WO2020016859A2 - Motion prediction based on updated motion vectors - Google Patents

Abstract

A method for video processing, comprising: determining a current block with motion vectors; generating updated motion vectors based on specific prediction mode; and performing, based on the updated motion vectors, a conversion between the current block and a bitstream representation of a video data including the current block, wherein the specific prediction mode includes one or more of bi-directional optical flow (BIO) refinement, a decoder-side motion vector refinement (DMVR), frame-rate up conversion (FRUC) techniques or a template matching technique.

Description

MOTION PREDICTION BASED ON UPDATED MOTION VECTORS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Under the applicable patent law and/or rules pursuant to the Paris Convention, this application is made to claim the priority to and benefit of International Patent Application No. PCT/CN2018/096384, filed on July 20, 2018, entitled“MOTION PREDICTION BASED ON UPDATED MOTION VECTORS”. The entire disclosure of International Patent

Application No. PCT/CN2018/096384 is incorporated by reference as part of the disclosure of this application.

TECHNICAL FIELD

[0002] This patent document relates to video encoding and decoding techniques, devices and systems.

BACKGROUND

[0003] In spite of the advances in video compression, digital video still accounts for the largest bandwidth use on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, it is expected that the bandwidth demand for digital video usage will continue to grow.

SUMMARY

[0004] Devices, systems and methods related to digital video coding, and specifically, motion prediction based on updated motion vectors 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.

In one representative aspect, the disclosed technology may be used to provide a method for video processing. This method includes: determining a current block with motion vectors; generating updated motion vectors based on specific prediction mode; and performing, based on the updated motion vectors, a conversion between the current block and a bitstream representation of a video data including the current block, wherein the specific prediction mode includes one or more of bi-directional optical flow (BIO) refinement, a decoder-side motion vector refinement (DMVR), frame-rate up conversion (FRUC) techniques or a template matching technique. [0005] In another representative aspect, the disclosed technology may be used to provide processing video data. This method includes: determining a current block and corresponding neighboring blocks; and constructing a final prediction block of the current block as weighted sum of a prediction block derived from a motion vector of the current block and prediction blocks derived from motion vectors of one or more of neighboring blocks; and performing, based on the final prediction block of the current block, a conversion between the current block and a bitstream representation of a video data including the current block; wherein a short-tap interpolation filter is used for constructing the final prediction block of the current block.

[0006] In yet another representative aspect, the above- described method is embodied in the form of processor-executable code and stored in a computer-readable program medium.

[0007] In yet another representative aspect, a device that is configured or operable to perform the above-described method is disclosed. The device may include a processor that is

programmed to implement this method.

[0008] In yet another representative aspect, a video decoder apparatus may implement a method as described herein.

[0009] The above and other aspects and features of the disclosed technology are described in greater detail in the drawings, the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 shows an example of constructing a merge candidate list.

[0011] FIG. 2 shows an example of positions of spatial candidates.

[0012] FIG. 3 shows an example of candidate pairs subject to a redundancy check of spatial merge candidates.

[0013] 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.

[0014] FIG. 5 shows an example of motion vector scaling for temporal merge candidates.

[0015] FIG. 6 shows an example of candidate positions for temporal merge candidates.

[0016] FIG. 7 shows an example of generating a combined bi-predictive merge candidate.

[0017] FIG. 8 shows an example of constructing motion vector prediction candidates.

[0018] FIG. 9 shows an example of motion vector scaling for spatial motion vector candidates. [0019] FIG. 10 shows an example of motion prediction using the alternative temporal motion vector prediction (ATMVP) algorithm for a coding unit (CU).

[0020] 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.

[0021] FIGS. 12A and 12B show example snapshots of sub-block when using the overlapped block motion compensation (OBMC) algorithm.

[0022] FIG. 13 shows an example of neighboring samples used to derive parameters for the local illumination compensation (LIC) algorithm.

[0023] FIG. 14 shows an example of a simplified affine motion model.

[0024] FIG. 15 shows an example of an affine motion vector field (MVF) per sub-block.

[0025] FIG. 16 shows an example of motion vector prediction (MVP) for the AF INTER affine motion mode.

[0026] FIGS. 17A and 17B show example candidates for the AF MERGE affine motion mode.

[0027] FIG. 18 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.

[0028] FIG. 19 shows an example of template matching in the FRUC algorithm.

[0029] FIG. 20 shows an example of unilateral motion estimation in the FRUC algorithm.

[0030] FIG. 21 shows an example of an optical flow trajectory used by the bi-directional optical flow (BIO) algorithm.

[0031] FIGS. 22A and 22B show example snapshots of using of the bi-directional optical flow (BIO) algorithm without block extensions.

[0032] FIG. 23 shows an example of the decoder-side motion vector refinement (DMVR) algorithm based on bilateral template matching.

[0033] FIG. 24 shows an example of a template definition used in transform coefficient context modelling.

[0034] FIG. 25 shows an example of inner and boundary sub-blocks in a PU/CU.

[0035] FIG. 26 shows a flowchart of an example method for video coding in accordance with the presently disclosed technology.

[0036] FIG. 27 shows a flowchart of another example method for video coding in accordance with the presently disclosed technology.

[0037] FIG. 28 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.

[0038] FIG. 29 shows a flowchart of yet another example method for video processing in accordance with the presently disclosed technology.

[0039] FIG. 30 shows a flowchart of yet another example method for processing video data in accordance with the presently disclosed technology.

DETAILED DESCRIPTION

[0040] Due to the increasing demand of higher resolution video, video coding methods and techniques are ubiquitous in modern technology. 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. There are complex relationships between the video quality, the amount of data used to represent the video (determined by the bit rate), the complexity of the encoding and decoding algorithms, sensitivity to data losses and errors, ease of editing, random access, and end-to-end delay (latency). 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.

[0041] 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.

1. Examples of inter-prediction in HEVC/H.265

[0042] 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.

1.1 Examples of prediction modes [0043] Each inter-predicted PU (prediction unit) has motion parameters for one or two reference picture lists. In some embodiments, motion parameters include a motion vector and a reference picture index. In other embodiments, the usage of one of the two reference picture lists may also be signaled using inter _predjdc. In yet other embodiments, motion vectors may be explicitly coded as deltas relative to predictors.

[0044] When a CU is coded with skip mode, one PU is associated with the CU, and there are no significant residual coefficients, no coded motion vector delta or reference picture index. 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.

[0045] 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.

[0046] 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.

1.1.1 Embodiments of constructing candidates for merge mode

[0047] When a PU is predicted using merge mode, an index pointing to an entry in the merge candidates list is parsed from the bitstream and used to retrieve the motion information. The construction of this list can be summarized according to the following sequence of steps:

[0048] Step 1 : Initial candidates derivation

[0049] Step 1.1 : Spatial candidates derivation

[0050] Step 1.2: Redundancy check for spatial candidates

[0051] Step 1.3: Temporal candidates derivation

[0052] Step 2: Additional candidates insertion

[0053] Step 2.1 : Creation of bi-predictive candidates

[0054] Step 2.2: Insertion of zero motion candidates

[0055] 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. For 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 2Nx2N prediction unit.

