of FIG. 1.
  • a video sequence typically includes an ordered set of frames or pictures.
  • Each frame may include three sample arrays, denoted SL, SCb, and SCr.
  • SL is a two-dimensional array of luma samples.
  • SCb is a two-dimensional array of Cb chroma samples.
  • SCr is a two-dimensional array of Cr chroma samples.
  • a frame may be monochrome and therefore includes only one two-dimensional array of luma samples.
  • video encoder 20 (or more specifically partition unit 45) generates an encoded representation of a frame by first partitioning the frame into a set of coding tree units (CTUs).
  • a video frame may include an integer number of CTUs ordered consecutively in a raster scan order from left to right and from top to bottom.
  • Each CTU is a largest logical coding unit and the width and height of the CTU are signaled by the video encoder 20 in a sequence parameter set, such that all the CTUs in a video sequence have the same size being one of 128x 128, 64x64, 32x32, and 16x 16.
  • the present application is not necessarily limited to a particular size. As shown in FIG.
  • each CTU may comprise one coding tree block (CTB) of luma samples, two corresponding coding tree blocks of chroma samples, and syntax elements used to code the samples of the coding tree blocks.
  • the syntax elements describe properties of different types of units of a coded block of pixels and how the video sequence can be reconstructed at the video decoder 30, including inter or intra prediction, intra prediction mode, motion vectors, and other parameters.
  • a CTU may comprise a single coding tree block and syntax elements used to code the samples of the coding tree block.
  • a coding tree block may be an NxN block of samples.
  • video encoder 20 may recursively perform tree partitioning such as binary-tree partitioning, quad-tree partitioning or a combination of both on the coding tree blocks of the CTU and divide the CTU into smaller coding units (CUs).
  • tree partitioning such as binary-tree partitioning, quad-tree partitioning or a combination of both on the coding tree blocks of the CTU and divide the CTU into smaller coding units (CUs).
  • FIG. 4C the 64x64 CTU 400 is first divided into four smaller CU, each having a block size of 32x32.
  • CU 410 and CU 420 are each divided into four CUs of 16x16 by block size.
  • the two 16x16 CUs 430 and 440 are each further divided into four CUs of 8x8 by block size.
  • each leaf node of the quad-tree corresponding to one CU of a respective size ranging from 32x32 to 8x8.
  • each CU may comprise a coding block (CB) of luma samples and two corresponding coding blocks of chroma samples of a frame of the same size, and syntax elements used to code the samples of the coding blocks.
  • CB coding block
  • a CU may comprise a single coding block and syntax structures used to code the samples of the coding block.
  • video encoder 20 may further partition a coding block of a CU into one or more MxN prediction blocks (PB).
  • a prediction block is a rectangular (square or non-square) block of samples on which the same prediction, inter or intra, is applied.
  • a prediction unit (PU) of a CU may comprise a prediction block of luma samples, two corresponding prediction blocks of chroma samples, and syntax elements used to predict the prediction blocks.
  • a PU may comprise a single prediction block and syntax structures used to predict the prediction block.
  • Video encoder 20 may generate predictive luma, Cb, and Cr blocks for luma, Cb, and Cr prediction blocks of each PU of the CU.
  • Video encoder 20 may use intra prediction or inter prediction to generate the predictive blocks for a PU. If video encoder 20 uses intra prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of the frame associated with the PU. If video encoder 20 uses inter prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of one or more frames other than the frame associated with the PU.
  • video encoder 20 may generate a luma residual block for the CU by subtracting the CU’s predictive luma blocks from its original luma coding block such that each sample in the CU’s luma residual block indicates a difference between a luma sample in one of the CU's predictive luma blocks and a corresponding sample in the CU's original luma coding block.
  • video encoder 20 may generate a Cb residual block and a Cr residual block for the CU, respectively, such that each sample in the CU's Cb residual block indicates a difference between a Cb sample in one of the CU's predictive Cb blocks and a
  • each sample in the CU's Cr residual block may indicate a difference between a Cr sample in one of the CU's predictive Cr blocks and a corresponding sample in the CU's original Cr coding block.
  • video encoder 20 may use quad-tree partitioning to decompose the luma, Cb, and Cr residual blocks of a CU into one or more luma, Cb, and Cr transform blocks.
