CN110740321A

CN110740321A - Motion prediction based on updated motion vectors

Info

Publication number: CN110740321A
Application number: CN201910663403.7A
Authority: CN
Inventors: 刘鸿彬; 张莉; 张凯; 王悦
Original assignee: Beijing ByteDance Network Technology Co Ltd; ByteDance Inc
Current assignee: Beijing ByteDance Network Technology Co Ltd; ByteDance Inc
Priority date: 2018-07-20
Filing date: 2019-07-22
Publication date: 2020-01-31
Anticipated expiration: 2039-07-22
Also published as: TW202008786A; TWI723472B; TWI734147B; WO2020016858A1; WO2020016859A3; TW202023283A; TWI709332B; WO2020016857A1; CN110740332B; CN110740327A; TW202008787A; CN110740332A; CN110740321B; WO2020016859A2; CN110740327B

Abstract

A video processing method includes determining that a current block is associated with a th reference motion vector and a second reference motion vector, generating an updated th reference motion vector and an updated second reference motion vector based on a sum of a scaled th motion refinement and the th reference motion vector and a sum of a scaled th motion refinement and the second reference motion vector, respectively, wherein the th motion refinement is derived based on a bi-directional optical flow mode, and performing a conversion between the current video block and a bitstream representation of video data including the current block based on the updated th reference motion vector and the updated second reference motion vector.

Description

Motion prediction based on updated motion vectors

Cross Reference to Related Applications

The present application claims priority and benefit from international patent application No. PCT/CN2018/096384 entitled "motion prediction based on updated motion vectors" filed on 2018, 7, 20, month, according to applicable patent laws and/or rules under the paris convention the entire disclosure of international patent application No. PCT/CN2018/096384 is incorporated by reference as part of the disclosure of the present application.

Technical Field

This document relates to video encoding and video decoding techniques, devices and systems.

Background

Despite advances in video compression, digital video still accounts for the largest bandwidth usage on the internet and other digital communication networks. As the number of connected user devices capable of receiving and displaying video increases, the bandwidth requirements for pre-counting digital video usage will continue to grow.

Disclosure of Invention

Devices, systems, and methods related to digital video coding are described, and in particular, motion prediction based on updated motion vectors. The described methods may be applied to existing video coding standards, such as High Efficiency Video Coding (HEVC), and future video coding standards or video codecs.

In representative aspects, the disclosed techniques may be used to provide a method of video encoding that includes determining that a current block is associated with a th reference motion vector and a second reference motion vector, generating an updated th reference motion vector and an updated second reference motion vector based on a sum of a scaled th motion refinement and the th reference motion vector and a sum of a scaled th motion refinement and the second reference motion vector, respectively, wherein the motion refinement is derived based on a bi-directional optical flow mode, and performing a conversion between the current video block and a bitstream representation of video data that includes the current block based on the updated th reference motion vector and the updated second reference motion vector.

In another representative aspects, the disclosed techniques can be used to provide another method for processing video data that includes receiving a bitstream representation of a current block of video data and generating the current block by selectively using motion compensation for Overlapped Blocks (OBMC) to process the bitstream representation based on characteristics of the current block without signaling an OBMC flag.

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

In yet another representative aspect, devices configured or operable to perform the above-described methods are disclosed.

In yet another representative aspects, a video decoder device may implement a method as described herein.

The above aspects and features and other aspects and features of the disclosed technology are described in more detail in the accompanying drawings, the description and the claims.

Drawings

Fig. 1 shows an example of building a Merge candidate list.

Fig. 2 shows an example of the positions of spatial candidates.

Fig. 3 shows an example of a candidate pair subjected to a redundancy check of a spatial Merge candidate.

Fig. 4A and 4B illustrate examples of the location of the second prediction unit PU based on the size and shape of the current block.

Fig. 5 shows an example of motion vector scaling for the temporal Merge candidate.

Fig. 6 shows an example of candidate positions for the time Merge candidate.

Fig. 7 shows an example of generating combined bidirectional predictive Merge candidates.

Fig. 8 shows an example of constructing a motion vector prediction candidate.

Fig. 9 shows an example of motion vector scaling for spatial motion vector candidates.

Fig. 10 shows an example of motion prediction using an Alternative Temporal Motion Vector Prediction (ATMVP) algorithm for a Coding Unit (CU).

Fig. 11 shows an example of a Coding Unit (CU) having sub-blocks and neighboring blocks used by a spatial motion vector prediction (STMVP) algorithm.

Fig. 12A and 12B show example snapshots of sub-blocks when using the motion compensation for Overlapped Blocks (OBMC) algorithm.

Fig. 13 shows an example of neighboring samples used to derive parameters for a Local Illumination Compensation (LIC) algorithm.

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

Fig. 15 shows an example of an affine Motion Vector Field (MVF) of each sub-block.

Fig. 16 shows an example of Motion Vector Prediction (MVP) for the AF _ INTER affine motion mode.

Fig. 17A and 17B show example candidates for the AF _ MERGE affine motion mode.

Fig. 18 shows an example of bilateral matching in a mode-matched motion vector derivation (PMMVD) mode, which is a special Merge mode based on a Frame Rate Up Conversion (FRUC) algorithm.

Fig. 19 shows an example of template matching in the FRUC algorithm.

Fig. 20 shows an example of uni-directional motion estimation in the FRUC algorithm.

FIG. 21 shows an example of an optical flow trace used by a bi-directional optical flow (BIO) algorithm.

FIGS. 22A and 22B show example snapshots using a bi-directional optical flow (BIO) algorithm without block expansion.

Fig. 23 shows an example of a decoder-side motion vector refinement (DMVR) algorithm based on two-sided template matching.

Fig. 24 shows an example of a template definition used in transform coefficient context modeling.

FIG. 25 shows examples of inner and boundary sub-blocks in a PU/CU.

Fig. 26 illustrates a flow diagram of an example method for video encoding in accordance with the presently disclosed technology.

Fig. 27 shows a flow diagram of another example methods for video encoding in accordance with the presently disclosed technology.

Fig. 28 is a block diagram of an example of a hardware platform for implementing the visual media decoding or visual media encoding techniques described in this document.

Detailed Description

Due to the increasing demand for higher resolution video, video encoding methods and techniques are ubiquitous in modern technology. Video codecs typically include electronic circuits or software that compress or decompress digital video, and are continually being improved to provide higher coding efficiency. The video codec converts uncompressed video into a compressed format and vice versa. There is a complex relationship between video quality, the amount of data used to represent the video (determined by the bit rate), the complexity of the encoding and decoding algorithms, the susceptibility to data loss and errors, the ease of editing, random access, and end-to-end delay (latency). The compression format typically conforms to a standard video compression specification, such as the High Efficiency Video Coding (HEVC) standard (also known as h.265 or MPEG-H part 2), the general video coding standard to be completed, or other current and/or future video coding standards.

Embodiments of the disclosed techniques 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 this document to improve the readability of the description, and do not limit the discussion or the embodiments (and/or implementations) in any way to only the corresponding sections.

1. Example of inter prediction in HEVC/H.265

Video coding standards have improved significantly over the years and now provide, in part, high coding efficiency and support for higher resolution. Recent standards such as HEVC and h.265 are based on hybrid video coding structures that utilize temporal prediction plus transform coding.

1.1 example of inter prediction

Each inter-predicted PU (prediction Unit) has motion parameters for or two reference picture lists in embodiments the motion parameters include a motion vector and a reference picture index in other embodiments, inter _ pred _ idc may also be used to signal the use of of the two reference picture lists.

When a CU is encoded using skip mode, PUs are associated with the CU, and there are no significant residual coefficients, there are no motion vector deltas or reference picture indices to encode.

When the signaling indicates that of the two reference picture lists are to be used, the PU is generated from blocks of samples.

When the signaling indicates that two reference picture lists are to be used, the PU is generated from two blocks of samples. This is called "bi-prediction". Bi-prediction can only be used for B slices.

