WO2020221256A1 - Symmetric motion vector difference coding - Google Patents

Symmetric motion vector difference coding Download PDF

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WO2020221256A1
WO2020221256A1 PCT/CN2020/087535 CN2020087535W WO2020221256A1 WO 2020221256 A1 WO2020221256 A1 WO 2020221256A1 CN 2020087535 W CN2020087535 W CN 2020087535W WO 2020221256 A1 WO2020221256 A1 WO 2020221256A1
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mvd
list
picture
poc
reference list
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PCT/CN2020/087535
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English (en)
French (fr)
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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 CN202080031971.6A priority Critical patent/CN113767638A/zh
Publication of WO2020221256A1 publication Critical patent/WO2020221256A1/en

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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
    • H04N19/102—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
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/105—Selection of the reference unit for prediction within a chosen coding or prediction mode, e.g. adaptive choice of position and number of pixels used for 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
    • H04N19/103—Selection of coding mode or of prediction mode
    • H04N19/109—Selection of coding mode or of prediction mode among a plurality of temporal predictive coding modes
    • 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
    • H04N19/17—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 an image region, e.g. an object
    • H04N19/176—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 an image region, e.g. an object the region being a block, e.g. a macroblock
    • 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
    • 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
    • H04N19/577—Motion compensation with bidirectional frame interpolation, i.e. using B-pictures

Definitions

  • This patent document relates to video coding techniques, devices and systems.
  • the present document describes various embodiments and techniques in which video coding or decoding is performed using motion vector difference coding that uses a symmetric coding or decoding technique.
  • a method of video processing includes determining to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures and performing the conversion using the SMVD mode.
  • the bitstream representation indicates to disable use of a motion vector difference (MVD) mode for one of the reference list 0 or the reference list 1.
  • another method of video processing includes determining to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in pictures from two target reference pictures from a reference list 0 and a reference list 1 of reference pictures and performing the conversion using the SMVD mode.
  • the bitstream representation includes a motion vector difference (MVD) information for the reference list 1.
  • another method of video processing includes determining to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in pictures from a reference list 0 and a reference list 1 of reference pictures and performing the conversion using the SMVD mode.
  • the SMVD generates the two additional motion candidates using a first step in which each reference picture list is parsed to identify target reference pictures.
  • another method of video processing includes determining, based on a condition to use a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures, and a decoder side motion vector difference (DMVD) coding mode for a conversion between a current video block and a bitstream representation of the current video block and performing the conversion based on the determining.
  • SMVD symmetric motion vector difference
  • DMVD decoder side motion vector difference
  • another method of video processing includes determining, based on a condition, whether or not to use an all-zero motion vector difference for a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures, and a decoder side motion vector difference (DMVD) coding mode for a conversion between a current video block and a bitstream representation of the current video block and performing the conversion based on the determining.
  • SMVD symmetric motion vector difference
  • DMVD decoder side motion vector difference
  • another method of video processing includes selecting a first reference picture and a second reference picture from a plurality of reference pictures associated with a current video block, and performing, based on the selected first and second reference pictures, a conversion between the current video block and a bitstream representation of the current video block, wherein a first distance between the first reference picture and a current picture comprising the current video block and a second distance between the second reference picture and the current picture are equal.
  • another method of video processing includes determining that a first distance between a first reference picture and a current picture comprising a current video block and a second distance between a second reference picture and the current picture are unequal, and disabling, based on the determining and for a conversion between the current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode for the current video block.
  • SMVD symmetric motion vector difference
  • another method of video processing includes deriving, for a current video block, a first motion vector difference (MVD) of a first reference picture list based on a second MVD of a second reference picture list, and performing, based on the deriving, a conversion between the current video block and a bitstream representation of the current video block, wherein the a range of the first MVD is restricted.
  • MVD motion vector difference
  • a method of video processing includes determining, for a conversion between a block of current picture of video and a bitstream representation of the first block, whether a symmetric motion vector difference (SMVD) mode is allowable for the block based on coding information of the block; and performing the conversion based on the determination.
  • SMVD symmetric motion vector difference
  • a method of video processing includes determining, for a conversion between a block of video and a bitstream representation of the first block, whether a symmetric motion vector (SMV) mode is allowable for the block according to the method of previous examples; and performing the conversion based on the determination.
  • SMV symmetric motion vector
  • a method of video processing includes determining, for a conversion between a block of a current picture of video and a bitstream representation of the block, whether a symmetric motion vector difference (SMVD) mode is allowable for the block, wherein whether the SMVD mode is allowable depends on a derivation process of two target reference pictures of the current picture, which includes a first step for searching a forward target reference picture in the reference picture list 0 and searching a backward target reference picture in the reference picture list 1, and a second step for searching a backward target reference picture in the reference picture list 0 and searching a forward target reference picture in the reference picture list 1, outputs of the first step and the second step being independent of each other; and performing the conversion based on the determination.
  • SMVD symmetric motion vector difference
  • a method of video processing includes deriving, for a conversion between a block of a current picture of video and a bitstream representation of the block, a second motion vector difference (MVD) of one reference picture list from a first MVD associated with the other reference picture list, wherein an MVD includes both a horizontal component and a vertical component; applying a range restriction on at least one of the first MVD and the second MVD; and performing the conversion based on at least one of the restricted first MVD and the restricted second MVD.
  • MVD motion vector difference
  • a video processing apparatus includes a processor configured to perform an-above disclosed method.
  • the apparatus may further perform video encoding or video decoding.
  • a computer readable medium has code for processor-implementation of the above-described methods stored on it.
  • FIG. 1 depicts an example derivation process for merge candidates list construction.
  • FIG. 2 shows examples of positions of spatial merge candidates.
  • FIG. 3 shows examples of candidate pairs considered for redundancy check of spatial merge candidates.
  • FIG. 4A-4B show example positions for the second PU of N ⁇ 2N and 2N ⁇ N partitions.
  • FIG. 5 is an illustration of motion vector scaling for temporal merge candidate.
  • FIG. 6 shows examples of candidate positions for temporal merge candidate, C0 and C1.
  • FIG. 7 shows an example of combined bi-predictive merge candidate.
  • FIG. 8 summarizes derivation process for motion vector prediction candidate.
  • FIG. 9 shows an illustration of motion vector scaling for spatial motion vector candidate.
  • FIG. 10 shows an example of decoder side motion vector refinement (DMVR) based on bilateral template matching.
  • FIG. 11 shows an example of MVD (0, 1) mirrored between list 0 and list 1 in DMVR.
  • FIG. 12 shows examples of motion vectors (MVs) that may be checked in one iteration.
  • FIG. 13 is an example illustration for symmetrical mode.
  • FIG. 14 is a block diagram of an example of a hardware platform used for implementing methods described in the present document.
  • FIG. 15 is a flowchart for an example method of video processing.
  • FIG. 16 is a flowchart for an example method of video processing.
  • FIG. 17 is a flowchart for an example method of video processing.
  • FIG. 18 is a flowchart for an example method of video processing.
  • FIG. 19 is a flowchart for an example method of video processing.
  • Section headings are used in the present document to facilitate ease of understanding and do not limit the embodiments disclosed in a section to only that section.