  • a transform block is a rectangular (square or non-square) block of samples on which the same transform is applied.
  • a transform unit (TU) of a CU may comprise a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax elements used to transform the transform block samples.
  • each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block.
  • the luma transform block associated with the TU may be a sub-block of the CU's luma residual block.
  • the Cb transform block may be a sub-block of the CU's Cb residual block.
  • the Cr transform block may be a sub-block of the CU's Cr residual block.
  • a TU may comprise a single transform block and syntax structures used to transform the samples of the transform block.
  • Video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU.
  • a coefficient block may be a two-dimensional array of transform coefficients.
  • a transform coefficient may be a scalar quantity.
  • Video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU.
  • Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.
  • After generating a coefficient block (e.g., a luma coefficient block, a Cb coefficient block or a Cr coefficient block), video encoder 20 may quantize the coefficient block.
  • Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression.
  • video encoder 20 may entropy encode syntax elements indicating the quantized transform coefficients.
  • video encoder 20 may perform Context- Adaptive Binary
  • video encoder 20 may output a bitstream that includes a sequence of bits that forms a representation of coded frames and associated data, which is either saved in storage device 32 or transmitted to destination device 14.
  • CAB AC Arithmetic Coding
  • video decoder 30 may parse the bitstream to obtain syntax elements from the bitstream. Video decoder 30 may reconstruct the frames of the video data based at least in part on the syntax elements obtained from the bitstream. The process of reconstructing the video data is generally reciprocal to the encoding process performed by video encoder 20. For example, video decoder 30 may perform inverse transforms on the coefficient blocks associated with TUs of a current CU to reconstruct residual blocks associated with the TUs of the current CU. Video decoder 30 also reconstructs the coding blocks of the current CU by adding the samples of the predictive blocks for PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. After reconstructing the coding blocks for each CU of a frame, video decoder 30 may reconstruct the frame.
  • video coding achieves video compression using primarily two modes, i.e., intra-frame prediction (or intra-prediction) and inter-frame prediction (or inter prediction). It is noted that IBC could be regarded as either intra-frame prediction or a third mode. Between the two modes, inter-frame prediction contributes more to the coding efficiency than intra-frame prediction because of the use of motion vectors for predicting a current video block from a reference video block.
  • motion vector predictor MVP
  • a set of rules need to be adopted by both video encoder 20 and video decoder 30 for constructing a motion vector candidate list (also known as a“merge list”) for a current CU using those potential candidate motion vectors associated with spatially neighboring CUs and/or temporally collocated CUs of the current CU and then selecting one member from the motion vector candidate list as a motion vector predictor for the current CU.
  • a motion vector candidate list also known as a“merge list”
  • each inter-prediction CU has three motion vector prediction modes including inter (which is also referred to as“advanced motion vector prediction” (AMVP)), skip, and merge for constructing the motion vector candidate list. Under each mode, one or more motion vector candidates may be added to the motion vector candidate list according to the algorithms described below.
  • inter which is also referred to as“advanced motion vector prediction” (AMVP)
  • AVP advanced motion vector prediction
  • a motion vector competition (MVC) scheme is introduced to select a motion vector from a given candidate set of motion vectors, i.e., the motion vector candidate list, that includes spatial and temporal motion vector candidates.
  • the motion vector predictor candidates can also be derived from the so-called“history-based motion vector prediction” (HMVP) table.
  • HMVP history-based motion vector prediction
  • the HMVP table houses a predefined number of motion vector predictors, each having been used for encoding/decoding a particular CU of the same row of CTUs (or sometimes the same CTU). Because of the spatial/temporal proximity of these CUs, there is a high likelihood that one of the motion vector predictors in the HMVP table may be reused for encoding/decoding different CUs within the same row of CTUs. Therefore, it is possible to achieve a higher code efficiency by including the HMVP table in the process of constructing the motion vector candidate list.
  • the HMVP table has a fixed length (e.g., 5) and is managed in a quasi-First-In-First-Out (FIFO) manner. For example, a motion vector is reconstructed for a CU when decoding one inter-coded block of the CU.
  • the HMVP table is updated on-the-fly with the reconstructed motion vector because such motion vector could be the motion vector predictor of a subsequent CU.
  • the reconstructed motion vector is different from other existing motion vectors in the HMVP table or (ii) the reconstructed motion vector is the same as one of the existing motion vectors in the HMVP table.
