WO2020063598A1

WO2020063598A1 - A video encoder, a video decoder and corresponding methods

Info

Publication number: WO2020063598A1
Application number: PCT/CN2019/107608
Authority: WO
Inventors: Sriram Sethuraman; Jeeva Raj A; Sagar KOTECHA
Original assignee: Huawei Technologies Co., Ltd.
Priority date: 2018-09-25
Filing date: 2019-09-24
Publication date: 2020-04-02

Abstract

A method for determining availability of refined motion vectors of a spatially neighboring set includes determining that the refined motion vectors of the spatially neighboring set are available when the refined motion vectors have been computed in a pipeline stage ahead of a data pre-fetch stage of the current set, setting a top-right spatial neighbor block as unavailable when the top-right spatial neighbor block belongs to a top-right CTB, and partitioning a coding unit normatively into as many sub-coding units as a number of concurrency sets that the coding unit spans so that the data pre-fetch stage and a decoder-side motion vector refinement and motion compensation stage for each sub-coding unit occur independent of other sub coding-units, and concurrently with other coding or sub-coding units that belong to a current concurrency set.

Description

A VIDEO ENCODER, A VIDEO DECODER AND CORRESPONDING METHODS

CROSS REFERENCE OF RELATED APPLICATIONS

This application claims priority to Indian Patent Application No. IN201831036149, filed on September 25, 2018, which is incorporated by reference herein in its entirety.

TECHNICAL FIELD

Embodiments of the present invention generally relate to the field of video coding, and more particularly to inter prediction with the decoder-side motion derivation (DMVR) .

BACKGROUND OF THE INVENTION

Video coding (video encoding and decoding) is used in a wide range of digital video applications, for example broadcast digital TV, video transmission over internet and mobile networks, real-time conversational applications such as video chat, video conferencing, DVD and Blu-ray discs, video content acquisition and editing systems, and camcorders of security applications.

Since the development of the block-based hybrid video coding approach in the H. 261 standard in 1990, new video coding techniques and tools were developed and formed the basis for new video coding standards. Further video coding standards comprise MPEG-1 video, MPEG-2 video, ITU-T H. 262/MPEG-2, ITU-T H. 263, ITU-T H. 264/MPEG-4, Part 10, Advanced Video Coding (AVC) , ITU-T H. 265/High Efficiency Video Coding (HEVC) , ITU-T H. 266/Versatile video coding (VVC) and extensions, e.g. scalability and/or three-dimensional (3D) extensions, of these standards. As the video creation and use have become more and more ubiquitous, video traffic is the biggest load on communication networks and data storage, accordingly, one of the goals of the video coding standards is to achieve a bitrate reduction compared to its predecessor without sacrificing picture quality. Even the latest High Efficiency video coding (HEVC) can compress video about twice as much as AVC without sacrificing quality, it is hunger for new technology to further compress video as compared with HEVC. Inter-picture prediction makes use of the temporal correlation between pictures in order to derive a motion-compensated prediction (MCP) for a block of image samples.

Inter-picture prediction makes use of the temporal correlation between pictures in order to derive a motion-compensated prediction (MCP) for a block of image samples.

For this block-based MCP, a video picture is divided into rectangular blocks. Assuming homogeneous motion inside one block and that moving objects are larger than one block, for each block, a corresponding block in a previously decoded picture can be found that serves as a predictor. The general concept of MCP based on a translational motion model is illustrated in FIG. 1. Using a translational motion model, the position of the block in a previously decoded picture is indicated by a motion vector (Δx, Δy) where Δx specifies the horizontal and Δy specifies the vertical displacement relative to the position of the current block. The motion vectors (Δx, Δy) could be of fractional sample accuracy to more accurately capture the movement of the underlying object. Interpolation is applied on the reference pictures to derive the prediction signal when the corresponding motion vector has fractional sample accuracy. The previously decoded picture is referred to as the reference picture and indicated by a reference index Δt to a reference picture list. These translational motion model parameters, i.e. motion vectors and reference indices, are further referred to as motion data. Two kinds of inter-picture prediction are allowed in modern video coding standards, namely uni-prediction and bi-prediction.

In case of bi-prediction, two sets of motion data (Δx ₀, Δy ₀, Δt ₀ and Δx ₁, Δy ₁, Δt ₁) are used to generate two MCPs (possibly from different pictures) , which are then combined to obtain the final MCP. Per default, this is done by averaging but in case of weighted prediction, different weights can be applied to each MCP, e.g. to compensate for scene fade outs. The reference pictures that can be used in bi-prediction are stored in two separate lists, namely list 0 and list 1. In order to limit the memory bandwidth in slices allowing bi-prediction, the HEVC standard restricts PUs with 4×8 and 8×4 luma prediction blocks to use uni-prediction only. Motion data is derived at the encoder using a motion estimation process. Motion estimation is not specified within video standards so different encoders can utilize different complexity-quality tradeoffs in their implementations.

An overview block diagram of the HEVC inter-picture prediction is shown in FIG. 2. The motion data of a block is correlated with the neighboring blocks. To exploit this correlation, motion data is not directly coded in the bitstream but predictively coded based on neighboring motion data. In HEVC, two concepts are used for that. The predictive coding of the motion vectors was improved in HEVC by introducing a new tool called advanced motion vector prediction (AMVP) where the best predictor for each motion block is signaled to the decoder. In addition, a new technique called inter-prediction block merging derives all motion data of a block from the neighboring blocks replacing the direct and skip modes in H. 264/AVC.

Motion data coding module

Different kinds of inter prediction methods are implemented in the motion data coding module. Generally, the methods are referred to as inter prediction modes. Several inter prediction modes are discussed below.

Advanced Motion Vector Prediction

As in previous video coding standards, the HEVC motion vectors are coded in terms of horizontal (x) and vertical (y) components as a difference to a motion vector predictor (MVP) .

The calculation of both motion vector difference (MVD) components is shown in Eq. (1.1) and (1.2) .

MVD _X = Δx -MVP _X (1.1)

MVD _Y = Δy -MVP _Y (1.2)

Motion vectors of the current block are usually correlated with the motion vectors of neighboring blocks in the current picture or in the earlier coded pictures. This is because neighboring blocks are likely to correspond to the same moving object with similar motion and the motion of the object is not likely to change abruptly over time. Consequently, using the motion vectors in neighboring blocks as predictors reduces the size of the signaled motion vector difference. The MVPs are usually derived from already decoded motion vectors from spatially neighboring blocks or from temporally neighboring blocks in the co-located picture. In some cases, the zero motion vector can also be used as MVP. In H. 264/AVC, this is done by doing a component wise median of three spatially neighboring motion vectors. Using this approach, no signaling of the predictor is required. Temporal MVPs from a co-located picture are only considered in the so called temporal direct mode of H. 264/AVC. The H. 264/AVC direct modes are also used to derive other motion data than the motion vectors.

In HEVC, the approach of implicitly deriving the MVP was replaced by a technique known as motion vector competition, which explicitly signals which MVP from a list of MVPs is used for motion vector derivation. The variable coding quadtree block structure in HEVC can result in one block having several neighboring blocks with motion vectors as potential MVP candidates. The initial design of Advanced Motion Vector Prediction (AMVP) included five MVPs from three different classes of predictors: three motion vectors from spatial neighbors, the median of the three spatial predictors and a scaled motion vector from a co-located, temporally neighboring block. Furthermore, the list of predictors was modified by reordering to place the most probable motion predictor in the first position and by removing redundant candidates to assure minimal signaling overhead. Then, significant simplifications of the AMVP design are developed such as removing the median predictor, reducing the number of candidates in the list from five to two, fixing the candidate order in the list and reducing the number of redundancy checks. The final design of the AMVP candidate list construction includes the following two MVP candidates: a. up to two spatial candidate MVPs that are derived from five spatially neighboring blocks; b. one temporal candidate MVPs derived from two temporal, co-located blocks when both spatial candidate MVPs are not available or they are identical; c. zero motion vectors when the spatial, the temporal or both candidates are not available.

As already mentioned, two spatial MVP candidates A and B are derived from five spatially neighboring blocks which are shown in the right part of FIG. 3. The locations of the spatial candidate blocks are the same for both AMVP and inter-prediction block merging. The derivation process flow for the two spatial candidates A and B is depicted in FIG. 4. For candidate A, motion data from the two blocks A0 and A1 at the bottom left corner is taken into account in a two-pass approach. In the first pass, it is checked whether any of the candidate blocks contain a reference index that is equal to the reference index of the current block. The first motion vector found will be taken as candidate A. When all reference indices from A0 and A1 are pointing to a different reference picture than the reference index of the current block, the associated motion vector cannot be used as is. Therefore, in a second pass, the motion vectors need to be scaled according to the temporal distances between the candidate reference picture and the current reference picture. Eq. (1.3) shows how the candidate motion vector mv _cand is scaled according to a scale factor ScaleFactor. ScaleFactor is calculated based on the temporal distance between the current picture and the reference picture of the candidate block td and the temporal distance between the current picture and the reference picture of the current block tb. The temporal distance is expressed in terms of difference between the picture order count (POC) values which define the display order of the pictures. The scaling operation is basically the same scheme that is used for the temporal direct mode in H. 264/AVC. This factoring allows pre-computation of ScaleFactor at slice-level since it only depends on the reference picture list structure signaled in the slice header. Note that the MV scaling is only performed when the current reference picture and the candidate reference picture are both short-term reference pictures. Parameter td is defined as the POC difference between the co-located picture and the reference picture of the co-located candidate block.

mv = sign (mv _cand ·ScaleFactor) · ( (|mv _cand ·ScaleFactor| + 2 ⁷) >> 8) (1.3)

ScaleFactor = clip (-2 ¹², 2 ¹² -1, (tb ·tx + 2 ⁵) >> 6) (1.4)

For candidate B, the candidates B0 to B2 are checked sequentially in the same way as A0 and A1 are checked in the first pass. The second pass, however, is only performed when blocks A0 and A1 do not contain any motion information, i.e., blocks A0 and A1 are not available or coded using intra-picture prediction. Then, candidate A is set equal to the non-scaled candidate B, if found, and candidate B is set equal to a second, non-scaled or scaled variant of candidate B. The second pass searches for non-scaled as well as for scaled MVs derived from candidates B0 to B2. Overall, this design allows to process A0 and A1 independently from B0, B1, and B2. The derivation of B should only be aware of the availability of both A0 and A1 in order to search for a scaled or an additional non-scaled MV derived from B0 to B2. This dependency is acceptable given that it significantly reduces the complex motion vector scaling operations for candidate B. Reducing the number of motion vector scaling represents a significant complexity reduction in the motion vector predictor derivation process.

In HEVC, the block to the bottom right and at the center of the current block have been determined to be the most suitable to provide a good temporal motion vector predictor (TMVP) . These candidates are illustrated in the left part of FIG. 3 where C0 represents the bottom right neighbor and C1 represents the center block. Here again, motion data of C0 is considered first and, if not available, motion data from the co-located candidate block at the center is used to derive the temporal MVP candidate C. The motion data of C0 is also considered as not being available when the associated PU belongs to a CTU beyond the current CTU row. This minimizes the memory bandwidth requirements to store the co-located motion data. In contrast to the spatial MVP candidates, where the motion vectors may refer to the same reference picture, motion vector scaling is mandatory for the TMVP. Hence, the same scaling operation as for the spatial MVPs is used.

While the temporal direct mode in H. 264/AVC always refers to the first reference picture in the second reference picture list, list 1, and is only allowed in bi-predictive slices, HEVC offers the possibility to indicate for each picture which reference picture is considered as the co-located picture. This is done by signaling in the slice header the co-located reference picture list and reference picture index as well as requiring that these syntax elements in all slices in a picture should specify the same reference picture.

Since the temporal MVP candidate introduces additional dependencies, it might be desirable to disable its usage for error robustness reasons. In H. 264/AVC there is the possibility to disable the temporal direct mode for bi-predictive slices in the slice header (direct_spatial_mv_pred_flag) . HEVC syntax extends this signaling by allowing to disable the TMVP at sequence level or at picture level (sps/slice_temporal_mvp_enabled_flag) . Although the flag is signaled in the slice header, it is a requirement of bitstream conformance that its value shall be the same for all slices in one picture. Since the signaling of the picture-level flag depends on the SPS flag, signaling it in the PPS would introduce a parsing dependency between SPS and PPS. Another advantage of this slice header signaling is that if a user wants to change only the value of this flag and no other parameter in the PPS, there is no need to transmit a second PPS.

In general, motion data signaling in HEVC is similar as in H. 264/AVC. An inter-picture prediction syntax element, inter_pred_idc, signals whether reference list 0, reference list 1 or both are used. For each MCP obtained from one reference picture list, the corresponding reference picture (Δt) is signaled by an index to the reference picture list, ref_idx_l0/1, and the MV (Δx, Δy) is represented by an index to the MVP, mvp_l0/1_flag, and its MVD. A newly introduced flag in the slice header, mvd_l1_zero_flag, indicates whether the MVD for the second reference picture list is equal to zero and therefore not signaled in the bitstream. When the motion vector is fully reconstructed, a final clipping operation assures that the values of each component of the final motion vector will always be in the range of -2 ¹⁵ to 2 ¹⁵ -1, inclusive.

Inter-picture Prediction Block Merging

The AMVP list only contains motion vectors for one reference list while a merge candidate contains all motion data including the information whether one or two reference picture lists are used as well as a reference index and a motion vector for each list. Overall, the merge candidate list is constructed based on the following candidates: a. up to four spatial merge candidates that are derived from five spatially neighboring blocks; b. one temporal merge candidate derived from two temporal, co-located blocks; c. additional merge candidates including combined bi-predictive candidates and zero motion vector candidates.

