Methods, computing devices, non-transitory computer-readable storage media, computer program products, and methods of storing a bitstream for video decoding

Abstract

A method, computing device, non-transitory computer-readable storage medium, computer program product, and method of storing a bitstream for video decoding are provided. A computing device performs a method of decoding video data by determining a collocated picture of a current coding unit, locating spatially neighboring blocks of the current coding unit corresponding to the collocated picture, determining a motion shift vector of the current coding unit from one or more motion vectors associated with the spatially neighboring blocks according to a predefined fixed order, and reconstructing a subblock-based temporal motion vector for a respective subblock of a plurality of subblocks in the current coding unit from a corresponding subblock in the collocated picture based on the motion shift vector.

Description

[0001] This application is a divisional application of application number 202080036321.0, filed on June 5, 2020, entitled “Sub-block temporal motion vector prediction for video coding”. TECHNICAL FIELD

[0002] The present application generally relates to video data encoding and decoding, and in particular, to methods and systems for sub-block motion vector prediction during video data encoding and decoding. BACKGROUND

[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 gaming consoles, smart phones, video teleconferencing devices, video streaming devices, etc. The digital video can be stored on a suitable digital storage media or transmitted via a digital TV broadcast, a cable TV network, a satellite TV network, an Internet TV network, a wireless network or other means. Electronic devices can implement video compression / decompression standards, such as 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, to transmit, receive, encode, decode, and / or store digital video data. Video compression typically involves performing spatial (intra-frame) prediction and / or temporal (inter-frame) prediction to reduce or remove redundancy inherent in the video data. For block-based video coding, a video frame is partitioned into one or more slices, each slice having multiple video blocks, which can also be referred to as coding tree units (CTUs). Each CTU can contain one coding unit (CU) or recursively split into smaller CUs until a predefined minimum CU size is reached. Each CU, also referred to as a leaf CU, contains one or more transform units (TUs) and each CU also contains one or more prediction units (PUs). Each CU can be coded in intra, inter, or IBC modes. Video blocks in intra coded (I) slices of a video frame are coded using spatial prediction with respect to reference samples in neighboring blocks within the same video frame. Video blocks in inter coded (P or B) slices of a video frame can be coded by using either spatial prediction with respect to reference samples in neighboring blocks within the same video frame or temporal prediction with respect to reference samples in other reference video frames.

[0004] A prediction block for a current video block to be coded is derived based on either spatial or temporal prediction of previously coded reference blocks, e.g., neighboring blocks. The process of finding the reference blocks can be done through block matching algorithms. Residual data representing pixel differences between the current block to be coded and the prediction block is referred to as a residual block or prediction error. Inter coded blocks are coded according to the residual block and a motion vector pointing to a reference block in a reference frame that forms the prediction block. The process of determining the motion vector is commonly referred to as motion estimation. Intra coded blocks are coded according to an intra prediction mode and the residual block. To further compress, the residual block is transformed from the pixel domain to a transform domain, e.g., frequency domain, resulting in residual transform coefficients that can then be quantized. The quantized transform coefficients, which are initially arranged in a two-dimensional array, can be scanned to produce a one-dimensional vector, and then entropy coded into a video bitstream for even more compression.

[0005] The coded 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 sent to the electronic device wired or wirelessly. The electronic device then performs video decompression, which is the reverse process of video compression described above, e.g., obtaining the syntax elements from the bitstream by parsing the coded video bitstream, and reconstructing the digital video data from the coded video bitstream into its original format based at least in part on the syntax elements obtained from the bitstream, and presents the reconstructed digital video data on a display of the electronic device.

[0006] As the quality of digital videos increases from high definition to 4K x 2K or even 8K x 4K, the amount of video data to be encoded / decoded exponentially increases. It is a long-standing challenge in how to more efficiently code / decode video data while maintaining the image quality of the decoded video data. SUMMARY

[0007] This disclosure describes implementations related to video data encoding and decoding, and more specifically, implementations related to systems and methods of sub-block motion vector prediction.

[0008] According to a first aspect of the disclosure, a method of decoding a current coding unit in a current picture, comprising: determining a collocated picture of the current picture; determining a motion shift vector of the current coding unit according to motion vectors of spatial neighboring blocks of the current coding unit, wherein the motion shift vector indicates a shift of spatial positions between a sub-block of a plurality of sub-blocks in the current coding unit and a corresponding sub-block in the collocated picture; reconstructing a sub-block based temporal motion vector of the sub-block of the plurality of sub-blocks in the current coding unit from the corresponding sub-block in the collocated picture based on the motion shift vector.

[0009] According to a second aspect of the present application, 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.

[0010] According to a third aspect of the present application, 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. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings, included to provide a further understanding of the implementations and are incorporated in and constitute a part of this specification, illustrate the described implementations and together with the description serve to explain the basic principles. Like reference numerals refer to corresponding parts throughout.

[0012] Figure 1 is a block diagram illustrating an exemplary video encoding and decoding system in accordance with some implementations of the present disclosure.

[0013] Figure 2 is a block diagram illustrating an exemplary video encoder in accordance with some implementations of the present disclosure.

[0014] Figure 3 is a block diagram illustrating an exemplary video decoder in accordance with some implementations of the present disclosure.

[0015] Figures 4A to 4E is a block diagram illustrating how a frame is recursively partitioned into multiple video blocks of different sizes and shapes in accordance with some implementations of the present disclosure.

[0016] Figure 5 is a block diagram illustrating spatial neighboring positions and temporal collocated block positions of a current CU to be encoded in accordance with some implementations of the present disclosure.

[0017] Figures 6A to 6D is a block diagram illustrating steps for deriving a temporal motion vector predictor for a current block or a sub-block temporal motion vector predictor for a sub-block in the current block in accordance with some implementations of the present disclosure.

[0018] Figure 7 is a block diagram illustrating a process for determining an effective region for deriving a temporal motion vector predictor and a sub-block temporal motion vector predictor in accordance with some implementations of the present disclosure.

[0019] Figures 8A to 8B is a flowchart illustrating an exemplary process showing a video codec implementation of the techniques for deriving a sub-block temporal motion vector predictor in accordance with some implementations of the present disclosure. DETAILED DESCRIPTION

[0020] Reference will now be made in detail to specific implementations, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous non-limiting specific details are set forth in order to assist in understanding the subject matter presented herein. But it will be apparent to one of ordinary skill in the art that the subject matter can be practiced without these specific details, and that numerous alternatives can be implemented. For example, it will be apparent to one of ordinary skill in the art that the subject matter presented herein can be implemented on many types of electronic devices with digital video capabilities.

[0021] Figure 1 FIG. 1 is a block diagram illustrating an example system 10 for encoding and decoding video blocks in parallel, in accordance with some implementations of the present disclosure. As shown in FIG. 1, 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 can comprise any of a 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 devices, etc. In some implementations, source device 12 and destination device 14 are equipped with wireless communication capabilities. Figure 1

[0022] In some implementations, destination device 14 can receive encoded video data to be decoded via a link 16. Link 16 can comprise any type of communication medium or device capable of moving the encoded video data from source device 12 to destination device 14. In one example, link 16 can comprise a communication medium to enable source device 12 to transmit encoded video data directly to destination device 14 in real-time. The encoded video data can be modulated according to a communication standard, such as a wireless communication protocol, and transmitted to destination device 14. The communication medium can comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium can 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 can include routers, switches, base stations, or any other equipment that can be useful to facilitate communication from source device 12 to destination device 14.

[0023] ​In some other embodiments, the encoded video data may be sent from the output interface 22 to a storage device 32. The encoded video data in the storage device 32 may then be accessed by the target device 14 via the input interface 28. The storage device 32 may include any of a variety of distributed or locally accessible data storage media, such as a hard drive, a Blu-ray disc, a DVD, a CD-ROM, a flash memory, a volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data. In another example, the storage device 32 may correspond to a file server or another intermediate storage device that can hold the encoded video data generated by the source device 12. The target device 14 may access the stored video data from the storage device 32 via streaming or downloading. The file server may be any type of computer capable of storing encoded video data and sending the encoded video data to the target device 14. Exemplary file servers include a web server (e.g., for a website), an FTP server, a network attached storage (NAS) device, or a local disk drive. Target device 14 may access the encoded video data via any standard data connection suitable for accessing encoded video data stored on a file server, including a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., DSL, cable modem, etc.), or a combination of both. The transmission of the encoded video data from storage device 32 may be a streaming transmission, a download transmission, or a combination of both.