  • the reconstructed motion vector is added to the HMVP table as the newest one if the HMVP table is not full. If the HMVP table is already full, the oldest motion vector in the HMVP table needs to be removed from the HMVP table first before the reconstructed motion vector is added as the newest one.
  • the HMVP table in this case is similar to a FIFO buffer such that the motion information located at the head of the FIFO buffer and associated with another previously inter-coded block is shifted out of the buffer so that the reconstructed motion vector is appended to the tail of the FIFO buffer as the newest member in the HMVP table.
  • the existing motion vector in the HMVP table that is substantially identical to the reconstructed motion vector is removed from the HMVP table before the reconstructed motion vector is added to the HMVP table as the newest one.
  • the HMVP table is also maintained in the form of a FIFO buffer, the motion vector predictors after the identical motion vector in the HMVP table are shifted forward by one element to occupy the space left by the removed motion vector and the reconstructed motion vector is then appended to the tail of the FIFO buffer as the newest member in the HMVP table.
  • the motion vectors in the HMVP table could be added to the motion vector candidate lists under different prediction modes such as AMVP, merge, skip, etc. It has been found that the motion information of previously inter-coded blocks stored in the HMVP table even not adjacent to the current block can be utilized for more efficient motion vector prediction.
  • video encoder 20 may generate one or more syntax elements for the corresponding MVP candidate and encode them into the video bitstream such that video decoder 30 can retrieve the MVP candidate from the video bitstream using the syntax elements.
  • different modes e.g., AMVP, merge, skip, etc.
  • the syntax elements include inter prediction indicators (List 0, List 1, or bi-directional prediction), reference indices, motion vector candidate indices, motion vector prediction residual signal, etc.
  • the motion vector prediction residual signal is also omitted.
  • FIG. 5A is a block diagram illustrating spatially neighboring and temporally collocated block positions of a current CU to be encoded/decoded in accordance with some implementations of the present disclosure.
  • a motion vector prediction (MVP) candidate list is constructed by first checking the availability of motion vectors associated with the spatially left and above neighboring block positions, and the availability of motion vectors associated with temporally collocated block positions and then the motion vectors in the FDMVP table.
  • some redundant MVP candidates are removed from the candidate list and, if necessary, zero-valued motion vector is added to make the candidate list to have a fixed length (note that different modes may have different fixed lengths).
  • video encoder 20 can select the best motion vector predictor from the candidate list and encode the corresponding index indicating the chosen candidate into the video bitstream.
  • the motion vector predictor (MVP) candidate list for the current CU may be constructed by performing the following steps in order under the AMVP mode:
  • the MVP candidate list after the previous step does not include two MVP candidates, derive up to one MVP candidate from the temporal collocated CUs (e.g ⁇ , TO)
  • an associated syntax element like a binary flag is encoded into the bitstream to indicate that which of the two MVP candidates within the candidate list is used for decoding the current CU.
  • the MVP candidate list for the current CU under the skip or merge mode may be constructed by performing a similar set of steps in order like the ones above. It is noted that one special kind of merge candidate called“pair-wise merge candidate” is also included into the MVP candidate list for the skip or merge mode.
  • the pair wise merge candidate is generated by averaging the MVs of the two previously derived merge-mode motion vector candidates.
  • the size of the merge MVP candidate list (e.g., from 1 to 6) is signaled in a slice header of the current CU.
  • an index of the best merge candidate is encoded using truncated unary binarization (TU). The first bin of the merge index is coded with context and bypass coding is used for other bins.
  • TU truncated unary binarization
  • the history-based MVPs can be added to either the
  • the motion information of a previously inter-coded CU is stored in the HMVP table and used as a MVP candidate for the current CU.
  • the HMVP table is maintained during the encoding/decoding process. Whenever there is a non-sub-block inter- coded CU, the associated motion vector information is added to the last entry of the HMVP table as a new candidate while the motion vector information stored in the first entry of the HMVP table is removed from therein (if the HMVP table is already full and there is no identical duplicate of the associated motion vector information in the table). Alternatively, the identical duplicate of the associated motion vector information is removed from the table before the associated motion vector information is added to the last entry of the HMVP table.
  • IBC intra block copy
  • BM block matching
  • An IBC-coded CU is treated as the third prediction mode other than the intra or inter prediction modes.