The first candidates in the merge candidate list are the spatial neighbors. Up to four candidates are inserted in the merge list by sequentially checking A1, B1, B0, A0 and B2, in that order, according to the right part of FIG. 3.

Instead of just checking whether a neighboring block is available and contains motion information, some additional redundancy checks are performed before taking all the motion data of the neighboring block as a merge candidate. These redundancy checks can be divided into two categories for two different purposes: a. avoid having candidates with redundant motion data in the list; b. prevent merging two partitions that could be expressed by other means which would create redundant syntax.

When N is the number of spatial merge candidates, a complete redundancy check would consist of

motion data comparisons. In case of the five potential spatial merge candidates, ten motion data comparisons would be needed to assure that all candidates in the merge list have different motion data. During the development of HEVC, the checks for redundant motion data have been reduced to a subset in a way that the coding efficiency is kept while the comparison logic is significantly reduced. In the final design, no more than two comparisons are performed per candidate resulting in five overall comparisons. Given the order of {A1, B1, B0, A0, B2} , B0 only checks B1, A0 only A1 and B2 only A1 and B1. In an embodiment of the partitioning redundancy check, the bottom PU of a 2N×N partitioning is merged with the top one by choosing candidate B1. This would result in one CU with two PUs having the same motion data which could be equally signaled as a 2N×2N CU. Overall, this check applies for all second PUs of the rectangular and asymmetric partitions 2N×N, 2N×nU, 2N×nD, N×2N, nR×2N and nL×2N. It is noted that for the spatial merge candidates, only the redundancy checks are performed and the motion data is copied from the candidate blocks as it is. Hence, no motion vector scaling is needed here.

The derivation of the motion vectors for the temporal merge candidate is the same as for the TMVP. Since a merge candidate comprises all motion data and the TMVP is only one motion vector, the derivation of the whole motion data only depends on the slice type. For bi-predictive slices, a TMVP is derived for each reference picture list. Depending on the availability of the TMVP for each list, the prediction type is set to bi-prediction or to the list for which the TMVP is available. All associated reference picture indices are set equal to zero. Consequently for uni-predictive slices, only the TMVP for list 0 is derived together with the reference picture index equal to zero.

When at least one TMVP is available and the temporal merge candidate is added to the list, no redundancy check is performed. This makes the merge list construction independent of the co-located picture which improves error resilience. Consider the case where the temporal merge candidate would be redundant and therefore not included in the merge candidate list. In the event of a lost co-located picture, the decoder could not derive the temporal candidates and hence not check whether it would be redundant. The indexing of all subsequent candidates would be affected by this.

For parsing robustness reasons, the length of the merge candidate list is fixed. After the spatial and the temporal merge candidates have been added, it can happen that the list has not yet the fixed length. In order to compensate for the coding efficiency loss that comes along with the non-length adaptive list index signaling, additional candidates are generated. Depending on the slice type, up to two kind of candidates are used to fully populate the list: a. Combined bi-predictive candidates; b. Zero motion vector candidates.

In bi-predictive slices, additional candidates can be generated based on the existing ones by combining reference picture list 0 motion data of one candidate with and the list 1 motion data of another one. This is done by copying Δx ₀, Δy ₀, Δt ₀ from one candidate, e.g., the first one, and Δx ₁, Δy ₁, Δt ₁ from another, e.g. the second one. The different combinations are predefined and given in Table 1.1.

Table 1.

When the list is still not full after adding the combined bi-predictive candidates, or for uni-predictive slices, zero motion vector candidates are calculated to complete the list. All zero motion vector candidates have one zero displacement motion vector for uni-predictive slices and two for bi-predictive slices. The reference indices are set equal to zero and are incremented by one for each additional candidate until the maximum number of reference indices is reached. If that is the case and there are still additional candidates missing, a reference index equal to zero is used to create these. For all the additional candidates, no redundancy checks are performed as it turned out that omitting these checks will not introduce a coding efficiency loss.

For each PU coded in inter-picture prediction mode, a merge_flag indicates that block merging is used to derive the motion data. The merge_idx further determines the candidate in the merge list that provides all the motion data needed for the MCP. Besides this PU-level signaling, the number of candidates in the merge list is signaled in the slice header. Since the default value is five, it is represented as a difference to five (five_minus_max_num_merge_cand) . That way, the five is signaled with a short codeword for the 0 whereas using only one candidate, is signaled with a longer codeword for the 4. Regarding the impact on the merge candidate list construction process, the overall process remains the same although it terminates after the list contains the maximum number of merge candidates. In the initial design, the maximum value for the merge index coding was given by the number of available spatial and temporal candidates in the list. When, e.g., only two candidates are available, the index can be efficiently coded as a flag. But, in order to parse the merge index, the whole merge candidate list has to be constructed to know the actual number of candidates. Assuming unavailable neighboring blocks due to transmission errors, it would not be possible to parse the merge index anymore.

A crucial application of the block merging concept in HEVC is its combination with a skip mode. In previous video coding standards, the skip mode was used to indicate for a block that the motion data is inferred instead of explicitly signaled and that the prediction residual is zero, i.e., no transform coefficients are transmitted. In HEVC, at the beginning of each CU in an inter-picture prediction slice, a skip_flag is signaled that implies the following: a. the CU only contains one PU (2N×2N partition type) ; b. the merge mode is used to derive the motion data (merge_flag equal to 1) ; c. no residual data is present in the bitstream.

A parallel merge estimation level was introduced in HEVC that indicates the region in which merge candidate lists can be independently derived by checking whether a candidate block is located in that merge estimation region (MER) . A candidate block that is in the same MER is not included in the merge candidate list. Hence, its motion data does not need to be available at the time of the list construction. When this level is, e.g., 32, all prediction units in a 32×32 area can construct the merge candidate list in parallel since all merge candidates that are in the same 32×32 MER, are not inserted in the list. As shown in FIG. 5, there is a CTU partitioning with seven CUs and ten PUs. All potential merge candidates for the first PU0 are available because they are outside the first 32×32 MER. For the second MER, merge candidate lists of PUs 2-6 cannot include motion data from these PUs when the merge estimation inside that MER should be independent. Therefore, when looking at a PU5 for example, no merge candidates are available and hence not inserted in the merge candidate list. In that case, the merge list of PU5 consists only of the temporal candidate (if available) and zero MV candidates. In order to enable an encoder to trade-off parallelism and coding efficiency, the parallel merge estimation level is adaptive and signaled as log2_parallel_merge_level_minus2 in the picture parameter set.

Sub-CU based motion vector prediction

During the development of the new video coding technique, with QTBT, each CU can have at most one set of motion parameters for each prediction direction. Two sub-CU level motion vector prediction methods are considered in the encoder by splitting a large CU into sub-CUs and deriving motion information for all the sub-CUs of the large CU. Alternative temporal motion vector prediction (ATMVP) method allows each CU to fetch multiple sets of motion information from multiple blocks smaller than the current CU in the collocated reference picture. 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 spatially neighboring motion vector.

To preserve more accurate motion field for sub-CU motion prediction, the motion compression for the reference frames is currently disabled.

Alternative temporal motion vector prediction

In the alternative temporal motion vector prediction (ATMVP) method, the motion vectors temporal motion vector prediction (TMVP) is modified by fetching multiple sets of motion information (including motion vectors and reference indices) from blocks smaller than the current CU. As shown in FIG. 6, the sub-CUs are square N×N blocks (N is set to 4 by default) .

ATMVP predicts the motion vectors of the sub-CUs within a CU in two steps. The first step is to identify the corresponding block in a reference picture with a so-called temporal vector. The reference picture is called the motion source picture. The second step is to split the current CU into sub-CUs and obtain the motion vectors as well as the reference indices of each sub-CU from the block corresponding to each sub-CU, as shown in FIG. 6.

In the first step, a reference picture and the corresponding block is determined by the motion information of the spatially neighboring blocks of the current CU. To avoid the repetitive scanning process of neighboring blocks, the first merge candidate in the merge candidate list of the current CU 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, in ATMVP, 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.

In the second step, a corresponding block of the sub-CU is identified by the temporal vector in the motion source picture, by adding the temporal vector to the coordinate of the current CU. For each sub-CU, the motion information of its corresponding block (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 N×N block is identified, it is converted to the motion vectors and reference indices of the current sub-CU, in the same way as TMVP of HEVC, wherein motion scaling and other procedures apply. For example, the decoder checks whether the low-delay condition (i.e., 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 (the motion vector corresponding to reference picture list X) to predict motion vector MVy (with X being equal to 0 or 1 and Y being equal to 1-X) for each sub-CU.

Spatial-temporal motion vector prediction

In this method, the motion vectors of the sub-CUs are derived recursively, following raster scan order. As shown in FIG. 7, it is considered that an 8×8 CU which contains four 4×4 sub-CUs A, B, C, and D. The neighboring 4×4 blocks in the current frame are labelled as a, b, c, and d.

The motion derivation for sub-CU A starts by identifying its two spatial neighbors. The first neighbor is the N×N block above sub-CU A (block c) . If this block c is not available or is intra coded the other N×N blocks above sub-CU A are checked (from left to right, starting at block c) . The second neighbor is a block to the left of the sub-CU A (block b) . If block b is not available or is intra coded other blocks to the left of sub-CU A are checked (from top to bottom, starting at block b) . 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 is derived by following the same procedure of TMVP derivation as specified in HEVC. The motion information of the collocated block at location D is fetched and scaled accordingly. Finally, after retrieving and scaling the motion information, all available motion vectors (up to 3) are averaged separately for each reference list. The averaged motion vector is assigned as the motion vector of the current sub-CU.

Combined with Merge mode

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. Up to seven merge candidates are 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 HM, which means, for each CU in P or B slice, two more RD checks is needed for the two additional merge candidates.

Pattern matched motion vector derivation

Pattern matched motion vector derivation (PMMVD) mode is based on Frame-Rate Up Conversion (FRUC) techniques. With this mode, motion information of a block is not signalled but derived at the decoder side.

A FRUC flag is signalled for a CU when its merge flag is true. When the FRUC flag is false, a merge index is signalled and the regular merge mode is used. When the FRUC flag is true, an additional FRUC mode flag is signalled to indicate which method (bilateral matching or template matching) is to be used to derive motion information for the block.

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. That is the two matching modes (bilateral matching and template matching) are both 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, the FRUC flag is set to true for the CU and the related matching mode is used.

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 which 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 and 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.

For example, the following derivation process is performed for a W×H CU motion information derivation. At the first stage, MV for the whole W×H CU is derived. At the second stage, the CU is further split into M×M sub-CUs. The value of M is calculated as in Eq. (1.8) , 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.

As shown in FIG. 8, 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 in two different reference pictures. Under the assumption of a continuous motion trajectory, the motion vectors MV0 and MV1 pointing to the two reference blocks shall be proportional to the temporal distances, i.e., TD0 and TD1, between the current picture and the two reference pictures. When the current picture is temporally between the two reference pictures 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.

In the bilateral matching merge mode, bi-prediction is always applied since 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. There is no such limitation for the template matching merge mode. In the template matching merge mode, the encoder can choose among uni-prediction from list0, uni-prediction from list1 or bi-prediction for a CU. The selection is based on a template matching cost as follows:

If costBi <= factor *min (cost0, cost1)

bi-prediction is used;

Otherwise, if cost0 <= cost1

uni-prediction from list0 is used;

Otherwise,

uni-prediction from list1 is used;

where cost0 is the SAD of list0 template matching, cost1 is the SAD of list1 template matching and costBi is the SAD of bi-prediction template matching. The value of factor is equal to 1.25, which means that the selection process is biased toward bi-prediction. The inter prediction direction selection is only applied to the CU-level template matching process.

As shown in FIG. 9, template matching is used to derive motion information of the current CU by finding the closest match between a template (top and/or left neighbouring blocks of the current CU) in the current picture and a block (same size to the template) in a reference picture. Except the aforementioned FRUC merge mode, the template matching is also applied to AMVP mode. With template matching method, a new candidate is 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 (meaning remove the second existing AMVP candidate) . When applied to AMVP mode, only CU level search is applied.

The MV candidate set at CU level consists of: a. original AMVP candidates if the current CU is in AMVP mode; b. all merge candidates; c. several MVs in the interpolated MV field; d. top and left neighbouring motion vectors.

It is noted that the interpolated MV field mentioned above is generated before coding a picture 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. First, the motion field of each reference picture in both reference lists is traversed at 4×4 block level. For each 4×4 block, if the motion associated to the block passing through a 4×4 block in the current picture, as shown in FIG. 10, 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 4×4 block, the block’s motion is marked as unavailable in the interpolated motion field.

When using bilateral matching, each valid MV of a merge candidate is 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, refa) at reference list A. Then the reference picture refb of its paired bilateral MV is found in the other reference list B so that refa and refb are temporally at different sides of the current picture. If such a refb is not available in reference list B, refb is determined as a reference which is different from refa and its temporal distance to the current picture is the minimal one in list B. After refb is determined, MVb is derived by scaling MVa based on the temporal distance between the current picture and refa, refb.

Four MVs from the interpolated MV field are also 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.

At the CU level, up to 15 MVs for AMVP CUs and up to 13 MVs for merge CUs are added to the candidate list.

The MV candidate set at sub-CU level consists of: a. an MV determined from a CU-level search; b. top, left, top-left and top-right neighbouring MVs; c. scaled versions of collocated MVs from reference pictures; d. up to 4 ATMVP candidates; e. up to 4 STMVP candidates.

The scaled MVs from reference pictures are derived as follows. All 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 are limited to the four first ones.