1.1.2 Constructing spatial merge candidates

[0056] In the derivation of spatial merge candidates, a maximum of four merge candidates are selected among candidates located in the positions depicted in FIG. 2. The order of derivation is Ai_, Bi_, Bo_, Ao and B₂. Position B₂ is considered only when any PU of position Ai, Bi, B₀, A₀ is not available (e.g. because it belongs to another slice or tile) or is intra coded. After candidate at position Ai 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.

[0057] 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. 3 are considered and a candidate is only added to the list if the corresponding candidate used for redundancy check has not the same motion information. Another source of duplicate motion information is the“ second PU” associated with partitions different from 2Nx2N. As an example, FIG. 4A and 4B depict the second PU for the case of Nx2N and 2NxN, respectively. When the current PU is partitioned as Nx2N, candidate at position Ai is not considered for list

construction. In some embodiments, 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. Similarly, position Bi is not considered when the current PU is partitioned as 2NxN.

1.1.3 Constructing temporal merge candidates

[0058] In this step, only one candidate is added to the list. Particularly, in the derivation of this temporal merge candidate, 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.

[0059] 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.

[0060] In the co-located PU (Y) belonging to the reference frame, the position for the temporal candidate is selected between candidates Co and Ci, as depicted in FIG. 6. If PU at position Co is not available, is intra coded, or is outside of the current CTU, position Ci is used. Otherwise, position Co is used in the derivation of the temporal merge candidate.

1.1.4 Constructing additional types of merge candidates

[0061] Besides spatio-temporal 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.

[0062] FIG. 7 shows an example of this process, wherein two candidates in the original list (710, on the left), which have mvLO and refldxLO or mvLl and refldxLl, are used to create a combined bi-predictive merge candidate added to the final list (720, on the right).

[0063] 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.

1.1.5 Examples of motion estimation regions for parallel processing [0064] To speed up the encoding process, 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. To mitigate the trade-off between coding efficiency and processing latency, a motion estimation region (MER) 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. When a MER is defined, merge candidates falling in the same region are marked as unavailable and therefore not considered in the list construction.

1.2 Embodiments of advanced motion vector prediction (AMVP)

[0065] 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.

1.2.1 Examples of constructing motion vector prediction candidates

[0066] FIG. 8 summarizes derivation process for motion vector prediction candidate, and may be implemented for each reference picture list with refidx as an input.

[0067] In motion vector prediction, two types of motion vector candidates are considered: spatial motion vector candidate and temporal motion vector candidate. For 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.

[0068] For temporal motion vector candidate derivation, 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.

1.2.2 Constructing spatial motion vector candidates

[0069] In the derivation of spatial motion vector candidates, 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 Ao, Ai,and scaled Ao, scaled Ai. The order of derivation for the above side of the current PU is defined as Bo, Bi, B₂, scaled Bo, scaled Bi, scaled B₂. For each side there are therefore four cases that can be used as motion vector candidate, with two cases not required to use spatial scaling, and two cases where spatial scaling is used. The four different cases are summarized as follows:

[0070] — No spatial scaling

[0071] (1) Same reference picture list, and same reference picture index (same POC)

[0072] (2) Different reference picture list, but same reference picture index (same POC)

[0073] — Spatial scaling

[0074] (3) Same reference picture list, but different reference picture index (different

POC)

[0075] (4) Different reference picture list, and different reference picture index (different

POC)

[0076] 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.

[0077] As shown in the example in FIG. 9, for the spatial scaling case, 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.

1.2.3 Constructing temporal motion vector candidates [0078] Apart from the reference picture index derivation, all processes for the derivation of temporal merge candidates are the same as for the derivation of spatial motion vector candidates (as shown in the example in FIG. 6). In some embodiments, the reference picture index is signaled to the decoder.

2. Example of inter prediction methods in Joint Exploration Model (JEM)

[0079] In some embodiments, future video coding technologies are explored using a reference software known as the Joint Exploration Model (JEM). In JEM, sub-block based prediction is adopted in several coding tools, such as affine prediction, alternative temporal motion vector prediction (ATMVP), spatial-temporal motion vector prediction (STMVP), bi directional optical flow (BIO), Frame-Rate Up Conversion (FRUC), Locally Adaptive Motion Vector Resolution (LAMVR), Overlapped Block Motion Compensation (OBMC), Local Illumination Compensation (LIC), and Decoder-side Motion Vector Refinement (DMVR).

2.1 Examples of sub-CU based motion vector prediction

[0080] In the JEM with quadtrees plus binary trees (QTBT), each CU can have at most one set of motion parameters for each prediction direction. In some embodiments, 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. In spatial-temporal motion vector prediction (STMVP) method motion vectors of the sub-CUs are derived recursively by using the temporal motion vector predictor and spatial neighbouring motion vector. In some embodiments, and to preserve more accurate motion field for sub-CU motion prediction, the motion compression for the reference frames may be disabled.

2.1.1 Examples of alternative temporal motion vector prediction (ATMVP)

[0081] In the ATMVP method, 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.

[0082] 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.

[0083] In the first step, a reference picture 1050 and the corresponding block is determined by the motion information of the spatial neighboring blocks of the current CU 1000. To avoid the repetitive scanning process of neighboring blocks, 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.

[0084] In the second step, 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. For each sub-CU, the motion information of its corresponding block (e.g., the smallest motion grid that covers the center sample) is used to derive the motion information for the sub-CU. After the motion information of a corresponding NxN 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. For example, the decoder checks whether the low-delay condition (e.g. the POCs of all reference pictures of the current picture are smaller than the POC of the current picture) is fulfilled and possibly uses motion vector MVx (e.g., the motion vector corresponding to reference picture list X) to predict motion vector MVy (e.g., with X being equal to 0 or 1 and Y being equal to l-X) for each sub-CU.

2.1.2 Examples of spatial- temporal motion vector prediction (STMVP)

[0085] In the STMVP method, the motion vectors of the sub-CUs are derived recursively, following raster scan order. FIG. 11 shows an example of one CU with four sub-blocks and neighboring blocks. Consider an 8x8 CU 1100 that includes four 4x4 sub-CUs A (1101), B (1102), C (1103), and D (1104). The neighboring 4x4 blocks in the current frame are labelled as a (1111), b (1112), c (11 13), and d (1114).

[0086] The motion derivation for sub-CU A starts by identifying its two spatial neighbors. The first neighbor is the NxN block above sub-CU A 1101 (block e l l 13). If this block c (1113) is not available or is intra coded the other NxN 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. Next, 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. Finally, after retrieving and scaling the motion information, 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.

2.1.3 Examples of sub-CU motion prediction mode signaling

[0087] In some embodiments, 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. In some embodiments, e.g., JEM, all bins of the merge index are context coded by CABAC (Context-based Adaptive Binary Arithmetic Coding). In other embodiments, e.g., HEVC, only the first bin is context coded and the remaining bins are context by-pass coded.

2.2 Examples of adaptive motion vector difference resolution

[0088] In some embodiments, motion vector differences (MVDs) (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. In the JEM, a locally adaptive motion vector resolution (LAMVR) is introduced. In the JEM, 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.