  • the IBC mode can be signaled as IBC AMVP mode or IBC skip/merge mode as follows: - IBC AMVP mode: a block vector difference (BVD) between the actual block vector of a CU and a block vector predictor of the CU selected from block vector candidates of the CU is encoded in the same way as a motion vector difference is encoded under the AMVP mode described above.
  • the block vector prediction method uses two block vector candidates as predictors, one from left neighbor and the other one from above neighbor (if IBC coded). When either neighbor is not available, a default block vector will be used as a block vector predictor. A binary flag is signaled to indicate the block vector predictor index.
  • the IBC AMVP candidate list consists of spatial and HMVP candidates.
  • a merge candidate index is used to indicate which of the block vector candidates in the merge candidate list (also known as a“merge list”) from neighboring IBC coded blocks is used to predict the block vector for the current block.
  • the IBC merge candidate list consists of spatial, HMVP, and pairwise candidates.
  • WPP wavefront parallel processing
  • FIG. 5B is a block diagram illustrating multi-threaded encoding of multiple rows of CTUs of a picture using wavefront parallel processing (WPP) in accordance with some implementations of the present disclosure.
  • WPP wavefront parallel processing
  • a video coder such as video encoder 20 and video decoder 30, may divide the coding tree units (CTUs) of the picture 500 into a plurality of wavefronts, each wavefront corresponding to a respective row of CTUs in the picture.
  • CTUs coding tree units
  • the video coder may start coding a top wavefront, e.g., using a first coder core or thread. After the video coder has coded two or more CTUs of the top wavefront, the video coder may start coding a second-to- top wavefront in parallel with coding the top wavefront, e.g., using a second, parallel coder core or thread. After the video coder has coded two or more CTUs of the second-to-top wavefront, the video coder may start coding a third-to-top wavefront in parallel with coding the higher wavefronts, e.g., using a third, parallel coder core or thread. This pattern may continue down the wavefronts in the picture 500.
  • each CTU of the CTU group may belong to a unique wavefront of the picture and the CTU may be offset from a CTU in a respective, above wavefront by at least two columns of CTUs of the picture.
  • the video coder may initialize a context for a current wavefront for performing context adaptive binary arithmetic coding (CAB AC) of the current wavefront based on data of the first two blocks of the above wavefront, as well as one or more elements of a slice header for a slice including the first code block of the current wavefront.
  • CAB AC context adaptive binary arithmetic coding
  • the video coder may perform CABAC initialization of a subsequent wavefront (or CTU row) using the context states after coding two CTUs of a CTU row above the subsequent CTU row.
  • a video coder (or more specifically, a thread of the video coder) may code at least two blocks of a wavefront above the current wavefront, assuming the current wavefront is not the top row of CTUs of a picture.
  • the video coder may then initialize a CABAC context for the current wavefront after coding at least two blocks of a wavefront above the current wavefront.
  • each CTU row of the picture 500 is a separated partition and has an associated thread (WPP Thread 1, WPP Thread 2, ...) such that the number of CTU rows in the picture 500 can be encoded in parallel.
  • the HMVP table uses a global motion vector (MV) buffer to store previously reconstructed motion vectors
  • this HMVP table cannot be implemented on the WPP-enabled parallel encoding scheme described above in connection with FIG. 5B.
  • the fact that the global MV buffer is shared by all the threads of the encoding/decoding process of a video coder prevents the WPP threads after the first WPP thread (i.e., WPP Thread 1) from being started since these WPP threads have to wait for the HMVP table update from the last CTU (i.e., rightmost CTU) of the first WPP thread (i.e., the first CTU row) to be completed.
  • each wavefront of CTU row has its own buffer for storing an HMVP table corresponding to the CTU row being processed by a corresponding WPP thread when WPP is enabled at the video coder.
  • each CTU row having its own HMVP table is equivalent to resetting the HMVP table before coding a first CU of the CTU row.
  • the HMVP table reset is to flush out all the motion vectors in the HMVP table resulting from coding of another CTU row.
  • the reset operation is to set the size of the available motion vector predictors in the HMVP table to be zero.
  • the reset operations could be to set the reference index of all the entries in the HMVP table to be an invalid value such as -1.
