WO2020192747A1 - Alignement de précision d'informations de mouvement dans une prédiction de vecteur de mouvement avancée affine - Google Patents

Alignement de précision d'informations de mouvement dans une prédiction de vecteur de mouvement avancée affine Download PDF

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WO2020192747A1
WO2020192747A1 PCT/CN2020/081575 CN2020081575W WO2020192747A1 WO 2020192747 A1 WO2020192747 A1 WO 2020192747A1 CN 2020081575 W CN2020081575 W CN 2020081575W WO 2020192747 A1 WO2020192747 A1 WO 2020192747A1
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precision
flag
motion vector
equal
block
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PCT/CN2020/081575
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Hongbin Liu
Li Zhang
Kai Zhang
Yue Wang
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Beijing Bytedance Network Technology Co., Ltd.
Bytedance Inc.
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Priority to CN202080025121.5A priority Critical patent/CN113661709A/zh
Publication of WO2020192747A1 publication Critical patent/WO2020192747A1/fr

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/134—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or criterion affecting or controlling the adaptive coding
    • H04N19/157—Assigned coding mode, i.e. the coding mode being predefined or preselected to be further used for selection of another element or parameter
    • H04N19/159—Prediction type, e.g. intra-frame, inter-frame or bidirectional frame prediction
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/13—Adaptive entropy coding, e.g. adaptive variable length coding [AVLC] or context adaptive binary arithmetic coding [CABAC]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/1887—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being a variable length codeword
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/503—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving temporal prediction
    • H04N19/51—Motion estimation or motion compensation
    • H04N19/513—Processing of motion vectors
    • H04N19/517—Processing of motion vectors by encoding
    • H04N19/52—Processing of motion vectors by encoding by predictive encoding

Definitions

  • This patent document relates to video coding and decoding techniques, devices and systems.
  • Devices, systems and methods related to digital video coding, and specifically, to motion vector predictor derivation and signaling for affine mode with adaptive motion vector resolution (AMVR) are described.
  • the described methods may be applied to both the existing video coding standards (e.g., High Efficiency Video Coding (HEVC) ) and future video coding standards or video codecs.
  • HEVC High Efficiency Video Coding
  • the disclosed technology may be used to provide a method for visual media processing.
  • This method includes during a conversion between a current video block and a bitstream representation of the current video block, using syntax elements composed of multiple bins for processing the current video block, wherein the syntax elements are selected according to a context model such that a first context model is applied for selecting a first bin of a first syntax element and a second context model is applied for selecting all bins excluding the first bin of the first syntax element.
  • the disclosed technology may be used to provide a method for visual media processing.
  • This method includes making a determination of using a precision from a precision set as a target precision of a motion vector (MVD) that is computed as a difference between a motion vector and a motion vector predictor (MVP) associated with a current video block; in response to detecting that the target precision is different from the precision of the MVP, converting the precision of the MVP to the target precision; and generating a reconstructed motion vector using the MVP with the target precision and the MVD, during a normal inter mode or an affine inter mode coding of the current video block, wherein the reconstructed motion vector is used for processing of subsequent video blocks.
  • MVP motion vector predictor
  • the disclosed technology may be used to provide a method for visual media processing.
  • This method includes during a conversion between a video block and a bitstream representation of the current video block, identifying that a precision of a motion vector predictor (MVP) associated with the current video block is different from a precision of a motion vector difference (MVD) that is computed as a difference between the MVP and a motion vector associated with the current video block; in response to the detecting, converting the precision of the MVD to the precision of the MVP; and reconstructing the motion vector associated with the current video block using the precision of the MVP for processing subsequent video blocks.
  • MVP motion vector predictor
  • MVP motion vector difference
  • the above-described method is embodied in the form of processor-executable code and stored in a computer-readable program medium.
  • a device that is configured or operable to perform the above-described method.
  • the device may include a processor that is programmed to implement this method.
  • a video encoder apparatus may implement a method as described herein.
  • a video decoder apparatus may implement a method as described herein.
  • FIG. 1 shows an example of constructing a merge candidate list.
  • FIG. 2 shows an example of positions of spatial candidates.
  • FIG. 3 shows an example of candidate pairs subject to a redundancy check of spatial merge candidates.
  • FIGS. 4A and 4B show examples of the position of a second prediction unit (PU) based on the size and shape of the current block.
  • FIG. 5 shows an example of motion vector scaling for temporal merge candidates.
  • FIG. 6 shows an example of candidate positions for temporal merge candidates.
  • FIG. 7 shows an example of generating a combined bi-predictive merge candidate.
  • FIG. 8 shows an example of constructing motion vector prediction candidates.
  • FIG. 9 shows an example of motion vector scaling for spatial motion vector candidates.
  • FIG. 10 shows an example of motion prediction using the alternative temporal motion vector prediction (ATMVP) algorithm for a coding unit (CU) .
  • ATMVP alternative temporal motion vector prediction
  • FIG. 11 shows an example of a coding unit (CU) with sub-blocks and neighboring blocks used by the spatial-temporal motion vector prediction (STMVP) algorithm.
  • CU coding unit
  • STMVP spatial-temporal motion vector prediction
  • FIGS. 12A and 12B show example snapshots of sub-block when using the overlapped block motion compensation (OBMC) algorithm.
  • OBMC overlapped block motion compensation
  • FIG. 13 shows an example of neighboring samples used to derive parameters for the local illumination compensation (LIC) algorithm.
  • LIC local illumination compensation
  • FIG. 14 shows an example of a simplified affine motion model.
  • FIG. 15 shows an example of an affine motion vector field (MVF) per sub-block.
  • FIG. 16 shows an example of motion vector prediction (MVP) for the AF_INTER affine motion mode.
  • FIGS. 17A and 17B show examples of the 4-parameter and 6-parameter affine models, respectively.
  • FIGS. 18A and 18B show example candidates for the AF_MERGE affine motion mode.
  • FIG. 19 shows an example of bilateral matching in pattern matched motion vector derivation (PMMVD) mode, which is a special merge mode based on the frame-rate up conversion (FRUC) algorithm.
  • PMMVD pattern matched motion vector derivation
  • FRUC frame-rate up conversion
  • FIG. 20 shows an example of template matching in the FRUC algorithm.
  • FIG. 21 shows an example of unilateral motion estimation in the FRUC algorithm.
  • FIG. 22 shows an example of an optical flow trajectory used by the bi-directional optical flow (BIO) algorithm.
  • FIGS. 23A and 23B show example snapshots of using of the bi-directional optical flow (BIO) algorithm without block extensions.
  • FIG. 24 shows an example of the decoder-side motion vector refinement (DMVR) algorithm based on bilateral template matching.
  • FIG. 25 shows a flowchart of an example method for video coding.
  • FIG. 26 is a block diagram of an example of a hardware platform for implementing a visual media decoding or a visual media encoding technique described in the present document.
  • FIG. 27 shows an example of symmetrical mode.
  • FIG. 28 is a block diagram of an example video processing system in which disclosed techniques may be implemented.
  • FIG. 29 shows a flowchart of an example method for video processing.
  • FIG. 30 shows a flowchart of an example method for video processing.
  • FIG. 31 shows a flowchart of an example method for video processing.
  • Video codecs typically include an electronic circuit or software that compresses or decompresses digital video, and are continually being improved to provide higher coding efficiency.
  • a video codec converts uncompressed video to a compressed format or vice versa.
  • the compressed format usually conforms to a standard video compression specification, e.g., the High Efficiency Video Coding (HEVC) standard (also known as H. 265 or MPEG-H Part 2) , the Versatile Video Coding standard to be finalized, or other current and/or future video coding standards.
  • HEVC High Efficiency Video Coding
  • MPEG-H Part 2 MPEG-H Part 2
  • Embodiments of the disclosed technology may be applied to existing video coding standards (e.g., HEVC, H. 265) and future standards to improve compression performance. Section headings are used in the present document to improve readability of the description and do not in any way limit the discussion or the embodiments (and/or implementations) to the respective sections only.
  • Video coding standards have significantly improved over the years, and now provide, in part, high coding efficiency and support for higher resolutions.
  • Recent standards such as HEVC and H. 265 are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized.
  • Each inter-predicted PU has motion parameters for one or two reference picture lists.
  • motion parameters include a motion vector and a reference picture index.
  • the usage of one of the two reference picture lists may also be signaled using inter_pred_idc.
  • motion vectors may be explicitly coded as deltas relative to predictors.
  • a merge mode is specified whereby the motion parameters for the current PU are obtained from neighboring PUs, including spatial and temporal candidates.
  • the merge mode can be applied to any inter-predicted PU, not only for skip mode.
  • the alternative to merge mode is the explicit transmission of motion parameters, where motion vector, corresponding reference picture index for each reference picture list and reference picture list usage are signaled explicitly per each PU.
  • the PU When signaling indicates that one of the two reference picture lists is to be used, the PU is produced from one block of samples. This is referred to as 'uni-prediction' . Uni-prediction is available both for P-slices and B-slices.
  • the PU When signaling indicates that both of the reference picture lists are to be used, the PU is produced from two blocks of samples. This is referred to as 'bi-prediction' . Bi-prediction is available for B-slices only.
  • Step 1 Initial candidates derivation
  • Step 1.1 Spatial candidates derivation
  • Step 1.2 Redundancy check for spatial candidates
  • Step 1.3 Temporal candidates derivation
  • Step 2 Additional candidates insertion
  • Step 2.1 Creation of bi-predictive candidates
  • Step 2.2 Insertion of zero motion candidates
  • FIG. 1 shows an example of constructing a merge candidate list based on the sequence of steps summarized above.
  • For spatial merge candidate derivation a maximum of four merge candidates are selected among candidates that are located in five different positions.
  • temporal merge candidate derivation a maximum of one merge candidate is selected among two candidates. Since constant number of candidates for each PU is assumed at decoder, additional candidates are generated when the number of candidates does not reach to maximum number of merge candidate (MaxNumMergeCand) which is signalled in slice header. Since the number of candidates is constant, index of best merge candidate is encoded using truncated unary binarization (TU) . If the size of CU is equal to 8, all the PUs of the current CU share a single merge candidate list, which is identical to the merge candidate list of the 2N ⁇ 2N prediction unit.
  • TU truncated unary binarization
  • a maximum of four merge candidates are selected among candidates located in the positions depicted in FIG. 2.
  • the order of derivation is A 1 , B 1 , B 0 , A 0 and B 2 .
  • Position B 2 is considered onlywhen any PU of position A 1 , B 1 , B 0 , A 0 is not available (e.g. because it belongs to another slice or tile) or is intra coded.
  • candidate at position A 1 is added, the addition of the remaining candidates is subject to a redundancy check which ensures that candidates with same motion information are excluded from the list so that coding efficiency is improved.
  • FIGS. 4A and 4B depict the second PU for the case of N ⁇ 2N and 2N ⁇ N, respectively.
  • candidate at position A 1 is not considered for list construction.
  • adding this candidate may lead to two prediction units having the same motion information, which is redundant to just have one PU in a coding unit.
  • position B 1 is not considered when the current PU is partitioned as 2N ⁇ N.
  • a scaled motion vector is derived based on co-located PU belonging to the picture which has the smallest POC difference with current picture within the given reference picture list.
  • the reference picture list to be used for derivation of the co-located PU is explicitly signaled in the slice header.
  • FIG. 5 shows an example of the derivation of the scaled motion vector for a temporal merge candidate (as the dotted line) , which is scaled from the motion vector of the co-located PU using the POC distances, tb and td, where tb is defined to be the POC difference between the reference picture of the current picture and the current picture and td is defined to be the POC difference between the reference picture of the co-located picture and the co-located picture.
  • the reference picture index of temporal merge candidate is set equal to zero. For a B-slice, two motion vectors, one is for reference picture list 0 and the other is for reference picture list 1, are obtained and combined to make the bi-predictive merge candidate.
  • the position for the temporal candidate is selected between candidates C 0 and C 1 , as depicted in FIG. 6. If PU at position C 0 is not available, is intra coded, or is outside of the current CTU, position C 1 is used. Otherwise, position C 0 is used in the derivation of the temporal merge candidate.