  • certain embodiments are described with reference to Versatile Video Coding or other specific video codecs, the disclosed techniques are applicable to other video coding technologies also.
  • video processing encompasses video coding or compression, video decoding or decompression and video transcoding in which video pixels are represented from one compressed format into another compressed format or at a different compressed bitrate.
  • This patent document is related to video coding technologies. Specifically, it is related to symmetric motion vector difference coding. It may be applied to the existing video coding standard like HEVC, or the standard (Versatile Video Coding) to be finalized. It may be also applicable to future video coding standards or video codec.
  • Video coding standards have evolved primarily through the development of the well-known ITU-T and ISO/IEC standards.
  • the ITU-T produced H. 261 and H. 263, ISO/IEC produced MPEG-1 and MPEG-4 Visual, and the two organizations jointly produced the H. 262/MPEG-2 Video and H. 264/MPEG-4 Advanced Video Coding (AVC) and H. 265/HEVC standards.
  • AVC H. 264/MPEG-4 Advanced Video Coding
  • H. 265/HEVC High Efficiency Video Coding
  • the video coding standards are based on the hybrid video coding structure wherein temporal prediction plus transform coding are utilized.
  • Joint Video Exploration Team JVET was founded by VCEG and MPEG jointly in 2015.
  • JVET Joint Exploration Model
  • 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. Usage of one of the two reference picture lists may also be signalled 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 neighbouring 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 (to be more precise, motion vector differences (MVD) compared to a motion vector predictor) , corresponding reference picture index for each reference picture list and reference picture list usage are signalled explicitly per each PU.
  • MDV motion vector differences
  • Such a mode is named Advanced motion vector prediction (AMVP) in this disclosure.
  • the PU When signalling 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.
  • Bi-prediction When signalling 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.
  • inter prediction is used to denote prediction derived from data elements (e.g., sample values or motion vectors) of reference pictures other than the current decoded picture.
  • data elements e.g., sample values or motion vectors
  • a picture can be predicted from multiple reference pictures.
  • the reference pictures that are used for inter prediction are organized in one or more reference picture lists.
  • the reference index identifies which of the reference pictures in the list should be used for creating the prediction signal.
  • a single reference picture list, List 0 is used for a P slice and two reference picture lists, List 0 and List 1 are used for B slices. It should be noted reference pictures included in List 0/1 could be from past and future pictures in terms of capturing/display order.
  • Step 1.2 Redundancy check for spatial candidates
  • steps are also schematically depicted in FIG. 1.
  • 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 obtained from step 1 does not reach the 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
  • FIG. 1 depicts an example derivation process for merge candidates list construction.
  • 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 only when 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.
  • a redundancy check To reduce computational complexity, not all possible candidate pairs are considered in the mentioned redundancy check. Instead only the pairs linked with an arrow in FIG.
  • FIG. 4A-4B depict the second PU for the case of N ⁇ 2N and 2N ⁇ N, respectively.
  • candidate at position A1 is not considered for list construction. In fact, by adding this candidate will lead to two prediction units having the same motion information, which is redundant to just have one PU in a coding unit.
  • position B1 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 signalled in the slice header.
  • the scaled motion vector for temporal merge candidate is obtained as illustrated by the dotted line in FIG.
  • tb is defined to be the POC difference between the reference picture of the current picture and the current picture
  • 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.
  • the position for the temporal candidate is selected between candidates C0 and C1, as depicted in FIG. 6. If PU at position C0 is not available, is intra coded, or is outside of the current coding tree unit (CTU aka. LCU, largest coding unit) row, position C1 is used. Otherwise, position C0 is used in the derivation of the temporal merge candidate.
  • CTU current coding tree unit
  • Zero merge candidate Combined bi-predictive merge candidates are generated by utilizing spatial and 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. As an example, FIG.
  • 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. Finally, no redundancy check is performed on these candidates.
  • AMVP exploits spatio-temporal correlation of motion vector with neighbouring PUs, which is used for explicit transmission of motion parameters.
  • a motion vector candidate list is constructed by firstly checking availability of left, above temporally neighbouring 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) .
  • the maximum value to be encoded is 2 (see FIG. 8) .
  • FIG. 8 summarizes derivation process for motion vector prediction candidate.
  • 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 depicted 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 depicted 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 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, as depicted as FIG. 9.
  • the main 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.
  • AMVR Adaptive motion vector difference resolution
  • TPM Triangular prediction mode
  • ATMVP Advanced TMVP
  • GBI Generalized Bi-Prediction
  • BIO Bi-directional Optical flow
  • QuadTree/BinaryTree/MulitpleTree (QT/BT/TT) structure is adopted to divide a picture into square or rectangle blocks.
  • separate tree (a. k. a. Dual coding tree) is also adopted in VVC for I-frames.
  • VVC VVC
  • the coding block structure are signaled separately for the luma and chroma components.
  • 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.
  • MV motion vector
  • DMVR decoder-side motion vector refinement
  • the motion vectors are 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.
  • An example is depicted in FIG. 10.
  • the 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. 10.
  • 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.
  • the 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. 10, are used for generating the final bi-prediction results.
  • a sum of absolute differences (SAD) is used as the cost measure.
  • SAD sum of absolute differences
  • MVD mirroring between list 0 and list 1 is assumed as shown in FIG. 11 and bilateral matching is performed to refine the MVs, i.e., to find the best MVD among several MVD candidates.
  • MVL0 L0X, L0Y
  • MVL1 L1X, L1Y
  • the MVD denoted by (MvdX, MvdY) for list 0 that could minimize the cost function (e.g., SAD) is defined as the best MVD.
  • the SAD function it is defined as the SAD between the reference block of list 0 derived with a motion vector (L0X+MvdX, L0Y+MvdY) in the list 0 reference picture and the reference block of list 1 derived with a motion vector (L1X-MvdX, L1Y-MvdY) in the list 1 reference picture.
  • the motion vector refinement process may iterate twice. In each iteration, at most 6 MVDs (with integer-pel precision) may be checked in two steps, as shown in FIG. 12. In the first step, MVD (0, 0) , (-1, 0) , (1, 0) , (0, -1) , (0, 1) are checked. In the second step, one of the MVD (-1, -1) , (-1, 1) , (1, -1) or (1, 1) may be selected and further checked. Suppose function Sad (x, y) returns SAD value of the MVD (x, y) . The MVD, denoted by (MvdX, MvdY) , checked in the second step is decided as follows:
  • the starting point In the first iteration, the starting point is the signaled MV, and in the second iteration, the starting point is the signaled MV plus the selected best MVD in the first iteration.
  • DMVR applies only when one reference picture is a preceding picture and the other reference picture is a following picture, and the two reference pictures are with same picture order count distance from the current picture.
  • DMVR may be enabled:
  • DMVR enabling flag in the SPS i.e., sps_dmvr_enabled_flag
  • TPM flag inter-affine flag and subblock merge flag (either ATMVP or affine merge)
  • MMVD flag are all equal to 0
  • the current CU height is greater than or equal to 8
  • Number of luma samples (CU width*height) is greater than or equal to 64
  • the parametric error surface fit is computed only if the center position is the best cost position in a given iteration.