[0024] like Figure 1 As shown in , 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 for receiving video from a video content provider, and / or a computer graphics system for generating computer graphics data as source video, or a combination of such sources. As an example, if video source 18 is a camera of a security monitoring system, source device 12 and target device 14 may form a camera phone or video phone. However, the embodiments described in this application are generally applicable to video encoding / decoding and may be applied to wireless and / or wired applications.

[0025] Captured, pre-captured, or computer-generated video may be encoded by video encoder 20. The encoded video data may be sent directly to target device 14 via output interface 22 of source device 12. The encoded video data may also (or alternatively) be stored on storage device 32 for later access by target device 14 or other devices for decoding and / or playback. Output interface 22 may further include a modem and / or a transmitter.

[0026] Target device 14 includes an input interface 28, a video decoder 30, and a display device 34. Input interface 28 can include a receiver and / or a modem and receive encoded video data over link 16. The encoded video data communicated over link 16 or provided on a storage device 32 can include various syntax elements generated by video encoder 20 for use by video decoder 30 when decoding video data. Such syntax elements can be included within the encoded video data transmitted on a communication medium, stored on a storage medium, or stored on a file server.

[0027] In some implementations, target device 14 can include a display device 34, which can be an integrated display device and an external display device configured to communicate with target device 14. Display device 34 displays the decoded video data to a user and can include any of various 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.

[0028] Video encoder 20 and video decoder 30 can operate according to a proprietary standard or industry standard, such as VVC, HEVC, MPEG-4, Part 10, Advanced Video Coding (AVC), or extensions thereof. It is to be understood that the present application is not limited to a specific video coding / decoding standard and can be applicable to other video coding / decoding standards. In general, it is contemplated that video encoder 20 of source device 12 can be configured to encode video data according to any of these current or future standards. Similarly, it is also contemplated that video decoder 30 of target device 14 can be configured to decode video data according to any of these current or future standards.

[0029] Video encoder 20 and video decoder 30 can 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. When implemented partially in software, an electronic device can 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 can be included in one or more encoders or decoders, either of which can be integrated as part of a combined encoder / decoder (CODEC) in a respective device.

[0030] Figure 2is a block diagram illustrating an example video encoder 20, in accordance with some implementations described in this application. Video encoder 20 can perform intra-prediction encoding and inter-prediction encoding of video blocks within a video frame. Intra-prediction encoding relies on spatial prediction to reduce or remove spatial redundancy in the video data within a given video frame or picture. Inter-prediction encoding relies on temporal prediction to reduce or remove temporal redundancy in the video data within neighboring video frames or pictures of a video sequence.

[0031] As Figure 2 As shown in FIG. 1, 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. In some implementations, 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) can be positioned between summer 62 and DPB 64 to filter block boundaries to remove blockiness artifacts from reconstructed video. In addition to the deblocking filter, an in-loop filter (not shown) can be used to filter the output of summer 62. Video encoder 20 can take the form of a fixed or programmable hardware unit, or can be dispersed in one or more of the illustrated fixed or programmable hardware units.

[0032] Video data memory 40 can store video data to be encoded by the components of video encoder 20. The video data in video data memory 40 can be obtained, for example, from video source 18. DPB 64 is a buffer that stores reference video data used by video encoder 20 (e.g., in intra- or inter-prediction encoding mode) when encoding video data. Video data memory 40 and DPB 64 can be formed by any of a variety of memory devices. In various examples, video data memory 40 can be on-chip with other components of video encoder 20, or off-chip relative to those components.

[0033] As Figure 2As shown in FIG. 1, after receiving video data, partitioning unit 45 within prediction processing unit 41 partitions the video data into video blocks. This partitioning can also include partitioning of video frames into slices, tiles, or other larger coding units (CUs) in accordance with a predefined splitting structure, such as a quadtree structure, associated with the video data. Video frames can be divided into multiple video blocks (or sets of video blocks referred to as tiles). Prediction processing unit 41 can select one of a plurality of possible predictive encoding modes, such as one of a plurality of intra-predictive encoding modes or one of a plurality of inter-predictive encoding modes, for the current video block based on error results (e.g., rate and distortion levels). Prediction processing unit 41 can provide the resulting intra- or inter-predicted 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 at a later time. Prediction processing unit 41 also provides syntax elements, such as motion vectors, intra-mode indicators, partitioning information, and other such syntax information, to entropy encoding unit 56.

[0034] To select an appropriate intra-predictive encoding mode for a current video block, intra-prediction processing unit 46 within prediction processing unit 41 can perform intra-predictive encoding of the current video block in relation to one or more neighboring blocks in the same frame as the current block being encoded to provide spatial prediction. Motion estimation unit 42 and motion compensation unit 44 within prediction processing unit 41 perform inter-predictive encoding of the current video block in relation to one or more predictive blocks in one or more reference frames to provide temporal prediction. Video encoder 20 can perform multiple encoding passes, e.g., to select a suitable encoding mode for each block of video data.

[0035] In some implementations, motion estimation unit 42 determines an inter-prediction mode for a current video frame by generating motion vectors according to a predetermined pattern within a sequence of video frames, the motion vectors indicating displacement of a prediction unit (PU) of a video block within the current video frame relative to a prediction block within a reference video frame. Motion estimation performed by motion estimation unit 42 is a process of generating motion vectors that estimate motion for video blocks. For example, a motion vector can indicate displacement of a PU of a video block within a current video frame or picture relative to a prediction block (or other coding unit) within a reference frame that is relevant to a current block (or other coding unit) being encoded within the current frame. The predetermined pattern can designate video frames in the sequence as P-frames or B-frames. Intra-BC unit 48 can determine vectors (e.g., block vectors) for intra-BC encoding in a similar manner as motion vectors determined by motion estimation unit 42 for inter-prediction, or can utilize block vectors determined by motion estimation unit 42.

[0036] In terms of pixel differences, a prediction block is a block of a reference frame that is deemed to closely match a PU of a video block to be encoded, and pixel differences can be determined by a sum of absolute differences (SAD), a sum of squared differences (SSD), or other difference metrics. In some implementations, video encoder 20 can calculate values for sub-integer pixel positions of reference frames stored in DPB 64. For example, video encoder 20 can interpolate values for quarter-pel positions, eighth-pel positions, or other fractional-pel positions of a reference frame. Thus, motion estimation unit 42 can perform a motion search with respect to both full-pel positions and fractional-pel positions and output motion vectors with fractional-pel precision.

[0037] Motion estimation unit 42 calculates motion vectors for PUs of a video block in an inter-predicted coded frame by comparing a location of the PU to a location of a prediction 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 vectors to motion compensation unit 44, which then sends to entropy encoding unit 56.

[0038] Motion compensation performed by motion compensation unit 44 can involve extracting or generating a prediction block based on the motion vectors determined by motion estimation unit 42. Upon receiving a motion vector for a PU of a current video block, motion compensation unit 44 can locate the prediction block pointed to by the motion vector in one of the reference frame lists, retrieve the prediction block from DPB 64, and forward the prediction block to summer 50. Summer 50 then forms a residual video block of pixel difference values by subtracting pixel values of the prediction block provided by motion compensation unit 44 from pixel values of the current video block being encoded. The pixel difference values forming the residual video block can include luma difference components or chroma difference components, or both. Motion compensation unit 44 can also generate semantic elements associated with a video block of a video frame for use by video decoder 30 when decoding the video block of the video frame. The semantic elements can include, for example, semantic elements defining motion vectors used to identify the prediction block, any flags indicating the prediction mode, or any other semantic information described herein. It is noted that motion estimation unit 42 and motion compensation unit 44 can be highly integrated, but are illustrated separately for conceptual purposes.

[0039] In some implementations, intra BC unit 48 can generate vectors and extract prediction blocks in a manner similar to that described above in connection with motion estimation unit 42 and motion compensation unit 44, but the prediction blocks are in the same frame as the current block being coded, and the vectors are referred to as block vectors rather than motion vectors. In particular, intra BC unit 48 can determine an intra prediction mode to be used for coding the current block. In some examples, intra BC unit 48 can code the current block using various intra prediction modes, e.g., during a separate encoding pass, and test their performance through rate-distortion analysis. Next, intra BC unit 48 can select a suitable intra prediction mode to use among the various tested intra prediction modes and generate an intra mode indicator accordingly. For example, intra BC unit 48 can compute rate-distortion values for the various tested intra prediction modes using rate-distortion analysis, and select the intra prediction mode with the best rate-distortion characteristics among the tested modes as the suitable intra prediction mode to use. Rate-distortion analysis generally determines the amount of distortion (or error) between a coded block and the original uncoded block that was coded to generate the coded block, and the bit rate (i.e., number of bits) used to produce the coded block. Intra BC unit 48 can compute the rate from the distortion and the rate for various coded blocks to determine which intra prediction mode exhibits the best rate-distortion values for the block.