At the sub-CU level, up to 17 MVs are added to the candidate list.

Motion vector refinement

Motion vector can be refined by different methods combining with the different inter prediction modes.

MV refinement in FRUC

MV refinement is a pattern based MV search with the criterion of bilateral matching cost or template matching cost. In the current development, 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.

Decoder-side motion vector refinement

In bi-prediction operation, for the prediction of one block region, two prediction blocks, formed using a MV of list0 and a MV of list1, 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 is 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.

In DMVR, a bilateral template is generated as the weighted combination (i.e., average) of the two prediction blocks, from the initial MV0 of list0 and MV1 of list1, respectively, as shown in FIG. 11. 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 current development, 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. 11, are used for generating the final bi-prediction results. A sum of absolute differences (SAD) is used as the cost measure.

DMVR is applied for the merge mode of bi-prediction with one MV from a reference picture in the past and another MV from a reference picture in the future, without the transmission of additional syntax elements.

Motion data precision and Motion data storage reduction

The usage of the TMVP, in AMVP as well as in the merge mode, requires the storage of the motion data (including motion vectors, reference indices and coding modes) in co-located reference pictures. Considering the granularity of motion representation, the memory size needed for storing motion data can be significant. HEVC employs motion data storage reduction (MDSR) to reduce the size of the motion data buffer and the associated memory access bandwidth by sub-sampling motion data in the reference pictures. While H. 264/AVC is storing these information on a 4×4 block basis, HEVC uses a 16×16 block where, in case of sub-sampling a 4×4 grid, the information of the top-left 4×4 block is stored. Due to this sub-sampling, MDSR impacts on the quality of the temporal prediction.

Furthermore, there is a tight correlation between the position of the MV used in the co-located picture, and the position of the MV stored by MDSR. During the standardization process of HEVC, it turned out that storing the motion data of the top left block inside the 16×16 area together with the bottom right and center TMVP candidates provide the best tradeoff between coding efficiency and memory bandwidth reduction.

Higher motion vector storage accuracy

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 current development, 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.

Fractional sample interpolation module

When a motion vector points to a fractional sample position, motion compensated interpolation is needed. For the luma interpolation filtering, an 8-tap separable DCT-based interpolation filter is used for 2/4 precision samples and a 7-tap separable DCT-based interpolation filter is used for 1/4 precisions samples, as shown in Table 1.2.

Table 1.2

Position	Filter coefficients
1/4	{-1, 4, -10, 58, 17, -5, 1}
2/4	{-1, 4, -11, 40, 40, -11, 4, -1}
3/4	{1, -5, 17, 58, -10, 4, -1}

Similarly, a 4-tap separable DCT-based interpolation filter is used for the chroma interpolation filter, as shown in Table 1.3.

Table 1.3

Position	Filter coefficients
1/8	{-2, 58, 10, -2}
2/8	{-4, 54, 16, -2}
3/8	{-6, 46, 28, -4}
4/8	{-4, 36, 36, -4}
5/8	{-4, 28, 46, -6}
6/8	{-2, 16, 54, -4}
7/8	{-2, 10, 58, -2}

For the vertical interpolation for 4: 2: 2 video and the horizontal and vertical interpolation for 4: 4: 4 chroma channels, the odd positions in Table 1.3 are not used, resulting in 1/4 ^th chroma interpolation.

For the bi-directional prediction, the bit-depth of the output of the interpolation filter is maintained to 14-bit accuracy, regardless of the source bit-depth, before the averaging of the two prediction signals. The actual averaging process is done implicitly with the bit-depth reduction process as:

predSamples [x, y ] = (predSamplesL0 [x, y ] + predSamplesL1 [x, y ] + offset ) >> shift (1.9)

shift = 15 –BitDepth (1.10)

offset = 1 << (shift –1 ) (1.11)

To reduce complexity, bi-linear interpolation instead of regular 8-tap HEVC interpolation is used for both bilateral matching and template matching.

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 is the 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:

where w is a weighting factor which is empirically set to 4, MV and MV ^s indicate the current MV and the starting MV, respectively. SAD is still used as the matching cost of template matching at sub-CU level search.

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.

SUMMARY

The present disclosure describes techniques for determining the availability of refined motion vector of a spatially spatially neighboring set and for pre-fetching data into a block processing pipeline. In some embodiments, the neighboring set includes at least one coding unit or sub-coding unit within a coding tree block (CTB) for a current set, and the method includes determining that the refined motion vectors of the spatially neighboring set are available when the refined motion vectors have been computed in a pipeline stage ahead of a data pre-fetch stage of the current set, setting a top-right spatial neighbor block as unavailable when the top-right spatial neighbor block belongs to a top-right CTB, and partitioning a coding unit normatively into as many sub-coding units as a number of concurrency sets that the coding unit spans so that the data pre-fetch stage and a decoder-side motion vector refinement and motion compensation stage for each sub-coding unit occur independent of other sub coding-units, and concurrently with other coding or sub-coding units that belong to a current concurrency set.

In other embodiments, a method for pre-fetching data into a block processing pipeline is provided. The block processing pipeline includes a plurality of pipeline slots each configured to process a pixel block. An input frame is partitioned into rows of coding tree blocks (CTBs) each comprising one or more coding unit (CUs) . Each of the CUs includes a number of concurrency sets. The method includes pre-fetching data for a given CTB into a pipeline slot, by the video coding apparatus, using unrefined motion vectors (MVs) of a neighbor CU that falls in a preceding pipeline slot to a concurrency set of a current CU, using refined MVs of a neighbor CU that does not fall in a same concurrency set as a refinement start MV, and using padded samples based on a configurable search range around the given CTB.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the general concept of MCP based on a translational motion model.

FIG. 2 shows an overview block diagram of the HEVC inter-picture prediction.

FIG. 3 shows two spatial MVP candidates A and B are derived from five spatially neighboring blocks.

FIG. 4 shows the derivation process flow for the two spatial MVP candidates A and B.

FIG. 5 shows an example of a CTU partitioning with seven CUs and ten PUs.

FIG. 6 shows the sub-CUs are square N×N blocks (N is set to 4 by default) .

FIG. 7 shows an 8×8 CU which contains four 4×4 sub-CUs A, B, C, and D.

FIG. 8 shows 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 in two different reference pictures.

FIG. 9 shows a template matching is used to derive motion information of the current CU by finding the closest match between a template (top and/or left neighbouring blocks of the current CU) in the current picture and a block (same size to the template) in a reference picture.

FIG. 10 shows the motion associated to the block passing through a 4×4 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 and the scaled motion is assigned to the block in the current frame.

FIG. 11 shows a bilateral template is generated as the weighted combination (i.e., average) of the two prediction blocks, from the initial MV0 of list0 and MV1 of list1, respectively.

FIG. 12 shows an exemplary diagram of a regular pipeline at CTB level according to an embodiment of the present disclosure.

FIG. 13 shows an example that none of the CTB in the current row at the DMA stage have the top row DMVR+MC stage completed according to an embodiment of the present disclosure.

FIG. 14 shows the processing pipeline with N=2.

FIG. 15 shows the pipeline of using a 1-level deep quad-tree split of a CTB and with lag of 2 CTBs between two consecutive CTB rows.

FIG. 16A shows top-right neighbor b0 coding unit is considered as available for AMVP and merge list construction normatively only if it belongs to top CTU according to an embodiment of the present disclosure.

FIG. 16B shows the exemplary removal of top-right CTU’s motion vectors for the prediction/merge motion vectors for the coding units in the current CTU according to an embodiment of the present disclosure.

FIG. 17A is a conceptual block diagram illustrating an example coding system according to an embodiment of the present disclosure.

FIG. 17B is a block diagram of an example coding system according to another embodiment of the present disclosure.

FIG. 18 is a conceptual block diagram illustrating an example video encoder according to an embodiment of the present disclosure.

FIG. 19 is a conceptual block diagram illustrating an example video decoder according to an embodiment of the present disclosure.

FIG. 20 is a schematic diagram of a video coding device encoder according to an embodiment of the present disclosure.

FIG. 21 is a simplified block diagram of an apparatus that may be configured to be either or both of a source device and a destination device from FIG. 17 according to an embodiment of the present disclosure.

FIG. 22 is a simplified flowchart illustrating a method for predicting a current block using a refined motion vector according to an embodiment of the present disclosure.

FIG. 23 is a simplified flowchart illustrating a method for predicting a current block using a refined motion vector according to another embodiment of the present disclosure.

FIG. 24 is a simplified block diagram of an inter-prediction apparatus that may be configured to perform the method of FIG. 22 according to an embodiment of the present disclosure.

FIG. 25 is a simplified block diagram of an inter-prediction apparatus that may be configured to perform the method of FIG. 23 according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

In the absence of any decoder side motion vector derivation, the motion vectors and reference indices of coding units that are coded with any inter-coding mode are reconstructed or inferred without any pixel level operations on any coding unit within that frame. The differential coding of a motion vector using an appropriately scaled version of an already reconstructed motion vector of a spatial or temporally co-located or interpolated neighbor as well as the process of inheriting a reconstructed motion vector through a merge process are computationally simple and hence the dependent reconstruction or inheritance process does not pose any major decoder-side design complexity issue.

The decoder-side motion vector refinement (DMVR) or pattern matched motion vector derivation (PMMVD) schemes proposed up to now allow the refined motion vector (s) of a spatially neighboring coding unit to be employed as motion vector predictor (s) in the differential coding of the motion vector (s) of a current coding unit. This results in significant coding gains through either the reduction in motion vector delta (MVD) coding bits with the spatially neighboring CU’s refinement MVs when the current CU is INTER/AFFINE-INTER and through improved starting point for current CU’s refinement when it is a CU that employs DMVR/PMMVD. However, this significantly impacts the concurrency in processing of the coding units of the current frame as the motion compensation or refinement followed by motion compensation for a given coding unit cannot start until the final motion vector of the spatially neighboring CU on which the current CU depends on. Even one refinement based dependency in the chain will stall the processing pipeline until that dependency is resolved. Given that motion based partitioning can have a wide range of granularities (from a complete coding tree block being one CU to as small as a 4x4 CU) , the sequential dependency results in reduced parallelism that will affect the timing within which the tasks of fetching the required reference data and performing decoder-side MV refinement and/or motion compensated prediction need to be completed. This will result in a significant over-design (e.g. higher clock, wider execution units, wider buses, etc. ) to handle the worst-case timing and significant under-utilization of the designed execution units in the average cases.

On the other hand, when the dependency issue is resolved by forcing all CUs in the current access unit to not use the refined motion vector of any coding unit as a predictor or starting point for refinement, the coding gains suffer significantly. This is because the RDO process decides DMVR/PMMVD to be superior to the other inter-coding modes. But in the absence of the decoder-side refinement, the MVD coding bits increase significantly (when compared to the no DMVR/PMMVD case) and also the starting points for the refinements end up being inferior. Hence there is a significant compression loss by not using any refined MVs.

Hence there is a need for a method that arrives at a suitable trade-off between the coding loss and the complexity increase by allowing refined motion vectors within the current access unit to be used as a predictor or as a starting point for other refinements.

The proposed method determines the availability of refined motion vectors of spatially neighboring coding units in such a way that a set of coding units or sub-coding units within a coding tree block (CTB) can configure their data pre-fetch in a concurrent manner in a given stage of a regular pipeline and also perform their refinement process in a concurrent manner in the next stage of that regular pipeline. In some embodiments, the concept of a lag between the top CTB row and current CTB row is utilized in determining such availability. Also, the concept of a concurrency set is introduced to normatively partition some coding units, when necessary, into sub-coding-units to meet the concurrency requirements of the pipeline. Compared to not using any refined motion vector from the current picture, the proposed approach provides a higher coding gain while ensuring that the dependency does not overly constrain the hardware implementation of the refinement process.

Also, by pre-fetching around an unrefined motion vector and using a normative padding process to access samples that go outside the normative amount of pre-fetched samples, the pipeline latency is further reduced to make even left or top-right CTB refined MVs to be used for refinement of current CTB CUs. The process is also extended to finer granularities than CTB level.

Another aspect is not using the motion vectors of the spatially neighbor block as predictors if the spatially neighbor block belongs to the top-right CTB.

Given that decoder-side motion vector refinement/derivation is a normative aspect of a coding system, the encoder will also have to perform the same error surface technique in order to not have any drift between the encoder’s reconstruction and the decoder’s reconstruction. Hence, all aspects of all embodiments are applicable to both encoding and decoding systems.

All embodiments are applicable to both PMMVD and DMVR methods.

Though terms such as data pre-fetch stage and refinement/motion compensation processing stage are used to explain the underlying design requirements, it should be understood that they are only notional stages and actual hardware implementations can choose to perform their designs differently as long as the availabilities of refined MVs are determined appropriately.

Embodiment 1

By considering a regular CTB level pipeline design, each processing stage should be preceded by a data pre-fetch stage. Both the data fetch stage and processing stage should be able to use the entire time of the pipeline slot (pipeline stage) . FIG. 12 shows an exemplary diagram of a regular pipeline at CTB level according to an embodiment of the present disclosure. The pipeline is two stages deep and requires two pipeline time intervals t1 and t2 to fill each of the two stages. In stage 1, the decoder fetches a pixel block TN+1 from memory using direct memory access (DMA) in the pipeline. In stage 2, the decoder performs a decoder-side MV refinement (DMVR) and a motion compensation (MC) of the fetched pixel block TN+1. In other words, at time t1, new pixel block TN+1 is loaded to the pipeline. At time t2, TN+2 is loaded (shaded box denoted the fetched pixel block using DMA) and pixel block TN+1 (blank box denoted the processed pixel block) is processed in stage 2.