  • Symmetric motion vector difference (SMVD) is applied for motion information coding in bi-prediction.
  • variables RefIdxSymL0 and RefIdxSymL1 to indicate the reference picture index of list 0/1 used in SMVD mode, respectively, are derived with the following steps. When at least one of the two variables are equal to -1, SMVD mode shall be disabled.
  • RefIdxSymL0 and RefIdxSymL0 specifying the list 0 and list 1 reference picture indices for symmetric motion vector differences, i.e., when sym_mvd_flag is equal to 1 for a coding unit.
  • Step #1 first loop each reference picture list
  • variable currPic specifies the current picture.
  • RefIdxSymL0 is set equal to -1.
  • RefIdxSymL0 is set to i:
  • DiffPicOrderCnt (currPic, RefPicList [0] [i] ) ⁇ DiffPicOrderCnt (currPic, RefPicList [0] [RefIdxSymL0] ) or RefIdxSymL0 is equal to -1.
  • RefIdxSymL1 is set equal to -1.
  • RefIdxSymL1 is set to i:
  • Step #2 second loop each reference picture list
  • RefIdxSymL1 is equal to -1 or RefIdxSymL1 is equal to -1, the following applies:
  • RefIdxSymL0 is set to i:
  • RefIdxSymL1 is set to i:
  • DiffPicOrderCnt (currPic, RefPicList [1] [i] ) ⁇ DiffPicOrderCnt (currPic, RefPicList [1] [RefIdxSymL1] ) or RefIdxSymL1 is equal to -1.
  • 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. 13 is an example illustration for symmetrical mode.
  • abs_mvd_greater0_flag [compIdx] specifies whether the absolute value of a motion vector component difference is greater than 0.
  • abs_mvd_greater1_flag [compIdx] specifies whether the absolute value of a motion vector component difference is greater than 1.
  • abs_mvd_minus2 [compIdx] plus 2 specifies the absolute value of a motion vector component difference.
  • abs_mvd_minus2 [compIdx] When abs_mvd_minus2 [compIdx] is not present, it is inferred to be equal to -1.
  • mvd_sign_flag [compIdx] specifies the sign of a motion vector component difference as follows:
  • lMvd [compIdx] shall be in the range of -215 to 215 -1, inclusive.
  • motion vector differences are derived as follows:
  • MotionModelIdc [x0] [y0] is equal to 0, the variable MvdLX [x0] [y0] [compIdx] , with X being 0 or 1, specifies the difference between a list X vector component to be used and its prediction.
  • 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.
  • the variable MvdCpLX [x0] [y0] [cpIdx] [compIdx] specifies the difference between a list X vector component to be used and its prediction.
  • 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, the array index cpIdx specifies the control point index.
  • the current SMVD may have the following problems:
  • SMVD is disallowed when mvd_l1_zero_flag is true, which may be inefficient.
  • the target reference picture index of list 0 and 1 used in SMVD mode are derived in the slice level with two steps:
  • step b the second step (i.e., step b) needs to be invoked for all of the following cases:
  • list 1 only has forward reference pictures, and list 0 only have backward reference pictures;
  • the current design has the restriction of finding forward from list 0 and backward from list 1; and vice versa. For example, if list 0 and list 1 have both forward and backward reference pictures, but the closest reference picture in list 0 is from backward, and the closet in list 1 is from forward. With current design, there is no chance to select the closest one from backward in list 0.
  • list 0 have both forward and backward reference pictures and list 1 only have forward reference pictures, with current design, it will identify two forward reference pictures, which is conflict with the concept of the SMVD design.
  • DMVR is disabled in SMVD mode though symmetric MVD is assumed in both DMVR and SMVD
  • MVD for list 1 is derived from the signaled MVD for list 0, i.e., opposite of both horizontal and vertical component of the MVD for list 0. Such assumption is that the two reference pictures are with same distance to the current picture. However, it is not always true.
  • VVC defines a range of MVD that MVD should be within [-2 15 , 2 15 -1] .
  • MVD for list 1 is derived from the signaled MVD for list 0 may exceed the constrains on MVD.
  • decoder side motion vector derivation includes methods like DMVR and FRUC which perform motion estimation to derive or refine the block/sub-block motion information, and BIO which performs sample-wise motion refinement.
  • the unequal weights applied to prediction blocks may refer to that used in the GBI process, LIC process, weighted prediction process or other encoding/decoding process of a coding tool that need to apply additional operations to prediction blocks instead of average of two prediction blocks etc. al.
  • the reference picture in list 0 and list 1 are Ref0 and Ref1 respectively
  • the POC distance between the current picture and Ref0 is PocDist0 (e.g., absolute value of (POC of current picture minus POC of Ref0) )
  • the POC distance between Ref1 and the current picture is PocDist1 (e.g., absolute value of (POC of Ref1 minus POC of current picture) )
  • width and height of the block as W and H respectively.
  • function abs (x) returns the absolute value of x.
  • All-zero MVD represents the case that all MVDs (including both x and y components) to be signaled are equal to zero.
  • currPocDiffL0 POC (current picture) –POC (RefIdxL0)
  • currPocDiffL1 POC (current picture) –POC (RefIdxL1)
  • Abs (x) x > 0? x : -x.
  • the SMVD mode may still be enabled for a block.
  • the MVD for reference picture list 1 is not forced to be zero (e.g. mvd_l1_zero_flag is equal to 1) , but it could be derived from the associated MVD for reference picture list 0.
  • X may be equal to 0.
  • SMVD may be disallowed when MVD in list X is indicated to be forced to zero.
  • the reference list with associated MVD to be signaled (or to be derived) may be also signaled in the bitstream.
  • indication of the reference picture list that the associated MVD need to be signaled may be signaled in the sequence/picture/slice/tile/video unit-level, such as SPS/PPS/slice header.
  • the reference list with associated MVD to be signaled (or to be derived) may be derived according to reference pictures in the reference picture lists.
  • the reference list with associated MVD to be signaled (or to be derived) may be derived according to the target two reference pictures.
  • MVD for list 0 may be signaled. Otherwise, MVD for list 1 may be signaled.
  • MVD for list 1 may be signaled. Otherwise, MVD for list 0 may be signaled.
  • MVD for list 0 may be signaled. Otherwise, MVD for list 1 may be signaled.
  • MVD for list 1 may be signaled. Otherwise, MVD for list 0 may be signaled.
  • MVD for list 0 may be signaled. Otherwise, MVD for list 1 may be signaled.
  • MVD for list 1 may be signaled. Otherwise, MVD for list 0 may be signaled.
  • the reference list with associated MVD to be signaled (or to be derived) may be also changed from one video unit (e.g., slice/tile group/tile/brick/CU) to another one.
  • the selection of reference list with associated MVD to be signaled may depend on the reference pictures information of neighboring blocks.
  • the reference picture list with the smaller absolute POC distances between PocDist0 and PocDist1 (wherein the two reference pictures are the two utilized in SMVD) is chosen.
  • PocDist0 is smaller than PocDist1
  • MVD of list 0 is signaled
  • MVD of list 1 is derived.
  • the reference picture list with the larger absolute POC distances between PocDist0 and PocDist1 (wherein the two reference pictures are the two utilized in SMVD) is chosen.