  • the HMVP table is reset to be empty without affecting the coding of another wavefront of CTUs by another WPP thread.
  • the HMVP table can be reset to be empty before the coding of each individual CTU.
  • the motion vectors in the HMVP table are limited to a particular CTU and there is probably a higher chance of a motion vector within the HMVP table being selected as a motion vector of a current CU within the particular CTU.
  • FIG. 6 is a block diagram illustrating an exemplary modified insertion order of merge motion vector prediction candidates (also known as a merge candidate) in a merge motion vector prediction candidate list (also known as a merge list or a merge candidate list) in accordance with some implementations of the present disclosure.
  • Table 602 shows an exemplary unmodified order of insertion of various merge candidates into the merge list
  • table 604 shows an exemplary modified order of insertion of various merge candidates.
  • the insertion of merge candidates into the merge list will be described as being performed by a prediction processing unit (e.g., prediction processing unit 81 of FIG. 3).
  • Each merge candidate comprises motion information from an associated CU, such as (1) motion vector, (2) a signal (“Inter Dir”) indicating whether a reference list L0 or a reference list Ll is used, (3) a reference index selecting a reference from either L0 or Ll.
  • motion information such as (1) motion vector, (2) a signal (“Inter Dir”) indicating whether a reference list L0 or a reference list Ll is used, (3) a reference index selecting a reference from either L0 or Ll.
  • the candidate list has a fixed length (e.g., six).
  • the prediction processing unit adds the merge MVP candidates to the candidate list in the following order:
  • the prediction processing unit adds to the merge list up to a predefined number (e.g., four) of spatial merge candidates from the spatially neighboring CUs Al, Bl, B0, A0, and B2, in this particular order.
  • a predefined number e.g., four
  • the prediction processing unit only adds a merge candidate from B2 if no merge candidate is available from the previous four CUs (Al, Bl, B0, and A0).
  • the merge candidate of a CU is not available if the CU is intra coded (thus no motion information at all) or if the CU belongs to another slice or tile.
  • the addition of the remaining spatial merge candidates to the candidate list is subject to a redundancy check.
  • the prediction processing unit performs the redundancy check to ensure that merge candidates with same motion information are excluded from being added to the candidate list so that coding efficiency can be improved.
  • the prediction processing unit adds to the merge list up to a predefined number (e.g., one) of temporal merge candidate from the temporally collocated picture frames at position TO and Tl, in this particular order.
  • a predefined number e.g., one
  • the prediction processing unit adds to the merge list up to a predefined number (e.g., one) of temporal merge candidate from the temporally collocated picture frames at position TO and Tl, in this particular order.
  • a scaled motion vector is derived from the motion vectors of the collocated picture (e.g., the collocated picture was previously coded in a reference list L0 or Ll).
  • the scaled motion vector for the temporal merge candidate is scaled from the selected motion vector of the collocated PU of the collocated picture using the POC distance
  • the prediction processing unit adds up to a predefined number (e.g., five) of HMVP merge candidates to the merge list.
  • the HMVP merge candidates are derived as explained in FIG. 5A and the related description.
  • a special condition associated with adding the HMVP merge candidates is that, the HMVP merge candidate cannot be added to the last slot of the merge list. For example, if there are four spatial/temporal merge candidates have been added to the merge list already, and there are two HMVP merge candidates available, only one of the two HMVP candidates can be added to the merge list.
  • the prediction processing unit adds up to a predefined number (e.g., one) of averaged merge candidates to the merge list.
  • the averaged merge candidates are generated by averaging (e.g., averaging the motion vectors) a selected group (e.g., a pair) of merge candidates already stored in the merge list.
  • the averaged motion vectors are calculated separately for each reference list of the selected pair of merge candidates. If both motion vectors of the selected pair of merge candidates are available in one reference list but the reference pictures are different, the motion vector associated with the larger merge index is scaled to the reference picture of the merge candidate with the smaller merge index to calculate the averaged merge candidate. If only one motion vector is available, the motion vector is used as the“averaged” merge candidate. If no motion vector is available (e.g., no candidate has been previously inserted into the merge list), no averaged merge candidate is inserted to the merge list.
  • averaging e.g., averaging the motion vectors
  • a selected group e.g., a
  • the prediction processing unit adds one or more zero motion merge candidates to the merge list so that the merge list reaches its maximum capacity.