1.1.1 example of constructing candidates for Merge mode

When predicting a PU using the Merge mode, an index pointing to an entry in the Merge candidate list (mergecandidates list) is parsed from the bitstream and used to retrieve motion information. The construction of this list can be summarized according to the following sequence of steps:

step 1: initial candidate derivation

Step 1.1: spatial candidate derivation

Step 1.2: redundancy check of spatial candidates

Step 1.3: temporal candidate derivation

Step 2: additional candidate insertions

Step 2.1: creating bi-directional prediction candidates

Step 2.2: inserting zero motion candidates

FIG. 1 shows an example of building a Merge candidate list based on the sequence of steps summarized above.A maximum of four Merge candidates are selected among the candidates located at five different positions for spatial Merge candidate derivation.A maximum of Merge candidates are selected among the two candidates for temporal Merge candidate derivation.As the number of candidates per PU is assumed to be constant at the decoder, additional candidates are generated when the number of candidates does not reach the maximum Merge candidate number (MaxNumMergeCand) signaled in the slice header.

1.1.2 construction of spatial Merge candidates

In the derivation of spatial Merge candidates, a maximum of four Merge candidates are selected among the candidates located in the positions depicted in FIG. 2. The order of derivation is A₁、B₁、B₀、A₀And B₂. Only when in position A₁、B₁、B₀When any PU of A0 is not available (e.g., because the PU belongs to another stripes (slice) or slices (tile)) or is intra-codedThen, position B is considered₂. At the addition position A₁After the candidate of (a), the addition of the remaining candidates is subjected to a redundancy check that ensures that candidates with the same motion information are excluded from the list, thereby improving coding efficiency.

Instead, only the pairs linked to the arrows in FIG. 3 are considered, and the corresponding candidates for redundancy check are only added to the list if they have different motion information, the other sources of duplicate motion information are "second PUs" associated with a partition other than 2Nx2N, as an example, FIGS. 4A and 4B depict the second PU. for the N x2N and 2N x N cases, respectively, position A when the current PU is partitioned into N x2N₁In embodiments, adding this candidate may result in two prediction units with the same motion information, which is redundant to only PUs in a coding unit₁。

1.1.3 construction time Merge candidates

In particular, in the derivation of this temporal Merge candidate, scaled motion vectors are derived based on co-located (co-located) PUs belonging to pictures with the smallest POC difference with respect to the current picture within a given reference picture list.

FIG. 5 shows an example of derivation of a scaled motion vector for a temporal Merge candidate (e.g., dashed line) scaled from the motion vector of a co-located PU using POC distances tb and td, where tb is defined as the POC difference between a reference picture of a current picture and the current picture and td is defined as the POC difference between a reference picture of a co-located picture and the co-located picture.

As shown in FIG. 6, in the co-located PU (Y) belonging to the reference frame, in the candidate C₀And C₁Selects a location for the time candidate. If at position C₀Where PU is not available, intra-coded or outside the current CTU, then position C is used₁. Otherwise, position C is used in the derivation of the time Merge candidate₀。

1.1.4 construction of additional types of Merge candidates

In addition to the spatio-temporal Merge candidates, there are two additional types of Merge candidates, a combined bi-directional prediction Merge candidate and a zero Merge candidate.

Fig. 7 shows an example of this process in which two candidates with mvL0 and refIdxL0 or mvL1 and refIdxL1 in the original list (710, on the left) are used to create a combined bipredictive Merge candidate that is added to the final list (720, on the right).

These candidates have a zero spatial displacement and a reference picture index that starts from zero and increases each time a new zero motion candidate is added to the list.

1.1.5 examples of motion estimation regions for parallel processing

To mitigate the tradeoff 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 a "log 2_ parallel _ Merge _ level _ minus 2" syntax element, when the MER is defined, the Merge candidates that fall into the same region are marked as unavailable and are therefore also not considered in list construction.

1.2 example of Advanced Motion Vector Prediction (AMVP)

The motion vector candidate list is constructed by first checking the availability of the neighboring PU position to the left, above in time, removing the redundant candidates, and adding a zero vector to make the candidate list a constant length.

1.2.1 example of constructing motion vector prediction candidates

Fig. 8 summarizes the derivation process for motion vector prediction candidates and may be implemented for each reference picture list with refidx as input.

In motion vector prediction, two types of motion vector candidates are considered: spatial motion vector candidates and temporal motion vector candidates. As previously shown in fig. 2, for spatial motion vector candidate derivation, two motion vector candidates are finally derived based on the motion vectors of each PU located at five different positions.

For temporal motion vector candidate derivation motion vector candidates are selected from two candidates derived based on two different co-located positions after the th list of spatio-temporal candidates is made, duplicate motion vector candidates in the list are removed, if the number of potential candidates is greater than 2, the motion vector candidate whose reference image index within the associated reference image list is greater than 1 is removed from the list, if the number of spatio-temporal motion vector candidates is less than 2, an additional zero motion vector candidate is added to the list.

1.2.2 construction of spatial motion vector candidates

In the derivation of spatial motion vector candidates, a maximum of two candidates are considered among five potential candidates from PUs located at positions as previously shown in fig. 2, which are the same as those of the motion Merge. The derivation order of the left side of the current PU is defined as A₀、A₁And scaled A₀Zoom of A₁. The derivation order of the upper side of the current PU is defined as B₀、B₁、B₂Zoomed B₀Zoomed B₁Zoomed B₂Thus, for each side, there are four cases that can be used as motion vector candidates, two of which do not require the use of spatial scaling and two of which use spatial scaling.

No spatial scaling

(1) Same reference picture list, and same reference picture (same POC)

(2) Different reference picture lists, but the same reference picture (same POC)

Spatial scaling

(3) Same reference picture list, but different reference pictures (different POCs)

(4) Different reference picture lists, and different reference pictures (different POCs)

The case of no spatial scaling is checked first, followed by the case of allowing spatial scaling. Regardless of the reference picture list, spatial scaling is considered when POC is different between the reference pictures of the neighboring PU and the reference pictures of the current PU. If all PUs of the left candidate are not available or are intra coded, scaling of the above motion vector is allowed to aid in the parallel derivation of the left and above MV candidates. Otherwise, no spatial scaling is allowed for the upper motion vectors.

As shown in the example in fig. 9, for the spatial scaling case, the motion vectors of neighboring PUs are scaled in a similar way as for the temporal scaling differences are that the reference picture list and index of the current PU are given as input and the actual scaling procedure is the same as for the temporal scaling procedure.

1.2.3 constructing temporal motion vector candidates

All procedures 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) except for the reference picture index derivation, in embodiments, the reference picture index is signaled to the decoder.

2. Example of inter-frame prediction method in Joint Exploration Model (JEM)

In JEM, sub-block based prediction, 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), is employed in several coding tools.

2.1 example of sub-CU-based motion vector prediction

In a JEM with a quadtree plus binary tree (QTBT), each CU may have a set of up to motion parameters for each prediction direction in embodiments, two sub-CU level motion vector prediction methods are considered in the encoder by dividing the large CU into sub-CUs and deriving motion information for all of the sub-CUs of the large CU.

2.1.1 example of Alternative Temporal Motion Vector Prediction (ATMVP)

In the ATMVP method, a Temporal Motion Vector Prediction (TMVP) method is modified by acquiring a plurality of sets of motion information (including a motion vector and a reference index) from a block smaller than a current CU.

Fig. 10 shows an example of the ATMVP motion prediction process for a CU 1000. the ATMVP method predicts the motion vectors of sub-CUs 1001 within the CU1000 in two steps, step is to use the temporal vectors to identify corresponding blocks 1051 in the reference picture 1050, the reference picture 1050 is also called a motion source picture, the second step is to divide the current CU1000 into sub-CUs 1001 and obtain the motion vectors and reference indices for each sub-CU from the blocks corresponding to each sub-CU.