[0089] For a 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. When 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.

[0090] When the first MVD resolution flag of a CU is zero, or not coded for a CU (meaning all MVDs in the CU are zero), the quarter luma sample MV resolution is used for the CU. When a CU uses integer-luma sample MV precision or four-luma-sample MV precision, the MVPs in the AMVP candidate list for the CU are rounded to the corresponding precision.

[0091] In the encoder, 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. To accelerate encoder speed, the following encoding schemes are applied in the JEM:

[0092] — During RD check of a CU with normal quarter luma sample MVD resolution, 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.

[0093] — RD check of a CU with 4 luma sample MVD resolution is conditionally invoked. For a CU, when RD cost integer luma sample MVD resolution is much larger than that of quarter luma sample MVD resolution, the RD check of 4 luma sample MVD resolution for the CU is skipped.

2.3 Examples of higher motion vector storage accuracy

[0094] In HEVC, motion vector accuracy is one-quarter pel (one-quarter luma sample and one-eighth chroma sample for 4:2:0 video). In the JEM, 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. For the CU coded with normal AMVP mode, either the integer-pel or quarter-pel motion is used.

[0095] 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. 2.4 Examples of overlapped block motion compensation (OBMC)

[0096] In the JEM, OBMC can be switched on and off using syntax at the CU level. When OBMC is used in the JEM, 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. In the JEM, an MC block corresponds to a coding block. When a CU is coded with sub-CU mode (includes sub-CU merge, affine and FRUC mode), each sub block of the CU is a MC block. To process CU boundaries in a uniform fashion, OBMC is performed at sub-block level for all MC block boundaries, where sub-block size is set equal to 4x4, as shown in FIGS. 12A and 12B.

[0097] FIG. 12A shows sub-blocks at the CU/PU boundary, and the hatched sub-blocks are where OBMC applies. Similarly, FIG. 12B shows the sub-Pus in ATMVP mode.

[0098] When OBMC applies to the current sub-block, besides current motion vectors, motion vectors of four connected neighboring sub-blocks, if available and are not identical to the current motion vector, 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.

[0099] 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. When 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. The 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. In this case 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.

[00100] In the JEM, for a CU with size less than or equal to 256 luma samples, a CU level flag is signaled to indicate whether OBMC is applied or not for the current CU. For the CUs with size larger than 256 luma samples or not coded with AMVP mode, OBMC is applied by default. At the encoder, when OBMC is applied for a CU, its impact is taken into account during the motion estimation stage. 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.

2.5 Examples of local illumination compensation (LIC)

[00101] 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).

[00102] When LIC applies for a CU, a least square error method is employed to derive the parameters a and b by using the neighboring samples of the current CU and their corresponding reference samples. 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.

[00103] When a CU is coded with merge mode, 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.

[00104] 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. When LIC is enabled for a CU, the mean- removed sum of absolute difference (MR-SAD) and mean-removed sum of absolute Hadamard- transformed difference (MR-SATD) are used, instead of SAD and SATD, for integer pel motion search and fractional pel motion search, respectively.

[00105] To reduce the encoding complexity, the following encoding scheme is applied in the JEM:

[00106] — 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.

2.6 Examples of affine motion compensation prediction

[00107] In HEVC, only a translation motion model is applied for motion compensation prediction (MCP). However, the camera and objects may have many kinds of motion, e.g. zoom in/out, rotation, perspective motions, and/or other irregular motions. JEM, on the other hand, applies a simplified affine transform motion compensation prediction. FIG. 14 shows an example of an affine motion field of a block 1400 described by two control point motion vectors Vo and Vi. The motion vector field (MVF) of the block 1400 can be described by the following equation:

[00109] As shown in FIG. 14, (vox, vo_y) is motion vector of the top-left corner control point, and (vi_x, vi_y) is motion vector of the top-right corner control point. To simplify the motion compensation prediction, sub-block based affine transform prediction can be applied. The sub block size MxN is derived as follows:

[00111] Here, 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 Eq. (1). M and N can be adjusted downward if necessary to make it a divisor of w and h, respectively.

[00112] FIG. 15 shows an example of affine MVF per sub-block for a block 1500. To derive motion vector of each MxN sub-block, the motion vector of the center sample of each sub-block can be calculated according to Eq. (1), and rounded to the motion vector fraction accuracy (e.g., 1/16 in JEM). Then the motion compensation interpolation filters can be applied to generate the prediction of each sub-block with derived motion vector. After the MCP, the high accuracy motion vector of each sub-block is rounded and saved as the same accuracy as the normal motion vector.

[00113] In the JEM, there are two affine motion modes: AF INTER mode and AF MERGE mode. For CUs with both width and height larger than 8, 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. In the AF INTER mode, a candidate list with motion vector pair {(v₀, v_x) |v₀ =

(v_A, ^V _B< ^vc)_< ^vi ⁼

i^s constructed using the neighboring blocks.

[00114] FIG. 16 shows an example of motion vector prediction (MVP) for a block 1600 in the AF INTER mode. As shown in FIG. 16, vo 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. The approach to select vi 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. When the candidate list is larger than 2, 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. In some embodiments, 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.

[00115] When a CU is applied in AF MERGE mode, it gets the first block coded with an affine mode from the valid neighboring reconstructed blocks. FIG. 17A shows an example of the selection order of candidate blocks for a current CU 1700. As shown in FIG. 17A, the selection order can be from left (1701), above (1702), above right (1703), left bottom (1704) to above left (1705) of the current CU 1700. FIG. 17B shows another example of candidate blocks for a current CU 1700 in the AF MERGE mode. If the neighboring left bottom block 1701 is coded in affine mode, as shown in FIG. 17B, the motion vectors v₂, vi and v₄ of the top left corner, above right corner, and left bottom corner of the CU containing the sub-block 1701 are derived. The motion vector vo of the top left corner on the current CU 1700 is calculated based on v2, v3 and v4. The motion vector vl of the above right of the current CU can be calculated accordingly. [00116] After the CPMV of the current CU vO and vl are computed according to the affine motion model in Eq. (1), the MVF of the current CU can be generated. In order to identify whether the current CU is coded with AF MERGE mode, an affine flag can be signaled in the bitstream when there is at least one neighboring block is coded in affine mode.

2.7 Examples of pattern matched motion vector derivation (PMMVD)

[00117] 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.

[00118] A FRUC flag can be signaled for a CU when its merge flag is true. When the FRUC flag is false, a merge index can be signaled and the regular merge mode is used. When the FRUC flag is true, 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.

[00119] At the encoder side, 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.

[00120] Typically, 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. At CU level, an initial motion vector is derived for the whole CU based on bilateral matching or template matching. First, 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. Then 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. Subsequently, the motion information is further refined at sub-CU level with the derived CU motion vectors as the starting points.

[00121] For example, the following derivation process is performed for a W X H CU motion information derivation. At the first stage, MV for the whole W x H CU is derived. At the second stage, the CU is further split into M x M sub-CUs. The value of M is calculated as in Eq. (3), 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.