  • merge candidates there are two additional types of merge candidates: combined bi-predictive merge candidate and zero merge candidate.
  • Combined bi-predictive merge candidates are generated by utilizing spatio-temporal merge candidates.
  • Combined bi-predictive merge candidate is used for B-Slice only.
  • the combined bi-predictive candidates are generated by combining the first reference picture list motion parameters of an initial candidate with the second reference picture list motion parameters of another. If these two tuples provide different motion hypotheses, they will form a new bi-predictive candidate.
  • FIG. 7 shows an example of this process, wherein two candidates in the original list (710, on the left) , which have mvL0 and refIdxL0 or mvL1 and refIdxL1, are used to create a combined bi-predictive merge candidate added to the final list (720, on the right) .
  • Zero motion candidates are inserted to fill the remaining entries in the merge candidates list and therefore hit the MaxNumMergeCand capacity. These candidates have zero spatial displacement and a reference picture index which starts from zero and increases every time a new zero motion candidate is added to the list. The number of reference frames used by these candidates is one and two for uni-and bi-directional prediction, respectively. In some embodiments, no redundancy check is performed on these candidates.
  • motion estimation can be performed in parallel whereby the motion vectors for all prediction units inside a given region are derived simultaneously.
  • the derivation of merge candidates from spatial neighborhood may interfere with parallel processing as one prediction unit cannot derive the motion parameters from an adjacent PU until its associated motion estimation is completed.
  • a motion estimation region may be defined.
  • the size of the MER may be signaled in the picture parameter set (PPS) using the "log2_parallel_merge_level_minus2" syntax element.
  • AMVP Advanced Motion Vector Prediction
  • AMVP exploits spatio-temporal correlation of motion vector with neighboring PUs, which is used for explicit transmission of motion parameters. It constructs a motion vector candidate list by firstly checking availability of left, above temporally neighboring PU positions, removing redundant candidates and adding zero vector to make the candidate list to be constant length. Then, the encoder can select the best predictor from the candidate list and transmit the corresponding index indicating the chosen candidate. Similarly with merge index signaling, the index of the best motion vector candidate is encoded using truncated unary. The maximum value to be encoded in this case is 2 (see FIG. 8) . In the following sections, details about derivation process of motion vector prediction candidate are provided.
  • FIG. 8 summarizes derivation process for motion vector prediction candidate, and may be implemented for each reference picture list with refidx as an input.
  • motion vector candidate two types are considered: spatial motion vector candidate and temporal motion vector candidate.
  • spatial motion vector candidate derivation two motion vector candidates are eventually derived based on motion vectors of each PU located in five different positions as previously shown in FIG. 2.
  • one motion vector candidate is selected from two candidates, which are derived based on two different co-located positions. After the first list of spatio-temporal candidates is made, duplicated motion vector candidates in the list are removed. If the number of potential candidates is larger than two, motion vector candidates whose reference picture index within the associated reference picture list is larger than 1 are removed from the list. If the number of spatio-temporal motion vector candidates is smaller than two, additional zero motion vector candidates is added to the list.
  • a maximum of two candidates are considered among five potential candidates, which are derived from PUs located in positions as previously shown in FIG. 2, those positions being the same as those of motion merge.
  • the order of derivation for the left side of the current PU is defined as A 0 , A 1 , and scaled A 0 , scaled A 1 .
  • the order of derivation for the above side of the current PU is defined as B 0 , B 1 , B 2 , scaled B 0 , scaled B 1 , scaled B 2 .
  • the no-spatial-scaling cases are checked first followed by the cases that allow spatial scaling. Spatial scaling is considered when the POC is different between the reference picture of the neighbouring PU and that of the current PU regardless of reference picture list. If all PUs of left candidates are not available or are intra coded, scaling for the above motion vector is allowed to help parallel derivation of left and above MV candidates. Otherwise, spatial scaling is not allowed for the above motion vector.
  • the motion vector of the neighbouring PU is scaled in a similar manner as for temporal scaling.
  • One difference is that the reference picture list and index of current PU is given as input; the actual scaling process is the same as that of temporal scaling.
  • the reference picture index is signaled to the decoder.
  • JEM Joint Exploration Model
  • affine prediction alternative temporal motion vector prediction
  • STMVP spatial-temporal motion vector prediction
  • BIO bi-directional optical flow
  • FRUC Frame-Rate Up Conversion
  • LAMVR Locally Adaptive Motion Vector Resolution
  • OBMC Overlapped Block Motion Compensation
  • LIC Local Illumination Compensation
  • DMVR Decoder-side Motion Vector Refinement
  • each CU can have at most one set of motion parameters for each prediction direction.
  • two sub-CU level motion vector prediction methods are considered in the encoder by splitting a large CU into sub-CUs and deriving motion information for all the sub-CUs of the large CU.
  • Alternative temporal motion vector prediction (ATMVP) method allows each CU to fetch multiple sets of motion information from multiple blocks smaller than the current CU in the collocated reference picture.
  • STMVP spatial-temporal motion vector prediction
  • motion vectors of the sub-CUs are derived recursively by using the temporal motion vector predictor and spatial neighbouring motion vector.
  • the motion compression for the reference frames may be disabled.
  • the temporal motion vector prediction (TMVP) method is modified by fetching multiple sets of motion information (including motion vectors and reference indices) from blocks smaller than the current CU.
  • FIG. 10 shows an example of ATMVP motion prediction process for a CU 1000.
  • the ATMVP method predicts the motion vectors of the sub-CUs 1001 within a CU 1000 in two steps.
  • the first step is to identify the corresponding block 1051 in a reference picture 1050 with a temporal vector.
  • the reference picture 1050 is also referred to as the motion source picture.
  • the second step is to split the current CU 1000 into sub-CUs 1001 and obtain the motion vectors as well as the reference indices of each sub-CU from the block corresponding to each sub-CU.
  • a reference picture 1050 and the corresponding block is determined by the motion information of the spatial neighboring blocks of the current CU 1000.
  • the first merge candidate in the merge candidate list of the current CU 1000 is used.
  • the first available motion vector as well as its associated reference index are set to be the temporal vector and the index to the motion source picture. This way, the corresponding block may be more accurately identified, compared with TMVP, wherein the corresponding block (sometimes called collocated block) is always in a bottom-right or center position relative to the current CU.
  • a corresponding block of the sub-CU 1051 is identified by the temporal vector in the motion source picture 1050, by adding to the coordinate of the current CU the temporal vector.
  • the motion information of its corresponding block e.g., the smallest motion grid that covers the center sample
  • the motion information of a corresponding N ⁇ N block is identified, it is converted to the motion vectors and reference indices of the current sub-CU, in the same way as TMVP of HEVC, wherein motion scaling and other procedures apply.
  • the decoder checks whether the low-delay condition (e.g.
  • motion vector MVx e.g., the motion vector corresponding to reference picture list X
  • motion vector MVy e.g., with X being equal to 0 or 1 and Y being equal to 1-X
  • FIG. 11 shows an example of one CU with four sub-blocks and neighboring blocks.
  • an 8 ⁇ 8 CU 1100 that includes four 4 ⁇ 4 sub-CUs A (1101) , B (1102) , C (1103) , and D (1104) .
  • the neighboring 4 ⁇ 4 blocks in the current frame are labelled as a (1111) , b (1112) , c (1113) , and d (1114) .
  • the motion derivation for sub-CU A starts by identifying its two spatial neighbors.
  • the first neighbor is the N ⁇ N block above sub-CU A 1101 (block c 1113) . If this block c (1113) is not available or is intra coded the other N ⁇ N blocks above sub-CU A (1101) are checked (from left to right, starting at block c 1113) .
  • the second neighbor is a block to the left of the sub-CU A 1101 (block b 1112) . If block b (1112) is not available or is intra coded other blocks to the left of sub-CU A 1101 are checked (from top to bottom, staring at block b 1112) .
  • the motion information obtained from the neighboring blocks for each list is scaled to the first reference frame for a given list.
  • temporal motion vector predictor (TMVP) of sub-block A 1101 is derived by following the same procedure of TMVP derivation as specified in HEVC.
  • the motion information of the collocated block at block D 1104 is fetched and scaled accordingly.
  • all available motion vectors are averaged separately for each reference list. The averaged motion vector is assigned as the motion vector of the current sub-CU.
  • the sub-CU modes are enabled as additional merge candidates and there is no additional syntax element required to signal the modes.
  • Two additional merge candidates are added to merge candidates list of each CU to represent the ATMVP mode and STMVP mode. In other embodiments, up to seven merge candidates may be used, if the sequence parameter set indicates that ATMVP and STMVP are enabled.
  • the encoding logic of the additional merge candidates is the same as for the merge candidates in the HM, which means, for each CU in P or B slice, two more RD checks may be needed for the two additional merge candidates.
  • all bins of the merge index are context coded by CABAC (Context-based Adaptive Binary Arithmetic Coding) .
  • CABAC Context-based Adaptive Binary Arithmetic Coding
  • motion vector differences (between the motion vector and predicted motion vector of a PU) are signalled in units of quarter luma samples when use_integer_mv_flag is equal to 0 in the slice header.
  • LAMVR locally adaptive motion vector resolution
  • MVD can be coded in units of quarter luma samples, integer luma samples or four luma samples.
  • the MVD resolution is controlled at the coding unit (CU) level, and MVD resolution flags are conditionally signalled for each CU that has at least one non-zero MVD components.
  • a first flag is signalled to indicate whether quarter luma sample MV precision is used in the CU.
  • the first flag (equal to 1) indicates that quarter luma sample MV precision is not used, another flag is signalled to indicate whether integer luma sample MV precision or four luma sample MV precision is used.
  • the quarter luma sample MV resolution is used for the CU.
  • the MVPs in the AMVP candidate list for the CU are rounded to the corresponding precision.
  • CU-level RD checks are used to determine which MVD resolution is to be used for a CU. That is, the CU-level RD check is performed three times for each MVD resolution.
  • the following encoding schemes are applied in the JEM:
  • the motion information of the current CU (integer luma sample accuracy) is stored.
  • the stored motion information (after rounding) is used as the starting point for further small range motion vector refinement during the RD check for the same CU with integer luma sample and 4 luma sample MVD resolution so that the time-consuming motion estimation process is not duplicated three times.
  • motion vector accuracy is one-quarter pel (one-quarter luma sample and one-eighth chroma sample for 4: 2: 0 video) .
  • the accuracy for the internal motion vector storage and the merge candidate increases to 1/16 pel.
  • the higher motion vector accuracy (1/16 pel) is used in motion compensation inter prediction for the CU coded with skip/merge mode.
  • the integer-pel or quarter-pel motion is used for the CU coded with normal AMVP mode.
  • SHVC upsampling interpolation filters which have same filter length and normalization factor as HEVC motion compensation interpolation filters, are used as motion compensation interpolation filters for the additional fractional pel positions.
  • the chroma component motion vector accuracy is 1/32 sample in the JEM, the additional interpolation filters of 1/32 pel fractional positions are derived by using the average of the filters of the two neighbouring 1/16 pel fractional positions.
  • OBMC Overlapped Block Motion Compensation
  • OBMC can be switched on and off using syntax at the CU level.
  • the OBMC is performed for all motion compensation (MC) block boundaries except the right and bottom boundaries of a CU. Moreover, it is applied for both the luma and chroma components.
  • an MC block corresponds to a coding block.
  • sub-CU mode includes sub-CU merge, affine and FRUC mode
  • each sub-block of the CU is a MC block.
  • sub-block size is set equal to 4 ⁇ 4, as shown in FIGS. 12A and 12B.
  • FIG. 12A shows sub-blocks at the CU/PU boundary, and the hatched sub-blocks are where OBMC applies.
  • FIG. 12B shows the sub-Pus in ATMVP mode.
  • motion vectors of four connected neighboring sub-blocks are also used to derive prediction block for the current sub-block. These multiple prediction blocks based on multiple motion vectors are combined to generate the final prediction signal of the current sub-block.