  • list X (X being 0 or 1) may be chosen.
  • one of the two target reference pictures is forward (i.e., its POC is smaller than the current POC) and the other is backward (i.e., its POC is larger than the current POC) .
  • all reference pictures in list 0 and list 1 may be checked in order to find a first reference picture whose POC is closest to the current POC among all the POCs of reference pictures which are smaller than the current POC, and a second reference picture whose POC is closest to the current POC among all the POCs of reference pictures which are bigger than the current POC.
  • SMVD is disabled. That is, the signaling of all SMVD related syntaxes are skipped.
  • both target reference picture indices could be found in either the first (searching forward in list 0 for the target reference picture in list 0, and searching backward in list 1 for the target reference picture in list 1) or second step (searching backward in list 0 for the target reference picture in list 0, and searching forward in list 1 for the target reference picture in list 1) ; or (not all are found in the first step, or in the second step) SMVD is disabled.
  • the target reference picture indices are reset to be unavailable (e.g. resetting RefIdxSymL0 and RefIdxSymL1 to -1) .
  • additional check of POC distances is added after the target reference picture derivation process and the target reference pictures may be reset to be unavailable (e.g., resetting RefIdxSymL0 and RefIdxSymL1 to -1) .
  • the target reference pictures used in SMVD may be derived with two dependent checks (one loop for each reference picture list) .
  • the first check is to find one reference picture in list X (X being 0 or 1) .
  • the second check to find one reference picture in list Y according to the output of the first check and reference pictures in list Y (Y being 1-X) .
  • the given order is the ascending/descending order of reference picture index.
  • the reference picture which has the smallest (or greatest) POC distance e.g., Abs (POC (reference picture) –POC (current picture)
  • RefInLX the target reference picture for list X
  • the target reference picture for list Y shall be with greater POC value compared to current picture.
  • the target reference picture for list Y shall be with smaller POC value compared to current picture.
  • the target reference picture for list Y shall be the one with the smallest POC distance compared to current picture among all backward (if RefInLX is forward) or forward reference pictures (if RefInLX is backward) in list Y.
  • SMVD Whether SMVD is allowed or not may depend on the coding information of the block.
  • the coding information may include MVD precision information, weights of the prediction samples in bi-prediction.
  • SMVD may be disallowed when unequal weights are selected for the bi-predicted blocks.
  • unequal weights mode may be disallowed in SMVD mode.
  • SMVD may be disallowed for certain MVD/MV precision.
  • AMVR may be disallowed in SMVD mode.
  • DMVR or/and other DMVD methods may be enabled in SMVD mode.
  • MV/MVD precision is N-pel
  • DMVR or/and other DMVD methods may be used to refine the MVD by mvdDmvr.
  • mvdDmvr is with M-pel precision.
  • N, M 1/16, 1/8, 1/4, 1/2, 1, 2, 4, 8, 16 etc.
  • M may be smaller than or equal to N.
  • MVD may be not signaled in SMVD mode, instead, DMVR or/and other DMVD methods may be applied to generate the MVD.
  • AMVR information may be not signaled, and the MV/MVD precision may be derived to be with a predefined value (e.g., MVD is with 1/4-pel precision) .
  • indication of whether DMVR or/and other DMVD methods are applied or not may be signaled in SMVD mode.
  • MVD may be not signaled.
  • such indication may be signaled for certain MV/MVD precisions.
  • such indication may be signaled for 1-pel or/and 4-pel MV/MVD precisions.
  • such indication may be signaled only when PocDist0 is equal to PocDist1 and Ref0 is a preceding picture and Ref1 is a following picture of the current picture in display order.
  • such indication may be signaled only when PocDist0 is equal to PocDist1 and Ref0 is a following picture and Ref1 is a preceding picture of the current picture in display order.
  • the coding information may include SMVD mode information, motion information of the block.
  • all-zero MVD may be disallowed in SMVD mode.
  • vertical MVD may be decreased by 1 (e.g. if vertical MVD is positive) or increased by 1 (e.g. if vertical MVD is negative) before encoding and may be increased by 1 (if vertical MVD is positive) or decreased by 1 (if vertical MVD is negative) after decoding.
  • horizontal MVD may be decreased by 1 (e.g. if horizontal MVD is positive) or increased by 1 (e.g. if horizontal MVD is negative) before encoding and may be increased by 1 (if horizontal MVD is positive) or decreased by 1 (if horizontal MVD is negative) after decoding.
  • all-zero MVD may be disallowed in non-SMVD mode.
  • K MVD components in total in non-SMVD mode if the first K –1 MVD components are zero. Then, instead of directly encoding the Kth MVD component, it may be decreased by 1 (e.g. if it is positive) or increased by 1 (e.g. if it is negative) before encoding and may be increased by 1 (e.g. if it is positive) or decreased by 1 (e.g. if it is negative) after decoding.
  • one reference picture is from list 0 and the other from list 1.
  • one reference picture is a forward reference picture from list 0 and the other is a backward reference picture from list 1.
  • one reference picture is a backward reference picture from list 0 and the other is a forward reference picture from list 1.
  • one reference picture is a backward reference picture and the other is a forward reference picture, with both from the same reference picture list.
  • target reference pictures may be selected according to the POC distances to the current picture, such as using current way, or the above methods.
  • currPocDiffL0 ! currPocDiffL1
  • SMVD related syntax elements such as sym_mvd_flag
  • SMVD is inferred not be used.
  • a coding method which derives the MVD of reference picture list X from the signaled MVD of reference picture list Y (with Y being 1-X) according to POC values of two reference pictures and current picture.
  • the signaled MVD for reference picture list Y is MvdLY with its horizontal and vertical component denoted by MvdLY [0] and MvdLY [1]
  • the MVD for reference picture list X denoted by (MvdLX [0] , MvdLX [1] ) may be derived by the following method:
  • MvdLX [0] MvdLY [0] * (POC (targetRef in List X) -POC(current picture) ) / (POC (targetRef in List Y) -POC (current picture) ) .
  • MvdLX [1] MvdLY [1] * (POC (targetRef in List X) -POC(current picture) ) / (POC (targetRef in List Y) -POC (current picture) ) .
  • the above methods may be applied to the SMVD mode wherein instead of always using the opposite MVD of list 0 as the MVD for list 1, it is proposed to scale the MVD of list 0 according to POC distances when deriving the MVD of list 1.
  • the above methods may be applicable the symmetric MV coding mode wherein the information of MV of one reference picture list may not be signaled but derived from the other reference picture list via scaling.
  • the x component and/or the y component of the second MVD derived from the first MVD with the SMVD method should be in a predefined range.
  • the x component and/or the y component of the second MVD should be clipped or conditionally modified according to a predefined range.
  • N is an integer such as 16 or 18.
  • N may be 15 or 17.
  • N is an integer such as 16 or 18.
  • N may be 15 or 17.
  • N is an integer such as 16 or 18.
  • N may be 15 or 17.
  • the x component and/or the y component of the second MVD should be within a predefine range in a conformance bit-stream.
  • the x component and/or the y component of the second MVD should be within the range of [-2 N , 2 N -1] inclusively in a conformance bit-stream.