[00123] FIG. 18 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 (1800) in two different reference pictures (1810, 1811). Under the assumption of continuous motion trajectory, the motion vectors MV0 (1801) and MV1 (1802) pointing to the two reference blocks are proportional to the temporal distances, e.g., TD0 (1803) and TD1 (1804), between the current picture and the two reference pictures. In some embodiments, when the current picture 1800 is temporally between the two reference pictures (1810, 1811) and the temporal distance from the current picture to the two reference pictures is the same, the bilateral matching becomes mirror based bi-directional MV.

[00124] FIG. 19 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 1900 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 1910. 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. If 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). When applied to AMVP mode, only CU level search is applied.

[00125] 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.

[00126] When using bilateral matching, each valid MV of a merge candidate can be used as an input to generate a MV pair with the assumption of bilateral matching. For example, one valid MV of a merge candidate is (MVa, ref_a) at reference list A. Then the reference picture reft of its paired bilateral MV is found in the other reference list B so that reft and reft are temporally at different sides of the current picture. If such a reft is not available in reference list B, reft is determined as a reference which is different from reft and its temporal distance to the current picture is the minimal one in list B. After reft is determined, MVb is derived by scaling MVa based on the temporal distance between the current picture and reft, reft.

[00127] In some implementations, 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. When FRUC is applied in AMVP mode, the original AMVP candidates are also added to CU level MV candidate set. In some implementations, at the CU level, 15 MVs for AMVP CUs and 13 MVs for merge CUs can be added to the candidate list.

[00128] 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. At the sub-CU level, one or more MVs (e.g., up to 17) are added to the candidate list.

[00129] Generation of an interpolated MV field. Before coding a frame, 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.

[00130] In some embodiments, the motion field of each reference pictures in both reference lists is traversed at 4x4 block level. FIG. 20 shows an example of unilateral Motion Estimation (ME) 2000 in the FRUC method. For each 4x4 block, if the motion associated to the block passing through a 4x4 block in the current picture and the block has not been assigned any interpolated motion, 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 4x4 block, the block’s motion is marked as unavailable in the interpolated motion field.

[00131] Interpolation and matching cost. When a motion vector points to a fractional sample position, motion compensated interpolation is needed. To reduce complexity, bi-linear interpolation instead of regular 8-tap HEVC interpolation can be used for both bilateral matching and template matching.

[00132] The calculation of matching cost is a bit different at different steps. When selecting the candidate from the candidate set at the CU level, the matching cost can be the absolute sum difference (SAD) of bilateral matching or template matching. After the starting MV is determined, the matching cost C of bilateral matching at sub-CU level search is calculated as follows:

[00134] Here, w is a weighting factor. In some embodiments, w can be empirically set to 4.

MV and MV^S indicate the current MV and the starting MV, respectively. S D may still be used as the matching cost of template matching at sub-CU level search.

[00135] In FRUC mode, 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.

[00136] MV refinement is a pattern based MV search with the criterion of bilateral matching cost or template matching cost. In the JEM, 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. For both CU and sub-CU level MV refinement, 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.

[00137] In the bilateral matching merge mode, 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. In the template matching merge mode, the encoder can choose among uni-prediction from listO, uni-prediction from listl, or bi prediction for a CU. The selection ca be based on a template matching cost as follows:

[00138] If costBi <= factor * min (costO, costl)

[00139] bi-prediction is used;

[00140] Otherwise, if costO <= costl

[00141] uni-prediction from listO is used;

[00142] Otherwise, [00143] uni-prediction from listl is used;

[00144] Here, costO is the SAD of listO template matching, costl is the SAD of listl template matching and costBi is the SAD of bi-prediction template matching. For example, when 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.

2.8 Examples of bi-directional optical flow (BIO)

[00145] The bi-directional optical flow (BIO) method is a sample- wise motion refinement performed on top of block- wise motion compensation for bi-prediction. In some

implementations, the sample-level motion refinement does not use signaling.

[00146] Let 7® be the luma value from reference k (k= 0, 1 ) after block motion compensation, and denote dl^/dx and dl^(k) /dy as the horizontal and vertical components of the I ^k gradient, respectively. Assuming the optical flow is valid, the motion vector field ( v_x , v_y) is given by:

[00147] dl^{k)/dt +v_x dl^{k)/dx + v_y dl^{k)/dy = 0. Eq. (5)

[00148] Combining this optical flow equation with Hermite interpolation for the motion trajectory of each sample results in a unique third-order polynomial that matches both the function values I^(k) and derivatives dl^(k) / dx and dl^(k) / dy at the ends. The value of this polynomial at t= 0 is the BIO prediction:

[00150] FIG. 21 shows an example optical flow trajectory in the Bi-directional Optical flow (BIO) method. Here, t₀ and t_± denote the distances to the reference frames. Distances t₀ and t_± are calculated based on POC for Refo and Refi: To=POC(current) - POC(Refo), ti= POC(Refi) - POC(current). If both predictions come from the same time direction (either both from the past or both from the future) then the signs are different (e.g., t₀ t < 0). In this case, BIO is applied if the prediction is not from the same time moment (e.g., t₀ ¹ t₁). Both referenced regions have non-zero motion (e.g., ^{MVx 0}’ ^{MVy 0}’ ^{MVx 1}’ ^{MVy 1 ¹ 0} ) and the block motion vectors are proportional to the time distance (e.g.,

‘ ⁼ !^t ).

[00151] The motion vector field (v_x, v_y) is determined by minimizing the difference D between values in points A and B. FIGS. 22A-22B show an example of intersection of motion trajectory and reference frame planes. Model uses only first linear term of a local Taylor expansion for D:

[00153] All values in the above equation depend on the sample location, denoted as {V ,j' ). Assuming the motion is consistent in the local surrounding area, D can be minimized inside the (2M+l)x(2M+l) square window W centered on the currently predicted point (i,y), where M is equal to 2:

[00154] (v_x ,v_y ) = argmin åD²M Eq. (8)

[00155] For this optimization problem, 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:

[00160] In order to avoid division by zero or a very small value, regularization parameters r and m can be introduced in Eq. (9) and Eq. (10), where:

[00161] r = 500 4^d_8 Eq. (12)

[00162] m = 700 4^d_8 Eq. (13)

[00163] Here, d is bit depth of the video samples.

[00164] In order to keep the memory access for BIO the same as for regular bi-predictive motion compensation, all prediction and gradients values, 7®, dl^(k) / dx , dl^(k) / dy, are calculated for positions inside the current block. FIG. 22A shows an example of access positions outside of a block 2200. As shown in FIG. 22A, in Eq. (9), (2M+l)x(2M+l) square window W centered in currently predicted point on a boundary of predicted block needs to accesses positions outside of the block. In the JEM, values of 7®, dl^(k) / dx , dl^(k) / dy 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 2201, as shown in FIG. 22B.

[00165] With BIO, it is possible that the motion field can be refined for each sample. To reduce the computational complexity, a block-based design of BIO is used in the JEM. The motion refinement can be calculated based on a 4x4 block. In the block-based BIO, the values of S_n in Eq. (9) 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 4x4 block. More specifically, the following formula can used for block-based BIO derivation:

[00167] Here, b_k denotes the set of samples belonging to the k-th 4x4 block of the predicted block. s„ in Eq (9) and Eq (10) are replaced by (( s_n,bk ) » 4 ) to derive the associated motion vector offsets.