  • Prediction block based on motion vectors of a neighboring sub-block is denoted as PN, with N indicating an index for the neighboring above, below, left and right sub-blocks and prediction block based on motion vectors of the current sub-block is denoted as PC.
  • PN is based on the motion information of a neighboring sub-block that contains the same motion information to the current sub-block, the OBMC is not performed from PN. Otherwise, every sample of PN is added to the same sample in PC, i.e., four rows/columns of PN are added to PC.
  • weighting factors ⁇ 1/4, 1/8, 1/16, 1/32 ⁇ are used for PN and the weighting factors ⁇ 3/4, 7/8, 15/16, 31/32 ⁇ are used for PC.
  • the exception are small MC blocks, (i.e., when height or width of the coding block is equal to 4 or a CU is coded with sub-CU mode) , for which only two rows/columns of PN are added to PC.
  • weighting factors ⁇ 1/4, 1/8 ⁇ are used for PN and weighting factors ⁇ 3/4, 7/8 ⁇ are used for PC.
  • For PN generated based on motion vectors of vertically (horizontally) neighboring sub-block samples in the same row (column) of PN are added to PC with a same weighting factor.
  • a CU level flag is signaled to indicate whether OBMC is applied or not for the current CU.
  • OBMC is applied by default.
  • the prediction signal formed by OBMC using motion information of the top neighboring block and the left neighboring block is used to compensate the top and left boundaries of the original signal of the current CU, and then the normal motion estimation process is applied.
  • LIC is based on a linear model for illumination changes, using a scaling factor a and an offset b. And it is enabled or disabled adaptively for each inter-mode coded coding unit (CU) .
  • FIG. 13 shows an example of neighboring samples used to derive parameters of the IC algorithm. Specifically, and as shown in FIG. 13, the subsampled (2: 1 subsampling) neighbouring samples of the CU and the corresponding samples (identified by motion information of the current CU or sub-CU) in the reference picture are used. The IC parameters are derived and applied for each prediction direction separately.
  • the LIC flag is copied from neighboring blocks, in a way similar to motion information copy in merge mode; otherwise, an LIC flag is signaled for the CU to indicate whether LIC applies or not.
  • LIC When LIC is enabled for a picture, an additional CU level RD check is needed to determine whether LIC is applied or not for a CU.
  • MR-SAD mean- removed sum of absolute difference
  • MR-SATD mean-removed sum of absolute Hadamard-transformed difference
  • LIC is disabled for the entire picture when there is no obvious illumination change between a current picture and its reference pictures. To identify this situation, histograms of a current picture and every reference picture of the current picture are calculated at the encoder. If the histogram difference between the current picture and every reference picture of the current picture is smaller than a given threshold, LIC is disabled for the current picture; otherwise, LIC is enabled for the current picture.
  • FIG. 14 shows an example of an affine motion field of a block 1400 described by two control point motion vectors V 0 and V 1 .
  • the motion vector field (MVF) of the block 1400 can be described by the following equation:
  • (v 0x , v 0y ) is motion vector of the top-left corner control point
  • (v 1x , v 1y ) is motion vector of the top-right corner control point.
  • sub-block based affine transform prediction can be applied.
  • the sub-block size M ⁇ N is derived as follows:
  • MvPre is the motion vector fraction accuracy (e.g., 1/16 in JEM) .
  • (v 2x , v 2y ) is motion vector of the bottom-left control point, calculated according to Equation 1.
  • M and N can be adjusted downward if necessary to make it a divisor of w and h, respectively.
  • FIG. 15 shows an example of affine MVF per sub-block for a block 1500.
  • the motion vector of the center sample of each sub-block can be calculated according to Equation 1, and rounded to the motion vector fraction accuracy (e.g., 1/16 in JEM) .
  • the motion compensation interpolation filters can be applied to generate the prediction of each sub-block with derived motion vector.
  • the high accuracy motion vector of each sub-block is rounded and saved as the same accuracy as the normal motion vector.
  • affine motion modes there are two affine motion modes: AF_INTER mode and AF_MERGE mode.
  • AF_INTER mode can be applied.
  • An affine flag in CU level is signaled in the bitstream to indicate whether AF_INTER mode is used.
  • FIG. 16 shows an example of motion vector prediction (MVP) for a block 1600 in the AF_INTER mode.
  • v 0 is selected from the motion vectors of the sub-block A, B, or C.
  • the motion vectors from the neighboring blocks can be scaled according to the reference list.
  • the motion vectors can also be scaled according to the relationship among the Picture Order Count (POC) of the reference for the neighboring block, the POC of the reference for the current CU, and the POC of the current CU.
  • POC Picture Order Count
  • the approach to select v 1 from the neighboring sub-block D and E is similar. If the number of candidate list is smaller than 2, the list is padded by the motion vector pair composed by duplicating each of the AMVP candidates.
  • the candidates can be firstly sorted according to the neighboring motion vectors (e.g., based on the similarity of the two motion vectors in a pair candidate) . In some implementations, the first two candidates are kept.
  • a Rate Distortion (RD) cost check is used to determine which motion vector pair candidate is selected as the control point motion vector prediction (CPMVP) of the current CU.
  • An index indicating the position of the CPMVP in the candidate list can be signaled in the bitstream. After the CPMVP of the current affine CU is determined, affine motion estimation is applied and the control point motion vector (CPMV) is found. Then the difference of the CPMV and the CPMVP is signaled in the bitstream.
  • RD Rate Distortion
  • the MV may be derived as follows, e.g., it predicts mvd 1 and mvd 2 from mvd 0 .
  • the addition of two motion vectors e.g., mvA (xA, yA) and mvB (xB, yB)
  • mvA + mvB implies that the two components of newMV are set to (xA + xB) and (yA + yB) , respectively.
  • MV of 2 or 3 control points needs to be determined jointly. Directly searching the multiple MVs jointly is computationally complex.
  • a fast affine ME algorithm is adopted into VTM/BMS.
  • the affine parameters may be derived as:
  • the motion vectors can be rewritten in vector form as:
  • the MVD of AF_INTER may be derived iteratively.
  • MV i (P) the MV derived in the ith iteration for position P
  • dMV C i the delta updated for MV C in the ith iteration.
  • Pic ref the reference picture
  • Pic cur the current picture
  • Q P+MV i (P) . If the MSE is used as the matching criterion, then the function that needs to be minimized may be written as:
  • the term may be derived by setting the derivative of the error function to zero, and then computing delta MV of the control points (0, 0) and (0, w) according to as follows:
  • this MVD derivation process may be iterated n times, and the final MVD may be calculated as follows:
  • predicting delta MV of control point (0, w) denoted by mvd 1 from delta MV of control point (0, 0) , denoted by mvd 0 , results in only being encoded for mvd 1 .
  • FIG. 18A shows an example of the selection order of candidate blocks for a current CU 1800. As shown in FIG. 18A, the selection order can be from left (1801) , above (1802) , above right (1803) , left bottom (1804) to above left (1805) of the current CU 1800.
  • FIG. 18B shows another example of candidate blocks for a current CU 1800 in the AF_MERGE mode. If the neighboring left bottom block 1801 is coded in affine mode, as shown in FIG.
  • the motion vectors v 2 , v 3 and v 4 of the top left corner, above right corner, and left bottom corner of the CU containing the sub-block 1801 are derived.
  • the motion vector v 0 of the top left corner on the current CU 1800 is calculated based on v2, v3 and v4.
  • the motion vector v1 of the above right of the current CU can be calculated accordingly.
  • the MVF of the current CU can be generated.
  • an affine flag can be signaled in the bitstream when there is at least one neighboring block is coded in affine mode.
  • the PMMVD mode is a special merge mode based on the Frame-Rate Up Conversion (FRUC) method. With this mode, motion information of a block is not signaled but derived at decoder side.
  • FRUC Frame-Rate Up Conversion
  • a FRUC flag can be signaled for a CU when its merge flag is true.
  • a merge index can be signaled and the regular merge mode is used.
  • an additional FRUC mode flag can be signaled to indicate which method (e.g., bilateral matching or template matching) is to be used to derive motion information for the block.
  • the decision on whether using FRUC merge mode for a CU is based on RD cost selection as done for normal merge candidate. For example, multiple matching modes (e.g., bilateral matching and template matching) are checked for a CU by using RD cost selection. The one leading to the minimal cost is further compared to other CU modes. If a FRUC matching mode is the most efficient one, FRUC flag is set to true for the CU and the related matching mode is used.
  • multiple matching modes e.g., bilateral matching and template matching
  • motion derivation process in FRUC merge mode has two steps: a CU-level motion search is first performed, then followed by a Sub-CU level motion refinement.
  • CU level an initial motion vector is derived for the whole CU based on bilateral matching or template matching.
  • a list of MV candidates is generated and the candidate that leads to the minimum matching cost is selected as the starting point for further CU level refinement.
  • a local search based on bilateral matching or template matching around the starting point is performed.
  • the MV results in the minimum matching cost is taken as the MV for the whole CU.
  • the motion information is further refined at sub-CU level with the derived CU motion vectors as the starting points.
  • the following derivation process is performed for a W ⁇ H CU motion information derivation.
  • MV for the whole W ⁇ H CU is derived.
  • the CU is further split into M ⁇ M sub-CUs.
  • the value of M is calculated as in (16)
  • D is a predefined splitting depth which is set to 3 by default in the JEM. Then the MV for each sub-CU is derived.
  • FIG. 19 shows an example of bilateral matching used in the Frame-Rate Up Conversion (FRUC) method.
  • the bilateral matching is used to derive motion information of the current CU by finding the closest match between two blocks along the motion trajectory of the current CU (1900) in two different reference pictures (1910, 1911) .
  • the motion vectors MV0 (1901) and MV1 (1902) pointing to the two reference blocks are proportional to the temporal distances, e.g., TD0 (1903) and TD1 (1904) , between the current picture and the two reference pictures.
  • the bilateral matching becomes mirror based bi-directional MV.
  • FIG. 20 shows an example of template matching used in the Frame-Rate Up Conversion (FRUC) method.
  • Template matching can be used to derive motion information of the current CU 2000 by finding the closest match between a template (e.g., top and/or left neighboring blocks of the current CU) in the current picture and a block (e.g., same size to the template) in a reference picture 2010. Except the aforementioned FRUC merge mode, the template matching can also be applied to AMVP mode. In both JEM and HEVC, AMVP has two candidates. With the template matching method, a new candidate can be derived.
  • a template e.g., top and/or left neighboring blocks of the current CU
  • a block e.g., same size to the template
  • the newly derived candidate by template matching is different to the first existing AMVP candidate, it is inserted at the very beginning of the AMVP candidate list and then the list size is set to two (e.g., by removing the second existing AMVP candidate) .
  • the list size is set to two (e.g., by removing the second existing AMVP candidate) .
  • the MV candidate set at CU level can include the following: (1) original AMVP candidates if the current CU is in AMVP mode, (2) all merge candidates, (3) several MVs in the interpolated MV field (described later) , and top and left neighboring motion vectors.
  • each valid MV of a merge candidate can be used as an input to generate a MV pair with the assumption of bilateral matching.
  • one valid MV of a merge candidate is (MVa, ref a ) at reference list A.
  • the reference picture ref b of its paired bilateral MV is found in the other reference list B so that ref a and ref b are temporally at different sides of the current picture. If such a ref b is not available in reference list B, ref b is determined as a reference which is different from ref a and its temporal distance to the current picture is the minimal one in list B.
  • MVb is derived by scaling MVa based on the temporal distance between the current picture and ref a , ref b .
  • four MVs from the interpolated MV field can also be added to the CU level candidate list. More specifically, the interpolated MVs at the position (0, 0) , (W/2, 0) , (0, H/2) and (W/2, H/2) of the current CU are added.
  • the original AMVP candidates are also added to CU level MV candidate set.
  • 15 MVs for AMVP CUs and 13 MVs for merge CUs can be added to the candidate list.