[0040] In other examples, intra BC unit 48 can perform such functions for intra BC prediction according to the implementations described herein using motion estimation unit 42 and motion compensation unit 44 in whole or in part. In either case, for intra block copy, in terms of pixel difference, the prediction block can be a block that is deemed to closely match the block to be coded, the pixel difference can be determined by sum of absolute difference (SAD), sum of squared difference (SSD), or other difference metric, and the identification of the prediction block can include computing values for sub-integer pixel positions.

[0041] Whether the prediction block is from the same frame according to intra prediction or a different frame according to inter prediction, video encoder 20 can form pixel difference values by subtracting pixel values of the prediction block from pixel values of the current video block being coded, thereby forming a residual video block. The pixel difference values forming the residual video block can include both luma component differences and chroma component differences.

[0042] As an alternative to inter prediction performed by motion estimation unit 42 and motion compensation unit 44 or intra block copy prediction performed by intra BC unit 48, as described above, intra prediction processing unit 46 can intra predict the current video block. In particular, intra prediction processing unit 46 can determine an intra prediction mode to use for encoding the current block. To this end, intra prediction processing unit 46 may, for example, encode the current block using various intra prediction modes during a separate encoding pass, and intra prediction processing unit 46 (or, in some examples, a mode selection unit) can select an appropriate intra prediction mode to use from among the tested intra prediction modes. Intra prediction processing unit 46 can provide information indicating the selected intra prediction mode for the block to entropy encoding unit 56. Entropy encoding unit 56 can encode information indicating the selected intra prediction mode into the bitstream.

[0043] After prediction processing unit 41 determines a prediction block for the current video block via inter prediction or intra prediction, adder 50 forms a residual video block by subtracting the prediction block from the current video block. The residual video data in the residual block can be included in one or more transform units (TUs) and 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.

[0044] Transform processing unit 52 can send the resulting transform coefficients to quantization unit 54. Quantization unit 54 quantizes the transform coefficients to further reduce bit rate. The quantization process can also reduce the bit depth associated with some or all of the coefficients. The degree of quantization can be modified by adjusting a quantization parameter. In some examples, quantization unit 54 can then perform a scan of the matrix including the quantized transform coefficients. Alternatively, entropy encoding unit 56 can perform the scan.

[0045] Following quantization, entropy encoding unit 56 entropy encodes the quantized transform coefficients using, for example, context adaptive variable length coding (CAVLC), context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), Probability Interval Partitioning Entropy (PIPE) coding or another entropy encoding methodology or technique, into a video bitstream. The encoded bitstream can then be transmitted to video decoder 30, or archived (e.g., stored) on a storage device 32 for later transmission to or retrieval by video decoder 30. Entropy encoding unit 56 can also entropy encode motion vectors and other syntax elements for the current video frame being encoded.

[0046] The inverse quantization unit 58 and the inverse transform processing unit 60 apply inverse quantization and inverse transform, respectively, to reconstruct the residual video block in the pixel domain for generating a reference block used to predict other video blocks. As noted above, the motion compensation unit 44 can generate a motion compensated prediction block from one or more reference blocks of frames stored in the DPB 64. The motion compensation unit 44 can also apply one or more interpolation filters to the prediction block to calculate sub-integer pixel values for use in motion estimation.

[0047] The summer 62 adds the reconstructed residual block to the motion compensated prediction block produced by the motion compensation unit 44 to produce a reference block for storage in the DPB 64. The reference block can then be used by the intra BC unit 48, the motion estimation unit 42, and the motion compensation unit 44 as a prediction block to inter predict another video block in a subsequent video frame.

[0048] Figure 3 FIG. 1 is a block diagram illustrating an example video decoder 30 according to some embodiments of the present application. The video decoder 30 includes a video data memory 79, an entropy decoding unit 80, a prediction processing unit 81, an inverse quantization unit 86, an inverse transform processing unit 88, a summer 90, and a DPB 92. The prediction processing unit 81 further includes a motion compensation unit 82, an intra prediction unit 84, and an intra BC unit 85. The video decoder 30 can perform a decoding process substantially reciprocal to that described above in connection with the video encoder 20. Figure 2 The decoding process described in connection with the video encoder 20 is substantially reciprocal. For example, the motion compensation unit 82 can generate prediction data based on motion vectors received from the entropy decoding unit 80, while the intra prediction unit 84 can generate prediction data based on intra prediction mode indicators received from the entropy decoding unit 80.

[0049] In some examples, the units of the video decoder 30 can be tasked to perform embodiments of the present application. Moreover, in some examples, embodiments of the present disclosure can be dispersed among one or more of the units of the video decoder 30. For example, the intra BC unit 85 can perform embodiments of the present application, alone or in combination with other units of the video decoder 30, such as the motion compensation unit 82, the intra prediction unit 84, and the entropy decoding unit 80. In some examples, the video decoder 30 can not include the intra BC unit 85, and the functionality of the intra BC unit 85 can be performed by other components of the prediction processing unit 81, such as the motion compensation unit 82.

[0050] Video data memory 79 can store video data to be decoded by the other components of video decoder 30, such as an encoded video bitstream. The video data stored in video data memory 79 can 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 can 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-coding modes). Video data memory 79 and DPB 92 can 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. For Figure 3 illustrative purposes, video data memory 79 and DPB 92 are depicted as two distinct components of video decoder 30. But it will be readily apparent to one of ordinary skill in the art that video data memory 79 and DPB 92 can be provided by the same memory device or separate memory devices. In some examples, video data memory 79 can be on-chip with other components of video decoder 30, or off-chip relative to those components.

[0051] During the decoding process, video decoder 30 receives an encoded video bitstream that represents encoded video frames and associated syntax elements. Video decoder 30 can receive the syntax elements at the video frame level and / or 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, among other syntax elements. Entropy decoding unit 80 then forwards the motion vectors and other syntax elements to prediction processing unit 81.

[0052] When a video frame is coded as an intra-predicted coding (I) frame or intra-coded prediction blocks in other types of frames, intra-prediction unit 84 of prediction processing unit 81 can generate prediction data for a video block of the current video frame based on the intra-prediction mode signaled and reference data from previously decoded blocks of the current frame.

[0053] When a video frame is coded as an inter prediction coded (i.e., B or P) frame, motion compensation unit 82 of prediction processing unit 81 generates one or more prediction blocks for a video block of the current video frame based on motion vectors and other syntax elements received from entropy decoding unit 80. Each of the prediction blocks can be generated from a reference frame within one of the reference frame lists. Video decoder 30 can construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference frames stored in DPB 92.

[0054] In some examples, when a video block is encoded according to the intra BC mode described herein, intra BC unit 85 of prediction processing unit 81 generates a prediction block for the current video block based on block vectors and other syntax elements received from entropy decoding unit 80. The prediction block can be within a reconstructed region of the same picture as the current video block, as defined by video encoder 20.

[0055] Motion compensation unit 82 and / or intra BC unit 85 determine the prediction information for a video block of the current video frame by parsing the motion vectors and other syntax elements, and then use the prediction information to generate a prediction block for the current video block being decoded. For example, motion compensation unit 82 uses some of the received syntax elements to determine the prediction mode used to code the video block of the video frame (e.g., intra prediction or inter prediction), the 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 prediction coded video block of the frame, inter prediction status for each inter prediction coded video block of the frame, and other information used to decode the video block in the current video frame.

[0056] Similarly, intra BC unit 85 can use some of the received syntax elements, such as flags, to determine that the current video block is predicted using the intra BC mode, construction information for 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 used to decode the video block in the current video frame.

[0057] Motion compensation unit 82 can also perform interpolation to calculate interpolated values for sub-integer pixels of a reference block using interpolation filters as used by video encoder 20 during encoding of the video block. In this case, motion compensation unit 82 can determine the interpolation filters used by video encoder 20 from the received syntax elements, and use these interpolation filters to generate the prediction block.

[0058] 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 parameters that were calculated by video encoder 20 for each video block in the video frame to determine the 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 to reconstruct the residual block in the pixel domain.

[0059] After the motion compensation unit 82 or the intra BC unit 85 generates a prediction block for the current video block based on the vector and other semantic elements, the adder 90 reconstructs the decoded video block for the current video block by adding the residual block from the inverse transform processing unit 88 to the corresponding prediction block generated by the motion compensation unit 82 and the intra BC unit 85. A loop filter (not shown) may be located between the adder 90 and the DPB 92 to further process the decoded video block. The decoded video block in a given frame is then stored in the DPB 92, which stores reference frames for subsequent motion compensation of the next video block. The DPB 92, or a memory device separate from the DPB 92, may also store the decoded video for later presentation on a display device (e.g., Figure 1 on the display device 34).