In step , the reference picture 1050 and corresponding block are determined from motion information of spatially neighboring blocks of the current CU 1000. to avoid a repeated scanning process of the neighboring blocks, the Merge candidate in the Merge candidate list of the current CU1000 is used. the available motion vector and its associated reference index are set to the time vector and index of the motion source picture.

In a second step, the corresponding block of sub-CU 1051 is identified from the time vector in the motion source image 1050 by adding the time vector to the coordinates of the current CU. For each sub-CU, the motion information of its corresponding block (e.g., the minimum motion grid covering the center samples) is used to derive the motion information of the sub-CU. After identifying the motion information of the corresponding nxn block, it is converted into a motion vector and reference index of the current sub-CU in the same way as the TMVP of HEVC, in which motion scaling and other processes are applied. For example, the decoder checks whether a low delay condition is met (e.g., POC of all reference pictures of the current picture is less than POC of the current picture) and possibly uses a motion vector MVx (e.g., a motion vector corresponding to reference picture list X) for predicting a motion vector MVy of each sub-CU (e.g., where X equals 0 or 1 and Y equals 1-X).

2.1.2 example of spatial motion vector prediction (STMVP)

In the STMVP method, the motion vectors of sub-CUs are recursively derived in raster scan order.

Fig. 11 shows an example of CUs with four sub-blocks and neighboring blocks consider an 8 × 8CU 1100 that includes four 4 × 4 sub-CUs a (1101), B (1102), C (1103), and D (1104) the neighboring 4 × 4 blocks in the current frame are labeled (1111), B (1112), C (1113), and D (1114).

The th neighbor is the nxn block (block c 1113) above the sub-CU a 1101. if this block c (1113) is not available or intra coded, the other nxn blocks above the sub-CU a (1101) are checked (from left to right, starting from block c 1113) if this block c (1113) is not available or intra coded.the second neighbor is the block to the left of the sub-CU a1101 (block b 1112). if block b (1112) is not available or intra coded, the other blocks to the left of the sub-CU a1101 are checked (from top to bottom, starting from block b 1112).

2.1.3 example of sub-CU motion prediction mode signaling

In embodiments, sub-CU mode is enabled as additional Merge candidates and no additional syntax elements are needed to signal the mode.in other embodiments, up to seven Merge candidates may be used if the sequence parameter set indicates that ATMVP and STMVP are enabled.

2.2 example of adaptive motion vector disparity resolution

In embodiments, when use _ integer _ mv _ flag in slice header is equal to 0, Motion Vector Difference (MVD) between motion vector of PU and predicted motion vector is signaled in units of luma samples in JEM, local adaptive motion vector resolution (lamfr) is introduced in JEM, MVD can be coded in units of quarter luma samples, integer luma samples or four luma samples in JEM MVD controls MVD resolution at Coding Unit (CU) level and conditionally signals MVD resolution flag to each CU with at least non-zero MVD components.

For CUs with at least non-zero MVD components, flag is signaled to indicate whether to use -quarter luma sample MV precision in the CU when flag (equal to 1) indicates that -quarter luma sample MV precision is not used, another flags are signaled to indicate whether integer luma sample MV precision or four luma sample MV precision is used.

When the th MVD resolution flag of a CU is zero, or is not coded for the CU (meaning that all MVDs in the CU are zero), the quarter luma sample MV resolution is used for this CU. when the CU uses integer luma sample MV precision or four luma sample MV precision, the MVPs in the CU's AMVP candidate list are rounded to the corresponding precision.

In the encoder, CU level RD check is used to determine which MVD resolution will be used for the CU. In other words, the CU-level RD check is performed three times for each MVD resolution. To speed up the encoder speed, the following encoding scheme is applied in JEM.

Motion information (integer luma sample precision) for this current CU is stored during RD check of a CU with normal quarter luma sample MVD resolution for the same CU with integer luma samples and 4 luma sample MVD resolutions, the stored motion information (after rounding) is used as a starting point for further small range motion vector refinements during RD check, so that the time consuming motion estimation process is not repeated three times.

For a CU, when the RD cost of an integer luma sample MVD resolution is much greater than the RD cost of a quarter luma sample MVD resolution, the RD check of the 4 luma sample MVD resolutions for that CU is skipped.

2.3 example of higher motion vector storage precision

In HEVC, the motion vector precision is one-quarter pixels (pel) (one-quarter luma samples and one-eighth chroma samples for 4:2:0 video.) in JEM, the precision of the inner motion vector storage and the Merge candidate is increased to 1/16 pixels.

The chroma component motion vector precision is 1/32 samples in JEM, deriving 1/32 fractional-pel additional interpolation filters by using the average of the filters at two adjacent 1/16 fractional-pel positions.

2.4 example of motion Compensation (OBMC) for overlapping blocks

In JEM, OBMC may be switched using a syntax element at a CU level, when OBMC is used in JEM, OBMC is performed on all Motion Compensation (MC) block boundaries excluding a right side boundary and a bottom boundary of a CU.

Fig. 12A shows sub-blocks at the CU/PU boundary, the shaded sub-blocks being where OBMC is applied. Similarly, fig. 12B shows the sub-PU in ATMVP mode.

When OBMC is applied to the current sub-block, in addition to the current MV, the vectors of the four neighboring sub-blocks (if available and not exactly the same as the current motion vector) are also used to derive the prediction block for the current sub-block. The plurality of prediction blocks based on the plurality of motion vectors are combined to generate a final prediction signal of the current sub-block.

The prediction block based on the motion vector of the neighboring sub-blocks is represented as PN, where N indicates the indexes of the sub-blocks adjacent to the upper, lower, left, and right sides, and the prediction block based on the motion vector of the current sub-block is represented as PC. OBMC is not performed from the PN when the PN is based on motion information of neighboring sub-blocks and the motion information is the same as that of the current sub-block. Otherwise, each sample of PN is added to the same sample in the PC, i.e., four rows/columns of PN are added to the PC. The weighting factors {1/4,1/8,1/16,1/32} are for PN and the weighting factors {3/4,7/8,15/16,31/32} are for PC. The exception is that only two rows/columns of PN are added to the PC for small MC blocks (i.e., when the height or width of the coding block is equal to 4 or the CU uses sub-CU mode coding). In this case, the weighting factors {1/4,1/8} are used for PN, and the weighting factors {3/4,7/8} are used for PC. For a PN generated based on motion vectors of vertically (horizontally) adjacent sub-blocks, samples in the same row (column) of the PN are added to PCs having the same weighting factor.

In JEM, for CUs with a size less than or equal to 256 luma samples, a CU level flag is signaled to indicate whether OBMC is to be applied to the current CU. For CUs with a size larger than 256 luma samples or without AMVP mode coding, OBMC is applied by default. At the encoder, when OBMC is applied to a CU, its effect is taken into account during the motion estimation phase. The prediction signal formed by OBMC using the motion information of the top-neighboring block and the left-neighboring block is used to compensate the top boundary and the left boundary of the original signal of the current CU, and then the normal motion estimation process is applied.

2.5 example of Local Illumination Compensation (LIC)

LIC uses a scaling factor a and an offset b based on a linear model for the luminance variation. And, the LIC is adaptively enabled or disabled for each inter-mode coded Coding Unit (CU).

When LIC is applied to a CU, the parameters a and b are derived using the least square error method by using neighboring samples of the current CU and their corresponding reference samples. Fig. 13 shows an example of adjacent samples for deriving parameters of an IC algorithm. Specifically, and as shown in fig. 13, neighboring samples of the sub-sampling (2:1 sub-sampling) of the CU and corresponding samples in the reference image (which are identified by motion information of the current CU or sub-CU) are used. IC parameters are derived and applied separately for each prediction direction.

When a CU is encoded using the Merge mode, copying LIC flags from neighboring blocks in a manner similar to the motion information copy in the Merge mode; otherwise, the LIC flag is signaled to the CU to indicate whether LIC is applicable.