  • the MV candidate set at sub-CU level includes an MV determined from a CU-level search, (2) top, left, top-left and top-right neighboring MVs, (3) scaled versions of collocated MVs from reference pictures, (4) one or more ATMVP candidates (e.g., up to four) , and (5) one or more STMVP candidates (e.g., up to four) .
  • the scaled MVs from reference pictures are derived as follows. The reference pictures in both lists are traversed. The MVs at a collocated position of the sub-CU in a reference picture are scaled to the reference of the starting CU-level MV.
  • ATMVP and STMVP candidates can be the four first ones.
  • one or more MVs are added to the candidate list.
  • interpolated motion field is generated for the whole picture based on unilateral ME. Then the motion field may be used later as CU level or sub-CU level MV candidates.
  • FIG. 21 shows an example of unilateral Motion Estimation (ME) 2100 in the FRUC method.
  • ME unilateral Motion Estimation
  • the motion of the reference block is scaled to the current picture according to the temporal distance TD0 and TD1 (the same way as that of MV scaling of TMVP in HEVC) and the scaled motion is assigned to the block in the current frame. If no scaled MV is assigned to a 4 ⁇ 4 block, the block's motion is marked as unavailable in the interpolated motion field.
  • the matching cost is a bit different at different steps.
  • the matching cost can be the absolute sum difference (SAD) of bilateral matching or template matching.
  • SAD absolute sum difference
  • the matching cost C of bilateral matching at sub-CU level search is calculated as follows:
  • w is a weighting factor.
  • w can be empirically set to 4.
  • MV and MV s indicate the current MV and the starting MV, respectively.
  • SAD may still be used as the matching cost of template matching at sub-CU level search.
  • MV is derived by using luma samples only. The derived motion will be used for both luma and chroma for MC inter prediction. After MV is decided, final MC is performed using 8-taps interpolation filter for luma and 4-taps interpolation filter for chroma.
  • MV refinement is a pattern based MV search with the criterion of bilateral matching cost or template matching cost.
  • two search patterns are supported –an unrestricted center-biased diamond search (UCBDS) and an adaptive cross search for MV refinement at the CU level and sub-CU level, respectively.
  • UMBDS center-biased diamond search
  • the MV is directly searched at quarter luma sample MV accuracy, and this is followed by one-eighth luma sample MV refinement.
  • the search range of MV refinement for the CU and sub-CU step are set equal to 8 luma samples.
  • bi-prediction is applied because the motion information of a CU is derived based on the closest match between two blocks along the motion trajectory of the current CU in two different reference pictures.
  • the encoder can choose among uni-prediction from list0, uni-prediction from list1, or bi-prediction for a CU. The selection ca be based on a template matching cost as follows:
  • cost0 is the SAD of list0 template matching
  • cost1 is the SAD of list1 template matching
  • costBi is the SAD of bi-prediction template matching.
  • the value of factor is equal to 1.25, it means that the selection process is biased toward bi-prediction.
  • the inter prediction direction selection can be applied to the CU-level template matching process.
  • the bi-directional optical flow (BIO) method is a sample-wise motion refinement performed on top of block-wise motion compensation for bi-prediction.
  • the sample-level motion refinement does not use signaling.
  • the motion vector field (v x , v y ) is given by:
  • FIG. 22 shows an example optical flow trajectory in the Bi-directional Optical flow (BIO) method.
  • ⁇ 0 and ⁇ 1 denote the distances to the reference frames.
  • BIO is applied if the prediction is not from the same time moment (e.g., ⁇ 0 ⁇ 1 ) .
  • the motion vector field (v x , v y ) is determined by minimizing the difference ⁇ between values in points A and B.
  • FIGS. 9A-9B show an example of intersection of motion trajectory and reference frame planes. Model uses only first linear term of a local Taylor expansion for ⁇ :
  • the JEM uses a simplified approach making first a minimization in the vertical direction and then in the horizontal direction. This results in the following:
  • d is bit depth of the video samples.
  • FIG. 23A shows an example of access positions outside of a block 2300.
  • 2M+1) ⁇ (2M+1) square window ⁇ centered in currently predicted point on a boundary of predicted block needs to accesses positions outside of the block.
  • values of I (k) , outside of the block are set to be equal to the nearest available value inside the block. For example, this can be implemented as a padding area 2301, as shown in FIG. 23B.
  • BIO it is possible that the motion field can be refined for each sample.
  • a block-based design of BIO is used in the JEM.
  • the motion refinement can be calculated based on a 4x4 block.
  • the values of s n in Equation 30 of all samples in a 4x4 block can be aggregated, and then the aggregated values of s n in are used to derived BIO motion vectors offset for the 4 ⁇ 4 block. More specifically, the following formula can used for block-based BIO derivation:
  • b k denotes the set of samples belonging to the k-th 4x4 block of the predicted block.
  • s n in Equations 28 and 29 are replaced by ( (s n, bk ) >>4) to derive the associated motion vector offsets.
  • MV regiment of BIO may be unreliable due to noise or irregular motion. Therefore, in BIO, the magnitude of MV regiment is clipped to a threshold value.
  • the threshold value is determined based on whether the reference pictures of the current picture are all from one direction. For example, if all the reference pictures of the current picture are from one direction, the value of the threshold is set to 12 ⁇ 2 14-d ; otherwise, it is set to 12 ⁇ 2 13-d .
  • Gradients for BIO can be calculated at the same time with motion compensation interpolation using operations consistent with HEVC motion compensation process (e.g., 2D separable Finite Impulse Response (FIR) ) .
  • the input for the 2D separable FIR is the same reference frame sample as for motion compensation process and fractional position (fracX, fracY) according to the fractional part of block motion vector.
  • fracX, fracY fractional position
  • fracX, fracY fractional position
  • BIOfilterG For vertical gradient a gradient filter is applied vertically using BIOfilterG corresponding to the fractional position fracY with de-scaling shift d-8. The signal displacement is then performed using BIOfilterS in horizontal direction corresponding to the fractional position fracX with de-scaling shift by 18-d.
  • the length of interpolation filter for gradients calculation BIOfilterG and signal displacement BIOfilterF can be shorter (e.g., 6-tap) in order to maintain reasonable complexity.
  • Table 1 shows example filters that can be used for gradients calculation of different fractional positions of block motion vector in BIO.
  • Table 2 shows example interpolation filters that can be used for prediction signal generation in BIO.
  • Fractional pel position Interpolation filter for gradient (BIOfilterG) 0 ⁇ 8, -39, -3, 46, -17, 5 ⁇ 1/16 ⁇ 8, -32, -13, 50, -18, 5 ⁇
  • Fractional pel position Interpolation filter for prediction signal (BIOfilterS) 0 ⁇ 0, 0, 64, 0, 0, 0 ⁇ 1/16 ⁇ 1, -3, 64, 4, -2, 0 ⁇ 1/8 ⁇ 1, -6, 62, 9, -3, 1 ⁇ 3/16 ⁇ 2, -8, 60, 14, -5, 1 ⁇ 1/4 ⁇ 2, -9, 57, 19, -7, 2 ⁇ 5/16 ⁇ 3, -10, 53, 24, -8, 2 ⁇ 3/8 ⁇ 3, -11, 50, 29, -9, 2 ⁇ 7/16 ⁇ 3, -11, 44, 35, -10, 3 ⁇ 1/2 ⁇ 3, -10, 35, 44, -11, 3 ⁇
  • BIO can be applied to all bi-predicted blocks when the two predictions are from different reference pictures.
  • BIO can be disabled.
  • BIO is applied for a block after normal MC process.
  • BIO may not be applied during the OBMC process. This means that BIO is applied in the MC process for a block when using its own MV and is not applied in the MC process when the MV of a neighboring block is used during the OBMC process.
  • a bi-prediction operation for the prediction of one block region, two prediction blocks, formed using a motion vector (MV) of list0 and a MV of list1, respectively, are combined to form a single prediction signal.
  • the two motion vectors of the bi-prediction are further refined by a bilateral template matching process.
  • the bilateral template matching applied in the decoder to perform a distortion-based search between a bilateral template and the reconstruction samples in the reference pictures in order to obtain a refined MV without transmission of additional motion information.
  • a bilateral template is generated as the weighted combination (i.e. average) of the two prediction blocks, from the initial MV0 of list0 and MV1 of list1, respectively, as shown in FIG. 24.
  • the template matching operation consists of calculating cost measures between the generated template and the sample region (around the initial prediction block) in the reference picture. For each of the two reference pictures, the MV that yields the minimum template cost is considered as the updated MV of that list to replace the original one.
  • nine MV candidates are searched for each list. The nine MV candidates include the original MV and 8 surrounding MVs with one luma sample offset to the original MV in either the horizontal or vertical direction, or both.
  • the two new MVs i.e., MV0′ and MV1′ as shown in FIG. 24, are used for generating the final bi-prediction results.
  • a sum of absolute differences (SAD) is used as the cost measure.
  • DMVR is applied for the merge mode of bi-prediction with one MV from a reference picture in the past and another from a reference picture in the future, without the transmission of additional syntax elements.
  • JEM when LIC, affine motion, FRUC, or sub-CU merge candidate is enabled for a CU, DMVR is not applied.
  • Symmetric motion vector difference can be used to encode the MVD more efficiently.
  • variables BiDirPredFlag, RefIdxSymL0 and RefIdxSymL1 are derived as follows:
  • the forward reference picture in reference picture list 0 which is nearest to the current picture is searched. If found, RefIdxSymL0 is set equal to the reference index of the forward picture.
  • the backward reference picture in reference picture list 1 which is nearest to the current picture is searched. If found, RefIdxSymL1 is set equal to the reference index of the backward picture.
  • BiDirPredFlag is set equal to 1.
  • the backward reference picture in reference picture list 0 which is nearest to the current one is searched. If found, RefIdxSymL0 is set equal to the reference index of the backward picture.
  • the forward reference picture in reference picture list 1 which is nearest to the current one is searched. If found, RefIdxSymL1 is set equal to the reference index of the forward picture.
  • BiDirPredFlag is set equal to 1. Otherwise, BiDirPredFlag is set equal to 0.
  • a symmetrical mode flag indicating whether symmetrical mode is used or not is explicitly signaled if the prediction direction for the CU is bi-prediction and BiDirPredFlag is equal to 1.
  • MVD0 When the flag is true, only mvp_l0_flag, mvp_l1_flag and MVD0 are explicitly signaled.
  • the reference indices are set equal to RefIdxSymL0, RefIdxSymL1 for list 0 and list 1, respectively.
  • MVD1 is just set equal to –MVD0.
  • the final motion vectors are shown in below formula.
  • FIG. 27 shows examples of symmetrical mode.
  • CABAC Context-adaptive Binary Arithmetic Coding
  • n (offsetIdx ⁇ 3) -16 (35)
  • the two values assigned to pStateIdx and valMps for the initialization are derived from the luma's quantization parameter of slice denoted by SliceQpY. Given the variables m and n, the initialization is specified as follows:
  • preCtxState Clip3 (1, 126, ( (m *Clip3 (0, 51, SliceQp Y ) ) >> 4) + n)
  • pStateIdx valMps ? (preCtxState-64) : (63 -preCtxState)
  • Inputs to this process are the current pStateIdx, the decoded value binVal and valMps values of the context variable associated with ctxTable and ctxIdx.
  • Outputs of this process are the updated pStateIdx and valMps of the context variable associated with ctxIdx.
  • the context-adaptive binary arithmetic coder (BAC) in VVC has been changed in VVC which is different from that in HEVC in terms of both context updating process and arithmetic coder.
  • preCtxState Clip3 (0, 127, ( (m *Clip3 (0, 51, SliceQp Y ) ) >> 4) + n)
  • pStateIdx1 initStateIdxToState [preCtxState] (38)
  • Inputs to this process are the current pStateIdx0 and pStateIdx1, and the decoded value binVal.
  • Outputs of this process are the updated pStateIdx0 and pStateIdx1 of the context variable associated with ctxIdx.