[0060] In a typical video encoding process, a video sequence typically consists of an ordered set of frames or pictures. Each frame may include three sample arrays, denoted as 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. In other cases, a frame may be monochrome and therefore consist of only a two-dimensional array of luma samples.

[0061] like Figure 4A As shown in , the video encoder 20 (or more specifically, the segmentation unit 45) generates an encoded representation of a frame by first segmenting the frame into a set of coding tree units (CTUs). A video frame may include an integer number of CTUs ordered consecutively from left to right and from top to bottom in raster scan order. Each CTU is the largest logical coding unit, and the width and height of the CTU are signaled by the video encoder 20 in a sequence parameter set so that all CTUs in a video sequence have the same size, one of 128×128, 64×64, 32×32, and 16×16. However, it should be noted that the present application is not necessarily limited to a specific size. As Figure 4BAs illustrated in FIG. 1, each CTU can include 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 the properties of different types of units that code the pixel blocks 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. In monochrome pictures or pictures with three separate color planes, a CTU can include a single coding tree block and syntax elements used to code the samples of the coding tree block. A coding tree block can be an NxN block of samples.

[0062] To achieve better performance, the video encoder 20 can recursively perform tree partitioning, such as binary tree partitioning, ternary tree partitioning, quad-tree partitioning, or a combination of both, on the coding tree blocks of a CTU and divide the CTU into smaller coding units (CUs). As Figure 4C As depicted in FIG. 4, a 64x64 CTU 400 is first divided into four smaller CUs, each having a block size of 32x32. Among the four smaller CUs, the CU 410 and the CU 420 are each divided into four CUs having a block size of 16x16. The two 16x16 CUs 430 and 440 are each further divided into four CUs having a block size of 8x8. Figure 4D A quad-tree data structure showing the final result of the partitioning process of the CTU 400 as Figure 4C depicted in FIG. 4, each leaf node of the quad-tree corresponds to one CU of various sizes ranging from 32x32 to 8x8. Similar to the binary tree data structure depicted in FIG. 3, each CU can include one coding block (CB) of luma samples and two corresponding coding blocks of chroma samples of the same size, and syntax elements used to code the samples of the coding blocks. In monochrome pictures or pictures with three separate color planes, a CU can include a single coding block and syntax elements used to code the samples of the coding block. It should be noted that, Figure 4B Figure 4C and Figure 4D The quad-tree partitioning depicted in FIG. 4 is for illustrative purposes only, and one CTU can be split into multiple CUs based on quad-tree partitioning / ternary tree partitioning / binary tree partitioning to adapt to varying local characteristics. In a multi-type tree structure, one CTU is partitioned in a quad-tree structure, and each quad-tree leaf CU can be further partitioned in binary and ternary tree structures. As Figure 4E depicted in FIG. 5, a coding block having a width W and a height H has five possible partitioning types, i.e., quad partitioning, horizontal binary partitioning, vertical binary partitioning, horizontal ternary partitioning, and vertical ternary partitioning.

[0063] ​In some implementations, video encoder 20 can further partition the coding block of a CU into one or more MxN prediction blocks (PBs). 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 can comprise a prediction block of luma samples, two corresponding prediction blocks of chroma samples, and syntax elements used to perform prediction for the prediction block. In a monochrome picture or a picture having three separate color planes, a PU can comprise a single prediction block and syntax structures used to perform prediction for the prediction block. Video encoder 20 can generate prediction luma, Cb, and Cr blocks for each PU of a CU.

[0064] Video encoder 20 can use intra prediction or inter prediction to generate the prediction block for a PU. If video encoder 20 uses intra prediction to generate the prediction block for a PU, video encoder 20 can generate the prediction block for the PU based on decoded samples of the frame associated with the PU. If video encoder 20 uses inter prediction to generate the prediction block for a PU, video encoder 20 can generate the prediction block for the PU based on decoded samples of one or more frames other than the frame associated with the PU.

[0065] After video encoder 20 generates the prediction luma, Cb, and Cr blocks for one or more PUs of a CU, video encoder 20 can generate a luma residual block for the CU by subtracting the prediction luma blocks for the CU from the original luma coding block for the CU, such that each sample in the luma residual block for the CU indicates a difference between a luma sample in one of the prediction luma blocks for the CU and a corresponding sample in the original luma coding block for the CU. Similarly, video encoder 20 can generate Cb and Cr residual blocks for the CU, respectively, such that each sample in the Cb residual block for the CU indicates a difference between a Cb sample in one of the prediction Cb blocks for the CU and a corresponding sample in the original Cb coding block for the CU, and each sample in the Cr residual block for the CU can indicate a difference between a Cr sample in one of the prediction Cr blocks for the CU and a corresponding sample in the original Cr coding block for the CU.

[0066] Furthermore, as Figure 4CAs shown in , the video encoder 20 may use quadtree partitioning to decompose the luma residual block, Cb residual block, and Cr residual block of a CU into one or more luma transform blocks, Cb transform blocks, and Cr transform blocks. A transform block is a rectangular (square or non-square) block of samples to which the same transform is applied. A transform unit (TU) of a CU may include a transform block of luma samples, two corresponding transform blocks of chroma samples, and semantic elements for transforming the transform block samples. Thus, each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block. In some examples, the luma transform block associated with a TU may be a sub-block of the luma residual block of the CU. The Cb transform block may be a sub-block of the Cb residual block of the CU. The Cr transform block may be a sub-block of the Cr residual block of the CU. In a monochrome picture or a picture with three separate color planes, a TU may include a single transform block and a semantic structure for transforming the samples of the transform block.

[0067] Video encoder 20 may apply one or more transforms to the 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. Video encoder 20 may apply one or more transforms to the 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 the Cr transform block of a TU to generate a Cr coefficient block for the TU.

[0068] 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 the process by which transform coefficients are quantized to potentially reduce the amount of data used to represent the transform coefficients, thereby providing further compression. After video encoder 20 quantizes the coefficient block, video encoder 20 may entropy encode semantic elements indicating the quantized transform coefficients. For example, video encoder 20 may perform context-adaptive binary arithmetic coding (CABAC) on the semantic elements indicating the quantized transform coefficients. Finally, video encoder 20 may output a bitstream comprising a sequence of bits forming a representation of an encoded frame and associated data, which is stored in storage device 32 or transmitted to target device 14.

[0069] After receiving the bitstream generated by video encoder 20, video decoder 30 can parse the bitstream to obtain the semantic elements from the bitstream. Video decoder 30 can reconstruct the frames of the video data based at least in part on the semantic 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 can perform inverse transforms on the coefficient blocks associated with the TUs of the current CU to reconstruct the residual blocks associated with the TUs of the current CU. Video decoder 30 also reconstructs the coding block of the current CU by adding the samples of the prediction block for the PUs of the current CU to the 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 can reconstruct the frame.

[0070] As noted above, video coding primarily uses two modes (i.e., intra-frame prediction (or intra-prediction) and inter-frame prediction (or inter-prediction)) to achieve video compression. It should be noted that IBC can be considered as intra-prediction or a third mode. Between the two modes, inter-prediction contributes more to coding efficiency than intra-prediction due to the use of motion vectors to predict the current video block from the reference video blocks.

[0071] However, as video data capturing technology is constantly improving and finer video block sizes are used to preserve details in the video data, the amount of data required to represent the motion vectors for the current frame also increases substantially. One way to overcome this challenge is to benefit from the fact that not only a group of neighboring CUs in both spatial and temporal domains have similar video data for prediction purposes, but also the motion vectors between these neighboring CUs are similar. Therefore, it is possible to use the motion information (e.g., motion vectors) of the spatial neighboring CUs and / or temporal collocated CUs as an approximation of the motion information (e.g., motion vectors) of the current CU by exploring their spatial and temporal correlation, which is also referred to as the “motion vector predictor” (MVP) of the current CU.

[0072] Instead of encoding the actual motion vectors of the current CU determined by the motion estimation unit 42 into the video bitstream as described above in connection with Figure 2 Instead of encoding the actual motion vectors of the current CU determined by the motion estimation unit 42 into the video bitstream as described above in connection with

[0073] Similar to the process of selecting a prediction block in a reference frame during inter prediction of a coding block, both video encoder 20 and video decoder 30 need to employ a set of rules for constructing a motion vector candidate list (also referred to 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 the motion vector predictor for the current CU. By doing so, there is no need to send the motion vector candidate list itself between video encoder 20 and video decoder 30, and the index of the selected motion vector predictor within the motion vector candidate list is sufficient for video encoder 20 and video decoder 30 to use the same motion vector predictor within the motion vector candidate list to encode and decode the current CU.

