Patent Application
20250008082
This disclosure relates to video coding, including video encoding and video decoding.
Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio telephones, so-called “smart phones,” video teleconferencing devices, video streaming devices, and the like. Digital video devices implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, 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 of such standards, as well as proprietary video codecs/formats such as AOMedia Video 1 (AV1) developed by the Alliance for Open Media. The video devices may transmit, receive, encode, decode, and/or store digital video information more efficiently by implementing such video coding techniques.
Video coding techniques include spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as coding tree units (CTUs), coding units (CUs) and/or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.
In general, this disclosure describes techniques related to intra block copy and inter prediction in video coding systems. In particular, this disclosure describes techniques that may be used to derive a base block vector, a base motion vector, and a block vector difference candidate list, e.g., for intra-block copy (IBC) merge mode with block vector differences (IBC-MBVD) or IBC advanced motion vector prediction (IBC AMVP) mode. The techniques may further include derivation of a motion vector difference candidate list for affine merge with motion vector difference (MMVD) mode, geometric MMVD mode, or MMVD for regular merge mode.
In particular, a vector (such as a block vector for intra-block copy (IBC) mode or a motion vector for inter-prediction) may initially be predicted using merge mode vector prediction techniques, which generally include coding of a merge candidate index. A decoder-side motion vector refinement (DMVR) technique, such as template matching refinement, may be used to refine the vector predictor determined from the merge candidate. DMVR generally includes performing a search in a search area relative to a point indicated by the vector predictor to determine an offset to be applied to the vector predictor that results in a refined vector. Per the techniques of this disclosure, a search process may be signaled (e.g., represented by an encoded syntax element in a bitstream). Signaling the search process to be used may improve efficiency of the search process and yield an offset that results in a prediction block that best represents a current block, which may reduce the bitrate associated with coding residual data for the current block.
In one example, a method of decoding video data includes: determining that vector information for a current block of video data is to be coded using a merge with vector difference mode; determining a search process to be used to determine a vector difference for the vector information: selecting a merge candidate from a merge candidate list to determine a vector predictor for the vector information; performing the search process to determine the vector difference: applying the vector difference to the vector predictor to form a final vector; and forming a prediction block for the current block using the final vector.
In another example, a device for decoding video data includes: a memory configured to store video data; and a processing system comprising one or more processors implemented in circuitry, the processing system being configured to: determine that vector information for a current block of video data is to be coded using a merge with vector difference mode; determine a search process to be used to determine a vector difference for the vector information; select a merge candidate from a merge candidate list to determine a vector predictor for the vector information; perform the search process to determine the vector difference; apply the vector difference to the vector predictor to form a final vector; and form a prediction block for the current block using the final vector.
The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims.
In general, video encoding and video decoding includes coding a sequence of pictures that, when rapidly played, simulate motion in a scene. Each picture may be coded using block-based coding techniques, in which the picture is partitioned into blocks of various sizes. Each block may be coded using intra-prediction (relative to previously coded data of the current picture) or inter-prediction (relative to previously coded pictures of the video data). Intra-block copy (IBC) may be considered an intra-prediction technique that involves the use of a block vector to refer to a reference block to be used to predict the current block. Inter-prediction generally involves the use of a motion vector to refer to a reference block of a reference picture (i.e., a previously coded picture).
In addition, the vector (whether a block vector or a motion vector) may itself also be encoded. Merge mode vector coding generally involves constructing a merge candidate list, corresponding to merge candidates of spatial and/or temporal neighboring blocks to the current block. A video encoder may encode a merge candidate index referring to the merge candidate to be used to form a vector predictor for the current block. The vector predictor may then be refined using decoder-side motion vector refinement (DMVR) techniques. Although referred to as “decoder-side.” both the video encoder and the video decoder may perform DMVR. These techniques are referred to as “decoder-side” because, generally, DMVR involves performing a motion search by the video decoder to refine the vector predictor.
Per the techniques of this disclosure, the video encoder may signal a search process to be performed by the video decoder. The video encoder may test a variety of search processes and determine one of the search processes that most quickly results in a vector offset that best yields a prediction block for the current block. The search process may be signaled when merge with motion vector difference (MMVD) or merge with block vector difference (MBVD) is enabled for the current block. The video encoder may signal the appropriate search process in a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, a block header, or the like. Thus, the video decoder may determine the appropriate search process from the SPS, PPS, slice header, block header, or the like.