When LIC is enabled for an image, an additional CU level RD check is needed to determine whether to apply LIC to the CU. When LIC is enabled for a CU, the integer-pixel motion search and fractional-pixel motion search are performed separately, using the mean-removed sum of absolute differences (MR-SAD) and the mean-removed sum of absolute Hadamard-transformed differences (MR-SATD), instead of SAD and SATD.

To reduce the coding complexity, the following coding scheme is applied in JEM.

When there is no significant brightness variation between the current image and its reference image, LIC is disabled for the entire image. To identify this, at the encoder, a histogram of the current image and each reference image of the current image is computed. Disabling LIC for a current picture if the histogram difference between the current picture and each reference picture of the current picture is less than a given threshold; otherwise, the LIC is enabled for the current image.

Example of 2.6 affine motion compensated prediction

In HEVC, only the translational motion model is applied to Motion Compensated Prediction (MCP). however, cameras and objects may have multiple motions, such as zoom in/out, rotation, perspective motion, and other irregular motions₀And V₁An example of an affine motion field of block 1400 is described. The Motion Vector Field (MVF) of block 1400 may be described by the following equation:

as shown in FIG. 14, (v)_0x,v_0y) Is the motion vector of the control point of the left corner, (v)_1x,v_1y) Is the motion vector of the right corner control point. To simplify motion compensated prediction, sub-block based affine transform prediction may be applied. The subblock size M × N is derived as the following equation:

where MvPre is the motion vector fractional precision (e.g., 1/16 in JEM), (v)_2x,v_2y) Is the motion vector of the lower left control point, calculated according to equation (1). If desired, M and N can be adjusted downward to be divisors of w and h, respectively.

Fig. 15 shows an example of affine MVF of each sub-block of the block 1500. To derive the motion vector for each M × N sub-block, the motion vector for the center sample of each sub-block may be calculated according to equation (1) and rounded to motion vector fractional precision (e.g., 1/16 in JEM). A motion compensated interpolation filter may then be applied to generate a prediction for each sub-block using the derived motion vectors. After MCP, the high precision motion vector of each sub-block is rounded and saved with the same precision as the normal motion vector.

In JEM, there are two affine motion patterns: AF _ INTER mode and AF _ MERGE mode. For CUs with a width and height greater than 8, the AF _ INTER mode may be applied. An affine flag at the CU level is signaled in the bitstream to indicate whether AF _ INTER mode is used. In AF _ INTER mode, neighboring blocks are used to construct pairs of motion vectors { (v)₀,v₁)|v₀＝{v_A,v_B,v_c},v₁＝{v_D,v_E} of the candidate list.

Fig. 16 shows an example of Motion Vector Prediction (MVP) for a block 1600 in AF _ INTER mode. As shown in FIG. 16, v is selected from the motion vectors of blocks A, B or C₀. The motion vectors from the neighboring blocks may be scaled according to the reference list. The motion vector may also be scaled according to a relationship between a reference Picture Order Count (POC) of the neighboring block, the reference POC of the current CU, and the POC of the current CU. Selecting v from adjacent sub-blocks D and E₁When the candidate list is greater than 2, the candidates may be first classified according to neighboring motion vectors (e.g., based on the similarity of the two motion vectors in the candidate pair). in implementations, the first two candidates are retained.in implementations, a Rate Distortion (RD) cost check is used to determine which motion vector pair candidate to select as the Control Point Motion Vector Prediction (CPMVP) for the current CU.

When a CU is applied in AF _ MERGE mode, it gets the th block encoded using affine mode from the valid neighboring reconstructed blocks FIG. 17A shows an example of the selection order of candidate blocks for the current CU 1700 As shown in FIG. 17A, the selection order may be from left (1701), above (1702), above-right (1703), below-left (1704), to above-left (1705) of the current CU 1700. FIG. 17B showsAnother examples of candidate blocks for the current CU 1700 in AF _ MERGE mode are shown in fig. 17B, if the adjacent bottom left block 1701 is encoded in affine mode, then a motion vector v is derived that contains the top left corner, top right corner and bottom left corner of the CU of sub-block 1701₂、v₃And v₄. Based on v₂、v₃And v₄To calculate the motion vector v of the top left corner of the current CU 1700₀. The motion vector v at the top right of the current CU can be calculated accordingly₁。

Calculating the CPMV v of the current CU according to the affine motion model in equation (1)₀And v₁To identify whether the current CU uses AF _ MERGE mode encoding, an affine flag may be signaled in the bitstream when there are at least neighboring blocks encoded in affine mode.

2.7 example of motion vector derivation by Pattern matching (PMMVD)

Using this mode, the motion information of the block is not signaled, but is derived at the decoder side.

When the Merge flag of a CU is true, the FRUC flag may be signaled to the CU. When the FRUC flag is false, the Merge index may be signaled and the normal Merge mode used. When the FRUC flag is true, an additional FRUC mode flag may be signaled to indicate which method (e.g., bilateral matching or template matching) will be used to derive the motion information for the block.

For example, the various matching patterns (e.g., bilateral matching and template matching) for a CU are checked by using RD cost selection, the matching pattern that results in the least cost is compared with other CU patterns .

In general, the motion derivation process in FRUC Merge mode has two steps.cu-level motion search is performed first, followed by sub-CU-level motion refinement.at the CU level, an initial motion vector is derived for the entire CU based on bilateral matching or template matching.first, a list of MV candidates is generated and the candidate that results in the smallest matching cost is selected as the starting point for the further CU-level refinements.then, local search based on bilateral matching or template matching is performed around the starting point MV. that will result in the smallest matching cost as the entire cu.subsequently, the motion information is refined at the sub-CU level, with the derived CU motion vector as the starting point.

At stage , MV., which derives the overall WxHCU, at stage 3883 the CU is further split into M × M sub-CU. to compute the value of M as in equation (3), D is a predefined split depth, which is set to 3 by default in JEM.

Under the assumption of a continuous motion trajectory, the motion vectors MV0(1801) and MV1(1802) pointing to the two reference blocks are proportional to the temporal distance between the current image and the two reference images, e.g., TD0(1803) and TD1 (1804). in embodiments, the bilateral matching becomes a mirror-based bi-directional MV when the current image (1800) is temporally between the two reference images (1810,1811) and the temporal distance from the current image to the two reference images is the same.

In addition to the FRUC Merge mode described above, template matching may also be applied to AMVP mode.in both JEM and HEVC, AMVP has two candidates.

The CU-level MV candidate set may include: (1) the current CU is the original AMVP candidate if it 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.

When using bilateral matching, each valid MV of the Merge candidate may be used as an input to generate MV pairs assuming bilateral matching, e.g., valid MVs of the Merge candidate are in reference list A (MVa, ref)_a). Then, the reference picture ref of its paired bilateral MV is found in the other reference list B_bSo that ref_aAnd ref_bTemporally on different sides of the current image. If such a ref in list B is referenced_bIf not, then ref_bIs determined as being equal to ref_aDifferent references, and ref_bThe temporal distance to the current image is the minimum in list B. In the determination of ref_bThen, based on the current image and ref_a、ref_bThe temporal distance between them is derived by scaling MVa to derive MVb.

More specifically, interpolation MV. at positions (0,0), (W/2,0), (0, H/2), and (W/2, H/2) of the current CU is added when FRUC is applied to AMVP mode, the original AMVP candidate is also added to the CU level MV candidate set.

The sub-CU level MV candidate set includes (1) MVs determined from the CU level search, (2) top, left top, and right top neighboring MVs, (3) scaled versions of collocated MVs from the reference picture, (4) or more ATMVP candidates (e.g., up to four), and (5) or more STMVP candidates (e.g., up to four).

Generation of interpolated MV domains

Before encoding a frame, an interpolated motion field is generated for the entire image based on one-sided ME. The motion field may then be used later as a CU-level or sub-CU-level MV candidate.