[0074] In some implementations, each inter prediction CU has three motion vector prediction modes for constructing a motion vector candidate list, including an inter mode (which is also referred to as "advanced motion vector prediction" (AMVP)), a skip mode, and a merge mode. In each mode, one or more motion vector candidates can be added to the motion vector candidate list according to the algorithms described below. Ultimately, one of these motion vector candidates in the candidate list serves as the best motion vector predictor for the inter prediction CU to be encoded by video encoder 20 into a video bitstream or decoded by video decoder 30 from a video bitstream. To find the best motion vector predictor from the candidate list, 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) including spatial motion vector candidates and temporal motion vector candidates.

[0075] In addition to deriving motion vector predictor candidates from spatially neighboring CUs or temporally collocated CUs, motion vector predictor candidates can also be derived from a so-called "history-based motion vector prediction" (HMVP) table. The HMVP table contains a predefined number of motion vector predictors, each of which has been used to encode / decode a particular CU in the same row of CTUs (or sometimes the same CTU). Due to the spatial / temporal proximity of these CUs, it is highly likely that one of the motion vector predictors in the HMVP table can be reused to encode / decode a different CU within the same row of CTUs. Thus, it is possible to achieve higher coding efficiency by including the HMVP table in the process of constructing the motion vector candidate list.

[0076] In some embodiments, the HMVP table has a fixed length (e.g., 5) and is managed in a first-in, first-out (FIFO)-like manner. For example, when an inter-frame coded block of a CU is decoded, a motion vector is reconstructed for the CU. Because the reconstructed motion vector may be a motion vector predictor for a subsequent CU, such a motion vector is used to update the HMVP table in real time. When updating the HMVP table, there are two scenarios: (i) 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. For the first scenario, if the HMVP table is not full, the reconstructed motion vector is added to the HMVP table as the latest motion vector. If the HMVP table is full, before the reconstructed motion vector is added as the latest motion vector, the oldest motion vector in the HMVP table must first be removed from the HMVP table. In other words, in this case, the HMVP table is similar to a FIFO buffer, so that the motion information at the head of the FIFO buffer and associated with another previous inter-frame coded block is moved out of the buffer, so that the reconstructed motion vector is appended to the tail of the FIFO buffer as the latest member of the HMVP table. For the second scenario, before adding the reconstructed motion vector as the latest motion vector to the HMVP table, the existing motion vectors in the HMVP table that are substantially identical to the reconstructed motion vector are removed from the HMVP table. If the HMVP table is also maintained in the form of a FIFO buffer, the motion vector prediction value following the identical motion vector in the HMVP table is shifted forward by one element to occupy the space left by the removed motion vector, and then the reconstructed motion vector is appended to the end of the FIFO buffer as the latest member in the HMVP table.

[0077] Motion vectors in the HMVP table can be added to the motion vector candidate list under different prediction modes such as AMVP, merge, skip, etc. It has been found that the motion information of previous inter-coded blocks stored in the HMVP table can be used for more efficient motion vector prediction even if they are not adjacent to the current block.

[0078] After selecting one MVP candidate within the given candidate set of motion vectors for the current CU, video encoder 20 can generate one or more semantic elements for the corresponding MVP candidate and encode them into the video bitstream so that video decoder 30 can retrieve the MVP candidate from the video bitstream using the semantic elements. Depending on the particular mode used to build the motion vector candidate set, different modes (e.g., AMVP, merge, skip, etc.) have different sets of semantic elements. For the AMVP mode, the semantic elements include an inter prediction indicator (list 0, list 1, or bi-prediction), a reference index, a motion vector candidate index, a motion vector prediction residual signal, etc. For the skip mode and the merge mode, only a merge index is encoded into the bitstream because the current CU inherits other semantic elements including the inter prediction indicator, the reference index, and the motion vector from the neighboring CUs referred by the encoded merge index. In the case of a skip coded CU, the motion vector prediction residual signal is also omitted.

[0079] Figure 5 is a block diagram illustrating spatial neighboring block positions and temporal collocated block positions of a current CU to be coded / decoded according to some embodiments of the present disclosure. For a given mode, a motion vector prediction (MVP) candidate list is constructed by first checking the availability of motion vectors associated with the left spatial neighboring block position and the above spatial neighboring block position and the availability of motion vectors associated with the temporal collocated block position, and then checking the motion vectors in the HMVP table. During the process of constructing the MVP candidate list, some redundant MVP candidates are removed from the candidate list, and if necessary, a zero-valued motion vector is added to make the candidate list have a fixed length (note that different modes can have different fixed lengths). After constructing the MVP candidate list, video encoder 20 can select the best motion vector prediction value from the candidate list and encode the corresponding index indicating the selected candidate into the video bitstream.

[0080] In some embodiments, the candidate list (also referred to as the merge candidate list) is constructed by including the following five types of candidates in the following order:

[0081] 1. Spatial MVPs (i.e., motion vector predictors) from spatial neighboring CUs

[0082] 2. Temporal MVPs from collocated CUs

[0083] 3. History-based MVPs from the FIFO table

[0084] 4. Pairwise average MVPs

[0085] 5. Zero MV

[0086] In some embodiments, the size of the candidate list is signaled in the slice header, and the maximum allowed size of the candidate list is six (e.g., in VVC). For each CU coded in merge mode, the index of the best merge candidate is coded using truncated unary binarization (TU). The first bin of the merge index is coded with a context, and bypass coding is used for the other bins. In the following context of this disclosure, this extended merge mode is also referred to as regular merge mode, as its concept is the same as the merge mode used in HEVC.

[0087] Using Figure 5 As an example and assuming the candidate list has a fixed length of 2, the motion vector predictor (MVP) candidate list for the current CU can be constructed by performing the following steps in order in AMVP mode:

[0088] 1) Selecting MVP candidates from spatial neighboring CUs

[0089] a) Get at most one unscaled MVP candidate from one of the two left spatial neighboring CUs starting with A0 and ending with A1 ;

[0090] b) If no unscaled MVP candidate from the left is available in the previous step, get at most one scaled MVP candidate from one of the two left spatial neighboring CUs starting with A0 and ending with A1 ;

[0091] c) Get at most one unscaled MVP candidate from one of the three above spatial neighboring CUs starting with B0, then B1 and ending with B2;

[0092] d) If A0 and A1 are not available, or if they are coded in intra mode, get at most one scaled MVP candidate from one of the three above spatial neighboring CUs starting with B0, then B1 and ending with B2;

[0093] 2) If two MVP candidates are found in the previous step and they are the same, remove one of the two candidates from the MVP candidate list;

[0094] 3) Selecting MVP candidates from temporal collocated CUs

[0095] a) If the MVP candidate list after going through the previous steps does not include two MVP candidates, get at most one MVP candidate from the temporal collocated CU (e.g., T0);

[0096] 4) Selecting MVP candidates from the HMVP table

[0097] a) If the MVP candidate list after going through the previous steps does not include two MVP candidates, get at most two history-based MVPs from the HMVP table; and

[0098] 5) If the MVP candidate list after going through the previous steps does not include two MVP candidates, add at most two zero-valued MVPs to the MVP candidate list.

[0099] Since there are only two candidates in the AMVP mode MVP candidate list built above, the associated semantic elements (such as binary flags) are coded into the bitstream to indicate which of the two MVP candidates within the candidate list is used to decode the current CU.

[0100] In some embodiments, the MVP candidate list for the current CU in skip or merge mode can be built by performing a set of similar steps in the order of the steps as above. It should be noted that a special type of merge candidate, called "paired merge candidate", is also included into the MVP candidate list for skip or merge mode. The paired merge candidate is generated by averaging the MVs of 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 the slice header of the current CU. For each CU in merge mode, the index of the best merge candidate is coded using truncated unary binarization (TU). The first bin of the merge index is coded with a context, and for the other bins, bypass coding is used.

[0101] As mentioned above, history-based MVPs can be added to the AMVP mode MVP candidate list or the merge MVP candidate list after the spatial MVPs and temporal MVPs. The motion information of previously inter-coded CUs is stored in the HMVP table and used as MVP candidates for the current CU. The HMVP table is maintained during the encoding / decoding process. Whenever there is a non-subblock inter-coded CU, the associated motion vector information is added to the last entry of the HMVP table as a new candidate (if the HMVP table is full and there is no identical copy of the associated motion vector information in the table), while the motion vector information stored in the first entry of the HMVP table is removed from the HMVP table. Optionally, before the associated motion vector information is added to the last entry of the HMVP table, the identical copy of the associated motion vector information is removed from the table.