  • N is an integer such as 16 or 18.
  • N may be 15 or 17.
  • the x component and/or the y component of the second MVD should be within the range of [-2 N +1, 2 N -1] inclusively in a conformance bit-stream.
  • N is an integer such as 16 or 18.
  • N may be 15 or 17.
  • the x component and/or the y component of the first MVD should be clipped or conditionally modified according to a first predefined range so that the x component and/or the y component of the second MVD derived from the first MVD with the SMVD method can be in a second predefined range.
  • N is an integer such as 16 or 18.
  • N may be 15 or 17.
  • N is an integer such as 16 or 18.
  • N may be 15 or 17.
  • the x component and/or the y component of the first MVD should be within a first predefine range in a conformance bit-stream so that the x component and/or the y component of the second MVD derived from the first MVD with the SMVD method can be in a second predefined range.
  • the first predefine range may be different to the predefine range fir the signaled MVD when SMVD is not applied.
  • the x component and/or the y component of the first MVD should be within the range of [-2 N +1, 2 N -1] inclusively in a conformance bit-stream.
  • N is an integer such as 16 or 18.
  • N may be 15 or 17.
  • the MVD range for SMVD (or other tools that derives MVD from another reference picture list) may be set differently from those MVDs for non-SMVD coding tools.
  • the signaled MVD to be within [-2 N +SMVDFlag, 2 N -1] , wherein SMVDFlag is equal to 1 SMVD is applied and SMVDFlag is equal to 0 if SMVD is not applied.
  • the clipping or constraint on MVD may be performed before the MVD is modified according to the MV resolution.
  • the clipping or constraint on MVD may be performed after the MVD is modified according to the MV resolution.
  • the clipping or constraint on MVD may depend on the MV resolution.
  • VVC working draft version 5 The changes on top of VVC working draft version 5 are highlighted in bold face italics. Deleted texts are marked with strikethrough.
  • RefIdxSymL0 and RefIdxSymL0 specifying the list 0 and list 1 reference picture indices for symmetric motion vector differences, i.e., when sym_mvd_flag is equal to 1 for a coding unit.
  • variable currPic specifies the current picture.
  • RefIdxSymL0 is set equal to -1.
  • RefIdxSymL0 is set to i:
  • DiffPicOrderCnt (currPic, RefPicList [0] [i] ) ⁇ DiffPicOrderCnt (currPic, RefPicList [0] [RefIdxSymL0] ) or RefIdxSymL0 is equal to -1.
  • RefIdxSymL1 is set equal to -1.
  • RefIdxSymL1 is set to i:
  • RefIdxSymL0 is equal to -1 and or RefIdxSymL1 is equal to -1, the following applies:
  • RefIdxSymL0 is set to i:
  • RefIdxSymL1 is set to i:
  • DiffPicOrderCnt (currPic, RefPicList [1] [i] ) ⁇ DiffPicOrderCnt (currPic, RefPicList [1] [RefIdxSymL1] ) or RefIdxSymL1 is equal to -1.
  • RefIdxSymL0 and RefIdxSymL0 specifying the list 0 and list 1 reference picture indices for symmetric motion vector differences, i.e., when sym_mvd_flag is equal to 1 for a coding unit.
  • variable currPic specifies the current picture.
  • RefIdxSymL0 is set equal to -1.
  • RefIdxSymL0 is set to i:
  • DiffPicOrderCnt (currPic, RefPicList [0] [i] ) ⁇ DiffPicOrderCnt (currPic, RefPicList [0] [RefIdxSymL0] ) or RefIdxSymL0 is equal to -1.
  • RefIdxSymL1 is set equal to -1.
  • RefIdxSymL1 is set to i:
  • RefIdxSymL0 is equal to -1 or RefIdxSymL1 is equal to -1, the following applies:
  • RefIdxSymL0 is set equal to -1 and RefIdxSymL1 is set equal to -1
  • RefIdxSymL0 is set to i:
  • RefIdxSymL1 is set to i:
  • DiffPicOrderCnt (currPic, RefPicList [1] [i] ) ⁇ DiffPicOrderCnt (currPic, RefPicList [1] [RefIdxSymL1] ) or RefIdxSymL1 is equal to -1.
  • RefIdxSymL0 and RefIdxSymL0 specifying the list 0 and list 1 reference picture indices for symmetric motion vector differences, i.e., when sym_mvd_flag is equal to 1 for a coding unit.
  • variable currPic specifies the current picture.
  • RefIdxSymL0 is set equal to -1.
  • RefIdxSymL0 is set to i:
  • DiffPicOrderCnt (currPic, RefPicList [0] [i] ) ⁇ DiffPicOrderCnt (currPic, RefPicList [0] [RefIdxSymL0] ) or RefIdxSymL0 is equal to -1.
  • RefIdxSymL1 is set equal to -1.
  • RefIdxSymL1 is set to i:
  • RefIdxSymL0 is equal to -1 or RefIdxSymL1 is equal to -1, the following applies:
  • RefIdxSymL0 is set to i:
  • RefIdxSymL1 is set to i:
  • DiffPicOrderCnt (currPic, RefPicList [1] [i] ) ⁇ DiffPicOrderCnt (currPic, RefPicList [1] [RefIdxSymL1] ) or RefIdxSymL1 is equal to -1.
  • RefIdxSymL0 is set to -1 and RefIdxSymL1 is set to -1:
  • RefIdxSymL0 is set to -1 and RefIdxSymL1 is set to -1:
  • mvd_sign_flag [compIdx] specifies the sign of a motion vector component difference as follows:
  • lMvd [compIdx] shall be in the range of -2 15 to 2 15 -1, inclusive.
  • MvdL1 [x0] [y0] [0] and MvdL1 [x0] [y0] [1] shall be in the range of -215 to 215 -1, inclusive, after they are derived as:
  • FIG. 14 is a block diagram of a video processing apparatus 1400.
  • the apparatus 1400 may be used to implement one or more of the methods described herein.
  • the apparatus 1400 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on.
  • the apparatus 1400 may include one or more processors 1402, one or more memories 1404 and video processing hardware 1406.
  • the processor (s) 1402 may be configured to implement one or more methods described in the present document.
  • the memory (memories) 1404 may be used for storing data and code used for implementing the methods and techniques described herein.
  • the video processing hardware 1406 may be used to implement, in hardware circuitry, some techniques described in the present document.
  • FIG. 15 is a flowchart for an example method 1500 of video processing.
  • the method 1500 includes determining (1502) to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures.
  • the method 1500 includes performing (1504) the conversion using the SMVD mode.
  • the bitstream representation indicates to disable use of a motion vector difference (MVD) mode for one of the reference list 0 or the reference list 1.
  • a method of video processing comprising: determining to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures; and performing the conversion using the SMVD mode; wherein the bitstream representation indicates to disable use of a motion vector difference (MVD) mode for one of the reference list 0 or the reference list 1.
  • SMVD symmetric motion vector difference
  • bitstream representation indicates to disable use of the MVD mode for reference list 1
  • the conversion includes deriving a motion candidate corresponding to the reference list 1 from a motion candidate corresponding to the reference list 0 using a relationship.