Fig. 20 shows an example of uni-directional Motion Estimation (ME)2000 in the FRUC method for each 4x4 block, if the motion associated with the block passes through a 4x4 block in the current image and the block has not been assigned any interpolated motion, the motion of the reference block is scaled to the current image according to temporal distances TD0 and TD1 (in the same way as the 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 the 4x4 block, the motion of the block is marked as unavailable in the interpolated motion domain.

Interpolation and matching costs

When the motion vector points to a fractional sample position, motion compensated interpolation is required. To reduce complexity, both bilateral matching and template matching may use bilinear interpolation instead of conventional 8-tap HEVC interpolation.

The matching cost is calculated somewhat differently at different steps. When selecting candidates from the candidate set at the CU level, the matching cost may be a Sum of Absolute Differences (SAD) of bilateral matching or template matching. After determining the starting MV, the matching cost C for the bilateral matching of the sub-CU level search is calculated as follows:

where w is weighting factors in embodiments w is empirically set to 4, MV and MV^sIndicating the current MV and the starting MV, respectively. SAD may still be used as the matching cost for template matching for sub-CU level search.

In FRUC mode, MVs are derived by using only luminance samples. The derived motion will be used for the luminance and chrominance of the MC inter prediction. After the MV is determined, the final MC is performed using an 8-tap interpolation filter for luminance and a 4-tap interpolation filter for chrominance.

In JEM, two search modes are supported-unrestricted center-biased Diamond search (UCBDS) and adaptive Cross search (adaptive search) for MV refinement at the CU level and sub-CU level, respectively-for CU level and sub-CU level MV refinement, MV is searched directly at the quarter luma sample MV precision and then refined at the eighth luma sample MV.

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 images. In the template matching Merge mode, the encoder may select among unidirectional prediction from list 0, unidirectional prediction from list 1, or bi-directional prediction for a CU. The selection may be based on the template matching cost, as follows:

if costBi & gt factor & ltmin (cost0, cost1)

Using bi-directional prediction;

otherwise, if cost0< ═ cost1

Using one-way prediction from list 0;

if not, then,

using unidirectional prediction from list 1;

where cost0 is the SAD of the List 0 template match, cost1 is the SAD of the List 1 template match, and cost Bi is the SAD of the bidirectional prediction template match. For example, when the value of the factor is equal to 1.25, this means that the selection process is biased towards bi-directional prediction. Inter prediction direction selection may be applied to the CU level template matching process.

2.8 example of bidirectional optical flow (BIO)

The bi-directional optical flow (BIO) method is a sample-wise motion refinement performed on top of block-wise motion compensation for bi-directional prediction in implementations, sample-level motion refinement does not use signaling.

Let I^(k)Is the luminance value of reference k (k 0,1) after block motion compensation and will be

Are respectively represented as I^(k)The horizontal and vertical components of the gradient. Assuming that the optical flow is valid, the motion vector field (v)_x,v_y) Given by the following equation.

Combining the optical flow equation with Hermite interpolation to obtain the motion track of each sampling point, and matching the function value I^(k)Partial derivative of sum

The only third order polynomial the value of this polynomial is BIO prediction when t is 0:

fig. 21 shows an example of an optical flow trajectory in the bidirectional optical flow (BIO) method. Wherein, tau₀And τ₁Indicating the distance to the reference frame. Distance tau₀And τ₁Based on Ref₀And Ref₁To calculate the POC of: tau is₀POC (when)Pre) -POC (Ref0), τ₁POC (Ref1) -POC (current). If both predictions are from the same time direction (either from the past or the future), then the sign is different (e.g., τ)₀·τ₁<0). In this case, if the predictions are not from the same time instant (e.g., τ)₀≠τ₁) BIO is applied. Both reference regions have non-zero motion (e.g., MVx)₀,MVy₀,MVx₁,MVy₁Not equal to 0) and block motion vector to temporal distance (e.g., MVx)₀/MVx₁＝MVy₀/MVy₁＝-τ₀/τ₁) Is in direct proportion.

Determining a motion vector field (v) by minimizing the difference Δ between the values in points A and B_x,v_y) 22A and 22B show examples of the intersection of the motion trajectory and the reference frame plane the model uses only the th linear term for the local Taylor expansion of Δ:

assuming that the motion is -fold in the local surrounding area, Δ can be minimized within a (2M +1) × (2M +1) square window Ω centered on the current predicted point (i, j), where M equals 2:

for this optimization problem, JEM uses a simplified approach, first minimizing in the vertical direction, and then minimizing in the horizontal direction. This results in

Wherein,

to avoid division by zero or very small values, regularization parameters r and m are introduced in equations (9) and (10).

r＝500·4^d-8(12)

m＝700·4^d-8(13)

Where d is the bit depth of the video samples.

To keep the memory access for BIO the same as for conventional bi-predictive motion compensation, all predictions and gradient values I are computed for the position within the current block^(k)、FIG. 22A shows an example of an access location outside of block 2200. As shown in fig. 22A, in equation (9), (2M +1) × (2M +1) square window Ω centered on the current prediction point on the boundary of the prediction block needs to access the position outside the block. In JEM, I outside the block^(k)、

Is set equal to the nearest available value within the block. This may be accomplished, for example, as filling region 2201, as shown in fig. 22B.

Using BIO, it is possible that the motion field can be refined for each sample. To reduce computational complexity, a block-based BIO design may be used in JEM. The motion refinement may be calculated based on 4x4 blocks. In block-based BIO, s in equation (9) can be aggregated for all samples in a 4 × 4 block_nValue, and then polymerizing the polymerized s_nThe values are used for the derived BIO motion vector offset for the 4x4 block. More specifically, the following formula may be used for block-based BIO derivation:

wherein b is_kRepresentation of belonging toA set of samples of the kth 4x4 block of the prediction block. From ((s)_n,bk)>>4) S in substitution equation (9) and equation (10)_nTo derive the associated motion vector offset.

In cases, the MV group (region) of the BIO may be unreliable due to noise or irregular motion in the BIO, therefore, the magnitude of the MV group is limited to a threshold value¹⁴ ^-d(ii) a Otherwise, it is set to 12 × 2^13-d。

The gradient of the BIO may be computed simultaneously with the motion compensated interpolation using operations that result from the HEVC motion compensation process (e.g., a 2D separable finite impulse response FIR), in embodiments , the input to this 2D separable FIR is the same reference frame sample point as the motion compensation process and fractional position (fracX, fracY) based on the fractional portion of the block motion vector

The signal is vertically interpolated using the bialters first corresponding to the fractional position fracY with the de-scaling offset d-8, and then the gradient filter bialterg is applied in the horizontal direction corresponding to the fractional position fracX with the de-scaling offset 18-d. For vertical gradients

The signal shifting is performed in the horizontal direction using the bialters, first with respect to the fractional position fracY with the de-scaling offset d-8, vertically applying the gradient filter using the bialterg, and then with respect to the fractional position fracX with the de-scaling offset 18-d. The length of the interpolation filter used for gradient computation bialterg and signal displacement bialterf may be short (e.g., 6 taps) to maintain reasonable complexity. Table 1 shows an example filter that can be used for gradient calculations for different fractional positions of block motion vectors in a BIO. Table 2 shows an example interpolation filter that may be used for prediction signal generation in BIO.

Exemplary Filter for gradient computation in Table 1 BIO

Exemplary interpolation Filter for prediction Signal Generation in Table 2 BIO

Fractional pixel position	Interpolation filter for prediction signal (BIOfilters)
		0	{0,0,64,0,0,0}
1/16	{1,-3,64,4,-2,0}
		1/8	{1,-6,62,9,-3,1}
3/16	{2,-8,60,14,-5,1}
		1/4	{2,-9,57,19,-7,2}
5/16	{3,-10,53,24,-8,2}
		3/8	{3,-11,50,29,-9,2}
7/16	{3,-11,44,35,-10,3}
		1/2	{3,-10,35,44,-11,3}

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

To reduce computational complexity, BIO may not be applied during the OBMC process, meaning that BIO is applied to the MC process of a block when its own MVs are used, and BIO is not applied to the MC process when the MVs of neighboring blocks are used in the OBMC process.