[0102] As noted above, Intra Block Copy (IBC) can significantly improve the coding efficiency of screen content material. Since the IBC mode is implemented as a block-level coding mode, block matching (BM) is performed at the video encoder 20 to find the best block vector for each CU. Here, the block vector is used to indicate the displacement from the current block to a reference block that has been reconstructed within the current picture. The IBC mode is considered as the third prediction mode in addition to the intra prediction mode or the inter prediction mode.

[0103] At the CU level, the IBC mode can be signaled as the IBC AMVP mode or the IBC skip / merge mode as follows:

[0104] - IBC AMVP mode: The block vector difference (BVD) between the actual block vector of a CU and the block vector predictor of the CU selected from the block vector candidates of the CU is coded in the same way as the motion vector difference is coded in the AMVP mode described above. The block vector prediction method uses two block vector candidates as the predictor, one from the left neighboring block and the other from the above neighboring block (if IBC coded). When either neighboring block is not available, a default block vector will be used as the block vector predictor. A binary flag is signaled to indicate the block vector predictor index. The IBC AMVP candidate list consists of spatial candidates and HMVP candidates.

[0105] - IBC skip / merge mode: The merge candidate index is used to indicate which one of the block vector candidates in the merge candidate list (referred to as the "merge list" or "candidate list") from the neighboring IBC coded blocks is used to predict the block vector for the current block. The IBC merge candidate list consists of spatial candidates, HMVP candidates and pairwise candidates.

[0106] Figures 6A to 6D is a block diagram illustrating steps for deriving a temporal motion vector predictor (TMVP) for a current block or a sub-block temporal motion vector predictor (SbTMVP) for a sub-block of the current block according to some embodiments of the present disclosure.

[0107] In some embodiments, only one temporal motion vector predictor (TMVP) candidate is added to the merge candidate list, as with respect to Figure 5The first flag (sps_temporal_mvp_enabled_flag) is signaled in the sequence parameter set (SPS) of the picture and the second flag (slice_temporal_mvp_enabled_flag) is signaled in the slice header to indicate whether this TMVP candidate is enabled or disabled. Specifically, in deriving the temporal merge candidate, a scaled motion vector is derived from the MV of the co-located picture, which is a previously coded picture in the reference picture list. In deriving the temporal motion candidate, first an explicit flag (co-located_from_l0_flag) in the slice header is sent to the decoder to indicate whether the co-located picture is selected from the first reference frame list (list 0) or the second reference frame list (list 1). Further, the co-located reference index (co-located_ref_idx) is sent to indicate which picture in the used list is selected as the co-located picture for deriving the temporal motion candidate. The list 0 (also referred to as L0) and list 1 (also referred to as LI) MVs of the temporal motion candidate are independently derived based on the pre-defined order of the MVs of the different lists in the co-located block for the co-located picture according to the following pseudo code:

[0108]

[0109] Table 1: Pseudo code for deriving temporal MVs from co-located block for TMVP

[0110] As shown by the dashed line in Figure 6A , the scaled motion vector 602 for the temporal merge candidate is obtained, where the scaled motion vector 602 is scaled from the motion vector of the selected co-located block using the POC distance tb 604 and the POC distance td 606, where tb is defined as the POC difference between the reference picture of the current picture (e.g., current reference 608) and the current picture (e.g., current picture 610) and td is defined as the POC difference between the reference picture of the co-located picture (e.g., co-located reference 614) and the co-located picture (co-located picture 612). The reference picture index of the temporal merge candidate is set to equal to zero. The actual implementation of the scaling process is described in the HEVC specification. For B slices, two motion vectors (one for reference picture list 0 and the other for reference picture list 1) are obtained and combined to form a bi-predictive merge candidate.

[0111] As depicted in Figure 6B , in the co-located block (e.g., co-located block 620) belonging to the reference frame, the position of the temporal candidate is selected between candidate C0 and C1. If the block at position C0 is not available, the block at position C0 is intra coded, or the block at position C0 is outside the current CTU, then position C1 is used. Otherwise, position C0 is used in deriving the temporal merge candidate.

[0112] Some codec standards (e.g., VVC Test Model 1) support a sub-block based temporal motion vector prediction (SbTMVP) method. Similar to the temporal motion vector prediction (TMVP) in HEVC, SbTMVP uses the motion field in the co-located picture to improve the motion vector prediction and merge mode for the CU in the current picture. The same co-located picture used by TMVP is used for SbTMVP. SbTMVP differs from TMVP in two main aspects:

[0113] 1. TMVP predicts motion at the CU level, while SbTMVP predicts motion at the sub-CU level;

[0114] 2. When TMVP selects a temporal motion vector from a co-located block in a co-located picture (the co-located block is the bottom-right block or the center block relative to the current CU), SbTMVP applies a motion shift to the temporal motion information selected from the co-located picture, where the motion shift is obtained from the motion vector from one of the spatially neighboring blocks of the current CU.

[0115] Figures 6C to 6D The SbTMVP process is shown in FIG. Figure 6D The SbTMVP 632) predicts the current CU in two steps ( Figure 6D In the first step, check the motion vector of the sub-CU (e.g., sub-CU 634) within the current CU 636. Figure 6C A spatial neighbor A1 (e.g., spatial neighbor 638) in . If A1 has a spatial neighbor A1 that uses a co-located picture (e.g., Figure 6A 612) as its reference picture's motion vector, then this motion vector is selected as the motion shift to be applied (e.g., Figure 6D 630). If no such motion vector is identified, the motion shift is set to the zero-valued vector (0,0). The first available motion vector in List 0MV and List 1MV for block A1 is set as the motion shift. In this way, in SbTMVP, the corresponding block can be identified more accurately than in TMVP, where the corresponding block (sometimes called a co-located block) is always located in the lower right or center position relative to the current CU. The pseudo code for determining the motion shift is as follows.

[0116]

[0117] Pseudocode for determining motion shift of SbTMVP in VVC

[0118] The variables and functions used in the above table are shown below.

[0119] ColFromL0Flag: Semantics used to indicate whether the co-located picture comes from list 0 reference picture list

[0120] LDC: used to indicate whether all reference pictures have a smaller POC value than the current picture

[0121] CurrentSliceType: the type of the current slice (image)

[0122] count: The available number of exported merge candidates

[0123] interDirA1: interDir of the nth merge candidate (1: L0, 2: L1, or 3: Bi)

[0124] refIdxA1[0]: L0 motion information of the Nth merge candidate (e.g. MV, ref.index)

[0125] refIdxA1[1]: L1 motion information of the Nth merge candidate (e.g., MV, ref.index)

[0126] getRefPic(M, I): function used to obtain the reference picture with reference index equal to I from the reference picture list M.

[0127] In the second step, the motion shift identified in step 1 is applied (i.e., the motion shift is added to the coordinates of the current block) to obtain sub-CU level motion information (motion vector and reference index) from the co-located picture, as Figure 6D shown. Figure 6D The example in assumes that the motion shift is set to the motion of block A1. In actual implementation, the motion shift may be set to any one of the motions of blocks A1, A2, B1, or B2.

[0128] First, a representative sub-CU is selected, and the motion information of the corresponding block of the representative sub-CU is used as the default motion information. In the existing scheme of SbTMVP, the sub-CU located to the lower right of the center position of the current CU is selected as the representative sub-CU. When valid motion information cannot be derived from the corresponding block of the representative sub-CU as the default motion information, the SbTMVP candidate is considered unavailable. When the default motion information is available, proceed to the next step to derive motion information for each sub-CU in the current CU. Whenever no motion information is available for the corresponding block of any sub-CU, the default motion information will be used as the derived temporal motion for that sub-CU.

[0129] Then, for each sub-CU, the motion information of the corresponding block of the sub-CU in the same picture (the minimum motion grid covering the center sample) is used to derive the motion information of the sub-CU. After identifying the motion information of the same sub-CU, the motion information is converted into the motion vector and reference index of the current sub-CU in a manner similar to the TMVP process of HEVC, where temporal motion scaling is applied to align the reference picture of the temporal motion vector with the reference picture of the current CU.