In case of both top and current row starting at the same time, the decoder does not provide the spatial refined motion vector from the neighbors. The following figure shows the CTB pipeline cross rows when both row processing starts at the same time.

FIG. 13 shows an example showing that none of the CTB in the current row at the DMA stage have the top row DMVR+MC stage completed according to an embodiment of the present disclosure. Referring to FIG. 13, it can be seen that none of the CTB in the current row at the DMA stage have the top row DMVR+MC stage completed. This is similar to not using any refined motion vector from the current access unit for AMVP or as a starting motion vector for decoder-side motion refinement.

By introducing a lag of N CTBs (N > 0) between the current CTB row and its Top neighbor CTB row, Current CTB gets the refined motion vectors of some of the top CTB neighbors. FIG. 14 shows an example processing pipeline with N=2. In HEVC and AVC, intra prediction depends on completion of top right neighbor CTB. A lag value of N=2 will now bring a similar dependency for inter prediction.

Referring to FIG. 14, during the DMA or data pre-fetch stage of CN+1 1403 at time t4, both TN 1401 (at time t2) and TN+1 1402 (at time t3) DMVR+MC stage are completed, hence CN+1 1403 (at time t4) CTB can use the refined MVs of the Top and Top left CTBs for Inter MVP and as starting MVs for decoder-side MV refinement.

It should be noted that even with the concept of lag between consecutive CTB rows, any coding unit that is a spatial neighbor for a current CU within the current CTB is still considered unavailable. Also, given that data pre-fetch stage has been introduced as a pipeline stage, left and bottom-left neighbor CTBs are always considered as unavailable. Hence, this scheme is more beneficial when the maximum CTB size is smaller.

Table 3.1 provides the final refined MV availability status of spatial neighbor CTBs with lags of 0, 2, and 3.

Table 3.1

Summarizing the above, the proposed method aims to allow:

(a) concurrent data-prefetch of required reference samples for refinement and/or motion compensation of all coding units within a CTB that can occupy an entire pipeline stage; and,

(b) concurrent refinement and/or motion compensation of all coding units within a CTB that follows the data-prefetch stage in the pipeline and can occupy an entire pipeline stage.

To facilitate this, the following rules are applied to determine the availability of a spatial neighbor’s refined MV:

(i) The refined MVs of all coding units within the current CTB are assumed to be unavailable;

(ii) The refined MVs of neighbour coding units in the CTB to the left of the current CTB are assumed to be unavailable;

(iii) The refined MVs of neighbour coding units in the CTB to the top of the current CTB are considered available if those refined MVs are available before the start of the notional reference data pre-fetch stage of the current CTB, based on a configurable lag in the number of CTBs by which the notional reference data pre-fetch stage of the current CTB lags the notional reference data pre-fetch stage of its top neighbour CTB.

A lag value of zero is equivalent to all neighbour refined MVs being unavailable for AMVP or DMVR/PMMVD processes. A lag value of 2 is equivalent to the top-right dependency seen in intra prediction in HEVC/VVC and allows refined MVs of neighbour coding units falling within the top and top-left neighbour CTBs to be available. A lag value of 3 makes refined MVs of neighbour coding units falling within top-right CTB neighbour also to be available. The increased availabilities at non-zero lags improve the coding gains when compared to a lag value of zero. The impact is expected to be higher when the max CTB sizes are lower (e.g. 64 or 32, as compared to the default 128.

FIG. 22 is a simplified flowchart illustrating a method for predicting a current block using a refined motion vector according to an embodiment of the present disclosure. Referring to FIG. 22, the method includes:

S221: obtaining a neighboring refined MV from a particular position of a first neighboring block adjacent to the current block, wherein the first neighboring block belongs to a first picture region (PR) , and the current block belongs to a second PR which is adjacent to the top-left of the first PR.

S223: deriving a refined MV for the current block by using the neighboring refined MV as an initial MV of a DMVR processing of the current block.

S225: obtaining the predictor of the current block by using the refined MV.

FIG. 24 is a simplified block diagram of an inter-prediction apparatus 240 that may be configured to perform the method of FIG. 22 according to an embodiment of the present disclosure. Referring to FIG. 24, the inter prediction apparatus 240 includes a motion vector obtaining circuit 241 configured to or having the capability and function of performing the step S221, a refined motion vector deriving circuit 243 configured to or having the capability and function of performing the step S223, and a predicting circuit 245 configured to or having the capability and function of performing the S225. It should be noted that the inter prediction apparatus 240 may either be a part of an integral video coding device/chipset, or be a separate/individual component which communicates with the related parts of a video coding device/chipset to collaboratively code a video.

FIG. 23 is a simplified flowchart illustrating a method for predicting a current block using a refined motion vector according to another embodiment of the present disclosure. Referring to FIG. 23, the method includes:

S233: obtaining a second neighboring refined MV from a particular position of a second neighboring block adjacent to the current block, wherein the second neighboring block belongs to a third PR which is adjacent to the top of the second PR.

S235: determining an optimal neighboring referring MV from a candidate list which includes the first neighboring refined MV and second neighboring refined MV.

S237: deriving a refined MV for the current block by using the optimal neighboring referring MV as an initial MV of a DMVR processing of the current block.

S239: obtaining the predictor of the current block by using the refined MV.

In anr alternative embodiment, this method may also include a step of obtaining a first neighboring MV from a particular position of a third neighboring adjacent to the current block, wherein the third neighboring block belongs to a fourth PR which is adjacent to the top-right of the second PR, and the first neighboring MV is included in the candidate list. In addition, for the present invention, the MV in a neighboring block left to the current block may also be used to do the DMVR process of the current invention, and the corresponding process may be: obtaining a second neighboring MV from a particular position of a fourth neighboring block adjacent to the current block, wherein the fourth neighboring block belongs to a fifth PR which is adjacent to the left of the second PR, and second neighboring MV is included in the candidate list. The first neighboring MV is configured to derive a third neighboring refined MV of the third neighboring block and second neighboring MV is configured to derive a fourth neighboring refined MV of the fourth neighboring block.

FIG. 25 is a simplified block diagram of an inter-prediction apparatus that may be configured to perform the method of FIG. 23 according to an embodiment of the present disclosure. Referring to FIG. 25, the inter prediction apparatus 250 includes a motion vector obtaining circuit 251 configured to perform the steps S231 and S233, a refined motion vector deriving circuit 253 configured to perform the steps S235 and 237, and a predicting circuit configured to perform the step S239. It should be noted that the inter prediction apparatus 250 may either be a part of an integral video coding device/chipset, or be a separate/individual component which communicates with the related parts of a video coding device/chipset to collaboratively code a video.

Accordingly, technical features and benefits of this embodiment are improved coding gains due to increasing the availability of spatial refined motion vectors by introducing the CTB lag of N. “N” can be selected as per the design constraints of the video coding system.

Embodiment 2

In embodiment 1, all coding units at a CTB level are considered as part of a concurrency set such that their data-prefetches can occur concurrently during a pipeline stage while their refinement and motion compensation processing can occur concurrently during the following pipeline stage. In this embodiment, a concept of concurrency set that can exist at a sub-CTB level is introduced in order to further improve the coding gains by being able to use the final refined motion vectors in more cases.

For instance, there are cases where a larger CTB is force partitioned into quad-tree partitioned coding units that are coded in a recursive z-scan order.

As in PMMVD, it is also possible to force partition a given coding unit into sub-coding units. A concurrency set is defined as a set of pixels in a CTB that correspond to one partition of recursive quad-tree partition of the CTB. For instance, a concurrency set can be chosen as 64x64 or 32x32 for a CTB size of 128x128. A given coding unit that spans across more than one concurrency set is force partitioned for decoder-side motion vector refinement purposes into as many sub coding units (sub-CUs) as the number of concurrency sets that it spans. The dependency across these concurrency sets is assumed to be in a recursive z-scan order. Thus independent of the actual partitioning of the CTB into coding units, a concurrency set becomes an independent set of pixels, the processing for which can be performed concurrently to have a regular sub-CTB level pipeline that can have a data pre-fetch stage followed by a refinement and motion compensation stage in a manner similar to the CTB level pipeline in embodiment 1.

FIG. 15 shows an example pipeline of using a 1-level deep quad-tree split of a CTB and with lag of 2 CTBs between two consecutive CTB rows according to an embodiment of the present disclosure.

Referring to FIG. 15, the improvements in the availability of final refined spatial neighbor motion vectors can be seen. Concurrency set Z0 has all the neighbor concurrency sets available except bottom left, concurrency set Z1 has all top concurrency set neighbors available but left and bottom left concurrency set neighbors are not available, concurrency set Z2 has all concurrency set neighbors except Top right and bottom left concurrency sets, and concurrency set Z3 has only Top and top left concurrency sets available. This is summarized in the Table 3.2.

Table 3.2

Table 3.2 shows the refined spatial neighbor concurrency set availability status for 1-level deep quad-trees split with a lag of 2 CTBs between consecutive CTB rows. A lag of 2 means that the current row (second row) can begin to be processed after the top row (first row) is processed in an ordinary way, and the next row (third row) can begin to be processed after only twp CTB have been processed in the second row, and so on.

The technical features, benefits and advantages of this embodiment are the forced partitioning of a CTB into concurrency sets for performing the decoder-side motion vector refinement in a manner that is independent of the actual partitioning of the CTB makes more final refined motion vectors to be available in conjunction with the concept of a configurable CTB lag between consecutive CTB rows. This helps improve the coding gains relative to embodiment 1 while still allowing for a regular pipeline that allows for a data pre-fetch stage that precedes the decoder-side motion vector refinement and motion compensated prediction stage.

Embodiment 3

The search range for decoder-side motion vector refinement increases the worst-case external memory accesses and also the internal memory buffers. To counter this, some prior art methods do not bring any additional samples that are based on the search range, but only use the samples required for performing motion compensation using the merge mode motion vectors. Additional samples required for refinement are obtained purely through motion compensated interpolation that employs padding for the unavailable sample with the last available sample before it. It is also possible to arrive at a trade-off between external memory bandwidth and padding introduced coding efficiency reduction by fetching one or more lines of samples beyond just the samples required for motion compensation using the merge mode motion vectors without refinement, but still less than what are required for covering the entire refinement range.

In this embodiment, with such padded motion compensation, the pre-fetch for a given CTB (or a sub-partition of a CTB at the first level) is performed using the unrefined motion vectors of coding units in the causal neighbor CTBs when the refined neighbor CTB motion vectors are not available at the time of pre-fetch. The refined motion vector of a coding unit in the neighbor CTB can be used as the starting point for performing the refinement for a coding unit within the current CTB that merges with that coding unit in the neighbor CTB. Any unavailable samples relative to the pre-fetched data can be accessed or interpolated through padding. Thus, the use of padded samples obviates the need for pre-fetch to be performed only after the coding unit in the neighbor CTB completes its refinement, thus reducing the latency of the dependency. This method works reasonably well when the number of refinement search range iterations are low or when the refinement process exits early. The reduction of the pipeline latency implies that refined motion vectors of CTBs that are just one pipeline slot (pipeline stage) ahead of the current CTB can be used as the starting points for refinement in coding units within the current CTB. For example, even with a lag of 1 CTB between CTB rows, the top CTB’s refined MVs can be used for refinement of coding units within the current CTB. Also, the left CTB’s refined MVs can be used for refinement of coding units within the current CTB. Thus, barring the refined MVs of coding units within the current CTB, all other neighbor refined MVs can be employed to bring back the coding gains. The availabilities are summarized in Table 3.3 below.

Table 3.3

Table 3.3 shows the use of neighbor’s refined and unrefined MVs for pre-fetch and refinement based on neighbor CTB’s pipeline lag when CTB-row lag is equal 2 CTBs.

Similar to embodiment 2, when each CTB is quad-tree split at the first depth of splitting, it is possible to have a pipeline of pre-fetch followed by refinement that is at the granularity of a quarter of a CTB (QCTB) . In this case, with the pre-fetch based on unrefined neighbor QCTB MVs and with neighbor QCTB refined MVs as starting points for refinement with use of padding to get unavailable samples, the z-scan order of encoding the 4 QCTB coding units, more refined MVs can be tapped for refinement while still ensuring that the pre-fetch followed by refinement pipeline at the QCTB level can work. Table 3.4 below summarizes the MVs of neighbor used by each of the QCTBs within a CTB.

Table 3.4

Table 3.4 shows the use of neighbor’s refined and unrefined MVs for pre-fetch and refinement based on pipeline lag value of neighbor CU’s QCTB (quarter of a CTB) .

This embodiment enables even the left, top-right, and bottom-left neighbor’s refined MV to be used when the neighbor CU is in a neighbor CTB (or QCTB) and not within the current CTB (or QCTB) . This improves the coding gains while still ensuring a regular pipeline where pre-fetch is performed at CTB (or QCTB) level and refinement of all coding units within the current CTB (or QCTB) can be performed in parallel.

Embodiment 4

As per the 2-CTU lag pipeline discussed in embodiment 2, refined MVs from neighbor coding units in top left and top CTUs shall be used for by CUs within a current CTU as the center for DMVR, while only non-refined MVs from neighbor CUs in top right CTU can be used. For current CU, a0, a1, b0, b1 and b2 are used as the spatial neighbors for AMVP and merge list construction. A CTU (coding tree unit) is defined as having a luma CTB and the corresponding chroma CTBs and syntax elements. The quad-tree syntax of the CTU specifies the size and positions of its luma and chroma coding blocks (CBs) . One luma CB and two chroma CBs together with associated syntax form a coding unit (CU) .