  • shift1 (shiftIdx &3) + 3 + shift0 (39)
  • pStateIdx0 pStateIdx0 - (pStateIdx0 >> shift0) + (1023 *binVal >> shift0)
  • pStateIdx1 pStateIdx1 - (pStateIdx1 >> shift1) + (16383 *binVal >> shift1) (40)
  • MV/MV difference (MVD) could be selected from a set of multiple MV/MVD precisions for affine coded blocks, it remains uncertain how more accurate motion vectors may be obtained.
  • the MV/MVD precision information also plays an important role in determination of the overall coding gain of AMVR applied to affine mode, but achieving this goal remains uncertain.
  • Embodiments of the presently disclosed technology overcome the drawbacks of existing implementations, thereby providing video coding with higher coding efficiencies.
  • the derivation and signaling of motion vector predictors for affine mode with adaptive motion vector resolution (AMVR) may enhance both existing and future video coding standards, is elucidated in the following examples described for various implementations.
  • the examples of the disclosed technology provided below explain general concepts, and are not meant to be interpreted as limiting. In an example, unless explicitly indicated to the contrary, the various features described in these examples may be combined.
  • the following examples may be applied to affine mode or normal mode when AMVR is applied.
  • a precision Prec i.e., MV is with 1 / (2 ⁇ Prec) precision
  • MVPred MVPred X , MVPred Y
  • PredPrec PredPrec
  • offset0 and/or offset1 are set to (1 ⁇ n) >>1 or (1 ⁇ (n-1) ) .
  • offset0 and/or offset1 are set to 0.
  • an operation between two motion vectors means the operation will be applied to both the two components of the motion vector.
  • the operation may be only applied to the horizontal or vertical component of the two motion vectors.
  • the set of allowed MVD precisions may be different from picture to picture, from slice to slice, or from block to block.
  • the set of allowed MVD precisions may depend on coded information, such as block size, block shape. etc. al.
  • a set of allowed MV precisions may be pre-defined, such as ⁇ 1/16, 1/4, 1 ⁇ .
  • Indications of allowed MV precisions may be signaled in SPS/PPS/VPS/sequence header/picture header/slice header/group of CTUs, etc. al.
  • the signaling of selected MV precision from a set of allowed MV precisions further depend on number of allowed MV precisions for a block.
  • a syntax element is signaled to the decoder to indicate the used MVD precision in affine inter mode.
  • only one single syntax element is used to indicate the MVD precisions applied to the affine mode and the AMVR mode.
  • same semantics are used, that is, the same value of syntax element is mapped to the same MVD precision for the AMVR and affine mode.
  • the semantics of the single syntax element is different for the AMVR mode and the affine mode. That is, the same value of syntax element could be mapped to different MVD precision for the AMVR and affine mode.
  • MVD precision set is ⁇ 1, 1/4, 4 ⁇ -pel
  • the MVD precision syntax element in AMVR is reused in affine mode, i.e., only one single syntax element is used.
  • CABAC encoder/decoder when encoding/decoding this syntax element in CABAC encoder/decoder, same or different context models may be used for AMVR and affine mode.
  • this syntax element may have different semantics in AMVR and affine mode.
  • the syntax element equal to 0, 1 and 2 indicates 1/4-pel, 1-pel and 4-pel MV precision respectively in AMVR, while in affine mode, the syntax element equal to 0, 1 and 2 indicates 1/4-pel, 1/16-pel and 1-pel MV precision respectively.
  • MVD precision set for AMVR is ⁇ 1, 1/4, 4 ⁇ -pel while for affine, it is ⁇ 1/16, 1/4, 1 ⁇ -pel
  • the MVD precision syntax element in AMVR is reused in affine mode, i.e., only one single syntax element is used.
  • CABAC encoder/decoder when encoding/decoding this syntax element in CABAC encoder/decoder, same or different context models may be used for AMVR and affine mode.
  • this syntax element may have different semantics in AMVR and affine mode.
  • affine mode uses less MVD precisions than AMVR, the MVD precision syntax element in AMVR is reused in affine mode. However, only a subset of the syntax element values is valid for affine mode.
  • CABAC encoder/decoder when encoding/decoding this syntax element in CABAC encoder/decoder, same or different context models may be used for AMVR and affine mode.
  • this syntax element may have different semantics in AMVR and affine mode.
  • affine mode uses more MVD precisions than AMVR, the MVD precision syntax element in AMVR is reused in affine mode.
  • such syntax element is extended to allow more values in affine mode.
  • CABAC encoder/decoder when encoding/decoding this syntax element in CABAC encoder/decoder, same or different context models may be used for AMVR and affine mode.
  • this syntax element may have different semantics in AMVR and affine mode.
  • a new syntax element is used for coding the MVD precision of affine mode, i.e., two different syntax elements are used for coding the MVD precision of AMVR and affine mode.
  • MVDs for at least one control point is non-zero.
  • MVD of one control point e.g., the first CPMV
  • the syntax element for indication of MVD precisions for either affine mode or the AMVR mode may be coded with contexts and the contexts are dependent on coded information.
  • the contexts may depend on whether current block is coded with affine mode or not.
  • the context may depend on the block size/block shape/MVD precisions of neighboring blocks/temporal layer index/prediction directions, etc. al.
  • Whether to enable or disable the usage of multiple MVD precisions for the affine mode may be signaled in SPS/PPS/VPS/sequence header/picture header/slice header/group of CTUs, etc. al.
  • whether to signal the information of enable or disable the usage of multiple MVD precisions for the affine mode may depend on other syntax elements. For example, the information of enable or disable the usage of multiple MV and/or MVP and/or MVD precisions for the affine mode is signaled when affine mode is enabled; and is not signaled and inferred to be 0 when affine mode is disabled.
  • multiple syntax elements may be signaled to indicate the used MV and/or MVP and/or MVD precision (in the following discussion, they are all referred to as "MVD precision" ) in affine inter mode.
  • the syntax elements used to indicate the used MVD precision in affine inter mode and normal inter mode may be different.
  • the number of syntax elements to indicate the used MVD precision in affine inter mode and normal inter mode may be different.
  • a first syntax element (e.g. amvr_flag) may be signaled to indicate whether to apply AMVR in an affine-coded block.
  • the first syntax element is conditionally signaled.
  • signalling of the first syntax element is skipped when current block is coded with certain mode (e.g., CPR/IBC mode) .
  • signalling of the first syntax element is skipped when all CPMVs' MVDs (including both horizontal and vertical components) are all zero.
  • signalling of the first syntax element is skipped when one selected CPMVs' MVDs (including both horizontal and vertical components) are all zero.
  • the selected CPMV's MVD is the first CPMV's MVD to be coded/decoded.
  • signalling of the first syntax element is skipped when the usage of enabling multiple MVD precisions for affine-coded block is false.
  • the first syntax element may be signaled under the following conditions:
  • the selected CPMV's MVD is the first CPMV's MVD to be coded/decoded.
  • AMVR is not applied to an affine-coded block or the first syntax element is not present, a default MV and/or MVD precision is utilized.
  • the default precision is 1/4-pel.
  • the default precision is set to that used in motion compensation for affine coded blocks.
  • the MVD precision of affine mode is 1/4-pel if amvr_flag is equal to 0; otherwise the MVD precision of affine mode may be other values.
  • the additional MVD precisions may be further signaled via a second syntax element.
  • a second syntax element (such as amvr_coarse_precision_flag) may be signaled to indicate the MVD precision of affine mode.
  • whether the second syntax element is signaled may depend on the first syntax element. For example, the second syntax element is only signaled when the first syntax element is 1.
  • the MVD precision of affine mode is 1-pel if the second syntax element is 0; otherwise, the MVD precision of affine mode is 1/16-pel.
  • the MVD precision of affine mode is 1/16-pel if the second syntax element is 0; otherwise, the MVD precision of affine mode is full-pixel.
  • a syntax element used to indicate the used MVD precision in affine inter mode share the same context models as the syntax element with the same name but used to indicate the used MVD precision in normal inter mode.
  • a syntax element used to indicate the used MVD precision in affine inter mode use different context models as the syntax element with the same name but used to indicate the used MVD precision in normal inter mode.
  • Whether to apply or how to apply AMVR on an affine coded block may depend on the reference picture of the current block.
  • AMVR is not applied if the reference picture is the current picture, i.e., Intra block copying is applied in the current block.
  • RD cost real RD cost, or SATD/SSE/SAD cost plus rough bits cost
  • IMV 0 means 1/4 pel MV
  • IMV 1 means integer MV for AMVP mode and 1/16 pel MV for affine mode
  • IMV 2 means 4 pel MV for AMVP mode and integer MV for affine mode.
  • mergeCost real RD cost, or SATD/SSE/SAD cost plus rough bits cost
  • AMVR is disabled for affine mode of current CU if the best mode of its parent CU is not AF_INTER mode or AF_MERGE mode.
  • AMVR is disabled for affine mode of current CU if the best mode of its parent CU is not AF_INTER mode
  • AMVR is disabled for affine mode if affineCost0> th1*amvpCost0, wherein th1 is a positive threshold.
  • AMVR is disabled for affine mode if min (affineCost0, amvpCost0) > th2*mergeCost, wherein th2 is a positive threshold.
  • integer MV is disabled for affine mode if affineCost0>th3*affineCost1, wherein th3 is a positive threshold.
  • AMVR is disabled for AMVP mode if amvpCost0 > th4 *affineCost0, wherein th4 is a positive threshold.
  • AMVR is disabled for AMVP mode if min (affineCost0, amvpCost0) > th5*mergeCost, wherein th5 is a positive threshold.
  • 4/6 parameter affine models obtained in 1/16 MV may be used as a candidate start search point for other MV precisions.
  • 4/6 parameter affine models obtained in 1/4 MV may be used as a candidate start search point for other MV precisions.
  • AMVR for affine mode is not checked at encoder for the current block if its parent block does not choose the affine mode.
  • the percentage of affine-coded blocks with a certain MV precision is recorded. If the percentage is too low, then the checking of the corresponding MV precision is skipped.
  • previously coded frames with the same temporal layer are utilized to decide whether to skip a certain MV precision.
  • the faster updating speed is defined by (shiftIdx >> 2) + 2.
  • the slower updating speed is defined by (shiftIdx &3) + 3 +shift0
  • the conformance bitstream shall follow the rule that the derived faster updating speed shall be within [2, 5] inclusively.
  • the conformance bitstream shall follow the rule that the derived faster updating speed shall be within [3, 6] inclusively.
  • the neighboring block's AMVR mode index may be utilized and neighboring block's affine AMVR mode information is excluded.
  • Table 5 including Table 5-1 and 5-2
  • the context index offset ctxInc (condL && availableL) + (condA && availableA) + ctxSetIdx*3.
  • neighboring block's affine AMVR mode information may be further utilized but with a function instead of being directly used.
  • the function func as described in Table 6-1 may return true when the amvr_mode [xNbL] [yNbL] of an affine-coded neighboring block indicates a certain MV precision (such as the 1/4-pel MV precision) .
  • the function func as described in Table 6-2 may return true when the amvr_flag [xNbL] [yNbL] of an affine-coded neighboring block indicates a certain MV precision (such as the 1/4-pel MV precision) .
  • neighboring block's affine AMVR mode information may be further utilized for coding the first syntax element (e.g., amvr_flag) of the AMVR mode (which is applied to normal inter mode) .
  • Table 6-3 and 6-4 give some examples.
  • the AMVR mode information is represented by multiple syntax elements (e.g., the first and second syntax elements, denoted by amvr_flag, amvr_coarse_precision_flag)
  • the above syntax amvr_mode may be replaced by any of the multiple syntax elements and above methods may be still applied.
  • the neighboring block's AMVR mode information may be utilized for context coding.
  • the neighboring block's AMVR mode information is directly used.
  • An example is shown in Table 7.
  • the context index offset ctxInc (condL && availableL) + (condA && availableA) +ctxSetIdx*3.
  • the neighboring block's AMVR mode information is disallowed for context modeling.
  • An example is shown in Table 8.
  • neighboring block's AMVR mode information may be further utilized but with a function instead of being directly used.