  • a method of video processing comprising: determining to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in pictures from two target reference pictures from a reference list 0 and a reference list 1 of reference pictures; and performing the conversion using the SMVD mode; wherein the bitstream representation includes a motion vector difference (MVD) information for the reference list 1.
  • SMVD symmetric motion vector difference
  • a method of video processing comprising: determining to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in pictures from a reference list 0 and a reference list 1 of reference pictures; and performing the conversion using the SMVD mode; wherein the SMVD generates the two additional motion candidates using a first step in which each reference picture list is parsed to identify target reference pictures.
  • SMVD symmetric motion vector difference
  • a method of video processing comprising: determining to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures; and performing the conversion using the SMVD mode; wherein the SMVD generates the two additional motion candidates such that: both target reference picture indices are found in either a first step that includes searching forward in list 0 for the target reference picture in list 0, and searching backward in list 1 for the target reference picture in list 1, or in a second step that includes searching backward in list 0 for the target reference picture in list 0, and searching forward in list 1 for the target reference picture in list 1.
  • SMVD symmetric motion vector difference
  • a method of video processing comprising: determining to use, for a conversion between a current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures; and performing the conversion using the SMVD mode; wherein one of the two target reference picture has a picture order count greater than that of the current video block and another of the two target reference pictures has a picture order count less than that of the current video block.
  • SMVD symmetric motion vector difference
  • the SMVD mode further includes a step of ascertaining distances between picture order counts of the current video block and the two target reference pictures.
  • a method of video processing comprising: determining, based on a condition, whether or not to use a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures, for a conversion between a current video block and a bitstream representation of the current video block; and performing the conversion based on the determining.
  • SMVD symmetric motion vector difference
  • a method of video processing comprising: determining, based on a condition to use a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures, and a decoder side motion vector difference (DMVD) coding mode for a conversion between a current video block and a bitstream representation of the current video block; and performing the conversion based on the determining.
  • SMVD symmetric motion vector difference
  • DMVD decoder side motion vector difference
  • a method of video processing comprising: determining, based on a condition, whether or not to use an all-zero motion vector difference for a symmetric motion vector difference (SMVD) mode in which two additional motion candidates generated for the conversion based on symmetric displacement of reference blocks in two target reference pictures from a reference list 0 and a reference list 1 of reference pictures, and a decoder side motion vector difference (DMVD) coding mode for a conversion between a current video block and a bitstream representation of the current video block; and performing the conversion based on the determining.
  • SMVD symmetric motion vector difference
  • DMVD decoder side motion vector difference
  • a method for video processing comprising selecting a first reference picture and a second reference picture from a plurality of reference pictures associated with a current video block, and performing, based on the selected first and second reference pictures, a conversion between the current video block and a bitstream representation of the current video block, wherein a first distance between the first reference picture and a current picture comprising the current video block and a second distance between the second reference picture and the current picture are equal.
  • a method for video processing comprising determining that a first distance between a first reference picture and a current picture comprising a current video block and a second distance between a second reference picture and the current picture are unequal, and disabling, based on the determining and for a conversion between the current video block and a bitstream representation of the current video block, a symmetric motion vector difference (SMVD) mode for the current video block.
  • SMVD symmetric motion vector difference
  • bitstream representation excludes signaling one or more SMVD related syntax elements.
  • a method for video processing comprising deriving, for a current video block, a first motion vector difference (MVD) of a first reference picture list based on a second MVD of a second reference picture list, and performing, based on the deriving, a conversion between the current video block and a bitstream representation of the current video block, wherein the a range of the first MVD is restricted.
  • MVD motion vector difference
  • a video processing apparatus comprising a processor configured to implement one or more of examples 1 to 42.
  • a computer-readable medium having code stored thereon, the code, when executed by a processor, causing the processor to implement a method recited in any one or more of examples 1 to 42.
  • FIG. 16 is a flowchart for an example method 1600 of video processing.
  • the method 1600 includes, at 1602, determining, for a conversion between a block of current picture of video and a bitstream representation of the first block, whether a symmetric motion vector difference (SMVD) mode is allowable for the block based on coding information of the block; and at 1604, performing the conversion based on the determination.
  • SMVD symmetric motion vector difference
  • X 0.
  • the SMVD mode is allowed for the block.
  • the flag indicates the MVD in the reference list 1 is forced to be zero the MVD in the reference list 1 is forced to be zero, and the SMVD mode is allowed for the block.
  • the MVD in the reference list 1 when the flag indicates the MVD in the reference list 1 is forced to be zero, the MVD in the reference list 1 is not forced to be zero, but is derived from associated MVD in reference list 0, and the SMVD mode is allowed for the block.
  • the SMVD mode is disallowed for the block.
  • all related syntax elements for the SMVD mode are implicitly derived instead of being signaled.
  • the reference list Y for which the MVD need to be signaled is signaled by an indication of in the bitstream.
  • the indication is signaled in at least one of the sequence, picture, slice, tile, video unit level.
  • the indication is signaled in at least one of sequence parameter set (SPS) and picture parameter set (PPS) , picture header, slice header, and tile group header.
  • SPS sequence parameter set
  • PPS picture parameter set
  • the reference list Y for which the MVD need to be signaled is derived according to reference pictures in the reference lists.
  • the reference list Y for which the MVD need to be signaled is derived according to two reference pictures in the two reference lists and corresponding two parameters of Abs (currPocDiffL0) and Abs (currPocDiffL1) , where Abs (currPocDiffL0) indicates an absolute value of POC (picture order count) distance from the current picture to the reference picture in the reference list 0, and Abs (currPocDiffL1) indicates an absolute value of POC distance from the current picture to the reference picture in the reference list 1.
  • MVD for the reference list 0 is signaled, otherwise, MVD for the reference list 1 is signaled.
  • MVD for the reference list 1 is signaled, otherwise, MVD for the reference list 0 is signaled.
  • MVD for the reference list 0 is signaled, otherwise, MVD for the reference list 1 is signaled.
  • MVD for the reference list 1 is signaled, otherwise, MVD for the reference list 0 is signaled.
  • MVD for the reference list 0 is signaled, otherwise, MVD for the reference list 1 is signaled.
  • MVD for the reference list 1 is signaled, otherwise, MVD for the reference list 0 is signaled.
  • the reference list Y for which the MVD need to be signaled is changed from one video unit to another video unit.
  • the video unit includes at least one of slice, tile group, tile, brick and coding unit (CU) .
  • CU coding unit
  • selection of the reference list Y depends on reference pictures information of neighboring blocks of the block.
  • selection of the reference list Y depends on two reference pictures in the two reference lists and corresponding two parameters of PocDist0 and PocDist1, where PocDist0 is absolute value of picture order count (POC) distance from the reference picture in reference list 0 to the current picture, and PocDist1 is absolute value of POC distance from the reference picture in reference list 1 to the current picture.
  • POC picture order count
  • the reference list with a smaller absolute value of POC distances between PocDist0 and PocDist1 is selected as the reference list Y.
  • the reference list with a larger absolute value of POC distances between PocDist0 and PocDist1 is selected as the reference list Y.
  • either the reference list 0 or the reference list 1 is selected as the reference list Y.