In this embodiment, top-right neighbor b0 coding unit is considered as available for AMVP and merge list construction normatively only if it belongs to top CTU as shown in FIG. 16A, whereas it is considered as unavailable for AMVP and merge list construction normatively, if it belongs to top-right CTU (in addition to the cases of when top-right neighbor is outside the tile or frame boundaries or is intra-coded where they are already considered as unavailable) , as shown in FIG. 16B.

Since only refined MVs are used from the previous CTU row, a single line buffer to maintain the neighbor MVs from the top-CTU row are sufficient.

This embodiment helps to remove the entire dependency of top right CTU’s motion vectors for the prediction/merge MVs for the coding units in the current CTU. The line buffer requirement to store one unrefined MV per CTU for use by AMVP or merge list construction process is no longer required.

The present invention relates to versatile video coding standardization which was earlier pursued as a Joint Exploratory Model (JEM) within Joint Video Exploration Team which is a joint work between Q16 of VCEG and MPEG (SC29/WG11) . Document JVET-G1001 and other Huawei prior art relating to decoder side motion vector refinement and decoder side motion vector derivation can be used to get a list of contribution documents and patents related to this invention.

Besides the above discussion, the present invention can be implemented by the following encoding/decoding circuitry/system/apparatus or encoder/decoder.

In the following description, reference is made to the accompanying figures, which form part of the disclosure, and which show, by way of illustration, specific aspects of embodiments of the invention or specific aspects in which embodiments of the present invention may be used. It is understood that embodiments of the invention may be used in other aspects and comprise structural or logical changes not depicted in the figures. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

For instance, it is understood that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if one or a plurality of specific method steps are described, a corresponding device may include one or a plurality of units, e.g. functional units, to perform the described one or plurality of method steps (e.g. one unit performing the one or plurality of steps, or a plurality of units each performing one or more of the plurality of steps) , even if such one or more units are not explicitly described or illustrated in the figures. On the other hand, for example, if a specific apparatus is described based on one or a plurality of units, e.g. functional units, a corresponding method may include one step to perform the functionality of the one or plurality of units (e.g. one step performing the functionality of the one or plurality of units, or a plurality of steps each performing the functionality of one or more of the plurality of units) , even if such one or plurality of steps are not explicitly described or illustrated in the figures. Further, it is understood that the features of the various exemplary embodiments and/or aspects described herein may be combined with each other, unless specifically noted otherwise.

Video coding typically refers to the processing of a sequence of pictures, which form the video or video sequence. Instead of the term “picture” the term “frame” or “image” may be used as synonyms in the field of video coding. Video coding used in the present application (or present disclosure) indicates either video encoding or video decoding. Video encoding is performed at the source side, typically comprising processing (e.g. by compression) the original video pictures to reduce the amount of data required for representing the video pictures (for more efficient storage and/or transmission) . Video decoding is performed at the destination side and typically comprises the inverse processing compared to the encoder to reconstruct the video pictures. Embodiments referring to “coding” of video pictures (or pictures in general, as will be explained later) shall be understood to relate to either “encoding” or “decoding” for video sequence. The combination of the encoding part and the decoding part is also referred to as CODEC (Coding and Decoding) .

In case of lossless video coding, the original video pictures can be reconstructed, i.e., the reconstructed video pictures have the same quality as the original video pictures (assuming no transmission loss or other data loss during storage or transmission) . In case of lossy video coding, further compression, e.g., by quantization, is performed, to reduce the amount of data representing the video pictures, which cannot be completely reconstructed at the decoder, i.e. the quality of the reconstructed video pictures is lower or worse compared to the quality of the original video pictures.

Several video coding standards since H. 261 belong to the group of “lossy hybrid video codecs” (i.e. combine spatial and temporal prediction in the sample domain and 2D transform coding for applying quantization in the transform domain) . Each picture of a video sequence is typically partitioned into a set of non-overlapping blocks and the coding is typically performed on a block level. In other words, at the encoder the video is typically processed, i.e. encoded, on a block (video block) level, e.g. by using spatial (intra picture) prediction and temporal (inter picture) prediction to generate a prediction block, subtracting the prediction block from the current block (block currently processed/to be processed) to obtain a residual block, transforming the residual block and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression) , whereas at the decoder the inverse processing compared to the encoder is partially applied to the encoded or compressed block to reconstruct the current block for representation. Furthermore, the encoder duplicates the decoder processing loop such that both will generate identical predictions (e.g. intra-and inter predictions) and/or re-constructions for processing, i.e., coding, the subsequent blocks.

As used herein, the term “block” may a portion of a picture or a frame. For convenience of description, embodiments of the invention are described herein in reference to High-Efficiency Video Coding (HEVC) or the reference software of Versatile video coding (VVC) , developed by the Joint Collaboration Team on Video Coding (JCT-VC) of ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Motion Picture Experts Group (MPEG) . One of ordinary skill in the art will understand that embodiments of the invention are not limited to HEVC or VVC. It may refer to a CU, PU, and TU. In HEVC, a CTU is split into CUs by using a quad-tree structure denoted as coding tree. The decision whether to code a picture area using inter-picture (temporal) or intra-picture (spatial) prediction is made at the CU level. Each CU can be further split into one, two or four PUs according to the PU splitting type. Inside one PU, the same prediction process is applied and the relevant information is transmitted to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the PU splitting type, a CU can be partitioned into transform units (TUs) according to another quadtree structure similar to the coding tree for the CU. In the newest development of the video compression technical, Qual-tree and binary tree (QTBT) partitioning frame is used to partition a coding block. In the QTBT block structure, a CU can have either a square or rectangular shape. For example, a coding tree unit (CTU) is first partitioned by a quadtree structure. The quadtree leaf nodes are further partitioned by a binary tree structure. The binary tree leaf nodes are called coding units (CUs) , and that segmentation is used for prediction and transform processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. In parallel, multiply partition, for example, triple tree partition was also proposed to be used together with the QTBT block structure.

In the following embodiments of an encoder 20, a decoder 30 and a coding system 10 are described with reference to FIGS. 17 to 19.

FIG. 17A is a conceptual or schematic block diagram illustrating an example coding system 10, e.g. a video coding system 10 that may utilize techniques of the present disclosure. Encoder 20 (e.g. Video encoder 20) and decoder 30 (e.g. video decoder 30) of video coding system 10 represent examples of devices that may be configured to perform techniques in accordance with various examples described in the present disclosure. As shown in FIG. 17A, the coding system 10 comprises a source device 12 configured to provide encoded data 13, e.g. an encoded picture 13, e.g. to a destination device 14 for decoding the encoded data 13.

The source device 12 comprises an encoder 20, and may additionally, i.e. optionally, comprise a picture source 16, a pre-processing unit 18, e.g. a picture pre-processing unit 18, and a communication interface or communication unit 22.

The picture source 16 may comprise or be any kind of picture capturing device, for example for capturing a real-world picture, and/or any kind of a picture or comment (for screen content coding, some texts on the screen is also considered a part of a picture or image to be encoded) generating device, for example a computer-graphics processor for generating a computer animated picture, or any kind of device for obtaining and/or providing a real-world picture, a computer animated picture (e.g. a screen content, a virtual reality (VR) picture) and/or any combination thereof (e.g. an augmented reality (AR) picture) .

A (digital) picture is or can be regarded as a two-dimensional array or matrix of samples with intensity values. A sample in the array may also be referred to as pixel (short form of picture element) or a pel. The number of samples in horizontal and vertical direction (or axis) of the array or picture define the size and/or resolution of the picture. For representation of color, typically three color components are employed, i.e. the picture may be represented or include three sample arrays. In RBG format or color space a picture comprises a corresponding red, green and blue sample array. However, in video coding each pixel is typically represented in a luminance/chrominance format or color space, e.g. YCbCr, which comprises a luminance component denoted as Y (sometimes also L is used instead) and two chrominance components denoted as Cb and Cr. The luminance (or short luma) component Y represents the brightness or grey level intensity (e.g. like in a grey-scale picture) , while the two chrominance (or short chroma) components Cb and Cr represent the chromaticity or color information components. Accordingly, a picture in YCbCr format comprises a luminance sample array of luminance sample values (Y) , and two chrominance sample arrays of chrominance values (Cb and Cr) . Pictures in RGB format may be converted or transformed into YCbCr format and vice versa, the process is also known as color transformation or conversion. If a picture is monochrome, the picture may comprise only a luminance sample array.

The picture source 16 (e.g. video source 16) may be, for example a camera for capturing a picture, a memory, e.g. a picture memory, comprising or storing a previously captured or generated picture, and/or any kind of interface (internal or external) to obtain or receive a picture. The camera may be, for example, a local or integrated camera integrated in the source device, the memory may be a local or integrated memory, e.g. integrated in the source device. The interface may be, for example, an external interface to receive a picture from an external video source, for example an external picture capturing device like a camera, an external memory, or an external picture generating device, for example an external computer-graphics processor, computer or server. The interface can be any kind of interface, e.g. a wired or wireless interface, an optical interface, according to any proprietary or standardized interface protocol. The interface for obtaining the picture data 17 may be the same interface as or a part of the communication interface 22.

In distinction to the pre-processing unit 18 and the processing performed by the pre-processing unit 18, the picture or picture data 17 (e.g. video data 16) may also be referred to as raw picture or raw picture data 17. Pre-processing unit 18 is configured to receive the (raw) picture data 17 and to perform pre-processing on the picture data 17 to obtain a pre-processed picture 19 or pre-processed picture data 19. Pre-processing performed by the pre-processing unit 18 may, e.g., comprise trimming, color format conversion (e.g. from RGB to YCbCr) , color correction, or de-noising. It can be understood that the pre-processing unit 18 may be an optional component.

The encoder 20 (e.g. video encoder 20) is configured to receive the pre-processed picture data 19 and provide encoded picture data 21 (further details will be described below, e.g., based on FIG. 18 or FIG. 4) . Communication interface 22 of the source device 12 may be configured to receive the encoded picture data 21 and to transmit it to another device, e.g. the destination device 14 or any other device, for storage or direct reconstruction, or to process the encoded picture data 21 for respectively before storing the encoded data 13 and/or transmitting the encoded data 13 to another device, e.g. the destination device 14 or any other device for decoding or storing.

The destination device 14 comprises a decoder 30 (e.g. a video decoder 30) , and may additionally, i.e. optionally, comprise a communication interface or communication unit 28, a post-processing unit 32 and a display device 34.

The communication interface 28 of the destination device 14 is configured to receive the encoded picture data 21 or the encoded data 13, e.g. directly from the source device 12 or from any other source, e.g. a storage device, e.g. an encoded picture data storage device.

The communication interface 22 and the communication interface 28 may be configured to transmit or receive the encoded picture data 21 or encoded data 13 via a direct communication link between the source device 12 and the destination device 14, e.g. a direct wired or wireless connection, or via any kind of network, e.g. a wired or wireless network or any combination thereof, or any kind of private and public network, or any kind of combination thereof.

The communication interface 22 may be, e.g., configured to package the encoded picture data 21 into an appropriate format, e.g. packets, for transmission over a communication link or communication network.

The communication interface 28, forming the counterpart of the communication interface 22, may be, e.g., configured to de-package the encoded data 13 to obtain the encoded picture data 21.

Both, communication interface 22 and communication interface 28 may be configured as unidirectional communication interfaces as indicated by the arrow for the encoded picture data 13 in FIG. 17A pointing from the source device 12 to the destination device 14, or bi-directional communication interfaces, and may be configured, e.g. to send and receive messages, e.g. to set up a connection, to acknowledge and exchange any other information related to the communication link and/or data transmission, e.g. encoded picture data transmission.

The decoder 30 is configured to receive the encoded picture data 21 and provide decoded picture data 31 or a decoded picture 31 (further details will be described below, e.g., with reference to FIG. 19 or FIG. 21) . The post-processor 32 of destination device 14 is configured to post-process the decoded picture data 31 (also called reconstructed picture data) , e.g. the decoded picture 31, to obtain post-processed picture data 33, e.g. a post-processed picture 33. The post-processing performed by the post-processing unit 32 may comprise, e.g. color format conversion (e.g. from YCbCr to RGB) , color correction, trimming, or re-sampling, or any other processing, e.g. for preparing the decoded picture data 31 for display, e.g. by display device 34.

The display device 34 of the destination device 14 is configured to receive the post-processed picture data 33 for displaying the picture, e.g. to a user or viewer. The display device 34 may be or comprise any kind of display for representing the reconstructed picture, e.g. an integrated or external display or monitor. The displays may, e.g. comprise liquid crystal displays (LCD) , organic light emitting diodes (OLED) displays, plasma displays, projectors , micro LED displays, liquid crystal on silicon (LCoS) , digital light processor (DLP) or any kind of other display.

Although FIG. 17A depicts the source device 12 and the destination device 14 as separate devices, embodiments of devices may also comprise both or both functionalities, the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality. In such embodiments the source device 12 or corresponding functionality and the destination device 14 or corresponding functionality may be implemented using the same hardware and/or software or by separate hardware and/or software or any combination thereof.

As will be apparent to the skilled person based on the description, the existence and (exact) split of functionalities of the different units or functionalities within the source device 12 and/or destination device 14 as shown in FIG. 17A may vary depending on the actual device and application.

The encoder 20 (e.g. a video encoder 20) and the decoder 30 (e.g. a video decoder 30) each may be implemented as any of a variety of suitable circuitry, such as one or more microprocessors, digital signal processors (DSPs) , application-specific integrated circuits (ASICs) , field-programmable gate arrays (FPGAs) , discrete logic, hardware, or any combinations thereof. If the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Any of the foregoing (including hardware, software, a combination of hardware and software, etc. ) may be considered to be one or more processors. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device.