  • the function func as described in Table 9 may return true when the amvr_mode [xNbL] [yNbL] of an non-affine-coded neighboring block indicates a certain MV precision (such as the 1/4-pel MV precision) .
  • the affine AMVR mode information is represented by multiple syntax elements (e.g., the first and second syntax elements, denoted by amvr_flag, amvr_coarse_precision_flag)
  • the above syntax amvr_mode may be replaced by any of the multiple syntax elements and above methods may be still applied.
  • SMVD mode may be skipped depending on the currently selected best mode (i.e., CurBestMode) , the MVD precision in AMVR.
  • CurBestMode is merge mode or/and UMVE mode
  • SMVD mode may be not checked.
  • SMVD mode may be not checked.
  • CurBestMode is affine mode
  • SMVD mode may be not checked.
  • CurBestMode is sub-block merge mode
  • SMVD mode may be not checked.
  • SMVD mode may be not checked.
  • SMVD mode may be not checked.
  • above fast methods i.e., bullet 13. a ⁇ 13. f, may be applied only for some MVD precision.
  • above fast methods may be applied only when MVD precision is greater than or equal to a precision (for example, integer-pel precision) .
  • above fast methods may be applied only when MVD precision is greater than a precision (for example, integer-pel precision) .
  • above fast methods may be applied only when MVD precision is smaller than or equal to a precision (for example, integer-pel precision) .
  • above fast methods may be applied only when MVD precision is smaller than a precision (for example, integer-pel precision) .
  • Affine SMVD mode may be skipped depending on the currently selected best mode (i.e., CurBestMode) , the MVD precision in affine AMVR.
  • affine SMVD mode may be not checked.
  • affine SMVD mode may be not checked.
  • affine SMVD mode may be not checked.
  • affine SMVD mode may be not checked.
  • affine SMVD mode may be not checked.
  • above fast methods i.e., bullet 14. a ⁇ 14. e, may be applied only for some MVD precision.
  • affine MVD precision is greater than or equal to a precision (for example, integer-pel precision) .
  • above fast methods may be applied only when affine MVD precision is greater than a precision (for example, integer-pel precision) .
  • affine MVD precision is smaller than or equal to a precision (for example, integer-pel precision) .
  • above fast methods may be applied only when affine MVD precision is smaller than a precision (for example, integer-pel precision) .
  • the above proposed method may be applied under certain conditions, such as block sizes, slice/picture/tile types, or motion information.
  • a block size contains smaller than M*H samples, e.g., 16 or 32 or 64 luma samples, proposed method is not allowed.
  • X is set to 8.
  • X is set to 8.
  • th1 and/or th2 is set to 8.
  • th1 and/or th2 is set to 8.
  • whether to enable or disable the above methods and/or which method to be applied may be dependent on block dimension, video processing data unit (VPDU) , picture type, low delay check flag, coded information of current block (such as reference pictures, uni or bi-prediction) or previously coded blocks.
  • VPDU video processing data unit
  • picture type picture type
  • low delay check flag coded information of current block (such as reference pictures, uni or bi-prediction) or previously coded blocks.
  • the AMVR methods for affine mode may be performed in different ways when intra block copy (IBC, a.k.a. current picture reference (CPR) ) is applied or not.
  • IBC intra block copy
  • CPR current picture reference
  • AMVR for affine mode cannot be used if a block is coded by IBC.
  • AMVR for affine mode may be used if a block is coded by IBC, but the candidate MV/MVD/MVP precisions may be different to those used for non-IBC coded affine-coded block.
  • a syntax element (e.g. no_amvr_constraint_flag) equal to 1 specifies that it is a requirement of bitstream conformance that both the syntax element to indicate whether AMVR is enabled (e.g. sps_amvr_enabled_flag) and the syntax element to indicate whether affine AMVR is enabled (e.g. sps_affine_avmr_enabled_flag) shall be equal to 0.
  • the syntax element (e.g. no_amvr_constraint_flag) equal to 0 does not impose a constraint.
  • a syntax element e.g. no_affine_amvr_constraint_flag
  • no_affine_amvr_constraint_flag 1 specifies that it is a requirement of bitstream conformance that the syntax element to indicate whether affine AMVR is enabled (e.g. sps_affine_avmr_enabled_flag) shall be equal to 0.
  • the syntax element e.g. no_affine_amvr_constraint_flag
  • two contexts may be utilized.
  • selection of contexts may depend on whether the current block is affine coded or not.
  • the first syntax it may be coded with only one context and also for the second syntax, it may be coded with only one context.
  • the first syntax may be coded with only one context and also for the second syntax, it may be bypass coded.
  • the first syntax it may be bypass coded and also for the second syntax, it may be bypass coded.
  • SE For example, only the first bin of the syntax element SE is coded with arithmetic coding context (s) . All the following bins of SE are coded as bypass coding. SE may be
  • a syntax element SE is a binary value (i.e., it could be only either equal to 0 or 1) , it may be context coded.
  • a syntax element SE is a binary value (i.e., it could be only either equal to 0 or 1) , it may be bypass coded.
  • MVP motion vector prediction
  • MVD motion vector difference
  • MV reconstructed motion vector
  • MVP MVP ⁇ s if the original prediction of MVP is lower (or not higher) than the target precision. s is an integer, which may depend on the difference between the original precision and the target precision.
  • MVD MVD ⁇ s if the original precision of MVD is lower (or not higher) than the target precision. s is an integer, which may depend on the difference between the original precision and the target precision.
  • MV MV ⁇ s if the original precision of MV is lower (or not higher) than the target precision. s is an integer, which may depend on the difference between the original precision and the target precision.
  • MVP Shift (MVP, s) if the original prediction of MVP is higher (or not lower) than the target precision.
  • s is an integer, which may depend on the difference between the original precision and the target precision.
  • MVD Shift (MVD, s) if the original precision of MVD is higher (or not lower) than the target precision.
  • s is an integer, which may depend on the difference between the original precision and the target precision.
  • MV Shift (MV, s) if the original precision of MV is higher (or not lower) than the target precision.
  • s is an integer, which may depend on the difference between the original precision and the target precision.
  • MVP SatShift (MVP, s) if the original prediction of MVP is higher (or not lower) than the target precision.
  • s is an integer, which may depend on the difference between the original precision and the target precision.
  • MVD SatShift (MVD, s) if the original precision of MVD is higher (or not lower) than the target precision.
  • s is an integer, which may depend on the difference between the original precision and the target precision.
  • MV SatShift (MV, s) if the original precision of MV is higher (or not lower) than the target precision.
  • s is an integer, which may depend on the difference between the original precision and the target precision.
  • Embodiment 1 Indication of usage of affine AMVR mode
  • This section presents the signalling in SPS.
  • sps_affine_amvr_enabled_flag 1 specifies that adaptive motion vector difference resolution is used in motion vector coding of affine inter mode.
  • amvr_enabled_flag 0 specifies that adaptive motion vector difference resolution is not used in motion vector coding of affine inter mode.
  • Syntax of the affine AMVR mode information may reuse that for the AMVR mode information (applied to normal inter mode) .
  • different syntax elements may be utilized.
  • Affine AMVR mode information may be conditionally signaled. Different embodiments below show some examples of the conditions.
  • Embodiment #1 CU syntax table
  • Embodiment 2 An alternative CU syntax table design
  • Embodiment 3 A thirdCU syntax table design
  • Embodiment 4 syntax table design with different syntax for AMVR and affine AMVR mode
  • conditionsA is defined as follows:
  • conditionsA is defined as follows:
  • conditionsA is defined as follows:
  • X is being 0 or 1.
  • conditionsA is defined as follows:
  • conditionsB is defined as follows:
  • conditionsB is defined as follows:
  • conditionsB is defined as follows:
  • the context modeling and/or contexts used for the embodiments in 6.5 which are applied to Affine AMVR may be applied accordingly.
  • amvr_flag [x0] [y0] specifies the resolution of motion vector difference.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • amvr_flag [x0] [y0] 0 specifies that the resolution of the motion vector difference is 1/4 of a luma sample.
  • amvr_flag [x0] [y0] equal to 1 specifies that the resolution of the motion vector difference is further specified by amvr_coarse_precisoin_flag [x0] [y0] .
  • amvr_flag [x0] [y0] is inferred to be equal to 1.
  • amvr_flag [x0] [y0] is inferred to be equal to 0.
  • amvr_coarse_precisoin_flag [x0] [y0] 1 specifies that the resolution of the motion vector difference is four luma samples when inter_affine_flag is equal to 0, and 1 luma samples when inter_affine_flag is equal to 1.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • amvr_coarse_precisoin_flag [x0] [y0] When amvr_coarse_precisoin_flag [x0] [y0] is not present, it is inferred to be equal to 0.
  • MvShift is set equal to (amvr_flag [x0] [y0] +amvr_coarse_precisoin_flag [x0] [y0] ) ⁇ 1 and the variables MvdL0 [x0] [y0] [0] , MvdL0 [x0] [y0] [1] , MvdL1 [x0] [y0] [0] , MvdL1 [x0] [y0] [1] are modified as follows:
  • inter_affine_flag [x0] [y0] is equal to 1
  • the variable MvShift is set equal to (amvr_coarse_precisoin_flag ? (amvr_coarse_precisoin_flag ⁇ 1) : (- (amvr_flag ⁇ 1) ) ) and the variables MvdCpL0 [x0] [y0] [0] [0] , MvdCpL0 [x0] [y0] [0] [1] ,
  • the rounding process is modified that when the given rightShift value is equal to 0 (which happens for 1/16-pel precision) , the rounding offset is set to 0 instead of (1 ⁇ (rightShift-1) ) .
  • Output of this process is the rounded motion vector mvX.
  • the rounding process invoked in the affine motion vector derivation process are performed with the input of (MvShift + 2) instead of being fixed to be 2.
  • the number of control point motion vector predictor candidates in the list numCpMvpCandLX is set equal to 0.
  • variable availableFlagA is set equal to TRUE
  • variable availableFlagB is set equal to TRUE
  • the derivation process for temporal luma motion vector prediction as specified in clause 8.4.2.11 is with the luma coding block location (xCb, yCb) , the luma coding block width cbWidth, the luma coding block height cbHeight and refIdxLX as inputs, and with the output being the availability flag availableFlagLXCol and the temporal motion vector predictor mvLXCol.
  • the affine control point motion vector predictor cpMvpLX with X being 0 or 1 is derived as follows:
  • cpMvpLX cpMvpListLX [mvp_lX_flag [xCb] [yCb] ] (8-642)
  • a luma location (xCb, yCb) specifying the top-left sample of the current luma coding block relative to the top-left luma sample of the current picture
  • the first (top-left) control point motion vector cpMvLX [0] and the availability flag availableFlagLX [0] are derived in the following ordered steps:
  • the sample locations (xNbB2, yNbB2) , (xNbB3, yNbB3) and (xNbA2, yNbA2) are set equal to (xCb-1, yCb-1) , (xCb, yCb-1) and (xCb-1, yCb) , respectively.
  • the availability flag availableFlagLX [0] is set equal to 0 and both components of cpMvLX [0] are set equal to 0.
  • the availability derivation process for a coding block as specified in clause is invoked with the luma coding block location (xCb, yCb) , the luma coding block width cbWidth, the luma coding block height cbHeight, the luma location (xNbY, yNbY) set equal to (xNbTL, yNbTL) as inputs, and the output is assigned to the coding block availability flag availableTL.
  • DiffPicOrderCnt (RefPicListX [RefIdxLX [xNbTL] [yNbTL] ] , RefPicListX [refIdxLX] ) is equal to 0, and the reference picture corresponding to RefIdxLX [xNbTL] [yNbTL] is not the current picture, availableFlagLX [0] is set equal to 1 and the following assignments are made:
  • DiffPicOrderCnt (RefPicListY [RefIdxLY [xNbTL] [yNbTL] ] , RefPicListX [refIdxLX] ) is equal to 0, and the reference picture corresponding to RefIdxLY [xNbTL] [yNbTL] is not the current picture, availableFlagLX [0] is set equal to 1 and the following assignments are made:
  • the second (top-right) control point motion vector cpMvLX [1] and the availability flag availableFlagLX [1] are derived in the following ordered steps:
  • sample locations (xNbB1, yNbB1) and (xNbB0, yNbB0) are set equal to
  • the availability flag availableFlagLX [1] is set equal to 0 and both components of cpMvLX [1] are set equal to 0.