As an example, one of the search processes may be to perform an initial search using only integer-valued offsets, followed by a fractional-sample offset search. As another example, a search process may be to add only integer-valued offsets to a vector predictor, without performing a fractional-sample offset search (while the vector predictor may have integer or fractional sample precision). The integer search may include an exhaustive search over predefined vector predictor offsets. Alternatively, the integer search may be performed as a sequence of steps, where each step involves only candidates close to the best candidates evaluated in the previous step.
In the case that the fractional-sample search is performed, a list of fractional offsets may be used, such as {−½, ½, ¼, −¼, −¾, and ¾}. The fractional offsets may be searched together, where the best performing offset may be selected based on template matching (TM) cost. Alternatively, the fractional offset search may involve searching the ½ sample offset first, then perform a quarter-sample search around the best ½ sample candidate.
Furthermore, certain candidate offset values may be excluded from consideration if the candidate offset value would point to a location for which not all pixel values needed to determine a difference metric in a reference area are available. For example, to perform template matching, both the reference block and the pixels of the template(s) neighboring the reference block would need to be available in the reference area. Thus, if either the reference block or the template overlaps an unavailable area, the candidate offset value may be excluded from consideration.
In this manner, these techniques may improve the efficiency of performing the search process for identifying an appropriate offset to be applied to a vector predictor. Furthermore, these techniques may be used to select a search process that yields the best performance for predicting a current block, which may reduce the bitrate of the resulting bitstream, due to having smaller residual values.
As shown in
In the example of
System 100 as shown in
In general, video source 104 represents a source of video data (i.e., raw, uncoded video data) and provides a sequential series of pictures (also referred to as “frames”) of the video data to video encoder 200, which encodes data for the pictures. Video source 104 of source device 102 may include a video capture device, such as a video camera, a video archive containing previously captured raw video, and/or a video feed interface to receive video from a video content provider. As a further alternative, video source 104 may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. In each case, video encoder 200 encodes the captured, pre-captured, or computer-generated video data. Video encoder 200 may rearrange the pictures from the received order (sometimes referred to as “display order”) into a coding order for coding. Video encoder 200 may generate a bitstream including encoded video data. Source device 102 may then output the encoded video data via output interface 108 onto computer-readable medium 110 for reception and/or retrieval by, e.g., input interface 122 of destination device 116.
Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memories. In some examples, memories 106, 120 may store raw video data, e.g., raw video from video source 104 and raw, decoded video data from video decoder 300. Additionally or alternatively, memories 106, 120 may store software instructions executable by, e.g., video encoder 200 and video decoder 300, respectively. Although memory 106 and memory 120 are shown separately from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 may also include internal memories for functionally similar or equivalent purposes. Furthermore, memories 106, 120 may store encoded video data, e.g., output from video encoder 200 and input to video decoder 300. In some examples, portions of memories 106, 120 may be allocated as one or more video buffers, e.g., to store raw, decoded, and/or encoded video data.
Computer-readable medium 110 may represent any type of medium or device capable of transporting the encoded video data from source device 102 to destination device 116. In one example, computer-readable medium 110 represents a communication medium to enable source device 102 to transmit encoded video data directly to destination device 116 in real-time, e.g., via a radio frequency network or computer-based network. Output interface 108 may modulate a transmission signal including the encoded video data, and input interface 122 may demodulate the received transmission signal, according to a communication standard, such as a wireless communication protocol. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device 102 to destination device 116.
In some examples, source device 102 may output encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access encoded data from storage device 112 via input interface 122. Storage device 112 may include any of a variety of distributed or locally accessed data storage media such as a hard drive. Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data.
In some examples, source device 102 may output encoded video data to file server 114 or another intermediate storage device that may store the encoded video data generated by source device 102. Destination device 116 may access stored video data from file server 114 via streaming or download.
File server 114 may be any type of server device capable of storing encoded video data and transmitting that encoded video data to the destination device 116. File server 114 may represent a web server (e.g., for a website), a server configured to provide a file transfer protocol service (such as File Transfer Protocol (FTP) or File Delivery over Unidirectional Transport (FLUTE) protocol), a content delivery network (CDN) device, a hypertext transfer protocol (HTTP) server, a Multimedia Broadcast Multicast Service (MBMS) or Enhanced MBMS (eMBMS) server, and/or a network attached storage (NAS) device. File server 114 may, additionally or alternatively, implement one or more HTTP streaming protocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real Time Streaming Protocol (RTSP). HTTP Dynamic Streaming, or the like.