Source device 12 may be referred to as a video encoding device or a video encoding apparatus. Destination device 14 may be referred to as a video decoding device or a video decoding apparatus. Source device 12 and destination device 14 may be examples of video coding devices or video coding apparatuses.

Source device 12 and destination device 14 may comprise any of a wide range of devices, including any kind of handheld or stationary devices, e.g. notebook or laptop computers, mobile phones, smart phones, tablets or tablet computers, cameras, desktop computers, set-top boxes, televisions, display devices, digital media players, video gaming consoles, video streaming devices (such as content services servers or content delivery servers) , broadcast receiver device, broadcast transmitter device, or the like and may use no or any kind of operating system.

In some cases, the source device 12 and the destination device 14 may be equipped for wireless communication. Thus, the source device 12 and the destination device 14 may be wireless communication devices.

In some cases, video coding system 10 illustrated in FIG. 17A is merely an example and the techniques of the present application may apply to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between the encoding and decoding devices. In other examples, data is retrieved from a local memory, streamed over a network, or the like. A video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory. In some examples, the encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory.

It should be understood that, for each of the above examples described with reference to video encoder 20, video decoder 30 may be configured to perform a reciprocal process. With regard to signaling syntax elements, video decoder 30 may be configured to receive and parse such syntax element and decode the associated video data accordingly. In some examples, video encoder 20 may entropy encode one or more syntax elements into the encoded video bitstream. In such examples, video decoder 30 may parse such syntax element and decode the associated video data accordingly.

FIG. 17B is an illustrative diagram of another example video coding system 40 including encoder 20 of Fig. 18 and/or decoder 30 of Fig. 19 according to an exemplary embodiment. The system 40 can implement techniques in accordance with various examples described in the present application. In the illustrated implementation, video coding system 40 may include imaging device (s) 41, video encoder 100, video decoder 30 (and/or a video coder implemented via logic circuitry 47 of processing unit (s) 46) , an antenna 42, one or more processor (s) 43, one or more memory store (s) 44, and/or a display device 45.

As illustrated, imaging device (s) 41, antenna 42, processing unit (s) 46, logic circuitry 47, video encoder 20, video decoder 30, processor (s) 43, memory store (s) 44, and/or display device 45 may be capable of communication with one another. As discussed, although illustrated with both video encoder 20 and video decoder 30, video coding system 40 may include only video encoder 20 or only video decoder 30 in various examples.

As shown, in some examples, video coding system 40 may include antenna 42. Antenna 42 may be configured to transmit or receive an encoded bitstream of video data, for example. Further, in some examples, video coding system 40 may include display device 45. Display device 45 may be configured to present video data. As shown, in some examples, logic circuitry 47 may be implemented via processing unit (s) 46. Processing unit (s) 46 may include application-specific integrated circuit (ASIC) logic, graphics processor (s) , general purpose processor (s) , or the like. Video coding system 40 also may include optional processor (s) 43, which may similarly include application-specific integrated circuit (ASIC) logic, graphics processor (s) , general purpose processor (s) , or the like. In some examples, logic circuitry 47 may be implemented via hardware, video coding dedicated hardware, or the like, and processor (s) 43 may implemented general purpose software, operating systems, or the like. In addition, memory store (s) 44 may be any type of memory such as volatile memory (e.g., Static Random Access Memory (SRAM) , Dynamic Random Access Memory (DRAM) , etc. ) or non-volatile memory (e.g., flash memory, etc. ) , and so forth. In a non-limiting example, memory store (s) 44 may be implemented by cache memory. In some examples, logic circuitry 47 may access memory store (s) 44 (for implementation of an image buffer for example) . In other examples, logic circuitry 47 and/or processing unit (s) 46 may include memory stores (e.g., cache or the like) for the implementation of an image buffer or the like.

In some examples, video encoder 100 implemented via logic circuitry may include an image buffer (e.g., via either processing unit (s) 46 or memory store (s) 44) ) and a graphics processing unit (e.g., via processing unit (s) 46) . The graphics processing unit may be communicatively coupled to the image buffer. The graphics processing unit may include video encoder 100 as implemented via logic circuitry 47 to embody the various modules as discussed with respect to FIG. 18 and/or any other encoder system or subsystem described herein. The logic circuitry may be configured to perform the various operations as discussed herein.

Video decoder 30 may be implemented in a similar manner as implemented via logic circuitry 47 to embody the various modules as discussed with respect to decoder 30 of FIG. 19 and/or any other decoder system or subsystem described herein. In some examples, video decoder 30 may be implemented via logic circuitry may include an image buffer (e.g., via either processing unit (s) 420 or memory store (s) 44) ) and a graphics processing unit (e.g., via processing unit (s) 46) . The graphics processing unit may be communicatively coupled to the image buffer. The graphics processing unit may include video decoder 30 as implemented via logic circuitry 47 to embody the various modules as discussed with respect to FIG. 19 and/or any other decoder system or subsystem described herein.

In some examples, antenna 42 of video coding system 40 may be configured to receive an encoded bitstream of video data. As discussed, the encoded bitstream may include data, indicators, index values, mode selection data, or the like associated with encoding a video frame as discussed herein, such as data associated with the coding partition (e.g., transform coefficients or quantized transform coefficients, optional indicators (as discussed) , and/or data defining the coding partition) . Video coding system 40 may also include video decoder 30 coupled to antenna 42 and configured to decode the encoded bitstream. The display device 45 configured to present video frames.

ENCODER &ENCODING METHOD

FIG. 18 shows a schematic/conceptual block diagram of an example video encoder 20 that is configured to implement the techniques of the present disclosure. In the example of FIG. 18, the video encoder 20 comprises a residual calculation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, and inverse transform processing unit 212, a reconstruction unit 214, a buffer 216, a loop filter unit 220, a decoded picture buffer (DPB) 230, a prediction processing unit 260 and an entropy encoding unit 270. The prediction processing unit 260 may include an inter prediction unit 244, an intra prediction unit 254 and a mode selection unit 262. Inter prediction unit 244 may include a motion estimation unit and a motion compensation unit (not shown) . A video encoder 20 as shown in FIG. 18 may also be referred to as hybrid video encoder or a video encoder according to a hybrid video codec.

For example, the residual calculation unit 204, the transform processing unit 206, the quantization unit 208, the prediction processing unit 260 and the entropy encoding unit 270 form a forward signal path of the encoder 20, whereas, for example, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the buffer 216, the loop filter 220, the decoded picture buffer (DPB) 230, prediction processing unit 260 form a backward signal path of the encoder, wherein the backward signal path of the encoder corresponds to the signal path of the decoder (see decoder 30 in FIG. 19) .

The encoder 20 is configured to receive, e.g. by input 202, a picture 201 or a block 203 of the picture 201, e.g. picture of a sequence of pictures forming a video or video sequence. The picture block 203 may also be referred to as current picture block or picture block to be coded, and the picture 201 as current picture or picture to be coded (in particular in video coding to distinguish the current picture from other pictures, e.g. previously encoded and/or decoded pictures of the same video sequence, i.e. the video sequence which also comprises the current picture) .

Embodiments of the encoder 20 may comprise a partitioning unit (not depicted in FIG. 18) configured to partition the picture 201 into a plurality of blocks, e.g. blocks like block 203, typically into a plurality of non-overlapping blocks. The partitioning unit may be configured to use the same block size for all pictures of a video sequence and the corresponding grid defining the block size, or to change the block size between pictures or subsets or groups of pictures, and partition each picture into the corresponding blocks.

In one example, the prediction processing unit 260 of video encoder 20 may be configured to perform any combination of the partitioning techniques described above.

Like the picture 201, the block 203 again is or can be regarded as a two-dimensional array or matrix of samples with intensity values (sample values) , although of smaller dimension than the picture 201. In other words, the block 203 may comprise, e.g., one sample array (e.g. a luma array in case of a monochrome picture 201) or three sample arrays (e.g. a luma and two chroma arrays in case of a color picture 201) or any other number and/or kind of arrays depending on the color format applied. The number of samples in horizontal and vertical direction (or axis) of the block 203 define the size of block 203.

Encoder 20 as shown in FIG. 18 is configured to encode the picture 201 block by block, e.g. the encoding and prediction is performed per block 203.

The residual calculation unit 204 is configured to calculate a residual block 205 based on the picture block 203 and a prediction block 265 (further details about the prediction block 265 are provided later) , e.g. by subtracting sample values of the prediction block 265 from sample values of the picture block 203, sample by sample (pixel by pixel) to obtain the residual block 205 in the sample domain.

The transform processing unit 206 is configured to apply a transform, e.g. a discrete cosine transform (DCT) or discrete sine transform (DST) , on the sample values of the residual block 205 to obtain transform coefficients 207 in a transform domain. The transform coefficients 207 may also be referred to as transform residual coefficients and represent the residual block 205 in the transform domain.

The transform processing unit 206 may be configured to apply integer approximations of DCT/DST, such as the transforms specified for HEVC/H. 265. Compared to an orthogonal DCT transform, such integer approximations are typically scaled by a certain factor. In order to preserve the norm of the residual block which is processed by forward and inverse transforms, additional scaling factors are applied as part of the transform process. The scaling factors are typically chosen based on certain constraints like scaling factors being a power of two for shift operation, bit depth of the transform coefficients, tradeoff between accuracy and implementation costs, etc. Specific scaling factors are, for example, specified for the inverse transform, e.g. by inverse transform processing unit 212, at a decoder 30 (and the corresponding inverse transform, e.g. by inverse transform processing unit 212 at an encoder 20) and corresponding scaling factors for the forward transform, e.g. by transform processing unit 206, at an encoder 20 may be specified accordingly.

The quantization unit 208 is configured to quantize the transform coefficients 207 to obtain quantized transform coefficients 209, e.g. by applying scalar quantization or vector quantization. The quantized transform coefficients 209 may also be referred to as quantized residual coefficients 209. The quantization process may reduce the bit depth associated with some or all of the transform coefficients 207. For example, an n-bit Transform coefficient may be rounded down to an m-bit Transform coefficient during quantization, where n is greater than m.The degree of quantization may be modified by adjusting a quantization parameter (QP) . For example for scalar quantization, different scaling may be applied to achieve finer or coarser quantization. Smaller quantization step sizes correspond to finer quantization, whereas larger quantization step sizes correspond to coarser quantization. The applicable quantization step size may be indicated by a quantization parameter (QP) . The quantization parameter may for example be an index to a predefined set of applicable quantization step sizes. For example, small quantization parameters may correspond to fine quantization (small quantization step sizes) and large quantization parameters may correspond to coarse quantization (large quantization step sizes) or vice versa. The quantization may include division by a quantization step size and corresponding or inverse dequantization, e.g. by inverse quantization 210, may include multiplication by the quantization step size. Embodiments according to some standards, e.g. HEVC, may be configured to use a quantization parameter to determine the quantization step size. Generally, the quantization step size may be calculated based on a quantization parameter using a fixed point approximation of an equation including division. Additional scaling factors may be introduced for quantization and dequantization to restore the norm of the residual block, which might get modified because of the scaling used in the fixed point approximation of the equation for quantization step size and quantization parameter. In one example implementation, the scaling of the inverse transform and dequantization might be combined. Alternatively, customized quantization tables may be used and signaled from an encoder to a decoder, e.g. in a bitstream. The quantization is a lossy operation, wherein the loss increases with increasing quantization step sizes.

The inverse quantization unit 210 is configured to apply the inverse quantization of the quantization unit 208 on the quantized coefficients to obtain dequantized coefficients 211, e.g. by applying the inverse of the quantization scheme applied by the quantization unit 208 based on or using the same quantization step size as the quantization unit 208. The dequantized coefficients 211 may also be referred to as dequantized residual coefficients 211 and correspond -although typically not identical to the transform coefficients due to the loss by quantization -to the transform coefficients 207.

The inverse transform processing unit 212 is configured to apply the inverse transform of the transform applied by the transform processing unit 206, e.g. an inverse discrete cosine transform (DCT) or inverse discrete sine transform (DST) , to obtain an inverse transform block 213 in the sample domain. The inverse transform block 213 may also be referred to as inverse transform dequantized block 213 or inverse transform residual block 213.

The reconstruction unit 214 (e.g. Summer 214) is configured to add the inverse transform block 213 (i.e. reconstructed residual block 213) to the prediction block 265 to obtain a reconstructed block 215 in the sample domain, e.g. by adding the sample values of the reconstructed residual block 213 and the sample values of the prediction block 265.

In one embodiment, the buffer unit 216 (also referred to as “buffer” or “line buffer” 216) is configured to buffer or store the reconstructed block 215 and the respective sample values, for example for intra prediction. In further embodiments, the encoder may be configured to use unfiltered reconstructed blocks and/or the respective sample values stored in buffer unit 216 for any kind of estimation and/or prediction, e.g. intra prediction.

Embodiments of the encoder 20 may be configured such that, e.g. the buffer unit 216 is not only used for storing the reconstructed blocks 215 for intra prediction 254 but also for the loop filter unit 220 (not shown in FIG. 18) , and/or such that, e.g. the buffer unit 216 and the decoded picture buffer unit 230 form one buffer. Further embodiments may be configured to use filtered blocks 221 and/or blocks or samples from the decoded picture buffer 230 (both not shown in FIG. 18) as input or basis for intra prediction 254.