[00168] In some scenarios, 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 x 2^14-d; otherwise, it is set to 12 x 2^13-d.

[00169] 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)). In some embodiments, 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. For horizontal gradient dl /dx, a signal is first interpolated vertically using BlOfilterS corresponding to the fractional position fracY with de-scaling shift d 8. Gradient filter BIOfilterG is then applied in horizontal direction corresponding to the fractional position fracX with de-scaling shift by 18 d. For vertical gradient dl / dy, 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 BlOfilterS 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.

[00170] In the JEM, BIO can be applied to all bi-predicted blocks when the two predictions are from different reference pictures. When Local Illumination Compensation (LIC) is enabled for a CU, BIO can be disabled.

[00171] In some embodiments, OBMC is applied for a block after normal MC process. To reduce the computational complexity, 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.

2.9 Examples of decoder-side motion vector refinement (DMVR)

[00172] In a bi-prediction operation, for the prediction of one block region, two prediction blocks, formed using a motion vector (MV) of listO and a MV of listl , respectively, are combined to form a single prediction signal. In the decoder-side motion vector refinement (DMVR) method, 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.

[00173] In DMVR, a bilateral template is generated as the weighted combination (i.e.

average) of the two prediction blocks, from the initial MV0 of listO and MV1 of listl, respectively, as shown in FIG. 23. 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. In the JEM, 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. Finally, the two new MVs, i.e., MV0' and MV1' as shown in FIG. 23, are used for generating the final bi-prediction results. A sum of absolute differences (SAD) is used as the cost measure.

[00174] 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. In the JEM, when LIC, affine motion, FRUC, or sub-CU merge candidate is enabled for a CU, DMVR is not applied.

3. Examples of CABAC modifications

[00175] In the JEM, CABAC contains the following three major changes compared to the design in HEVC:

[00176] • Modified context modeling for transform coefficients [00177] • Multi-hypothesis probability estimation with context-dependent updating speed

[00178] · Adaptive initialization for context models

3.1 Examples of context modeling for transform coefficients

[00179] In HEVC, transform coefficients of a coding block are coded using non-overlapped coefficient groups (CGs), and each CG contains the coefficients of a 4x4 block of a coding block. The CGs inside a coding block, and the transform coefficients within a CG, are coded according to pre-defmed scan orders. The coding of transform coefficient levels of a CG with at least one non-zero transform coefficient may be separated into multiple scan passes. In the first pass, the first bin (denoted by binO, also referred as significant coejfi Jlag, which indicates the magnitude of the coefficient is larger than 0) is coded. Next, two scan passes for context coding the second/third bins (denoted by binl and bin2, respectively, also referred as

coejfi abs greater 1 Jlag and coejfi abs greater2 flag) may be applied. Finally, two more scan passes for coding the sign information and the remaining values (also referred as

coejfi abs level remaining) of coefficient levels are invoked, if necessary. Only bins in the first three scan passes are coded in a regular mode and those bins are termed regular bins in the following descriptions.

[00180] In the JEM, the context modeling for regular bins is changed. When coding bin i in the z-th scan pass (z being 0, 1, 2), the context index is dependent on the values of the z-th bins of previously coded coefficients in the neighbourhood covered by a local template. Specifically, the context index is determined based on the sum of the i-th bins of neighbouring coefficients.

[00181] As shown in FIG. 24, the local template contains up to five spatial neighbouring transform coefficients wherein x indicates the position of current transform coefficient and xi (i being 0 to 4) indicates its five neighbours. To capture the characteristics of transform coefficients at different frequencies, one coding block may be split into up to three regions and the splitting method is fixed regardless of the coding block sizes. For example, when coding binO of luma transform coefficients, one coding block is split into three regions marked with different colours, and the context index assigned to each region is listed. Luma and chroma components are treated in a similar way but with separate sets of context models. Moreover, the context model selection for binO (i.e., significant flags) of the luma component is further dependent on transform size.

3.2 Examples of multi-hypothesis probability estimation

[00182] The binary arithmetic coder is applied with a“multi-hypothesis” probability update model based on two probability estimates Po and Pi that are associated with each context model and are updated independently with different adaptation rates as follows:

[00184] Here,

1) represent the probabilities before and after decoding a bin, respectively. The variable M (being 4, 5, 6, 7) is a parameter which controls the probability updating speed for the context model with index equal to i; and k represents the precision of probabilities (here it is equal to 15).

[00185] The probability estimate P used for the interval subdivision in the binary arithmetic coder is the average of the estimates from the two hypotheses:

[00186] _P = (p_{r + Pr} )/₂ Eq. (16)

[00187] In the JEM, the value of the parameter M used in Equation (15) that controls the probability updating speed for each context model is assigned as follows:

[00188] At the encoder side, the coded bins associated with each context model are recorded. After one slice is coded, for each context model with index equal to i, the rate costs of using different values of M, (being 4, 5, 6, 7) are calculated and the one that provides the minimum rate cost is selected. For simplicity, this selection process is performed only when a new combination of slice type and slice-level quantization parameter are encountered.

[00189] A 1 bit flag is signalled for each context model i to indicate whether M is different from the default value 4. When the flag is 1, two bits are used to indicate whether M is equal to 5, 6, or 7.

3.3 Examples of initialization for context models

[00190] Instead of using fixed tables for context model initialization in HEVC, the initial probability states of context models for inter-coded slices can be initialized by copying states from previously coded pictures. More specifically, after coding a centrally-located CTU of each picture, the probability states of all context models are stored for potential use as the initial states of the corresponding context models on later pictures. In the JEM, the set of initial states for each inter-coded slice is copied from the stored states of a previously coded picture that has the same slice type and the same slice-level QP as the current slice. This lacks loss robustness, but is used in the current JEM scheme for coding efficiency experiment purposes.

4. Examples of related embodiments and methods

[00191] Methods related to the disclosed technology include extended LAMVR, wherein supported motion vector resolutions range from l/4-pel to 4-pel (l/4-pel, l/2-pel, l-pel, 2-pel and 4-pel). Information about the motion vector resolution is signaled at the CU level when MVD information is signaled.

[00192] Depending on the resolution of CU, both motion vector (MV) and motion vector predictor (MVP) of the CU are adjusted. If applied motion vector resolution is denoted as R (R could be ¼, ½, 1, 2, 4), MV (MV_X, MV_y) and MVP (MVP_X, MVP_y) are represented as follows:

[00193] (MV_X, MV_y) = (Round(MV_x / (R * 4)) * (R * 4), Round(MV_y / (R * 4)) * (R * 4))

[00194] (MVP_x, MVP_y) = (Round(MVP_x / (R * 4)) * (R * 4), Round(MVP_y / (R * 4)) * (R * 4))

[00195] Since the motion vector predictor and MV are both adjusted by an adaptive resolution, MVD (MVD_X, MVD_y) is also aligned to the resolution and, is signaled according to the resolution as follows:

[00196] (MVD_X, MVD_y) = ((MV_{X -}MVP_X) / (R * 4), (MV_{y -}MVP_y) /R * 4))

[00197] In this proposal, motion vector resolution index (MVR index) indicates MVP index as well as the motion vector resolution. As result, the proposed method has no MVP index signaling. The table shows what each value of MVR index represents.