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

In a bi-prediction operation, to predict block regions, two prediction blocks, formed using the Motion Vectors (MVs) of List 0 and the MVs of List 1, respectively, are combined to form a single prediction signal in a decoder-side motion vector refinement (DMVR) method, the two motion vectors of bi-prediction are further refined by a double-sided template matching process.

As shown in FIG. 23, in DMVR, two-sided templates are generated from the initial MV0 of List 0 and the MV1 of List 1, respectively, as a weighted combination (i.e., average) of the two prediction blocks the template matching operation includes computing a cost metric between the generated template and the sample region in the reference image (around the initial prediction block). for each of the two reference images, the MV yielding the smallest template cost is treated as the updated MV of the list to replace the original template. in JEM, for each list, nine MV candidates are searched, which include the original MV and 8 surrounding MVs, with luminance samples shifted to the original MV. last in the horizontal or vertical direction or in both directions, as shown in FIG. 23, two new MVs, MV0 'and MV1', are used to generate the final bi-directional prediction result.

DMVR is applied to the bidirectionally predicted Merge mode, using MVs from past reference pictures and another MV. from future reference pictures in JEM without transmitting additional syntax elements, DMVR is not applied when LIC, affine motion, FRUC or sub-CU Merge candidates are enabled for a CU.

Example of CABAC modification

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

context modeling of modified transform coefficients

Multi-hypothesis probability estimation with context-dependent update speed

Adaptive initialization of context models

3.1 example of context modeling of transform coefficients

In HEVC, transform coefficients of an encoded block are encoded using non-overlapping Coefficient Groups (CGs), and each CG contains coefficients of a 4 × 4 block of the encoded block, the CGs within the encoded block and the transform coefficients within the CGs are encoded according to a predefined scan order the encoding of transform coefficient levels of a CG having at least non-zero transform coefficients may be divided into multiple scan channels in the channel th bin (represented by bin0, also referred to as significant _ coeff _ flag, which indicates that the magnitude of the coefficients is greater than 0) is encoded next two scan channels for context coding the second/third bin (represented by bin1 and bin2, respectively, also referred to as coeff _ abs _ greater1_ flag and coeff _ abs _ greater2_ flag) may be applied.

In JEM, the context modeling of the regular bin is changed. When bin i is coded in the ith scan channel (i is 0,1,2), the context index depends on the value of the ith bin of previously coded coefficients in the neighborhood covered by the local template. Specifically, the context index is determined based on the sum of the ith bin of the neighboring coefficients.

As shown in FIG. 24, the local template contains up to five spatially adjacent transform coefficients, where x indicates the position of the current transform coefficient and xi (i is 0 to 4) indicates its five neighbors to capture the characteristics of the transform coefficients of different frequencies, coding blocks can be divided into up to three regions and the division method is fixed regardless of the coding block size.

3.2 example of Multi-hypothesis probability estimation

Binary arithmetic coder estimates P based on two probabilities associated with each context model₀And P₁The "multi-hypothesis" probability update model is applied and independently updated at different adaptation rates as follows:

wherein,

andrepresenting the probabilities before and after decoding the bin, respectively. Variable M_i(4, 5,6,7) is a parameter that controls the probability update speed of the context model with index equal to i; and k tableThe accuracy of the probability (here equal to 15) is shown.

The probability estimate P for an interval subdivision in a binary arithmetic encoder is the average of estimates from two hypotheses:

P＝(P₀ ^new+P₁ ^new)/2 (16)

in JEM, parameter M used in equation (15) for controlling the probability update speed of each context model_iThe values of (c) are assigned as follows:

on the encoder side, the coded bins associated with each context model are recorded after coding slices, for each context model with index equal to i, the calculation uses a different M_iRate cost of value (4, 5,6,7) and select M that provide the minimum rate cost_iThe value is obtained. For simplicity, this selection process is only performed when a new combination of slice type and slice-level quantization parameter is encountered.

Signaling a 1-bit flag for each context model i to indicate M_iWhether different from the default value of 4. When the flag is 1, two bits are used to indicate M_iWhether it is equal to 5,6 or 7.

3.3 example of initialization of context model

Instead of using a fixed table for initialization of context models in HEVC, the initial probability state of a context model for a slice of inter-coding may be initialized by copying the state from a previously coded picture. More specifically, after encoding the centrally located CTU for each picture, the probability states of all context models are stored to be used as initial states for the corresponding context models on subsequent pictures. In JEM, the initial state set of each inter-coded slice is copied from the storage state of the previously coded picture with the same slice type and the same slice level QP as the current slice. This lacks loss robustness, but is used for coding efficiency experimental purposes in the current JEM scheme.

4. Examples relating to embodiments and methods

Methods related to the disclosed technology include extended LAMVR, where the supported motion vector resolution ranges from 1/4 pixels to 4 pixels (1/4 pixels, 1/2 pixels, 1 pixel, 2 pixels, and 4 pixels). When the MVD information is signaled, information on the motion vector resolution is signaled at the CU level.

Both the Motion Vector (MV) and the Motion Vector Predictor (MVP) of the CU are adjusted depending on the resolution of the CU. If the applied motion vector resolution is denoted as R (R may be 1/4, 1/2, 1,2, 4), then MV (MV)_x，MV_y) And MVP (MVP)_x，MVP_y) Is represented as follows:

(MV_x,MV_y)＝(Round(MV_x/(R*4))*(R*4),Round(MV_y/(R*4))*(R*4))

(MVP_x,MVP_y)＝(Round(MVP_x/(R*4))*(R*4),Round(MVP_y/(R*4))*(R*4))

MVD (MVD) because both the motion vector predictor and the MV are adjusted by adaptive resolution_x，MVD_y) Also aligned with the resolution and signaled according to the resolution as follows:

(MVD_x,MVD_y)＝((MV_x–MVP_x)/(R*4),(MV_y–MVP_y)/R*4))

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

Table 3 example of MVR index representation

In the case of bi-prediction, the AMVR has 3 modes for each resolution. AMVR Bi-directional index indicates whether to signal the MVD of each reference List (List 0 or List 1)_x、MVD_y. An example definition of the AMVR bi-directional index is shown in the following table.

Example of Table 4 AMVR Bi-directional indexing

AMVR bidirectional indexing	List 0 (MVD)_x,MVD_y)	List 1 (MVD)_x,MVD_y)
			0	Signaling notification	Signaling notification
1	Non-signaling notification	Signaling notification
			2	Signaling notification	Non-signaling notification

5. Examples of existing implementations

In prior implementations using BIO, the calculated MV between the reference block/sub-block in List 0 (represented by refblk 0) and the reference block/sub-block in List 1 (refblk1) -is composed of (v @_x,v_y) Representation-only for motion compensation of the current block/sub-block and not for motion prediction, deblocking, OBMC, etc. of future coding blocks, which may be inefficient.

In another prior implementations using OBMC, for AMVP mode, it is determined at the encoder whether OBMC is enabled for a small block (width x height < > 256) and the decoder is signaled.

6. Example method for motion prediction based on updated MVs

The disclosed techniques, based on which motion prediction using updated motion vectors can enhance existing and future video coding standards, are set forth in the examples described below for various implementations.

With respect to terminology, reference pictures for current pictures from list 0 and list 1 are denoted as Ref0 and Ref1, respectively. Take tau₀POC (current) -POC (Ref0), τ₁POC (Ref1) -POC (current), and reference blocks for the current block from Ref0 and Ref1 are represented by refblk0 and refblk1, respectively. For the sub-block in the current block, the MV pointing to refblk1 of its corresponding sub-block in refblk0 is represented by (v)_x,v_y) And (4) showing. The MVs of the sub-blocks in Ref0 and Ref1 are respectively composed of (mvL0_x,mvL0_y) And (mvL 1)_x,mvL1_y) And (4) showing. As described in this patent document, the updated motion vector-based approach for motion prediction can be extended to existing and future video coding standards.