The loop filter unit 220 (also referred to as “loop filter” 220) is configured to filter the reconstructed block 215 to obtain a filtered block 221, e.g., to smooth pixel transitions or otherwise improve the video quality. The loop filter unit 220 represents one or more loop filters, such as a de-blocking filter, a sample-adaptive offset (SAO) filter or other filters, e.g., a bilateral filter, an adaptive loop filter (ALF) , a sharpening or smoothing filters, or collaborative filters. Although the loop filter unit 220 is shown in FIG. 18 as being an in-loop filter, in other configurations, the loop filter unit 220 may be implemented as a post-loop filter. The filtered block 221 may also be referred to as filtered reconstructed block 221. Decoded picture buffer 230 may store the reconstructed coding blocks after the loop filter unit 220 performs the filtering operations on the reconstructed coding blocks.

Embodiments of the encoder 20 (respectively loop filter unit 220) may be configured to output loop filter parameters (such as sample adaptive offset information) , e.g., directly or entropy encoded via the entropy encoding unit 270 or any other entropy coding unit, so that, e.g., a decoder 30 may receive and apply the same loop filter parameters for decoding.

The decoded picture buffer (DPB) 230 may be a reference picture memory that stores reference picture data for use in encoding video data by video encoder 20. The DPB 230 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) , including synchronous DRAM (SDRAM) , magnetoresistive RAM (MRAM) , resistive RAM (RRAM) , or other types of memory devices. The DPB 230 and the buffer 216 may be provided by the same memory device or separate memory devices. In some example, the decoded picture buffer (DPB) 230 is configured to store the filtered block 221. The decoded picture buffer 230 may be further configured to store other previously filtered blocks, e.g. previously reconstructed and filtered blocks 221, of the same current picture or of different pictures, e.g. previously reconstructed pictures, and may provide complete previously reconstructed, i.e. decoded, pictures (and corresponding reference blocks and samples) and/or a partially reconstructed current picture (and corresponding reference blocks and samples) , for example for inter prediction. In some example, if the reconstructed block 215 is reconstructed but without in-loop filtering, the decoded picture buffer (DPB) 230 is configured to store the reconstructed block 215.

The prediction processing unit 260, also referred to as block prediction processing unit 260, is configured to receive or obtain the block 203 (current block 203 of the current picture 201) and reconstructed picture data, e.g. reference samples of the same (current) picture from buffer 216 and/or reference picture data 231 from one or a plurality of previously decoded pictures from decoded picture buffer 230, and to process such data for prediction, i.e. to provide a prediction block 265, which may be an inter-predicted block 245 or an intra-predicted block 255.

Mode selection unit 262 may be configured to select a prediction mode (e.g. an intra or inter prediction mode) and/or a

corresponding prediction block

245 or 255 to be used as prediction block 265 for the calculation of the residual block 205 and for the reconstruction of the reconstructed block 215.

Embodiments of the mode selection unit 262 may be configured to select the prediction mode (e.g. from those supported by prediction processing unit 260) , which provides the best match or in other words the minimum residual (minimum residual means better compression for transmission or storage) , or a minimum signaling overhead (minimum signaling overhead means better compression for transmission or storage) , or which considers or balances both. The mode selection unit 262 may be configured to determine the prediction mode based on rate distortion optimization (RDO) , i.e. select the prediction mode which provides a minimum rate distortion optimization or which associated rate distortion at least a fulfills a prediction mode selection criterion.

In the following the prediction processing (e.g. prediction processing unit 260 and mode selection (e.g. by mode selection unit 262) performed by an example encoder 20 will be explained in more detail.

As described above, the encoder 20 is configured to determine or select the best or an optimum prediction mode from a set of (pre-determined) prediction modes. The set of prediction modes may comprise, e.g., intra-prediction modes and/or inter-prediction modes.

The set of intra-prediction modes may comprise 35 different intra-prediction modes, e.g., non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined in H. 265, or may comprise 67 different intra-prediction modes, e.g. non-directional modes like DC (or mean) mode and planar mode, or directional modes, e.g. as defined in H. 266 under development.

The set of inter-prediction modes depend on the available reference pictures (i.e., previous at least partially decoded pictures, e.g., stored in DBP 230) and other inter-prediction parameters, e.g., whether the whole reference picture or only a part (e.g., a search window area around the area of the current block) of the reference picture is used for searching for a best matching reference block, and/or e.g., whether pixel interpolation is applied (e.g. half/semi-pel and/or quarter-pel interpolation, or not) .

Additional to the above prediction modes, skip mode and/or direct mode may be applied.

The prediction processing unit 260 may be further configured to partition the block 203 into smaller block partitions or sub-blocks, e.g., iteratively using quad-tree-partitioning (QT) , binary partitioning (BT) or triple-tree-partitioning (TT) or any combination thereof, and to perform, e.g. the prediction for each of the block partitions or sub-blocks, wherein the mode selection comprises the selection of the tree-structure of the partitioned block 203 and the prediction modes applied to each of the block partitions or sub-blocks.

The inter prediction unit 244 may include motion estimation (ME) unit (not shown in FIG. 2) and motion compensation (MC) unit (not shown in FIG. 2) . The motion estimation unit is configured to receive or obtain the picture block 203 (current picture block 203 of the current picture 201) and a decoded picture 231, or at least one or a plurality of previously reconstructed blocks, e.g. reconstructed blocks of one or a plurality of other/different previously decoded pictures 231, for motion estimation. For example, a video sequence may comprise the current picture and the previously decoded pictures 231, or in other words, the current picture and the previously decoded pictures 231 may be part of or form a sequence of pictures forming a video sequence.

The encoder 20 may, e.g., be configured to select a reference block from a plurality of reference blocks of the same or different pictures of the plurality of other pictures and provide a reference picture (or reference picture index, …) and/or an offset (spatial offset) between the position (x, y coordinates) of the reference block and the position of the current block as inter prediction parameters to the motion estimation unit (not shown in FIG. 2) . This offset is also called motion vector (MV) .

The motion compensation unit is configured to obtain, e.g. receive, an inter prediction parameter and to perform inter prediction based on or using the inter prediction parameter to obtain an inter prediction block 245. Motion compensation, performed by motion compensation unit (not shown in FIG. 2) , may involve fetching or generating the prediction block based on the motion/block vector determined by motion estimation, possibly performing interpolations to sub-pixel precision. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that may be used to code a picture block. Upon receiving the motion vector for the PU of the current picture block, the motion compensation unit 246 may locate the prediction block to which the motion vector points in one of the reference picture lists. Motion compensation unit 246 may also generate syntax elements associated with the blocks and the video slice for use by video decoder 30 in decoding the picture blocks of the video slice.

The intra prediction unit 254 is configured to obtain, e.g. receive, the picture block 203 (current picture block) and one or a plurality of previously reconstructed blocks, e.g. reconstructed neighbor blocks, of the same picture for intra estimation. The encoder 20 may, e.g., be configured to select an intra prediction mode from a plurality of (predetermined) intra prediction modes.

The intra prediction unit 254 is further configured to determine based on intra prediction parameter, e.g. the selected intra prediction mode, the intra prediction block 255. In any case, after selecting an intra prediction mode for a block, the intra prediction unit 254 is also configured to provide intra prediction parameter, i.e., information indicative of the selected intra prediction mode for the block to the entropy encoding unit 270. In one example embodiment, the intra prediction unit 254 may be configured to perform any combination of the intra prediction techniques described below.

The entropy encoding unit 270 is configured to apply an entropy encoding algorithm or scheme (e.g. a variable length coding (VLC) scheme, an context adaptive VLC scheme (CALVC) , an arithmetic coding scheme, a context adaptive binary arithmetic coding (CABAC) , syntax-based context-adaptive binary arithmetic coding (SBAC) , probability interval partitioning entropy (PIPE) coding or another entropy encoding methodology or technique) on the quantized residual coefficients 209, inter prediction parameters, intra prediction parameter, and/or loop filter parameters, individually or jointly (or not at all) to obtain encoded picture data 21 which can be output by the output 272, e.g. in the form of an encoded bitstream 21. The encoded bitstream 21 may be transmitted to video decoder 30, or archived for later transmission or retrieval by video decoder 30. The entropy encoding unit 270 can be further configured to entropy encode the other syntax elements for the current video slice being coded.

Other structural variations of the video encoder 20 can be used to encode the video stream. For example, a non-transform based encoder 20 can quantize the residual signal directly without the transform processing unit 206 for certain blocks or frames. In another implementation, an encoder 20 can have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit.

FIG. 19 shows an exemplary video decoder 30 that is configured to implement the techniques of the present disclosure. The video decoder 30 configured to receive encoded picture data (e.g. encoded bitstream) 21, e.g., encoded by encoder 100, to obtain a decoded picture 131. During the decoding process, video decoder 30 receives video data, e.g., an encoded video bitstream that represents picture blocks of an encoded video slice and associated syntax elements, from video encoder 100.

In the example of FIG. 19, the decoder 30 comprises an entropy decoding unit 304, an inverse quantization unit 310, an inverse transform processing unit 312, a reconstruction unit 314 (e.g. a summer 314) , a buffer 316, a loop filter 320, a decoded picture buffer 330 and a prediction processing unit 360. The prediction processing unit 360 may include an inter prediction unit 344, an intra prediction unit 354, and a mode selection unit 362. Video decoder 30 may, in some examples, perform a decoding pass generally reciprocal to the encoding pass described with respect to video encoder 100 from FIG. 18.

The entropy decoding unit 304 is configured to perform entropy decoding to the encoded picture data 21 to obtain, e.g., quantized coefficients 309 and/or decoded coding parameters (not shown in FIG. 19) , e.g., (decoded) any or all of inter prediction parameters, intra prediction parameter, loop filter parameters, and/or other syntax elements. Entropy decoding unit 304 is further configured to forward inter prediction parameters, intra prediction parameter and/or other syntax elements to the prediction processing unit 360. Video decoder 30 may receive the syntax elements at the video slice level and/or the video block level.

The inverse quantization unit 310 may be identical in function to the inverse quantization unit 110, the inverse transform processing unit 312 may be identical in function to the inverse transform processing unit 112, the reconstruction unit 314 may be identical in function reconstruction unit 114, the buffer 316 may be identical in function to the buffer 116, the loop filter 320 may be identical in function to the loop filter 120, and the decoded picture buffer 330 may be identical in function to the decoded picture buffer 130.

The prediction processing unit 360 may comprise an inter prediction unit 344 and an intra prediction unit 354, wherein the inter prediction unit 344 may resemble the inter prediction unit 144 in function, and the intra prediction unit 354 may resemble the intra prediction unit 154 in function. The prediction processing unit 360 are typically configured to perform the block prediction and/or obtain the prediction block 365 from the encoded data 21 and to receive or obtain (explicitly or implicitly) the prediction related parameters and/or the information about the selected prediction mode, e.g. from the entropy decoding unit 304.

When the video slice is coded as an intra coded (I) slice, intra prediction unit 354 of prediction processing unit 360 is configured to generate prediction block 365 for a picture block of the current video slice based on a signaled intra prediction mode and data from previously decoded blocks of the current frame or picture. When the video frame is coded as an inter coded (i.e., B, or P) slice, inter prediction unit 344 (e.g. motion compensation unit) of prediction processing unit 360 is configured to produce prediction blocks 365 for a video block of the current video slice based on the motion vectors and other syntax elements received from entropy decoding unit 304. For inter prediction, the prediction blocks may be produced from one of the reference pictures within one of the reference picture lists. Video decoder 30 may construct the reference frame lists, List 0 and List 1, using default construction techniques based on reference pictures stored in DPB 330.

Prediction processing unit 360 is configured to determine prediction information for a video block of the current video slice by parsing the motion vectors and other syntax elements, and uses the prediction information to produce the prediction blocks for the current video block being decoded. For example, the prediction processing unit 360 uses some of the received syntax elements to determine a prediction mode (e.g., intra or inter prediction) used to code the video blocks of the video slice, an inter prediction slice type (e.g., B slice, P slice, or GPB slice) , construction information for one or more of the reference picture lists for the slice, motion vectors for each inter encoded video block of the slice, inter prediction status for each inter coded video block of the slice, and other information to decode the video blocks in the current video slice.

Inverse quantization unit 310 is configured to inverse quantize, i.e., de-quantize, the quantized transform coefficients provided in the bitstream and decoded by entropy decoding unit 304. The inverse quantization process may include use of a quantization parameter calculated by video encoder 100 for each video block in the video slice to determine a degree of quantization and, likewise, a degree of inverse quantization that should be applied.

Inverse transform processing unit 312 is configured to apply an inverse transform, e.g., an inverse DCT, an inverse integer transform, or a conceptually similar inverse transform process, to the transform coefficients in order to produce residual blocks in the pixel domain.

The reconstruction unit 314 (e.g. Summer 314) is configured to add the inverse transform block 313 (i.e. reconstructed residual block 313) to the prediction block 365 to obtain a reconstructed block 315 in the sample domain, e.g. by adding the sample values of the reconstructed residual block 313 and the sample values of the prediction block 365.

The loop filter unit 320 (either in the coding loop or after the coding loop) is configured to filter the reconstructed block 315 to obtain a filtered block 321, e.g., to smooth pixel transitions, or otherwise improve the video quality. In one example embodiment, the loop filter unit 320 may be configured to perform any combination of the filtering techniques described below. The loop filter unit 320 is intended to represent one or more loop filters such as a de-blocking filter, a sample-adaptive offset (SAO) filter or other filters, e.g. a bilateral filter or an adaptive loop filter (ALF) or a sharpening or smoothing filters or collaborative filters. Although the loop filter unit 320 is shown in FIG. 19 as being an in loop filter, in other configurations, the loop filter unit 320 may be implemented as a post loop filter.

The decoded video blocks 321 in a given frame or picture are then stored in decoded picture buffer 330, which stores reference pictures used for subsequent motion compensation.

The decoder 30 is configured to output the decoded picture 331, e.g. via output 332, for presentation or viewing to a user.