[0130] It should be noted that in the current design, only the motion field within the co-located CTU in the co-located picture plus one column to the right of the co-located CTU can be used for SbTMVP and TMVP derivation for each CU. Figure 7 As shown in , only the motion information within the co-located CTU plus one column of motion information to the right of the co-located CTU (CTU 2' is the co-located CTU of the current CU in this example) can be used for temporal MV derivation of SbTMVP and TMVP. In the following, for ease of explanation, we refer to this co-located CTU plus one column as the "valid area" for SbTMVP / TMVP derivation. In this context, whenever the corresponding N×N block in the co-located picture of the sub-CU is outside the valid area, the corresponding N×N block is replaced with an alternative N×N block located in the co-located CTU. The position of the alternative N×N block is derived by cropping the original position of the corresponding N×N block to be within the valid area using the following equation. In the following equations (for the positional clipping process for each sub-CU), CurPicWidthInSamplesY and CurPicHeightInSamplesY are the width and height of the codec picture, CTUWidthInSamplesX and CTUWidthInSamplesY are the width and height of the CTU, xCtb and yCtb are the horizontal and vertical positions of the top left sample of the co-located CTU. xColCtrCb and yColCtrCb are the horizontal and vertical positions of the representative sample of the sub-CU, and MotionShiftX and MotionShiftY are the x and y components of the motion shift, respectively. The functions Clip3(x,y,z) and Min(x,y) are defined below.

[0131]

[0132] The position (xColCb yColCb) of the co-located block in the co-located picture is derived as follows.

[0133]

[0134] In VVC, a combined subblock-based merge list is used to signal the subblock-based merge mode, where the combined subblock-based merge list includes both SbTMVP candidates and affine merge candidates. SbTMVP mode is enabled / disabled by a sequence parameter set (SPS) flag. If SbTMVP mode is enabled, SbTMVP predictors are added as the first entries of the list of subblock-based merge candidates, followed by affine merge candidates. The size of the subblock-based merge list is signaled in the SPS, and the maximum allowed size of the subblock-based merge list is 5 in VVC.

[0135] The sub-CU size used in SbTMVP is fixed to 8x8, and as done for affine merge mode, SbTMVP mode is only applied to CUs whose width and height are both greater than or equal to 8. Furthermore, in current VVC, for the temporal motion field memory used by TMVP and SbTMVP, motion field compression is performed at 8x8 granularity compared to 16x16 granularity in HEVC.

[0136] In some embodiments, the motion shift is always derived from the list 0 MV of the neighboring block; if the list 0 MV is not available, the list 1 MV of the neighboring block is used to derive the motion shift for SbTMVP. The pseudo code is described as follows:

[0137]

[0138] Pseudo code for determining the motion shift for SbTMVP

[0139] In some embodiments, the motion shift is always derived from the list 1 MV of the neighboring block; if the list 1 MV is not available, the list 0 MV of the neighboring block is used to derive the motion shift for SbTMVP. The pseudo code is described as follows:

[0140]

[0141] Pseudo code for determining the motion shift for SbTMVP

[0142] In some embodiments, whenever there is any corresponding block of a sub-CU that is outside the valid area, a zero vector is used as the motion shift vector to derive SbTMVP. By doing so, it is guaranteed that the corresponding blocks of all sub-CUs of the current CU are inside the valid area. Therefore, no position clipping process is needed for each sub-CU. There are many ways to determine whether there is any corresponding block of a sub-CU that is outside the valid area in the current CU. In one example, the corresponding block of the top-left NxN sub-CU and the corresponding block of the bottom-right NxN sub-CU are checked to see whether both corresponding blocks are inside the valid area. If either is outside the valid area, a zero vector is used as the motion shift vector; otherwise (both corresponding blocks are inside the valid area), the derived motion shift is used for SbTMVP.

[0143] In some embodiments, whenever there is any corresponding block of a sub-CU that is outside the valid area, SbTMVP is considered unavailable for the current CU.

[0144] In some embodiments, whenever there is any corresponding block of a sub-CU that is outside the valid area, the motion shift is modified to guarantee that the corresponding blocks of all sub-CUs are inside the valid area. Therefore, no position clipping process is needed for each sub-CU.

[0145] In some embodiments, a zero vector is always used for the motion shift derived for SbTMVP.

[0146] In some embodiments, it is proposed to use the default MV derived from a representative sub-CU as the MV for a sub-CU that has a corresponding block outside the valid area.

[0147] Figure 7A block diagram showing a valid region for determining TMVP and SbTMVP for deriving a coding block (e.g., current CU 702) in a current picture (e.g., current picture 704) is shown in accordance with some embodiments of the disclosure. The valid region is a region in a collocated picture (e.g., collocated picture 704') in which a corresponding CU (e.g., corresponding CU 702') of the current CU (e.g., current CU 702) is being searched for TMVP or SbTMVP. In some embodiments, the valid region is determined by a CTU (e.g., CTU 2') plus one column (e.g., one column of TMV buffer 706) for deriving TMVP and SbTMVP. The valid region constraint is a design to reduce memory usage. By constraining the valid region to be a collocated CTU plus one column, only the motion information within the valid region needs to be stored in internal memory (e.g., cache memory) to reduce the average cost (time or energy) of accessing temporal motion data from external memory. Currently, the maximum CTU size in VVC is 128x128 (the maximum CTU size can be determined later in VVC profile), and the CTU size can be set to be smaller than 128x128 (e.g., 64x64 or 32x32). In one example, when the CTU size is set to 64x64, the valid region is constrained to be a collocated 64x64 block plus one column. Since the design of the temporal MV buffer for the maximum CTU already exists, it can not be wise to use a valid region smaller than the maximum CTU size from the codec efficiency point of view. In some embodiments, the valid region is always fixed to be the maximum allowed CTU size plus one column regardless of what size of CTU is used.

[0148] In some embodiments, the valid region is modified to be only the collocated CTU.

[0149] According to embodiments, when the CTU size is equal to the maximum CTU size, the valid region is the collocated CTU plus one column. When the CTU size is smaller than the maximum CTU size, the valid region is modified to be the collocated CTU plus one column to the right of the collocated CTU and one row below the collocated CTU.

[0150] Figures 8A to 8B A flowchart showing an example process 800 showing techniques for video codec implementation to derive subblock temporal motion vector predictors is shown in accordance with some embodiments of the disclosure. Although process 800 can be a decoding process or an encoding process, for convenience, process 800 will be described as a decoding process performed by a video decoder (e.g., video decoder 30 of FIG. 1) in accordance with some embodiments of the disclosure. Figure 3

[0151] ​As a first step, the decoder determines a collocated picture for the current coding unit (805) (e.g., receives from the bitstream a first syntax element indicating whether the collocated picture for the current frame is from the first list or the second list; then receives from the bitstream a second syntax element indicating which frame in the selected list is used as the collocated frame). For example, referring to Figure 6A , the current CU 601 in the current picture 610 corresponds to a collocated CU 601'in the collocated picture 612.

[0152] Next, the decoder locates spatially neighboring blocks for the current coding unit (810). For example, referring to Figure 6D , the current coding unit (e.g., the current CU 636) has spatial neighbors 638 (block Al). In some embodiments, the spatially neighboring blocks are coding units or sub-blocks.

[0153] After locating the spatially neighboring blocks, the decoder then determines a motion shift vector for the current coding unit (815). The motion shift vector indicates a shift in spatial position between the current coding unit (e.g., the current CU 636) in the current picture (e.g., the current picture 610) and a corresponding collocated block (e.g., the spatially neighboring block 638') in the collocated picture (e.g., the collocated picture 612). Figure 6D Figure 6D Figure 6D Figure 6D

[0154] To determine the motion shift vector, the decoder sequentially checks each motion vector included in list 0 of the spatially neighboring blocks (820). In accordance with a determination that there is a motion vector in list 0 that uses the collocated picture as a reference picture for that motion vector (825): the decoder sets that motion vector in list 0 as the motion shift vector (830) (e.g., the motion shift vector 630), and abandons checking subsequent motion vectors in list 0 of the spatially neighboring blocks and motion vectors in list 1 (835). Thus, the search for a motion vector ends, and the first matching motion vector in list 0 will be used as the motion shift vector. In other words, the decoder always checks the motion vectors included in list 0 of the spatially neighboring blocks first before checking list 1 of the spatially neighboring blocks.

[0155] On the other hand, in accordance with a determination that there is no motion vector in list 0 that uses the collocated picture as a reference picture (840), the decoder sequentially checks each motion vector included in list 1 of the spatially neighboring blocks (845). That is, the decoder checks the motion vectors of list 1 of the spatially neighboring blocks only if the search of motion vectors in list 0 returns a negative result.