Example 1. It is proposed to modify the motion information of the BIO coding block (e.g. differently than used in motion compensation), which can be used later, such as in a subsequent motion prediction (e.g. TMVP) process.

(a) In examples, it is proposed to scale the MV (v) derived in the BIO_x,v_y) And adds it to the original MV (mvLX) of the current block/sub-block_x,mvLX_y) (X ═ 0 or 1). The updated MV is calculated as follows: mvL 0'_x＝-v_x*(τ₀/(τ₀+τ₁))+mvL0_x,mvL0’_y＝-v_y*(τ₀/(τ₀+τ₁))+mvL0_y,and mvL1’_x＝v_x*(τ₁/(τ₀+τ₁))+mvL1_x,mvL1’_y＝v_y*(τ₁/(τ₀+τ₁))+mvL1_y。

(i) In examples, the updated MV is used for future motion prediction (as in AMVP, Merge, and affine modes), deblocking (deblocking), OBMC, and so on.

(ii) Alternatively, the updated MV can only be used for motion prediction on CUs/PUs that are not immediately following it in decoding order.

(iii) Alternatively, the updated MV may only be used as TMVP in AMVP, Merge, or affine mode.

Example 2. It is proposed that for BIO, DMVR, FRUC, template matching or other methods that require updating MVs (or motion information including MVs and/or reference pictures) derived from the bitstream, the use of updated motion information may be constrained.

(a) In examples, updated motion information for sub-blocks may be stored, and for the other remaining sub-blocks, the non-updated motion information may be stored.

(b) In examples, if the MV (or motion information) is updated at the sub-block level, the updated MV is stored only for the inner sub-blocks (i.e., sub-blocks not at PU/CU/CTU boundaries) and then used for motion prediction, deblocking, OBMC, etc., as shown in fig. 25.

(c) In examples, the updated MV or motion information is not used for motion prediction and obmc.

(d) In examples, the updated MV or motion information is used only for motion compensation and temporal motion prediction, such as TMVP/ATMVP.

Example 3. It is proposed to implicitly enable/disable OBMC depending on coding mode, motion information, size or location of PU/CU/block and thus not to signal OBMC flag.

(a) In examples, OBMC is disabled for a PU/CU/block encoded in AMVP mode or AFFINE _ INTER mode if of the following conditions are met (where w and h are the width and height of the PU/CU/block).

(i)w×h<＝T

(ii)w<＝T&&h<＝T

(b) In examples, OBMC is always enabled for PU/CU/blocks encoded in both the Merge mode and the AFFINE _ Merge mode.

(c) Alternatively, in addition, vertical and horizontal OBMC are separately disabled/enabled. If the PU/CU/block height is less than T, then vertical OBMC is disabled. If the width of the PU/CU/block is less than T, horizontal OBMC is disabled.

(d) In examples, no neighboring MVs from the top row are used in OBMC for PU/CU/block/sub-block at the top CTU boundary.

(e) In examples, the neighboring MVs from the left column are not used in the OBMC for the PU/CU/block/sub-block at the left CTU boundary.

(f) In examples, only OBMC for uni-directionally predicted PU/CU/block/sub-block is enabled.

(g) In examples, OBMC is disabled for PU/CU/blocks whose MVD resolution is greater than or equal to an integer pixel.

Example 4. Whether OBMC is proposed to be enabled may depend on the motion information of the current PU/CU/block/sub-block and its neighboring PU/CU/block/sub-block.

(a) In examples, if a neighboring PU/CU/block/sub-block has motion information that is quite different (quadrature differential) from the current PU/CU/block/sub-block, its motion information is not used in OBMC.

(i) In examples, the neighboring PU/CU/block/sub-block has a different prediction direction or reference picture than the current PU/CU/block/sub-block.

(ii) In examples, the neighboring PU/CU/block/sub-block has the same prediction direction and reference picture as the current PU/CU/block/sub-block, however, the absolute horizontal/vertical MV difference between the neighboring PU/CU/block/sub-block and the current PU/CU/block/sub-block in the prediction direction X (X ═ 0 or 1) is greater than a given threshold MV _ TH.

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

(i) In examples, the neighboring PU/CU/block/sub-block has the same prediction direction and reference picture as the current PU/CU/block/sub-block, and the absolute horizontal/vertical MV difference between the neighboring PU/CU/block/sub-block and the current PU/CU/block/sub-block in all prediction directions is less than a given threshold MV _ TH.

Example 5. It is proposed that OBMC can be performed at block sizes different from the sub-block size in ATMVP/STMVP, affine mode, or other mode where each sub-block (size N × M) within a PU/CU has separate motion information.

(a) In examples, the sub-block size is 4 × 4, and OBMC is performed only at 8 × 8 block boundaries.

Example 6. How many rows/columns are proposed to be processed in OBMC may depend on PU/CU/block/sub-block size.

(a) In examples, if the width of the PU/CU/block/sub-block is greater than N, then 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.

(b) In examples, if the height of the PU/CU/block/sub-block is greater than N, then the upper 4 rows of the PU/CU/block/sub-block are processed, otherwise, only the upper 2 (or 1) rows of the PU/CU/block/sub-block are processed.

Example 7. It is proposed to enable/disable OBMC for luminance and chrominance components independently, and the rules described in examples 2 and 3 can be applied to each component separately.

Example 8. It is proposed to use a short-tap interpolation filter (such as a bilinear, 4-tap or 6-tap filter) when generating a prediction block using neighboring motion information.

(a) For sub-pixel positions, 4 pixels on the left/top side and 2 pixels on the right/bottom side are used for interpolation.

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

(a) The proposed method may be applied to certain modes, such as traditional translational motion (i.e. affine mode is disabled).

(b) The proposed method can be applied to certain block sizes.

(i) In examples, it only applies to blocks with w h ≧ T, where w and h are the width and height of the current block.

(ii) In another examples, it only applies to blocks where w ≧ T & & h ≧ T.

Example 10. The proposed method can be applied to all chroma components. Alternatively, they may be applied only to certain chrominance components. For example, they may be applied only to the luminance component.

The examples described above may be incorporated in the context of methods described below, e.g.,

methods

2600 and 2700, which may be implemented at a video decoder.

Fig. 26 shows a flow diagram 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.

The method 2600 includes, at step 2620, generating an updated th reference motion vector and an updated second reference motion vector based on the th motion vector and a weighted sum of the th reference motion vector and the second reference motion vector, respectively in embodiments , a th motion vector is derived based on the th reference motion vector from the th reference block and the second reference motion vector from the second reference block, and the current block is associated with the th reference block and the second reference block.

The method 2600 includes, at step 2630, processing the bitstream representation based on the updated th reference motion vector and the updated second reference motion vector to generate the current block.

In embodiments, and as described in the context of example 1, the th motion vector is derived based on bi-directional optical flow (BIO) refinement using the th reference motion vector and the second reference motion vector in an example, the weighted sum includes weights based on Picture Order Count (POC) of the current block, the th reference block, and the second reference block.

In embodiments, the processing may be based on bi-directional optical flow (BIO) refinement, decoder-side motion vector refinement (DMVR), Frame Rate Up Conversion (FRUC) techniques, or template matching techniques in examples, an updated th reference motion vector and an updated second reference motion vector are generated for inner sub-blocks that are not on the boundary of the current block in another example, an updated th reference motion vector and an updated second reference motion vector are generated for a subset of sub-blocks of the current block.

In embodiments, the processing does not include motion prediction or Overlapped Block Motion Compensation (OBMC).

Fig. 27 shows a flow diagram of another exemplary methods for video decoding method 2700 includes, at step 2710, receiving a bitstream representation of a current block of video data.

The method 2700 includes, at step 2720, generating the current block by selectively using Overlapped Block Motion Compensation (OBMC) to process the bitstream representation based on a characteristic of the current block without signaling an OBMC flag.