Other variations of the video decoder 30 can be used to decode the compressed bitstream. For example, the decoder 30 can produce the output video stream without the loop filtering unit 320. For example, a non-transform based decoder 30 can inverse-quantize the residual signal directly without the inverse-transform processing unit 312 for certain blocks or frames. In another implementation, the video decoder 30 can have the inverse-quantization unit 310 and the inverse-transform processing unit 312 combined into a single unit.

FIG. 20 is a schematic diagram of a video coding device 400 according to an embodiment of the disclosure. The video coding device 400 is suitable for implementing the disclosed embodiments as described herein. In an embodiment, the video coding device 400 may be a decoder such as video decoder 30 of FIG. 17A or an encoder such as video encoder 20 of FIG. 17A. In an embodiment, the video coding device 400 may be one or more components of the video decoder 30 of FIG. 17A or the video encoder 20 of FIG. 17A as described above.

The video coding device 400 comprises ingress ports 410 and receiver units (Rx) 420 for receiving data; a processor, logic unit, or central processing unit (CPU) 430 to process the data; transmitter units (Tx) 440 and egress ports 450 for transmitting the data; and a memory 460 for storing the data. The video coding device 400 may also comprise optical-to-electrical (OE) components and electrical-to-optical (EO) components coupled to the ingress ports 410, the receiver units 420, the transmitter units 440, and the egress ports 450 for egress or ingress of optical or electrical signals.

The processor 430 is implemented by hardware and software. The processor 430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor) , FPGAs, ASICs, and DSPs. The processor 430 is in communication with the ingress ports 410, receiver units 420, transmitter units 440, egress ports 450, and memory 460. The processor 430 comprises a coding module 470. The coding module 470 implements the disclosed embodiments described above. For instance, the coding module 470 implements, processes, prepares, or provides the various coding operations. The inclusion of the coding module 470 therefore provides a substantial improvement to the functionality of the video coding device 400 and effects a transformation of the video coding device 400 to a different state. Alternatively, the coding module 470 is implemented as instructions stored in the memory 460 and executed by the processor 430.

The memory 460 includes one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory 460 may be volatile and/or non-volatile and may be read-only memory (ROM) , random access memory (RAM) , ternary content-addressable memory (TCAM) , and/or static random-access memory (SRAM) .

FIG. 21 is a simplified block diagram of an apparatus 500 that may be used as either or both of the source device 310 and the destination device 320 from FIG. 17 according to an exemplary embodiment. The apparatus 500 can implement described techniques and embodiments of this present disclosure. The apparatus 500 can be in the form of a computing system including multiple computing devices, or in the form of a single computing device, for example, a mobile phone, a tablet computer, a laptop computer, a notebook computer, a desktop computer, and the like.

The apparatus 500 includes a processor 502 which can be a central processing unit. Alternatively, the processor 502 can be any other type of device or multiple devices capable of manipulating or processing information now-existing or hereafter developed. Although the disclosed implementations can be practiced with a single processor as shown, e.g., the processor 502, advantages in speed and efficiency can be achieved using more than one processor.

The apparatus 500 also includes a memory 504 which can be a read only memory (ROM) device or a random access memory (RAM) device in some embodiments. Any other suitable type of storage device can be used as the memory 504. The memory 504 can include code and data 506 that is accessed by the processor 502 using a bus 512. The memory 504 can further include an operating system 508 and application programs 510, the application programs 510 including at least one program that permits the processor 502 to perform the methods described here. For example, the application programs 510 can include applications 1 through N, which further include a video coding application that performs the methods described herein. The apparatus 500 can also include additional memory in the form of a secondary storage 514, which can, for example, be a memory card used with a mobile computing device. Because the video communication sessions may contain a significant amount of information, they can be stored in whole or in part in the secondary storage 514 and loaded into the memory 504 as needed for processing.

The apparatus 500 can also include one or more output devices, such as a display 518. The display 518 may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display 518 can be coupled to the processor 502 via the bus 512. Other output devices that permit a user to program or otherwise use the apparatus 500 can be provided in addition to or as an alternative to the display 518. When the output device is or includes a display, the display can be implemented in various ways, including by a liquid crystal display (LCD) , a cathode-ray tube (CRT) display, a plasma display or light emitting diode (LED) display, such as an organic LED (OLED) display.

The apparatus 500 can also include or be in communication with an image-sensing device 520, for example a camera, or any other image-sensing device 520 now existing or hereafter developed that can sense an image such as the image of a user operating the apparatus 500. The image-sensing device 520 can be positioned such that it is directed toward the user operating the apparatus 500. In an example, the position and optical axis of the image-sensing device 520 can be configured such that the field of vision includes an area that is directly adjacent to the display 518 and from which the display 518 is visible.

The apparatus 500 can also include or be in communication with a sound-sensing device 522, for example a microphone, or any other sound-sensing device now existing or hereafter developed that can sense sounds near the apparatus 500. The sound-sensing device 522 can be positioned such that it is directed toward the user operating the apparatus 500 and can be configured to receive sounds, for example, speech or other utterances, made by the user while the user operates the apparatus 500.

Although FIG. 21 depicts the processor 502 and the memory 504 of the apparatus 500 as being integrated into a single unit, other configurations can be utilized. The operations of the processor 502 can be distributed across multiple machines (each machine having one or more of processors) that can be coupled directly or across a local area or other network. The memory 504 can be distributed across multiple machines such as a network-based memory or memory in multiple machines performing the operations of the apparatus 500. Although depicted here as a single bus, the bus 512 of the apparatus 500 can be composed of multiple buses. Further, the secondary storage 514 can be directly coupled to the other components of the apparatus 500 or can be accessed via a network and can comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. The apparatus 500 can thus be implemented in a wide variety of configurations.

In one aspect of the present invention, a method for determining availability of refined motion vectors of a spatially neighboring set is provided. The method is presented for use in conjunction with FIGS. 1-21. In an embodiment, the neighboring set includes at least one coding unit or sub-coding unit within a coding tree block (CTB) for a current set, the method includes determining that the refined motion vectors of the spatially neighboring set are available when the refined motion vectors have been computed in a pipeline stage ahead of a data pre-fetch stage of the current set, setting a top-right spatial neighbor block as unavailable when the top-right spatial neighbor block belongs to a top-right CTB, and partitioning a coding unit normatively into as many sub-coding units as a number of concurrency sets that the coding unit spans so that the data pre-fetch stage and a decoder-side motion vector refinement and motion compensation stage for each sub-coding unit occur independent of other sub coding-units, and concurrently with other coding or sub-coding units that belong to a current concurrency set.

In one embodiment, the data data pre-fetch stage precedes the DMVR stage by a configurable lag comprising a number of CTBs. The refined motion vectors of the spatially neighboring set are unavailable for the DMVR process when the configurable lag comprises zero CTB. The refined motion vectors of the spatially neighboring set within top and top-left spatially neighboring CTBs are available for the DMVR process when the configurable lag comprises two CTBs. The refined motion vectors of the spatially neighboring set within top, top-left, and top-right spatially neighboring CTBs are available for the DMVR process when the configurable lag comprises three CTBs.

In one embodiment, the concurrency sets that the coding unit spans are quad-tree partitioned in a recursive z-scan order. The refined motion vectors of the spatially neighboring set within top and top-left spatially neighboring CTBs are available for the DMVR process of the quad-tree portioned concurrency sets when the configurable lag comprises two CTBs. In one embodiment, the method further includes performing the DMVR process using unrefined motion vectors of coding units in spatially neighboring CTBs, the refined motion vectors are determined to be unavailable at the pipeline stage. The technical featutres and benefits are discussed in

embodiments

1 and 2 and Table 3.1 and 3.2.

In another aspect of the present invention, a method for pre-fetching data into a block processing pipeline is provided. The block processing pipeline includes a plurality of pipeline slots each configured to process a pixel block. An input frame is partitioned into rows of coding tree blocks (CTBs) each comprising one or more coding unit (CUs) . Each of the CUs includes a number of concurrency sets. The method includes pre-fetching data for a given CTB into a pipeline slot, by the video coding apparatus, using unrefined motion vectors (MVs) of a neighbor CU that falls in a preceding pipeline slot to a concurrency set of a current CU, using refined MVs of a neighbor CU that does not fall in a same concurrency set as a refinement start MV, and using padded samples based on a configurable search range around the given CTB.

The methods described herein may be implemented in siftware, hardware, or a combination thereof. The variuosu embodiments described above are provided by way of illustration only and should not be condtrued to limit the appended claims. Those of skill in the art will readily recognize various modifications that could be made without departing from the scope of the present invention.

Claims

A method for determining availability of refined motion vectors of a spatially neighboring set comprising at least one coding unit or sub-coding unit within a coding tree block (CTB) for a current set, the method performed by a video coding apparatus and comprising:

determining, by the video coding apparatus, that the refined motion vectors of the spatially neighboring set are available when the refined motion vectors have been computed in a pipeline stage ahead of a data pre-fetch stage of the current set;

setting a top-right spatial neighbor block as unavailable when the top-right spatial neighbor block belongs to a top-right CTB; and

partitioning a coding unit normatively into as many sub-coding units as a number of concurrency sets that the coding unit spans so that the data pre-fetch stage and a decoder-side motion vector refinement (DMVR) process for each sub-coding unit occur independent of other sub coding-units, and concurrently with other coding or sub-coding units that belong to a current concurrency set.
The method of claim 1, wherein the data pre-fetch stage precedes the DMVR process by a configurable lag comprising a number of CTBs.
The method of claim 2, wherein the refined motion vectors of the spatially neighboring set are unavailable for the DMVR process when the configurable lag comprises zero CTB.
The method of claim 2, wherein the refined motion vectors of the spatially neighboring set within top and top-left spatially neighboring CTBs are available for the DMVR process when the configurable lag comprises two CTBs.
The method of claim 2, wherein the refined motion vectors of the spatially neighboring set within top, top-left, and top-right spatially neighboring CTBs are available for the DMVR process when the configurable lag comprises three CTBs.
The method of claim 2, wherein the concurrency sets that the coding unit spans are quad-tree partitioned in a recursive z-scan order.
The method of claim 6, wherein the refined motion vectors of the spatially neighboring set within top and top-left spatially neighboring CTBs are available for the DMVR process of the quad-tree partitioned concurrency sets when the configurable lag comprises two CTBs.
The method of claim 1, further comprising, when the refined motion vectors are determined to be unavailable at the pipeline stage:

performing the DMVR process using unrefined motion vectors of coding units in spatially neighboring CTBs.
A method for pre-fetching data into a block processing pipeline comprising a plurality of pipeline slots each configured to process a pixel block, wherein an input frame is partitioned into rows of coding tree blocks (CTBs) each comprising one or more coding units (CUs) each comprising a number of concurrency sets, the method performed by a video coding apparatus and comprising:

pre-fetching data for a given CTB into a pipeline slot, by the video coding apparatus, using unrefined motion vectors (MVs) of a neighbor coding unit (CU) that falls in a preceding pipeline slot to a concurrency set of a current CU;

using refined MVs of a neighbor CU that does not fall in a same concurrency set as a refinement start MV; and

using padded samples based on a configurable search range around the given CTB.
The method of claim 9, wherein pre-fetching the data for the given CTB is based on a refinement start MV of a neighbor CTB when the CTB of a neighbor CU has a lag equal to or greater than two CTBs and the start MV refinement is based on a refined MV of the neighbor CTB.
The method of claim 9, wherein pre-fetching the data for the given CTB is based on a refinement start MV of a neighbor CTB when the CTB of a neighbor CU has a lag equal to one CTB and the start MV refinement is based on a refined MV of the neighbor CTB.
The method of claim 9, wherein each of the CTBs is quad-tree split, and each of the pipeline slots has a granularity of a quarter of a CTB.
The method of claim 9, wherein the pipeline slot has a lag of two CTBs relative to the preceding pipeline slot, refined MVs from neighbor CUs in top-left and top CTUs are used and unrefined MVs from neighbor CUs in top-right CTU are used.
An inter prediction method for decoding/encoding a current block of a picture, the method comprising:

obtaining a first neighboring refined motion vector (MV) from a position of a first neighboring block adjacent to the current block, wherein the first neighboring block belongs to a first picture region (PR) , and the current block belongs to a second PR which is adjacent to a top-left block of the first PR;

obtaining a second neighboring refined MV from a position of a second neighboring block adjacent to the current block, wherein the second neighboring block belongs to a third PR which is adjacent to a top block of the second PR;

determining an optimal neighboring referring MV from a candidate list which includes the first neighboring refined MV and the second neighboring refined MV;

deriving a refined MV for the current block using the optimal neighboring referring MV as an initial MV of a decoder-side motion vector refinement (DMVR) process of the current block; and

obtaining a predictor of the current block using the refined MV.
The method of claim 14, further comprising:

obtaining the first neighboring MV from a position of a third neighboring block adjacent to the current block, wherein the third neighboring block belongs to a fourth PR which is adjacent to a top-right block of the second PR, and the first neighboring MV is included in the candidate list.
The method of claim 15, wherein the first neighboring MV is configured to derive a third neighboring refined MV of the third neighboring block.
The method of claim 14, further comprising:

obtaining the second neighboring MV from a position of a fourth neighboring block adjacent to the current block, wherein the fourth neighboring block belongs to a fifth PR which is adjacent to a left block of the second PR, and the second neighboring MV is included in the candidate list.
The method of claim 17, wherein the second neighboring MV is configured to derive a fourth neighboring refined MV of the fourth neighboring block.
The method of claim 14, wherein the picture region is a coding unit (CU) or a group of sub-coding tree units or a group of coding units.