[0156] ​​​​In searching for a motion vector in the list 1 of spatially neighboring blocks, the decoder determines whether a motion vector in the list 1 uses the collocated picture as a reference picture for the motion vector (850): if so, the decoder sets the motion vector in the list 1 as the motion shift vector (855), and abandons checking subsequent motion vectors in the list 1 (860). That is, the first matching motion vector in the list 1 will be used as the motion shift vector. If not, the decoder sets the motion shift vector to a zero-valued vector (870). Thus, the corresponding coding unit and the current coding unit are in the same relative position with respect to the collocated picture and the current picture (e.g., there is no motion shift between the current coding unit and the corresponding coding unit).

[0157] Finally, the decoder reconstructs the subblock-based temporal motion vector for the respective subblock of the plurality of subblocks in the current coding unit from the corresponding subblock in the collocated picture based on the motion shift vector (875). For example, with reference to Figure 6D , the subblock-based temporal motion vector for the respective subblock of the plurality of subblocks in the current coding unit is constructed by locating the corresponding subblock temporal motion vector 631 using the motion shift vector 630 after scaling (e.g., the scaling process described with respect to Figure 6A and related descriptions). In some embodiments, the subblock includes one or both temporal motion vectors from the list 0 and the list 1.

[0158] In some embodiments, reconstructing the subblock-based temporal motion vector for the respective subblock of the plurality of subblocks in the current coding unit from the corresponding subblock in the collocated picture based on the motion shift vector includes predicting the subblock-based temporal motion vector for the respective subblock of the plurality of subblocks in the current coding unit, including: searching for a collocated subblock corresponding to the respective subblock within a predefined region (e.g., an active region) in the collocated picture based on the motion shift vector; in accordance with a determination that the collocated subblock exists within the predefined region in the collocated picture: identifying one or both motion vectors of the collocated subblock; and setting the subblock-based temporal motion vector for the respective subblock to one or both motion vectors scaled based on a first picture order count (POC) distance (e.g., POC distance tb in Figure 6A ) between the current picture and a reference picture of the current picture and a second POC distance (e.g., POC distance td in Figure 6A ) between the collocated picture and a reference picture of the collocated picture. In some embodiments, in accordance with a determination that the collocated subblock does not exist within the predefined region in the collocated picture, the subblock-based temporal motion vector for the corresponding subblock is set to a zero-valued motion vector. In some other embodiments, in accordance with a determination that the collocated subblock does not exist within the predefined region in the collocated picture, a substitutable subblock within the predefined region in the collocated picture is set as the corresponding subblock. For example, the substitutable subblock is a boundary subblock within the predefined region closest to the collocated subblock.

[0159] In some embodiments, the predefined region has a size equal to the maximum allowable CTU size plus one column, regardless of the size of the CTU including the collocated coding unit.

[0160] In some embodiments, the decoder first checks the motion vectors in the list 1 of spatial neighboring blocks before checking the list 0 of spatial neighboring blocks.

[0161] In one or more examples, the functions described can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions can be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media can 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 the computer program from one place to another, e.g., according to a communication protocol. In this manner, computer- readable media generally can 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 can 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 disclosure. A computer program product can include a computer-readable medium.

[0162] The terminology used in the description of the implementations herein is for the purpose of describing particular implementations only and is not intended to limit the scope of the claims. As used in the description of the implementations and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and / or” as used herein refers to and encompasses 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,” when used in this specification, specify the presence of stated features, elements, and / or components, but do not preclude the presence or addition of one or more other features, elements, components, and / or groups thereof.

[0163] It will also be understood that, although the terms first, second, etc. can 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. For example, 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 present implementations. The first electrode and the second electrode are both electrodes, but they are not the same electrode.

[0164] The description of the application has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the application in the form disclosed. Many modifications, variations, and alternatives of the present application will be apparent to those of ordinary skill in the art, once the benefits of the present application have been explained. The embodiments were chosen and described in order to best explain the principles of the application and the practical application, and to enable others skilled in the art to understand the application of the various embodiments with various modifications as are suited to the particular use contemplated, and to best enable others skilled in the art to best utilize the application in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, it is to be understood that the scope of the claims is not to be limited to the specific examples disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims.

Claims

1. A method for video decoding, the method comprising: Obtaining a bitstream including a plurality of coding units divided into a video picture; Determining a collocated picture of the video picture; determining a motion shift vector for a current coding unit based on motion vectors of spatially neighboring blocks of the current coding unit, wherein the motion shift vector indicates a shift in spatial positions between subblocks of a plurality of subblocks in the current coding unit in the video picture and corresponding subblocks in the co-located picture; reconstructing a subblock-based temporal motion vector of the subblock of the plurality of subblocks in the current coding unit from a corresponding subblock in the co-located picture based on the motion shift vector; The determining of the motion shift vector of the current coding unit according to the motion vector of a spatially neighboring block of the current coding unit includes: deriving the motion shift vector from the motion vector associated with the first reference picture list, in a case where the motion vector of the spatially neighboring block associated with the first reference picture list uses the co-located picture as its reference picture; In a case where the motion vector of the spatially neighboring block associated with the first reference picture list does not use the co-located picture as its reference picture: deriving the motion shift vector from the motion vector associated with the second reference picture list, in a case where the motion vector of the spatially neighboring block associated with the second reference picture list uses the co-located picture as its reference picture; or determining the motion shift vector to be a zero-valued vector if the motion vector of the spatially neighboring block associated with the second reference picture list does not use the co-located picture as its reference picture; The reconstructing, based on the motion shift vector, the sub-block-based temporal motion vector of the sub-block of the multiple sub-blocks in the current coding unit from the corresponding sub-block in the co-located picture includes: determining, based on the motion shift vector, a co-located sub-block corresponding to the sub-block within a predefined area in the co-located picture, wherein, if a position determined based on the motion shift vector is outside the predefined area, clipping the position to be within the predefined area to determine a position of the co-located sub-block; and The sub-block based temporal motion vector of the sub-block is set to one or two scaled motion vectors derived based on one or two motion vectors of the co-located sub-block.

2. The method according to claim 1, wherein Setting the sub-block based temporal motion vector of the sub-block to one or two scaled motion vectors derived based on one or two motion vectors of the co-located sub-block comprises: The sub-block based temporal motion vector of the sub-block is set to: one or two scaled motion vectors derived based on one or two motion vectors of the co-located sub-block, a first picture order count (POC) distance between the video picture and a reference picture of the video picture, and a second POC distance between the co-located picture and the reference picture of the co-located picture.

3. The method of claim 1 , wherein reconstructing the subblock-based temporal motion vectors of the subblocks of the plurality of subblocks in the current coding unit from corresponding subblocks in the co-located picture based on the motion shift vector further comprises: According to determining that the co-located sub-block does not exist in the predefined area in the co-located picture: The sub-block based temporal motion vector of the sub-block is determined to be a zero-valued motion vector.

4. The method of claim 1 , wherein reconstructing the subblock-based temporal motion vectors of the subblocks of the plurality of subblocks in the current coding unit from corresponding subblocks in the co-located picture based on the motion shift vector further comprises: According to determining that the co-located sub-block does not exist in the predefined area in the co-located picture: A replaceable sub-block within the predefined area in the co-located picture is set as the corresponding sub-block, wherein the replaceable sub-block is a boundary sub-block within the predefined area that is closest to the co-located sub-block. The method according to claim 1 , wherein the spatially neighboring blocks of the current coding unit are coding units or sub-blocks of coding units. 6 . The method of claim 1 , wherein the predefined area has a size equal to a maximum allowable CTU size plus one column, and the size of the predefined area is independent of a size of a CTU including the co-located sub-block. The method of claim 6 , wherein the maximum allowable CTU size is 128×128.

8. A computing device comprising: one or more processors; a memory coupled to the one or more processors; as well as A plurality of programs are stored in the memory, and when the plurality of programs are executed by the one or more processors, the computing device performs the method for video decoding according to any one of claims 1 to 7.

9. A non-transitory computer-readable storage medium storing a plurality of programs for execution by a computing device having one or more processors, wherein the plurality of programs, when executed by the one or more processors, causes the computing device to perform the method for video decoding as described in any one of claims 1 to 7 to process a received video bitstream and store the processed video bitstream in the non-transitory computer-readable storage medium.

10. A computer program product comprising computer instructions, characterized in that When the computer instructions are executed by a processor, the method for video decoding according to any one of claims 1 to 7 is implemented.

11. A method of storing a bitstream, comprising storing the bitstream decoded by the method for video decoding according to any one of claims 1 to 7 in a non-transitory computer-readable storage medium.

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