  • two reference pictures both are selected from one same reference list.
  • one of the two reference pictures is forward reference picture whose POC is smaller than the current POC and the other is backward reference picture whose POC is larger than the current POC.
  • all reference pictures in the reference list 0 and the reference list 1 are checked in order to find a first reference picture whose POC is closest to the current POC among all the POCs of reference pictures which are smaller than the current POC, and a second reference picture whose POC is closest to the current POC among all the POCs of reference pictures which are larger than the current POC.
  • the SMVD mode includes a derivation process of target reference pictures, which includes a first step for searching a forward target reference picture in the reference list 0, and searching a backward target reference picture in the reference list 1, and a second step for searching a backward target reference picture in the reference list 0, and searching a forward target reference picture in the reference list 1.
  • the second step of the SMVD mode is skipped.
  • the second step of the SMVD mode is skipped.
  • the second step of the SMVD mode is skipped.
  • the SMVD mode is disallowed, and signaling of all SMVD related syntaxes are skipped.
  • the two target reference pictures found in the derivation process of target reference pictures include a forward reference picture whose POC is smaller than the current picture and a backward reference picture whose POC is larger than the current picture.
  • POC of the two target reference pictures are checked, and the target reference pictures are reset to be unavailable if the two target reference pictures both have smaller POCs than the current picture or larger POCs than the current picture.
  • the target reference pictures can be reset to be unavailable by resetting RefIdxSymL0 and RefIdxSymL1 to -1, where RefIdxSymL0 is index of the target reference picture in the reference list 0, and RefIdxSymL1 is index of the target reference picture in the reference list 0.
  • the SMVD mode includes a derivation process of target reference pictures, which removes the restriction of finding forward reference picture from reference list 0 and backward reference picture from reference list 1, or finding forward reference picture from reference list 1 and backward reference picture from reference list 0.
  • the target reference pictures used in SMVD mode are derived with two dependent checks including a first check and a second check, each check being used for one of the reference list 0 and the reference list 1.
  • the first check is to find one reference picture in the reference list X, where X being 0 or 1
  • POC distances between each reference pictures and the current picture are calculated regardless it is forward or backward according to a given order.
  • the given order is the ascending or descending order of reference picture index.
  • the reference picture which has the smallest POC distance is selected as the target reference picture for the reference list X and denoted by RefInLX.
  • the reference picture which has the greatest POC distance is selected as the target reference picture for the reference list X and denoted by RefInLX.
  • one reference picture is selected from the reference list Y according to the reference picture RefInLX as the target reference picture for the reference list Y.
  • the target reference picture for the reference list Y has a larger POC distance compared to the current picture.
  • the target reference picture for the reference list Y has a smaller POC distance compared to the current picture.
  • the target reference picture for the reference list Y is the one with the smallest POC distance compared to the current picture among all backward reference pictures.
  • the target reference picture for the reference list Y is the one with the smallest POC distance compared to the current picture among all forward reference pictures.
  • the coding information includes at least one of motion vector (MV) information, MVD precision information for the block and weights of prediction samples in bi-prediction.
  • MV motion vector
  • the SMVD mode is disallowed when unequal weights are selected for the bi-predicted blocks.
  • all related syntax elements related to the SMVD mode are not signaled and/or implicitly derived.
  • unequal weights are disallowed in the SMVD mode.
  • all syntax elements related to the unequal weights are not signaled and/or implicitly derived.
  • the SMVD mode is disallowed for certain MVD precision and/or MV precision.
  • N 1/4.
  • Adaptive motion vector difference resolution is disallowed in the SMVD mode.
  • decoder-side motion vector refinement or/and other decoder-side motion vector derivation (DMVD) methods are enabled in the SMVD mode.
  • DMVD decoder-side motion vector derivation
  • MV and/or MVD precision is N-pel
  • M is smaller than or equal to N.
  • the MVD in the SMVD mode, is derived by DMVR or/and other DMVD methods instead of being signaled.
  • AMVR information is not signaled, and the MV/MVD precision is derived to be with a predefined value, where the predefined value is 1/4-pel precision.
  • indication of whether DMVR or/and other DMVD methods are applied or not is signaled.
  • MVD is not signaled if DMVR or/and other DMVD methods are applied.
  • the indication is signaled for certain MV and/or MVD precisions.
  • the indication is signaled for 1-pel or/and 4-pel MV and/or MVD precisions.
  • the indication is signaled only when PocDist0 is equal to PocDist1, wherein PocDist0 is the POC distance between the current picture and Ref0 and PocDist1 is the POC distance between the current picture and Ref1, and Ref0 is a preceding picture and Ref1 is a following picture of the current picture in display order.
  • the indication is signaled only when PocDist0 is equal to PocDist1, wherein PocDist0 is the POC distance between the current picture and Ref0 and PocDist1 is the POC distance between the current picture and Ref1, and Ref0 is a following picture and Ref1 is a preceding picture of the current picture in display order.
  • whether all-zero MVD is allowed or not depends on the coding information of the block including SMVD mode information and motion information of the block.
  • all-zero MVD is disallowed in the SMVD mode.
  • vertical MVD is decreased by 1 if vertical MVD is positive or increased by 1 if vertical MVD is negative before encoding, and is increased by 1 if vertical MVD is positive or decreased by 1 if vertical MVD is negative after decoding.
  • horizontal MVD is decreased by 1 if horizontal MVD is positive or increased by 1 if horizontal MVD is negative before encoding, and is increased by 1 if horizontal MVD is positive or decreased by 1 if horizontal MVD is negative after decoding.
  • a higher priority is given to find two target reference pictures with the equal distance to the current picture instead of finding the closest reference pictures.
  • N when there are N pairs of reference pictures in the reference list 0 and the reference list 1, denoted by (RefL0i, RefL1i) with i being [0, N-1] , one of the N pairs is selected as the target two reference pictures used in the SMVD mode, where N is an integer.
  • one reference picture is from the reference list 0 and the other is from the reference list 1.
  • one reference picture is a forward reference picture from the reference list 0 and the other is a backward reference picture from the reference list 1.
  • one reference picture is a backward reference picture from the reference list 0 and the other is a forward reference picture from the reference list 1.
  • one reference picture is a backward reference picture and the other is a forward reference picture, with both from the same reference picture list.
  • N there are N pairs of reference pictures in the reference list 0 and the reference list 1, denoted by (RefL0i, RefL1i) with i being [0, N-1]
  • one of the N pairs with the smallest or largest absolute value of POC distances to the current picture is selected as the target two reference pictures used in the SMVD mode, where N is an integer.
  • target reference pictures are selected according to the POC distances to the current picture.
  • the SMVD mode is disallowed.
  • signaling of SMVD related syntax elements including sym_mvd_flag is skipped and the SMVD mode is inferred not be used.
  • the MVD of the reference picture list X is derived from the signaled MVD of reference picture list Y according to POC distances of two reference pictures and the current picture.