  • X is invoked with the luma coding block location (xCb, yCb) , the luma coding block width cbWidth, the luma coding block height cbHeight, the luma location (xNbY, yNbY) set equal to (xNbTR, yNbTR) as inputs, and the output is assigned to the coding block availability flag availableTR.
  • DiffPicOrderCnt (RefPicListX [RefIdxLX [xNbTR] [yNbTR] ] , RefPicListX [refIdxLX] ) is equal to 0, and the reference picture corresponding to RefIdxLX [xNbTR] [yNbTR] is not the current picture, availableFlagLX [1] is set equal to 1 and the following assignments are made:
  • DiffPicOrderCnt (RefPicListY [RefIdxLY [xNbTR] [yNbTR] ] , RefPicListX [refIdxLX] ) is equal to 0, and the reference picture corresponding to RefIdxLY [xNbTR] [yNbTR] is not the current picture, availableFlagLX [1] is set equal to 1 and the following assignments are made:
  • the third (bottom-left) control point motion vector cpMvLX [2] and the availability flag availableFlagLX [2] are derived in the following ordered steps:
  • sample locations (xNbA1, yNbA1) and (xNbA0, yNbA0) are set equal to (xCb-1, yCb+cbHeight-1) and (xCb-1, yCb+cbHeight) , respectively.
  • the availability flag availableFlagLX [2] is set equal to 0 and both components of cpMvLX [2] are set equal to 0.
  • DiffPicOrderCnt (RefPicListX [RefIdxLX [xNbBL] [yNbBL] ] , RefPicListX [refIdxLX] ) is equal to 0, and the reference picture corresponding to RefIdxLY [xNbBL] [yNbBL] is not the current picture, availableFlagLX [2] is set equal to 1 and the following assignments are made:
  • context increasement offset ctxInc (condL && availableL) + (condA && availableA) + ctxSetIdx*3.
  • ctxInc ( (condL && availableL)
  • amvr_flag is bypass coded.
  • amvr_coarse_precisoin_flag is bypass coded.
  • method 2500 may be implemented at a video decoder or a video encoder.
  • FIG. 25 shows a flowchart of an exemplary method for video decoding.
  • the method 2500 includes, at step 2510, making a determination of using (a) multiple motion vector difference (MVD) precisions or (b) adaptive motion vector difference resolution (AMVR) for affine coding of a current video block, and, at step 2520, performing, based on the determination, a conversion between the current video block and a bitstream representation of the current video block.
  • MVD multiple motion vector difference
  • AMVR adaptive motion vector difference resolution
  • the method 2500 includes, at step 2520, performing, based on the final motion vector, a conversion between the bitstream representation and the current block, which is coded using an affine inter mode or a normal inter mode with support for an adaptive motion vector resolution (AMVR) process.
  • the conversion generates the current block from the bitstream representation (e.g., as might be implemented in a video decoder) .
  • the conversion generates the bitstream representation from the current block (e.g., as might be implemented in a video encoder) .
  • a precision of the final motion vector is identical to a precision of a stored motion vector of the current block.
  • the precision of the final motion vector is 1/16-pel. In another example, the precision of the final motion vector is 1/8-pel.
  • the method 2500 further comprises the step of bypassing a scaling operation for the MVP upon determining that a precision of the MVD is fractional (e.g., a precision greater than 1-pel) . In other embodiments, the method 2500 further comprises the step of scaling the MVP upon determining that a precision of the MVD is less than or equal to 1-pel.
  • the current block is coded using the affine inter mode, and a signaled syntax element is indicative of a precision of a motion vector or a precision of a motion vector difference.
  • a value of 0, 1 or 2 for the signaled syntax element corresponds to the precision of the motion vector being 1/4-pel, 1/16-pel and 1-pel, respectively.
  • a value of 0, 1 or 2 for the signaled syntax element corresponds to the precision of the motion vector being 1/4-pel, 1-pel and 1/16-pel, respectively.
  • a value of 0, 1 or 2 for the signaled syntax element corresponds to the precision of the motion vector being 1/16-pel, 1/4-pel and 1-pel, respectively.
  • the AMVR process is enabled based on signaling in a sequence parameter set (SPS) , a picture parameter set (PPS) , a video parameter set (VPS) , a slice header, a tile header, a group of coding tree units (CTUs) , a coding unit (CU) , a prediction unit (PU) or a transform unit (TU) .
  • SPS sequence parameter set
  • PPS picture parameter set
  • VPS video parameter set
  • slice header a tile header
  • CTUs coding tree units
  • CU coding unit
  • PU prediction unit
  • TU transform unit
  • a set of allowed values for the precision of the motion vector or the precision of the motion vector difference is signaled in a sequence parameter set (SPS) , a picture parameter set (PPS) , a video parameter set (VPS) , a slice header, a tile header, a group of coding tree units (CTUs) , a coding unit (CU) , a prediction unit (PU) or a transform unit (TU) .
  • the set of allowed values is signaled for each coding tree unit (CTU) of the current block.
  • the set of allowed values is based on a coded mode or dimensions of the current block.
  • the set of allowed values is based a slice type, a temporal layer index or a low delay check flag. In yet another example, the set of allowed values is based on a precision of a motion vector stored in a decoded picture buffer.
  • the MVP may be based on a spatially or temporally neighboring block of the current block. In other implementations of the embodiments described above, the MVP may be a default MVP.
  • FIG. 26 is a block diagram of a video processing apparatus 2600.
  • the apparatus 2600 may be used to implement one or more of the methods described herein.
  • the apparatus 2600 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on.
  • the apparatus 2600 may include one or more processors 2602, one or more memories 2604 and video processing hardware 2606.
  • the processor (s) 2602 may be configured to implement one or more methods (including, but not limited to, method 2500) described in the present document.
  • the memory (memories) 2604 may be used for storing data and code used for implementing the methods and techniques described herein.
  • the video processing hardware 2606 may be used to implement, in hardware circuitry, some techniques described in the present document.
  • the video coding methods may be implemented using an apparatus that is implemented on a hardware platform as described with respect to FIG. 26.
  • a method for video coding comprising:
  • An apparatus in a video system comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to implement the method in any one of clauses 1 to 14.
  • a computer program product stored on a non-transitory computer readable media including program code for carrying out the method in any one of clauses 1 to 14.
  • FIG. 27 shows an example of symmetrical mode.
  • FIG. 28 is a block diagram showing an example video processing system 2800 in which various techniques disclosed herein may be implemented.
  • the system 2800 may include input 2802 for receiving video content.
  • the video content may be received in a raw or uncompressed format, e.g., 8 or 10 bit multi-component pixel values, or may be in a compressed or encoded format.
  • the input 2802 may represent a network interface, a peripheral bus interface, or a storage interface. Examples of network interface include wired interfaces such as Ethernet, passive optical network (PON) , etc. and wireless interfaces such as Wi-Fi or cellular interfaces.
  • PON passive optical network
  • the system 2800 may include a coding component 2804 that may implement the various coding or encoding methods described in the present document.
  • the coding component 2804 may reduce the average bitrate of video from the input 2802 to the output of the coding component 2804 to produce a coded representation of the video.
  • the coding techniques are therefore sometimes called video compression or video transcoding techniques.
  • the output of the coding component 2804 may be either stored, or transmitted via a communication connected, as represented by the component 2806.
  • the stored or communicated bitstream (or coded) representation of the video received at the input 2802 may be used by the component 2808 for generating pixel values or displayable video that is sent to a display interface 2810.
  • the process of generating user-viewable video from the bitstream representation is sometimes called video decompression.
  • certain video processing operations are referred to as "coding" operations or tools, it will be appreciated that the coding tools or operations are used at an encoder and corresponding decoding tools or operations that reverse the results of the coding will be performed by
  • peripheral bus interface or a display interface may include universal serial bus (USB) or high definition multimedia interface (HDMI) or Displayport, and so on.
  • storage interfaces include SATA (serial advanced technology attachment) , PCI, IDE interface, and the like.
  • FIG. 29 shows a flowchart of an example method for video processing. Steps of this flowchart show an implementation of the embodiments discussed in Example 21 in Section 4 of this document.
  • the process during a conversion between a current video block and a bitstream representation of the current video block uses syntax elements composed of multiple bins for processing the current video block, wherein the syntax elements are selected according to a context model such that a first context model is applied for selecting a first bin of a first syntax element and a second context model is applied for selecting all bins excluding the first bin of the first syntax element
  • FIG. 30 shows a flowchart of an example method for video processing. Steps of this flowchart show an implementation of the embodiments discussed in Example 22 in Section 4 of this document.
  • the process makes a determination of using a precision from a precision set as a target precision of a motion vector (MVD) that is computed as a difference between a motion vector and a motion vector predictor (MVP) associated with a current video block.
  • the process in response to detecting that the target precision is different from the precision of the MVP, converts the precision of the MVP to the target precision.
  • MVP motion vector predictor
  • the process generates a reconstructed motion vector using the MVP with the target precision and the MVD, during a normal inter mode or an affine inter mode coding of the current video block, wherein the reconstructed motion vector is used for processing of subsequent video blocks.
  • FIG. 31 shows a flowchart of an example method for video processing. Steps of this flowchart show an implementation of the embodiments discussed in Example 22 in Section 4 of this document.
  • the process during a conversion between a video block and a bitstream representation of the current video block identifies that a precision of a motion vector predictor (MVP) associated with the current video block is different from a precision of a motion vector difference (MVD) that is computed as a difference between the MVP and a motion vector associated with the current video block.
  • MVP motion vector predictor
  • MVP motion vector difference
  • the process in response to the detecting, converts the precision of the MVD to the precision of the MVP.
  • the process reconstructs the motion vector associated with the current video block using the precision of the MVP for processing subsequent video blocks.
  • a method for visual media processing comprising:
  • syntax elements composed of multiple bins for processing the current video block, wherein the syntax elements are selected according to a context model such that a first context model is applied for selecting a first bin of a first syntax element and a second context model is applied for selecting all bins excluding the first bin of the first syntax element.
  • A11 The method of clause A10, wherein an adaptive motion vector difference resolution (AMVR) is disabled for use during the conversion of the current video block or wherein the first syntax element is absent from the bitstream representation, and wherein the conversion uses a default motion vector or a default motion vector difference precision.
  • AMVR adaptive motion vector difference resolution
  • a method for visual media processing comprising:
  • offset0 and/or offset1 are set to (1 ⁇ n) >>1 and/or (1 ⁇ (n-1) ) and/or zero.
  • offset0 and/or offset1 are set to (1 ⁇ n) >>1 and/or (1 ⁇ (n-1) ) and/or zero.
  • a method for visual media processing comprising:
  • MVP motion vector predictor
  • MVPD motion vector difference
  • a video encoder apparatus comprising a processor configured to implement a method recited in any one or more of clauses A1-C3.
  • a video decoder apparatus comprising a processor configured to implement a method recited in any one or more of clauses A1-C3.
  • a computer readable medium having code stored thereon, the code embodying processor-executable instructions for implementing a method recited in any of or more of clauses A1-C3.
  • alf_ctb_flag [cIdx] [xCtb>>Log2CtbSize] [yCtb>>Log2CtbSize] 1 specifies that the adaptive loop filter is applied to the coding tree block of the colour component indicated by cIdx of the coding tree unit at luma location (xCtb, yCtb) .
  • alf_ctb_flag [cIdx] [xCtb>>Log2CtbSize] [yCtb>>Log2CtbSize] equal to 0 specifies that the adaptive loop filter is not applied to the coding tree block of the colour component indicated by cIdx of the coding tree unit at luma location (xCtb, yCtb) .