Table 3: Examples of MVR index representation

[00198] In the case of bi-prediction, AMVR has 3 modes for every resolution. AMVR Bi- Index indicates whether MVD_X, MVD_y of each reference list (list 0 or list 1) are signaled or not.

An example of the AMVR Bi-Index is defined as in the table below.

Table 4: Examples of the AMVR bi-index

5. Examples of existing implementations

[00199] In one existing implementation that uses BIO, the calculated MV between reference block/subblock in list 0 (denoted by refblkO) and reference block/subblock list 1 (refblkl), denoted by (v_x, v_y), is only used for motion compensation of the current block/subblock, and are not used for motion prediction, deblocking, OBMC etc. of future coded blocks, which may be inefficient.

[00200] In another existing implementation that uses OBMC, for AMVP mode, whether OBMC is enabled or not is decided at encoder and signaled to decoder for small blocks (width * height <= 256). This increases the encoder complexity. Meanwhile, for a given block/subblock, when OBMC is enabled, it is always applied to both luma and chroma, this may leads to coding efficiency drop.

6. Example methods for motion prediction based on updated MVs

[00201] Embodiments of the presently disclosed technology overcome the drawbacks of existing implementations, thereby providing video coding with higher coding efficiencies. The motion prediction using updated motion vectors, based on the disclosed technology, 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.

[00202] With regard to terminology, the reference picture of current picture from list 0 and list 1 is denoted RefO and Refl, respectively. Denote To=POC(current) - POC(RefO), ti= POC(Refl) - POC(current), and denote reference block of the current block from RefO and Refl by refblkO and refblkl respectively. For a sub-block in current block, MV of its corresponding sub-block in refblkO pointing to refblkl is denoted by (v_x, v_y). MVs of the sub-block in RefO and Refl are denoted by (mvL0_x, mvL0_y) and (mvLl_x, mvLl_y) respectively. The updated motion vector based methods for motion prediction may be extended, as described in this patent document, to existing and future video coding standards.

[00203] Example 1. It is proposed to modify the motion information of BIO coded blocks

(e.g., different from what has been used in motion compensation) which may be utilized later, such as in the following motion prediction (e.g., TMVP) process. [00204] (a) In one example, It is proposed that the MV (v_x, v_y) derived in BIO is scaled and added up to the original MV (mvLX_x, mvLX_y) (X = 0 or 1) of current block/subblock. The updated MV is calculated as: mvL0’_x = -v_x * (t₀/(t₀ + ti)) + mvL0_x, mvL0’_y = -v_y * (t₀/(t₀ + ti)) + mvL0_y, and mvLl’_x = v_x * (ti/(t₀ + ti)) + mvLl_x, mvLl \ = v * (ti/(t₀ + ti)) + mvLl_y.

[00205] (i) In one example, the updated MV is used for future motion prediction

(like in AMVP, merge and affine mode), deblocking, OBMC etc.

[00206] (ii) Alternatively, the updated MV can only be used in motion prediction of its non-immediately following CU/PUs in decoding order.

[00207] (iii) Alternatively, the updated MV can only be used as TMVP in AMVP, merge or affine mode.

[00208] Example 2 It is proposed that for BIO, DMVR, FRUC, template matching or other methods that require to update MV (or motion information including MV and/or reference pictures) from those derived from the bitstream, usage of the updated motion information may be constrained.

[00209] (a) If motion information could be updated at sub-block level, updated and non- updated motion information of different sub-blocks may be both stored. In one example, the updated motion information of some sub-blocks may be stored and for the other remaining sub blocks, the non-updated motion information are stored.

[00210] (b) In one example, if MV (or motion information) is updated at subblock level, the updated MV are only stored for inner subblocks, i.e., subblocks that are not at PU/CU/CTU boundary, and are then used for motion prediction, deblocking, OBMC etc. as shown in FIG. 25.

[00211] (c) In one example, the updated MV or motion information is not used for motion prediction and OBMC. Alternatively, in addition, the updated MV or motion information is not used for deblocking.

[00212] (d) In one example, the updated MV or motion information is only used for motion compensation and temporal motion prediction like TMVP/ATMVP.

[00213] Example 3 It is proposed that OBMC is implicitly enabled/disabled depending on the encoding mode, motion information, size or position of the PU/CU/block, and therefore no OBMC flag is signaled.

[00214] (a) In one example, OBMC is disabled for PFT/CU/block coded in AMVP mode or

AFFINE INTER mode if one of the following conditions is satisfied (where w and h are the width and height of the PU/CU/block).

[00215] (l) wxh <= T

[00216] (n) w <= T && h <= T

[00217] (b) In one example, OBMC is always enabled for PU/CU/block coded in merge mode and AFFINE MERGE mode.

[00218] (c) Alternatively, in addition, vertical and horizonal OBMC are disabled/enabled separately. If height of the PU/CU/block is smaller than T, vertical OBMC is disabled. If width of the PU/CU/block is smaller than T, horizonal OBMC is disabled.

[00219] (d) In one example, neighboring MV from above row is not used in OBMC for

PU/CU/block/sub-block at the top CTU boundary.

[00220] (e) In one example, neighboring MV from left column is not used in OBMC for

PU/CU/block/sub-block at the left CTU boundary.

[00221] (f) In one example, OBMC is only enabled for uni-predicted PU/CU/block/sub- block.

[00222] (g) In one example, OBMC is disabled for PU/CU/block whose MVD resolution is larger than or equal to integer pixel.

[00223] Example 4 It is proposed that whether OBMC is enabled or not may depend on the motion information of current PU/CU/block/sub-block and its neighboring PU/CU/block/sub- block.

[00224] (a) In one example, if a neighboring PU/CU/block/sub-block has quite different motion information from the current PU/CU/block/sub-block, its motion information is not used in OBMC.

[00225] (i) In one example, the neighboring PU/CU/block/sub-block has different prediction directions or reference pictures from the current PU/CU/block/sub-block.

[00226] (ii) In one example, the neighboring PU/CU/block/sub-block has same prediction directions and reference pictures with the current PU/CU/block/sub-block, however, absolute horizonal/vertical MV difference between the neighboring PU/CU/block/sub-block and the current PU/CU/block/sub-block in prediction direction X (X = 0 or 1) is larger than a given threshold MV TH.

[00227] (b) Alternatively, if a neighboring PU/CU/block/sub-block has similar motion information with the current PU/CU/block/sub-block, its motion information is not used in OBMC.

[00228] (i) In one example, the neighboring PU/CU/block/sub-block has same prediction directions and reference pictures with the current PU/CU/block/sub-block, and absolute horizonal/vertical MV difference between the neighboring PU/CU/block/sub-block and the current PU/CU/block/sub-block in all prediction directions are smaller than a given threshold MV TH.