  • the zero motion merge candidates have zero spatial displacement and a reference picture index that starts from 0 and increases by 1 for every new zero motion candidate added to the merge list (e.g., the third zero motion candidate will have a reference picture index of“3”). No redundancy check is performed on these zero motion merge candidates.
  • the prediction processing unit may add additional types of merge candidates such as non-adjacent spatial merge candidates and/or sub-block merge candidates to the merge list.
  • merge candidates such as non-adjacent spatial merge candidates and/or sub-block merge candidates.
  • spatial merge candidates from positions similar to those used in spatial merge candidates (e.g., A0-A1, B0-B2) are used, but being derived from the current CU, those positions are from outer reference areas containing the current CU.
  • the sub-block merge candidates are derived by partitioning the current CU into sub-blocks, identifying spatial and temporal motion vectors associated with each sub block, and averaging the identified spatial/temporal motion vectors.
  • Each merge candidate in the merge list is assigned a merge candidate index, representing the respective merge candidate’s position on the list.
  • the modified merge candidate insertion order illustrated in table 604 improves coding efficiency by allowing one or more averaged merge candidates to be inserted before the non-adjacent spatial merge candidates and the HMVP merge candidates.
  • the prediction processing unit computes a set of averaged merge candidates after finishing adding the spatial and temporal merge candidates to the merge list.
  • the prediction processing unit then adds a subset of the averaged merge candidates to the merge list.
  • the subset of averaged merge candidates can be the first two computed averaged merge candidates using a particular method (e.g., pairwise averaging).
  • the prediction processing unit then adds the HMVP merge candidates, the rest of the averaged merge candidates, and zero motion merge candidates, respectively (assuming there are enough slots in the merge list).
  • the prediction processing unit discards the remaining averaged merge candidates. Therefore, after the subset of averaged merge candidates, the prediction processing unit adds the HMVP merge candidates, and the zero motion merge candidates.
  • the prediction processing unit performs group-based redundancy checking when constructing the merge list.
  • the prediction processing unit performs either full redundancy checking, partial redundancy checking, or no redundancy checking for each group of candidates.
  • Full redundancy checking means that the redundancy checking is performed for each merge candidate against all the other candidates within the same group.
  • Partial checking means that the redundancy checking is performed for some merge candidates against some other merge candidates within the same group.
  • No redundancy checking means no redundancy check is performed for any merge candidates within the same group.
  • the prediction processing unit classifies the merge candidates as the following:
  • the prediction processing unit performs partial redundancy checking on group
  • the prediction processing unit performs partial redundancy checking on group 1 and 4, performs no redundancy checking on group 2, and performs full redundancy checking on group 3. [00112] In some embodiments, the prediction processing unit classifies the merge candidates as the following:
  • the non-adjacent spatial merge candidates can be divided into the first, second, ... Nth subsets based on the relative position of the non-adjacent spatial merge candidate with respect to the used reference frame.
  • the prediction processing unit performs partial redundancy checking on group 1, 4-1, 4-2, 4-3 ... 4-N, performs no redundancy checking on group 2, and full redundancy checking on group 3.
  • the prediction processing unit classifies the merge candidates as the following:
  • the prediction processing unit performs partial redundancy checking on groups 1-1, 1-2, ... l-N, performs no redundancy checking on group 2, and performs full redundancy checking on group 3. It should be noted that the partial redundancy checks described above are for illustrative purpose and it would be apparent for one skilled in the art to come up with the other possible redundancy check scenarios.
  • FIG. 7 is a flowchart illustrating an exemplary process 700 by which a video decoder implements the techniques of constructing a merge motion vector prediction candidate list (also known as merge list) in accordance with some implementations of the present disclosure.
  • a prediction processing unit e.g., the prediction processing unit 81 of FIG. 3.
  • the merge list can be set to having a maximum length (e.g., storing a maximum of 6 merge candidates), giving it characteristics similar to an array.
  • the merge list is configured to store all merge candidates computed by the prediction processing unit, giving it characteristics similar to a list.
  • the prediction processing unit can compute a merge candidate using one of many methods: using spatially neighboring blocks to generate spatial merge candidates, using temporally collocated blocks to generate temporal merge candidates, averaging motion vectors of existing merge candidates to generate averaged merge candidates, storing past motion information to generate history-based motion vector prediction (HMVP) candidates, and so on.