  • the MVD for the reference list Y is MvdLY with its horizontal and vertical component denoted by MvdLY [0] and MvdLY [1]
  • the MVD for the reference list X denoted by (MvdLX [0] , MvdLX [1] ) is derived as following:
  • MvdLX [0] MvdLY [0] * (POC (targetRef in List X) -POC (current picture) ) / (POC (targetRef in List Y) -POC (current picture) ) , and
  • MvdLX [1] MvdLY [1] * (POC (targetRef in List X) -POC (current picture) ) / (POC (targetRef in List Y) -POC (current picture) ) ,
  • POC targetRef in List X
  • POC targetRef in List Y
  • POC current picture
  • FIG. 17 is a flowchart for an example method 1700 of video processing.
  • the method 1700 includes, at 1702, determining, determining, for a conversion between a block of video and a bitstream representation of the first block, whether a symmetric motion vector (SMV) mode is allowable for the block according to the method of previous examples; and at 1704, performing the conversion based on the determination.
  • SMV symmetric motion vector
  • FIG. 18 is a flowchart for an example method 1800 of video processing.
  • the method 1800 includes, at 1802, determining, for a conversion between a block of a current picture of video and a bitstream representation of the block, whether a symmetric motion vector difference (SMVD) mode is allowable for the block, wherein whether the SMVD mode is allowable depends on a derivation process of two target reference pictures of the current picture, which includes a first step for searching a forward target reference picture in the reference picture list 0 and searching a backward target reference picture in the reference picture list 1, and a second step for searching a backward target reference picture in the reference picture list 0 and searching a forward target reference picture in the reference picture list 1, outputs of the first step and the second step being independent of each other; and at 1804, performing the conversion based on the determination.
  • SMVD symmetric motion vector difference
  • whether the SMVD mode is allowable is depends on whether both the target reference pictures are found in one step of the first step and the second step.
  • the SMVD mode is allowed.
  • the SMVD mode is allowed.
  • the SMVD mode is disallowed.
  • the second step is invoked.
  • both the target reference picture indices are reset to be unavailable.
  • the indices of the two target reference pictures include variables of RefIdxSymL0 and RefIdxSymL1, with RefIdxSymL0 indicating the target reference picture index in the reference picture list 0 and RefIdxSymL1 indicating the target reference picture index in the reference picture list 1.
  • resetting both the target reference picture indices to be unavailable comprises resetting both RefIdxSymL0 and RefIdxSymL1 to -1.
  • FIG. 19 is a flowchart for an example method 1900 of video processing.
  • the method 1900 includes, at 1902, deriving, for a conversion between a block of a current picture of video and a bitstream representation of the block, a second motion vector difference (MVD) of one reference picture list from a first MVD associated with the other reference picture list, wherein an MVD includes both a horizontal component and a vertical component; and at 1904, applying a range restriction on at least one of the first MVD and the second MVD; and at 1906, performing the conversion based on the determination.
  • MVD motion vector difference
  • the first MVD is included in the bitstream representation of the block.
  • the second MVD is derived from the first MVD in a symmetric motion vector difference (SMVD) mode.
  • SMVD symmetric motion vector difference
  • the horizontal component and/or the vertical component of the derived second MVD are restricted in a predefined range.
  • the horizontal component and/or the vertical component of the derived second MVD are clipped or conditionally modified according to the predefined range.
  • N 15, 16, 17 or 18.
  • N 15, 16, 17 or 18.
  • N 15, 16, 17 or 18.
  • the horizontal component and/or the vertical component of the derived second MVD are within a predefine range in a conformance bitstream.
  • the horizontal component and/or the vertical component of the derived second MVD are within the range of [-2 N , 2 N -1] inclusively in a conformance bitstream.
  • N 15, 16, 17 or 18.
  • the horizontal component and/or the vertical component of the derived second MVD are within the range of [-2 N +1, 2 N -1] inclusively in a conformance bitstream.
  • N 15, 16, 17 or 18.
  • the horizontal component and/or the vertical component of the first MVD are clipped or conditionally modified according to a first predefined range so that the horizontal component and/or the vertical component of the derived second MVD are in a second predefined range.
  • N 15, 16, 17 or 18.
  • N 15, 16, 17 or 18.
  • the horizontal component and/or the vertical component of the first MVD are within a first predefined range so that the horizontal component and/or the vertical component of the derived second MVD are in a second predefined range in a conformance bitstream.
  • the first predefined range is different to the predefined range for a signaled MVD wherein the SMVD mode is not applied.
  • the horizontal component and/or the vertical component of the first MVD is within the range of [-2 N +1, 2 N -1] inclusively in a conformance bitstream, N being an integer.
  • N 15, 16, 17 or 18.
  • the horizontal component and/or the vertical component of the first MVD is within the range of [-2 N +1, 2 N -1] inclusively in a conformance bitstream, N being an integer.
  • the first MVD is a signaled MVD
  • the range of the signaled MVD is set differently for SMVD mode or other tools that derives MVD from another reference picture list and for non-SMVD coding tools.
  • the signaled MVD is within a range of [-2 N +SMVDFlag, 2 N -1] , wherein SMVDFlag is equal to 1 when the SMVD mode is applied and SMVDFlag is equal to 0 when SMVD mode is not applied.
  • clipping or constraint on the MVD is performed before the MVD is modified according to precision of MV associated with the MVD.
  • clipping or constraint on the MVD is performed after the MVD is modified according to precision of MV associated with the MVD.
  • clipping or constraint on the MVD depend on precision of MV associated with the MVD.
  • the conversion generates the block of video from the bitstream representation.
  • the conversion generates the bitstream representation from the block of video.
  • the term conversion may refer to the generation of the bitstream representation for the current video block or generating the current video block from the bitstream representation.
  • the bitstream representation need not represent a contiguous group of bits and may be divided into bits that are included in header fields or in codewords representing coded pixel value information.
  • the applicability rule may be pre-defined and known to encoders and decoders.
  • the disclosed techniques may be embodied in video encoders or decoders to improve compression efficiency using techniques that include the use of various implementation rules of considerations regarding the use of a differential coding mode in intra coding, as described in the present document.
  • the disclosed and other solutions, examples, embodiments, modules and the functional operations described in this document can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this document and their structural equivalents, or in combinations of one or more of them.
  • the disclosed and other embodiments can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a computer readable medium for execution by, or to control the operation of, data processing apparatus.
  • the computer readable medium can be a machine-readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more them.
  • data processing apparatus encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers.
  • the apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.
  • a propagated signal is an artificially generated signal, e.g., a machine-generated electrical, optical, or electromagnetic signal, that is generated to encode information for transmission to suitable receiver apparatus.
  • a computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.
  • a computer program does not necessarily correspond to a file in a file system.
  • a program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document) , in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code) .
  • a computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.
  • the processes and logic flows described in this document can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output.
  • the processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit) .
  • processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer.
  • a processor will receive instructions and data from a read only memory or a random-access memory or both.
  • the essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data.
  • a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks.
  • mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks.
  • a computer need not have such devices.
  • Computer readable media suitable for storing computer program instructions and data include all forms of non-volatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto optical disks; and CD ROM and DVD-ROM disks.
  • semiconductor memory devices e.g., EPROM, EEPROM, and flash memory devices
  • magnetic disks e.g., internal hard disks or removable disks
  • magneto optical disks e.g., CD ROM and DVD-ROM disks.
  • the processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

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