[00229] Example 5. It is proposed that in ATMVP/STMVP, affine mode or other modes where each sub-block (with size NxM) within the PU/CU has individual motion information, OBMC may be performed at a block size different from the sub-block size.

[00230] (a) In one example, the sub-block size is 4x4 and OBMC is only performed at 8x8 block boundaries.

[00231] Example 6 It is proposed that how many rows/columns are processed in OBMC may depend on the PU/CU/block/sub-block size.

[00232] (a) In one example, if width of the PU/CU/block/sub-block is larger than N, 4 left columns of the PU/CU/block/sub-block are processed; otherwise, only 2 (or 1) left columns of the PU/CU/block/sub-block are processed.

[00233] (b) In one example, if height of the PU/CU/block/sub-block is larger than N, 4 above rows of the PU/CU/block/sub-block are processed; otherwise, only 2 (or 1) above rows of the PU/CU/block/sub-block are processed.

[00234] Example 7 It is proposed that OBMC is enabled/disabled for luma and chroma component independently, and the rules described in Examples 2 and 3 may be applied to each component individually.

[00235] Example 8 It is proposed that short-tap interpolation filter (like bilinear, 4-tap or 6- tap filter) is used when generating prediction blocks using neighboring motion information.

[00236] (a) In one example, asymmetric 6-tap filter is used for luma component. For a subpixel position, 4 pixels on the left/above side and 2 pixels on the right/below side are used for interpolation.

[00237] Example 9 The proposed methods may be applied to certain modes, block sizes/shapes, and/or certain sub-block sizes.

[00238] (a) The proposed methods may be applied to certain modes, such as conventional translational motion (i.e., affine mode is disabled). [00239] (b) The proposed methods may be applied to certain block sizes.

[00240] (i) In one example, it is only applied to a block with wxh>T, where w and h are the width and height of the current block.

[00241] (ii) In another example, it is only applied to a block with w>T && h>T.

[00242] Example 10. The proposed methods may be applied on all color components.

Alternatively, they may be applied only to some color components. For example, they may be only applied on the luma component.

[00243] The examples described above may be incorporated in the context of the methods described below, e.g., methods 2600 and 2700, which may be implemented at a video decoder.

[00244] FIG. 26 shows a flowchart of an exemplary method for video decoding. The method 2600 includes, at step 2610, receiving a bitstream representation of a current block of video data.

[00245] The method 2600 includes, at step 2620, generating updated first and second reference motion vectors based on a weighted sum of a first motion vector and first and second reference motion vectors, respectively. In some embodiments, the first motion vector is derived based on the first reference motion vector from a first reference block and the second reference motion vector from a second reference block, and the current block is associated with the first and second reference blocks.

[00246] The method 2600 includes, at step 2630, processing the bitstream representation based on the updated first and second reference motion vectors to generate the current block.

[00247] In some embodiments, and as described in the context of Example 1, the first motion vector is derived based on a bi-directional optical flow (BIO) refinement using the first and second reference motion vectors. In an example, the weighted sum comprises weights that are based on picture order counts (POCs) of the current block, the first reference block and the second reference block.

[00248] In some embodiments, the processing may be based on a bi-directional optical flow (BIO) refinement, a decoder-side motion vector refinement (DMVR), frame-rate up conversion (FRUC) techniques or a template matching technique. In one example, updated first and second reference motion vectors are generated for inner sub-blocks that are not on a boundary of the current block. In another example, the updated first and second reference motion vectors are generated for a subset of sub-blocks of the current block.

[00249] In some embodiments, the processing excludes motion prediction or overlapped block motion compensation (OBMC).

[00250] FIG. 27 shows a flowchart of another exemplary method for video decoding. The method 2700 includes, at step 2710, receiving a bitstream representation of a current block of video data with no OBMC flag is signaled.

[00251] The method 2700 includes, at step 2720, processing, based on a characteristic of the current block, the bitstream representation by selectively using overlapped block motion compensation (OBMC) to generate the current block.

[00252] In some embodiments, the characteristic comprises dimensions of the current block or a position of the current block in a picture. In other embodiments, the characteristic comprises motion information of the current block. In one example, OBMC may not be used if the motion information of the current block is different from motion information of a neighboring block. In another example, OBMC may be used if the motion information of the current block is identical to motion information of a neighboring block.

[00253] In some embodiments, and as described in the context of Example 7, OBMC may be applied to the luma and chroma components independently. In one example, OBMC is applied to a chroma component of the current block, and wherein OBMC is not applied to a luma component of the current block. In another example, OBMC is applied to a luma component of the current block, and wherein OBMC is not applied to a chroma component of the current block.

[00254] In some embodiments, and as described in the context of Example 6, processing the bitstream representation includes processing a predetermined number of row or columns of the current block using OBMC, and wherein the predetermined number is based on a size of a sub block of the current block.

7. Example implementations of the disclosed technology

[00255] FIG. 28 is a block diagram of a video processing apparatus 2800. The apparatus 2800 may be used to implement one or more of the methods described herein. The apparatus 2800 may be embodied in a smartphone, tablet, computer, Internet of Things (IoT) receiver, and so on. The apparatus 2800 may include one or more processors 2802, one or more memories 2804 and video processing hardware 2806. The processor(s) 2802 may be configured to implement one or more methods (including, but not limited to, methods 2600 and 2700) described in the present document. The memory (memories) 2804 may be used for storing data and code used for implementing the methods and techniques described herein. The video processing hardware 2806 may be used to implement, in hardware circuitry, some techniques described in the present document.

[00256] In some embodiments, the video coding methods may be implemented using an apparatus that is implemented on a hardware platform as described with respect to FIG. 28.

[00257] FIG. 29 shows a flowchart of another exemplary method for video processing. The method 2900 includes, at step 2910, determining a current block with motion vectors.

[00258] The method 2900 includes, at step 2920, generating updated motion vectors.

[00259] The method 2900 includes, at step 2930, performing, based on the updated motion vectors, a conversion between the current block and a bitstream representation of a video data including the current block.

[00260] FIG. 30 shows a flowchart of another exemplary method for processing video data. The method 3000 includes, at step 3010, determining a current block and corresponding neighboring blocks.

[00261] The method 3000 includes, at step 3020, constructing a final prediction block of the current block as weighted sum of a prediction block derived from a motion vector of the current block and prediction blocks derived from motion vectors of one or more of neighboring blocks. For example, a short-tap interpolation filter may be used for constructing the final prediction block of the current block.

[00262] The method 3000 includes, at step 3030, performing, based on the final prediction block of the current block, a conversion between the current block and a bitstream representation of a video data including the current block.

[00263] Some embodiments described herein may be captured using the following examples.

[00264] 1. A method for video processing, comprising: determining a current block with motion vectors; generating updated motion vectors based on specific prediction mode; and performing, based on the updated motion vectors, a conversion between the current block and a bitstream representation of a video data including the current block, wherein the specific prediction mode includes one or more of bi-directional optical flow (BIO) refinement, a decoder-side motion vector refinement (DMVR), frame-rate up conversion (FRUC) techniques or a template matching technique.