  • HMVP history-based motion vector prediction
  • Each merge candidate includes motion information indicating (1) a motion vector pointing from a block associated with the merge candidate to another block in the video signal, (2) reference lists (e.g., reference list L0 or Ll), (3) a flag indicating which reference list is used (e.g.,“inter dir” parameter), and (4) a reference index indicating which reference frame of a reference list is used.
  • reference lists e.g., reference list L0 or Ll
  • flag indicating which reference list is used e.g.,“inter dir” parameter
  • a reference index indicating which reference frame of a reference list is used.
  • Each merge candidate in the merge list is associated with a merge index.
  • the first candidate added to the merge list is represented by the merge index “0.”
  • merge candidates added early in the merge list will require less bit size to store their associated merge indices. For example,“0” requires only one bit to store (“0”), but“2” requires two bits to store (“10”), and 4 requires four bits to store“100”). Since the encoder stores in the video signal the merge index of the merge candidate to be used for a particular decoding process, it is preferable for to store merge candidates that are more likely to produce accurate prediction early in the merge list.
  • the prediction processing unit receives, from a bitstream representing encoded video signals, decoding information for a current coding block encoded in merge mode (710).
  • a coding block is encoded in merge mode if the motion information for decoding the coding block is shared from another coding block (e.g., a spatially neighboring coding block or a temporally collocated coding block), instead of being directly computed (e.g., the coding block is encoded using inter mode).
  • the prediction processing unit generates a merge list (also known as merge candidate list) for the current coding block (720).
  • the prediction processing unit starts with an empty merge list and computes multiple groups of merge candidates to be added to the merge list.
  • Each merge candidate includes respective motion information (e.g., motion vector, reference lists, reference frame index, etc.), and can be used by a motion
  • compensation unit (e.g., motion compensation unit 82) to generate a predicted unit for the current coding block.
  • the prediction processing unit first checks if at least one spatially neighboring block of the current coding block meets a first condition. If the first condition is met, the prediction processing unit inserts into the merge list a first group of spatial merge candidates (730).
  • the five possible spatial merge candidates are described with reference to FIG. 5A and FIG. 6.
  • the prediction processing unit checks the five spatial merge candidates in a predefined order, such as Al -> Bl -> B0 -> A0 -> B2. Other orders of checking the spatially neighboring blocks are also possible.
  • the first condition comprises that the spatially neighboring block (e.g., A0-A1, B0-B2) is inter-coded and contains motion information.
  • the spatially neighboring block e.g., A0-A1, B0-B2
  • the number of spatial merge candidates that can be added to the merge list is limited, and the first condition comprises that the maximum number of spatial merge candidates have not been reached in the merge list.
  • the prediction processing unit can only add up to four spatial merge candidates to the merge list, and checks all possible neighboring blocks (A0-A1, B0-B2) in the predefined order.
  • the first condition comprises that no previous spatial merge candidates have been added to the merge list.
  • the first condition may be that the merge candidate at B2 can only be added to the merge if no merge candidates at A0- Al, and B0-B1 has been added.
  • the prediction processing unit After finish adding the spatial merge candidates (if there is any to be added), the prediction processing unit checks if at least one temporally collocated block of the current block meets a second condition. If the second condition is met, the prediction processing unit adds to the merge list a second group of temporal merge candidates, each comprising motion information at temporally relocated blocks (740).
  • the two possible block locations e.g., TO and Tl
  • the prediction processing unit checks the two temporal merge candidates in a predefined order: TO -> Tl or Tl->T0.
  • the second condition comprises that the temporally collocated blocks (e.g., TO and Tl) are inter-coded and contains motion information.
  • the temporally collocated blocks e.g., TO and Tl
  • the number of temporal merge candidates that can be added to the merge list is limited, and the second condition comprises that the maximum number of temporal merge candidates have not been reached in the merge list.
  • the prediction processing unit can only add up to one temporal merge candidate to the merge list, and checks TO and Tl in the predefined order. Once a first temporal merge candidate has been added, the prediction processing unit forgoes adding the second temporal merge candidate, even if it contains valid motion information. Alternatively, the prediction processing unit can add all temporal merge candidates.