  • sao_merge_left_flag 1 specifies that the syntax elements sao_type_idx_luma, sao_type_idx_chroma, sao_band_position, sao_eo_class_luma, sao_eo_class_chroma, sao_offset_abs and sao_offset_sign are derived from the corresponding syntax elements of the left CTB.
  • sao_merge_left_flag 0 specifies that these syntax elements are not derived from the corresponding syntax elements of the left CTB. When sao_merge_left_flag is not present, it is inferred to be equal to 0.
  • sao_merge_up_flag 1 specifies that the syntax elements sao_type_idx_luma, sao_type_idx_chroma, sao_band_position, sao_eo_class_luma, sao_eo_class_chroma, sao_offset_abs and sao_offset_sign are derived from the corresponding syntax elements of the above CTB.
  • sao_merge_up_flag 0 specifies that these syntax elements are not derived from the corresponding syntax elements of the above CTB. When sao_merge_up_flag is not present, it is inferred to be equal to 0.
  • sao_type_idx_luma specifies the offset type for the luma component.
  • the array SaoTypeIdx [cIdx] [rx] [ry] specifies the offset type as specified in SAO offset type table for the CTB at the location (rx, ry) for the colour component cIdx.
  • the value of SaoTypeIdx [0] [rx] [ry] is derived as follows:
  • SaoTypeIdx [0] [rx] [ry] is set equal to sao_type_idx_luma.
  • SaoTypeIdx [0] [rx] [ry] is derived as follows:
  • SaoTypeIdx [0] [rx] [ry] is set equal to SaoTypeIdx [0] [rx-1] [ry] .
  • SaoTypeIdx [0] [rx] [ry] is set equal to SaoTypeIdx [0] [rx] [ry-1] .
  • SaoTypeIdx [0] [rx] [ry] is set equal to 0.
  • sao_type_idx_chroma specifies the offset type for the chroma components.
  • the values of SaoTypeIdx [cIdx] [rx] [ry] are derived as follows for cIdx equal to 1.. 2:
  • SaoTypeIdx [cIdx] [rx] [ry] is set equal to sao_type_idx_chroma.
  • SaoTypeIdx [cIdx] [rx] [ry] is derived as follows:
  • SaoTypeIdx [cIdx] [rx] [ry] is set equal to SaoTypeIdx [cIdx] [rx-1] [ry] .
  • SaoTypeIdx [cIdx] [rx] [ry] is set equal to SaoTypeIdx [cIdx] [rx] [ry-1] .
  • SaoTypeIdx [cIdx] [rx] [ry] is set equal to 0.
  • split_cu_flag 0 specifies that a coding unit is not split.
  • split_cu_flag 1 specifies that a coding unit is split into four coding units using a quad split as indicated by the syntax element split_qt_flag, or into two coding units using a binary split or into three coding units using a ternary split as indicated by the syntax element mtt_split_cu_binary_flag.
  • the binary or ternary split can be either vertical or horizontal as indicated by the syntax element mtt_split_cu_vertical_flag.
  • split_cu_flag When split_cu_flag is not present, the value of split_cu_flag is inferred as follows:
  • split_cu_flag is inferred to be equal to 1:
  • cbWidth is greater than pic_width_in_luma_samples.
  • cbHeight is greater than pic_height_in_luma_samples.
  • split_cu_flag is inferred to be equal to 0.
  • split_qt_flag specifies whether a coding unit is split into coding units with half horizontal and vertical size.
  • split_qt_flag If allowSplitQt is equal to TRUE, the value of split_qt_flag is inferred to be equal to 1.
  • split_qt_flag is inferred to be equal to 0.
  • mtt_split_cu_vertical_flag 0 specifies that a coding unit is split horizontally.
  • mtt_split_cu_vertical_flag 1 specifies that a coding unit is split vertically
  • mtt_split_cu_binary_flag 0 specifies that a coding unit is split into three coding units using a ternary split.
  • mtt_split_cu_binary_flag 1 specifies that a coding unit is split into two coding units using a binary split.
  • mtt_split_cu_binary_flag is inferred to be equal to ! mtt_split_cu_vertical_flag.
  • mtt_split_cu_binary_flag is inferred to be equal to mtt_split_cu_vertical_flag.
  • MttSplitMode [x0] [y0] [mttDepth] represents horizontal and vertical binary and ternary splittings of a coding unit within the multi-type tree.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • IsInSmr [x0] [y0] is equal to FALSE
  • mtt_split_cu_binary_flag is equal to 0 and cbWidth*cbHeight/4 is less than 32
  • – treeType is not equal to DUAL_TREE_CHROMA
  • cu_skip_flag [x0] [y0] 1 specifies that for the current coding unit, when decoding a P or B tile group, no more syntax elements except one or more of the following are parsed after cu_skip_flag [x0] [y0] : the IBC mode flag pred_mode_ibc_flag [x0] [y0] , the merge plus MVD flag mmvd_flag [x0] [y0] , the merge plus MVD index mmvd_merge_flag [x0] [y0] , the merge plus MVD distance index mmvd distance_idx [x0] [y0] , the merge plus MVD direction index mmvd_direction_idx [x0] [y0] , the merging candidate index merge_idx [x0] [y0] the subblock-based merge flag merge_subblock_flag [x0] [y0] , the subblock-based merging candidate index
  • cu_skip_flag [x0] [y0] 0 specifies that the coding unit is not skipped.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • pred_mode_ibc_flag 1 specifies that the current coding unit is coded in IBC prediction mode.
  • pred_mode_ibc_flag 0 specifies that the current coding unit is not coded in IBC prediction mode.
  • pred_mode_ibc_flag When pred_mode_ibc_flag is not present, it is inferred to be equal to the value of sps_ibc_enabled_flag when decoding an I tile group, and 0 when decoding a P or B tile group, respectively.
  • pred_mode_flag 0 specifies that the current coding unit is coded in inter prediction mode.
  • pred_mode_flag 1 specifies that the current coding unit is coded in intra prediction mode.
  • pred_mode_flag When pred_mode_flag is not present, it is inferred to be equal to 1 when decoding an I tile group, and equal to 0 when decoding a P or B tile group, respectively.
  • intra_luma_ref_idx [x0] [y0] specifies the intra prediction reference line index.
  • intra_subpartitions_mode_flag [x0] [y0] 1 specifies that the current intra coding unit is partitioned into NumIntraSubPartitions [x0] [y0] rectangular transform block subpartitions.
  • intra_subpartitions_mode_flag [x0] [y0] 0 specifies that the current intra coding unit is not partitioned into rectangular transform block subpartitions.
  • intra_subpartitions_split_flag [x0] [y0] specifies whether the intra subpartitions split type is horizontal or vertical. When intra_subpartitions_split_flag [x0] [y0] is not present, it is inferred as follows:
  • intra_subpartitions_split_flag [x0] [y0] is inferred to be equal to 0.
  • intra_subpartitions_split_flag [x0] [y0] is inferred to be equal to 1.
  • IntraSubPartitionsSplitType specifies the type of split used for the current luma coding block as illustrated in IntraSubPartitionsSplitType Table.
  • IntraSubPartitionsSplitType is derived as follows:
  • IntraSubPartitionsSplitType is set equal to 0.
  • IntraSubPartitionsSplitType is set equal to 1+intra_subpartitions_split_flag [x0] [y0] .
  • IntraSubPartitionsSplitType specifies the type of split used for the current luma coding block as illustrated in IntraSubPartitionsSplitType Table.
  • IntraSubPartitionsSplitType is derived as follows:
  • IntraSubPartitionsSplitType is set equal to 0.
  • IntraSubPartitionsSplitType is set equal to 1+intra_subpartitions_split_flag [x0] [y0] .
  • NumIntraSubPartitions specifies the number of transform block subpartitions an intra luma coding block is divided into. NumIntraSubPartitions is derived as follows:
  • IntraSubPartitionsSplitType is equal to ISP_NO_SPLIT
  • NumIntraSubPartitions is set equal to 1.
  • NumIntraSubPartitions is set equal to 2:
  • cbWidth is equal to 8 and cbHeight is equal to 4.
  • NumIntraSubPartitions is set equal to 4.
  • intra_luma_mpm_flag [x0] [y0] specifies the intra prediction mode for luma samples.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • intra_luma_mpm_flag [x0] [y0] is equal to 1, the intra prediction mode is inferred from a neighbouring intra-predicted coding unit.
  • intra_chroma_pred_mode [x0] [y0] specifies the intra prediction mode for chroma samples.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • merge_flag [x0] [y0] specifies whether the inter prediction parameters for the current coding unit are inferred from a neighbouring inter-predicted partition.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • merge_flag [x0] [y0] is inferred to be equal to 0.
  • inter_pred_idc [x0] [y0] specifies whether list0, list1, or bi-prediction is used for the current coding unit according to inter prediction mode table.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • inter_affine_flag [x0] [y0] 1 specifies that for the current coding unit, when decoding a P or B tile group, affine model based motion compensation is used to generate the prediction samples of the current coding unit.
  • inter_affine_flag [x0] [y0] 0 specifies that the coding unit is not predicted by affine model based motion compensation.
  • inter_affine_flag [x0] [y0] is not present, it is inferred to be equal to 0.
  • cu_affine_type_flag [x0] [y0] 1 specifies that for the current coding unit, when decoding a P or B tile group, 6-parameter affine model based motion compensation is used to generate the prediction samples of the current coding unit.
  • cu_affine_type_flag [x0] [y0] 0 specifies that 4-parameter affine model based motion compensation is used to generate the prediction samples of the current coding unit.
  • MotionMode1 Idc [x] [y] represents motion model of a coding unit as illustrated in MotionMode1 Idc Table.
  • the array indices x, y specify the luma sample location (x, y) relative to the top-left luma sample of the picture.
  • MotionModelIdc [x] [y] inter_affine_flag [x0] [y0] +cu_affine_type_flag [x0] [y0]
  • ref_idx_l0 [x0] [y0] specifies the list 0 reference picture index for the current coding unit.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • ref_idx_l0 [x0] [y0] is inferred to be equal to RefIdxSymL0.
  • mvp_l0_flag [x0] [y0] specifies the motion vector predictor index of list 0 where x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • ref_idx_l1 [x0] [y0] has the same semantics as ref_idx_l0, with l0, L0 and list 0 replaced by l1, L1 and list 1, respectively.
  • mvp_l1_flag [x0] [y0] has the same semantics as mvp_l0_flag, with l0 and list 0 replaced by l1 and list 1, respectively.
  • amvr_flag [x0] [y0] specifies the resolution of motion vector difference.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • amvr_flag [x0] [y0] 0 specifies that the resolution of the motion vector difference is 1/4 of a luma sample.
  • amvr_flag [x0] [y0] equal to 1 specifies that the resolution of the motion vector difference is further specified by amvr_precision_flag [x0] [y0] .
  • amvr_precision_flag [x0] [y0] 0 specifies that the resolution of the motion vector difference is one integer luma sample if inter_affine_flag [x0] [y0] is equal to 0, and 1/16 of a luma sample otherwise.
  • amvr_precision_flag [x0] [y0] 1 specifies that the resolution of the motion vector difference is four luma samples if inter_affine_flag [x0] [y0] is equal to 0, and one integer luma sample otherwise.
  • the array indices x0, y0 specify the location (x0, y0) of the top-left luma sample of the considered coding block relative to the top-left luma sample of the picture.
  • amvr_precision_flag [x0] [y0] When amvr_precision_flag [x0] [y0] is not present, it is inferred to be equal to 0.

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Abstract

La présente invention concerne un procédé de traitement multimédia visuel consistant à : pendant une conversion entre un bloc vidéo courant et une représentation de flux binaire du bloc vidéo courant, utiliser des éléments de syntaxe composés de multiples bacs pour traiter le bloc vidéo courant, les éléments de syntaxe étant sélectionnés selon un modèle de contexte, de telle sorte qu'un premier modèle de contexte soit appliqué pour sélectionner un premier bac d'un premier élément de syntaxe et un second modèle de contexte est appliqué pour sélectionner tous les bacs, à l'exclusion du premier bac du premier élément de syntaxe.
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