[00265] 2. The method of example 1, wherein the updated motion vectors are generated for a subset of sub-blocks of the current block.

[00266] 3. The method of example 2, wherein non-updated motion vectors and the updated motion vectors are all stored for the subset of sub-blocks of the current block, and only the non- updated motion vectors are stored for the remaining sub-blocks of the current block.

[00267] 4. The method of example 2, wherein the updated motion vectors are stored for the subset of sub-blocks of the current block, and non-updated motion vectors are stored for the remaining sub-blocks of the current block.

[00268] 5. The method of example 2, wherein the updated motion vectors are only stored for inner sub-blocks that are not on a boundary of a PU, CU, or CTU.

[00269] 6. The method of example 5, wherein the updated motion vectors are used for motion prediction, deblocking or overlapped block motion compensation (OBMC).

[00270] 7. The method of example 1, wherein the updated motion vectors are not used for motion prediction and overlapped block motion compensation (OBMC).

[00271] 8. The method of example 1, wherein the updated motion vectors are not used for deblocking.

[00272] 9. The method of example 1, wherein the updated motion vectors are used for motion compensation and/or temporal motion prediction.

[00273] 10. The method of example 9, wherein the temporal motion prediction includes temporal motion vector prediction (TMVP) and/or alternative temporal motion vector prediction (ATMVP).

[00274] 11. A method for processing video data, comprising: determining a current block and corresponding neighboring blocks; and constructing a final prediction block of the current block as weighted sum of a prediction block derived from a motion vector of the current block and prediction blocks derived from motion vectors of one or more of neighboring blocks; and performing, based on the final prediction block of the current block, a conversion between the current block and a bitstream representation of a video data including the current block; wherein a short-tap interpolation filter is used for constructing the final prediction block of the current block.

[00275] 12. The method of example 11, wherein the short-tap interpolation filter is bilinear, 4- tap or 6-tap filter.

[00276] 13. The method of example 12, wherein the short-tap interpolation filter is asymmetric

6-tap filter, and the filter is used for luma component, and wherein for a subpixel position, 4 pixels on the left/above side and 2 pixels on the right/below side are used for interpolation.

[00277] 14. The method of any one of examples 1 to 13, wherein the method is applied to translational motion and an affine mode is disabled.

[00278] 15. The method of any one of examples 1 to 13, wherein the method is only applied to a block with wxh>T, where w and h are the width and height of the current block, and T is a threshold.

[00279] 16. The method of any one of examples 1 to 13, wherein the method is only applied to a block with w>T and h>T where w and h are the width and height of the current block, and T is a threshold.

[00280] 17. The method of any one of examples 1 to 16, wherein the method is applied to all color components.

[00281] 18. The method of any one of examples 1 to 16, wherein the method is applied only to luma components.

[00282] 19. 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 examples 1 to 18.

[00283] 20. A computer program product stored on a non-transitory computer readable media, the computer program product including program code for carrying out the method in any one of examples 1 to 18.

[00284] From the foregoing, it will be appreciated that specific embodiments of the presently disclosed technology have been described herein for purposes of illustration, but that various modifications may be made without deviating from the scope of the invention. Accordingly, the presently disclosed technology is not limited except as by the appended claims.

[00285] Implementations of the subject matter and the functional operations described in this patent document can be implemented in various systems, digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible and non-transitory 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 of them. The term“data processing unit” or“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.

[00286] 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.

[00287] The processes and logic flows described in this specification 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).

[00288] 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. Generally, 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. Generally, 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. However, a computer need not have such devices.

Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[00289] It is intended that the specification, together with the drawings, be considered exemplary only, where exemplary means an example. As used herein, the singular forms“a”, “an” and“the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Additionally, the use of“or” is intended to include“and/or”, unless the context clearly indicates otherwise.

[00290] While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple

embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[00291] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all

embodiments.

Only a few implementations and examples are described and other implementations,

enhancements and variations can be made based on what is described and illustrated in this patent document.

Claims

CLAIMS What is claimed is:

1. A method for video processing, comprising:

determining a current block with motion vectors;

generating updated motion vectors based on specific prediction mode; and

performing, based on the updated motion vectors, a conversion between the current block and a bitstream representation of a video data including the current block, wherein the specific prediction mode includes one or more of bi-directional optical flow (BIO) refinement, a decoder- side motion vector refinement (DMVR), frame-rate up conversion (FRUC) techniques or a template matching technique.

2. The method of claim 1 , wherein the updated motion vectors are generated for a subset of sub-blocks of the current block.

3. The method of claim 2, wherein non- updated motion vectors and the updated motion vectors are all stored for the subset of sub-blocks of the current block, and only the non-updated motion vectors are stored for the remaining sub-blocks of the current block.

4. The method of claim 2, wherein the updated motion vectors are stored for the subset of sub-blocks of the current block, and non-updated motion vectors are stored for the remaining sub-blocks of the current block.

5. The method of claim 2, wherein the updated motion vectors are only stored for inner sub blocks that are not on a boundary of a PU, CU, or CTU.

6. The method of claim 5, wherein the updated motion vectors are used for motion prediction, deblocking or overlapped block motion compensation (OBMC).

7. The method of claim 1 , wherein the updated motion vectors are not used for motion prediction and overlapped block motion compensation (OBMC).

8. The method of claim 1, wherein the updated motion vectors are not used for deblocking.

9. The method of claim 1 , wherein the updated motion vectors are used for motion compensation and/or temporal motion prediction.

10. The method of claim 9, wherein the temporal motion prediction includes temporal motion vector prediction (TMVP) and/or alternative temporal motion vector prediction (ATMVP).

11. A method for processing video data, comprising:

determining a current block and corresponding neighboring blocks; and

constructing a final prediction block of the current block as weighted sum of a prediction block derived from a motion vector of the current block and prediction blocks derived from motion vectors of one or more of neighboring blocks; and

performing, based on the final prediction block of the current block, a conversion between the current block and a bitstream representation of a video data including the current block;

wherein a short-tap interpolation filter is used for constructing the final prediction block of the current block.

12. The method of claim 11, wherein the short-tap interpolation filter is bilinear, 4-tap or 6- tap filter.

13. The method of claim 12, wherein the short-tap interpolation filter is asymmetric 6-tap filter, and the filter is used for luma component, and wherein for a subpixel position, 4 pixels on the left/above side and 2 pixels on the right/below side are used for interpolation.

14. The method of any one of claims 1 to 13, wherein the method is applied to translational motion and an affine mode is disabled.

15. The method of any one of claims 1 to 13, wherein the method is only applied to a block with wxh>T, where w and h are the width and height of the current block, and T is a threshold.

16. The method of any one of claims 1 to 13, wherein the method is only applied to a block with w>T and h>T where w and h are the width and height of the current block, and T is a threshold.

17. The method of any one of claims 1 to 16, wherein the method is applied to all color components.

18. The method of any one of claims 1 to 16, wherein the method is applied only to luma components.

19. 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 claims 1 to 18.

20. A computer program product stored on a non-transitory computer readable media, the computer program product including program code for carrying out the method in any one of claims 1 to 18.