In the example of , OBMC may not be used if the motion information of the current block is different from the motion information of a neighboring block.

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

In embodiments, and as described in the context of example 6, processing the bitstream representation includes processing a predetermined number of rows 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

Fig. 28 is a block diagram of a video processing apparatus 2800 may be used to implement methods described herein apparatus 2800 may be implemented in a smartphone, tablet, computer, internet of things (IoT) receiver, etc. apparatus 2800 may include or more processors 2802, or more memories 2804, and video processing hardware 2806 ( or more) processor 2802 may be configured to implement or more methods described in this document (including but not limited to methods 2600 and 2700). ( or more) memory 2804 may be used to store data and code for implementing the methods and techniques described herein.

In embodiments, the video encoding method may be implemented using an apparatus implemented on a hardware platform as described with respect to fig. 28.

Various embodiments and techniques disclosed in this document may be described in the following list of examples.

1. A video processing method includes determining that a current block is associated with a th reference motion vector and a second reference motion vector, generating an updated th reference motion vector and an updated second reference motion vector based on a sum of a scaled th motion refinement and the th reference motion vector and a sum of a scaled th motion refinement and the second reference motion vector, respectively, wherein the th motion refinement is derived based on a bi-directional optical flow mode, and performing a conversion between the current video block and a bitstream representation of video data including the current block based on the updated th reference motion vector and the updated second reference motion vector.

2. The method of example 1, wherein the th reference motion vector relates to a th picture list of reference pictures and the second reference motion vector relates to another second picture list of reference pictures.

3. The method of example 1 or 2, wherein the motion refinement is scaled based on a Picture Order Count (POC) of the current block, a POC of the -th reference block, and a POC of the second reference block.

4. The method of example 3, wherein the POC difference τ₀And τ₁The calculation is as follows:

τ₀POC (current block) -POC ( th reference block),

τ₁POC (second reference block) -POC (current block).

5. The method of example 4, wherein generating the updated th reference motion vector and the updated second reference motion vector is as follows:

mvL0’_x＝-v_x*(τ₀/(τ₀+τ₁))+mvL0_x，

mvL0’_y＝-v_y*(τ₀/(τ₀+τ₁))+mvL0_y，

mvL1’_x＝v_x*(τ₁/(τ₀+τ₁))+mvL1_xand an

mvL1’_y＝v_y*(τ₁/(τ₀+τ₁))+mvL1_y，

Wherein (mvL 0'_x,mvL0’_y) Is the updated th reference motion vector, (mvL 1'_x,mvL1’_y) Is the updated second reference motion vector, (v)_x,v_y) Is the th motion refinement, (mvL 0)_x,mvL0_y) Is the th reference motion vector, and (mvL 1)_x,mvL1_y) Is the second reference motion vector.

6. The method of any of examples 1-5, wherein the updated motion vector is used for motion compensation (OBMC) for motion prediction, deblocking, or overlapping blocks.

7. The method of any of examples 1-6, wherein the updated motion vector is used as a Temporal Motion Vector Prediction (TMVP) in Advanced Motion Vector Prediction (AMVP), Merge mode, or affine mode.

8. The method of any of examples 1-6, wherein the updated motion vector is used only in motion prediction of non-immediately following Coding Units (CUs) or Prediction Units (PUs) in decoding order.

9. The method of any of examples 1-8, wherein the method is applied to translational motion and affine mode is disabled.

10. The method of any of examples 1-8, wherein the method is applied only to blocks w h ≧ T, where w and h are the width and height of the current block, and T is a threshold.

11. The method of any of examples 1-8, wherein the method is applied only to blocks that are w ≧ T and h ≧ T, where w and h are the width and height of the current block, and T is a threshold.

12. The method of any of examples 1-11, wherein the method is applied to all chroma components.

13. The method of any of examples 1-11, wherein the method is applied to only a luma component.

14. an apparatus in a video system, comprising a processor and a non-transitory memory having instructions thereon, wherein the instructions, when executed by the processor, cause the processor to implement the method of any of examples 1-13.

15. computer program product stored on a non-transitory computer readable medium, the computer program product comprising program code for carrying out the method of any of examples 1-13.

From the foregoing it will be appreciated that specific embodiments of the 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 disclosed technology is not to be restricted except in the spirit of the appended claims.

Implementations of the subject matter described in this specification can be implemented as or more computer program products, i.e., 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 combination of substances that affect a machine readable propagated signal, or a combination of or more thereof.

A computer program (also known as a program, 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.

The processes and logic flows described in this specification can be performed by or more programmable processors executing or more computer programs to perform functions by operating on input data and generating output.

Generally, a computer will also include or be operatively coupled to or more mass storage devices, such as magnetic, magneto-optical disks, or optical disks, for storing data from the or more mass storage devices, or for transferring data to the or more mass storage devices, or both.

As used herein, the singular forms "", "" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise, the use of "or" is intended to include "and/or" unless the context clearly indicates otherwise.

Although 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 specific to particular embodiments of particular inventions, in this patent document, some features described in the context of separate embodiments may also be implemented in combination in a single embodiment.

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 have been described, and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.

Claims

1, a video processing method, comprising:

determining that the current block is associated with a reference motion vector and a second reference motion vector;

generating an updated th reference motion vector and an updated second reference motion vector, respectively, based on a sum of the scaled th motion refinement and the th reference motion vector and a sum of the scaled th motion refinement and the second reference motion vector, wherein the th motion refinement is derived based on a bi-directional optical flow pattern, and

performing a conversion between a current video block and a bitstream representation of video data comprising the current block based on the updated th reference motion vector and the updated second reference motion vector.

2. The method of claim 1, wherein the th reference motion vector relates to a th picture list reference picture and the second reference motion vector relates to another second picture list reference pictures.

3. The method of claim 1 or 2, wherein the motion refinement is scaled based on a Picture Order Count (POC) of the current block, a POC of the -th reference block, and a POC of the second reference block.

4. The method of claim 3, wherein the POC difference τ₀And τ₁The calculation is as follows:

τ₀POC (current block) -POC ( th reference block),

τ₁POC (second reference block) -POC (current block).

5. The method of claim 4, wherein generating the updated th reference motion vector and the updated second reference motion vector is as follows:

mvL0’_x＝-v_x*(τ₀/(τ₀+τ₁))+mvL0_x，

mvL0’_y＝-v_y*(τ₀/(τ₀+τ₁))+mvL0_y，

mvL1’_x＝v_x*(τ₁/(τ₀+τ₁))+mvL1_xand an

mvL1’_y＝v_y*(τ₁/(τ₀+τ₁))+mvL1_y，

6. The method of any of claims 1-5 , wherein the updated motion vector is used for motion compensation (OBMC) for motion prediction, deblocking or overlapping blocks.

7. The method of any of claims 1-6, wherein the updated motion vector is used as a Temporal Motion Vector Prediction (TMVP) in Advanced Motion Vector Prediction (AMVP), Merge mode, or affine mode.

8. The method of any of claims 1-6 , wherein the updated motion vector is used only in motion prediction of non-immediately following Coding Units (CUs) or Prediction Units (PUs) in decoding order.

9. The method of any of claims 1-8, wherein the method is applied to translational motion and affine mode is disabled.

10. The method of any of claims 1-8, wherein the method is applied only to blocks of wx h ≧ T, where w and h are the width and height of the current block, and T is a threshold.

11. The method of any of claims 1-8, wherein the method is applied only to blocks of w ≧ T and h ≧ T, where w and h are a width and a height of the current block, and T is a threshold.

12. The method of any of claims 1-11 , wherein the method is applied to all chroma components.

13. The method of any of claims 1-11 , wherein the method is applied only to a luma component.

Apparatus in a video system of 14, , comprising a processor and a non-transitory memory having instructions thereon, wherein the instructions, when executed by the processor, cause the processor to implement the method of any of claims 1-13, .

Computer program product stored on a non-transitory computer readable medium, , the computer program product comprising program code for implementing the method of any of claims 1-13.