  • the prediction processing unit determines if an averaged merge candidate could be computed and added to the merge list (750). The prediction processing unit first checks if there are at least two merge candidates existing in the merge list (e.g., spatial or temporal merge candidates). If so, the prediction processing unit generates averaged merge candidates based on the existing at least two merge candidates.
  • the prediction processing unit performs pair-wise averaging to generate the averaged merge candidates. To do this, the prediction processing unit divides existing merge candidates into pairs based on their position in the merge list, and averages the motion vectors associated with each pair of merge candidates. The prediction processing unit can select the reference frame associated with either merge candidate in the pair as the reference frame for the averaged merge candidate.
  • the prediction processing unit generates an averaged merge candidate by averaging the motion vectors associated with all the existing merge candidates, and selecting a reference frame from the merge candidates as the reference frame for the averaged merge candidate.
  • the prediction processing unit may append all the averaged merge candidates to the merge list, or append only a subset of the averaged merge candidates to the merge list. The remaining averaged merge candidates can be appended to the merge list after the prediction processing unit appends the HMVP merge candidates.
  • the prediction processing unit After the prediction processing unit adds the averaged merge candidates to the merge list (if there is any to be added), the prediction processing unit determines if there are fewer than a maximum-allowed number of merge candidates in the merge list. If so, the prediction processing unit adds a fourth group of HMVP merge candidates to the merge list (760).
  • the HMVP merge candidates are computed according to the description with reference to FIG. 5 A.
  • a special condition is associated with the fourth group of HMVP merge candidates - a HMVP merge candidate cannot be the very last merge candidate in the merge list.
  • the prediction processing unit can only add up to 5 HMVP merge candidates.
  • the prediction processing unit after the prediction processing unit adds the fourth group of HMVP merge candidates to the merge list, the prediction processing unit further adds one or more averaged merge candidates to the merge list. For example, the prediction processing unit can add the first two averaged merge candidates to the merge list before the HMVP merge candidates, and the rest of the averaged merge candidates after the HMVP merge candidates.
  • the prediction processing unit performs redundancy check before adding the generated merge candidates (spatial merge candidates, temporal merge candidates, averaged merge candidates, etc.) to the merge list. Redundancy check is not performed on the HMVP merge candidates as it has already been performed when the HMVP merge candidates are first generated.
  • the prediction processing unit After generating the merge candidates and adding them to the merge list, the prediction processing unit receives a merge index from the bitstream (770).
  • the merge index indicates which merge candidate in the merge list is to be used for prediction block generation.
  • the prediction processing unit generates a prediction block for the current coding block by using the identified merge candidate (e.g., identified by the merge index) and a residual block (780). For example, the prediction processing unit can use the motion information to find a portion of another frame, and adds that frame portion to the residual block.
  • Computer- readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol.
  • computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non -transitory or (2) a communication medium such as a signal or carrier wave.
  • Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the implementations described in the present application.
  • a computer program product may include a computer- readable medium.
  • first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.
  • a first electrode could be termed a second electrode, and, similarly, a second electrode could be termed a first electrode, without departing from the scope of the implementations.
  • the first electrode and the second electrode are both electrodes, but they are not the same electrode.

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Abstract

Selon la présente invention, un dispositif informatique exécute un procédé de décodage de données vidéo en générant une liste de fusion. Le procédé consiste à : insérer dans la liste de fusion un premier groupe de candidats spatiaux de fusion ; ajouter à la liste de fusion un deuxième groupe de candidats temporels de fusion ; lorsque la présence d'au moins deux candidats de fusion est déterminée dans la liste de fusion, ajouter à la liste de fusion un troisième groupe de candidats de fusion moyennés sur la base des deux candidats de fusion ou plus ; lorsqu'il est déterminé que le nombre de candidats de fusion dans la liste de fusion est inférieur à un nombre maximum autorisé, ajouter à la liste de fusion un quatrième groupe de candidats de fusion HMVP (prédiction de vecteur de mouvement basée sur un historique) ; et recevoir, du train de bits, un indice de fusion identifiant un candidat de fusion dans la liste de fusion ; et générer un bloc de prédiction à l'aide du candidat de fusion identifié dans la liste de fusion.
PCT/US2019/050820 2018-09-12 2019-09-12 Modifications de la construction de la liste de candidats de fusion WO2020056143A1 (fr)

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