Destination device 116 may access encoded video data from file server 114 through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriber line (DSL), cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on file server 114. Input interface 122 may be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from file server 114, or other such protocols for retrieving media data.
Output interface 108 and input interface 122 may represent wireless transmitters/receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of a variety of IEEE 802.11 standards, or other physical components. In examples where output interface 108 and input interface 122 comprise wireless components, output interface 108 and input interface 122 may be configured to transfer data, such as encoded video data, according to a cellular communication standard, such as 4G, 4G-LTE (Long-Term Evolution), LTE Advanced, 5G. or the like. In some examples where output interface 108 comprises a wireless transmitter, output interface 108 and input interface 122 may be configured to transfer data, such as encoded video data, according to other wireless standards, such as an IEEE 802.11 specification, an IEEE 802.15 specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. In some examples, source device 102 and/or destination device 116 may include respective system-on-a-chip (SoC) devices. For example, source device 102 may include an SoC device to perform the functionality attributed to video encoder 200 and/or output interface 108, and destination device 116 may include an SoC device to perform the functionality attributed to video decoder 300 and/or input interface 122.
The techniques of this disclosure may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions. Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.
Input interface 122 of destination device 116 receives an encoded video bitstream from computer-readable medium 110 (e.g., a communication medium, storage device 112, file server 114, or the like). The encoded video bitstream may include signaling information defined by video encoder 200, which is also used by video decoder 300, such as syntax elements having values that describe characteristics and/or processing of video blocks or other coded units (e.g., slices, pictures, groups of pictures, sequences, or the like). Display device 118 displays decoded pictures of the decoded video data to a user. Display device 118 may represent any of a variety of display devices such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.
Although not shown in
Video encoder 200 and video decoder 300 each may be implemented as any of a variety of suitable encoder and/or decoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder 200 and video decoder 300 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. A device including video encoder 200 and/or video decoder 300 may comprise an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone.
Video encoder 200 and video decoder 300 may operate according to a video coding standard, such as ITU-T H.265, also referred to as High Efficiency Video Coding (HEVC) or extensions thereto, such as the multi-view and/or scalable video coding extensions. Alternatively, video encoder 200 and video decoder 300 may operate according to other proprietary or industry standards, such as ITU-T H.266, also referred to as Versatile Video Coding (VVC). In other examples, video encoder 200 and video decoder 300 may operate according to a proprietary video codec/format, such as AOMedia Video 1 (AV1), extensions of AV1, and/or successor versions of AV1 (e.g., AV2). In other examples, video encoder 200 and video decoder 300 may operate according to other proprietary formats or industry standards. The techniques of this disclosure, however, are not limited to any particular coding standard or format. In general, video encoder 200 and video decoder 300 may be configured to perform the techniques of this disclosure in conjunction with any video coding techniques that include performing a block vector search for intra-block copy mode.
In general, video encoder 200 and video decoder 300 may perform block-based coding of pictures. The term “block” generally refers to a structure including data to be processed (e.g., encoded, decoded, or otherwise used in the encoding and/or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and/or chrominance data. In general, video encoder 200 and video decoder 300 may code video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, rather than coding red, green, and blue (RGB) data for samples of a picture, video encoder 200 and video decoder 300 may code luminance and chrominance components, where the chrominance components may include both red hue and blue hue chrominance components. In some examples, video encoder 200 converts received RGB formatted data to a YUV representation prior to encoding, and video decoder 300 converts the YUV representation to the RGB format. Alternatively, pre- and post-processing units (not shown) may perform these conversions.
This disclosure may generally refer to coding (e.g., encoding and decoding) of pictures to include the process of encoding or decoding data of the picture. Similarly, this disclosure may refer to coding of blocks of a picture to include the process of encoding or decoding data for the blocks, e.g., prediction and/or residual coding. An encoded video bitstream generally includes a series of values for syntax elements representative of coding decisions (e.g., coding modes) and partitioning of pictures into blocks. Thus, references to coding a picture or a block should generally be understood as coding values for syntax elements forming the picture or block.
HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video coder (such as video encoder 200) partitions a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video coder partitions CTUs and CUs into four equal, non-overlapping squares, and each node of the quadtree has either zero or four child nodes. Nodes without child nodes may be referred to as “leaf nodes,” and CUs of such leaf nodes may include one or more PUs and/or one or more TUs. The video coder may further partition PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents partitioning of TUs. In HEVC, PUs represent inter-prediction data, while TUs represent residual data. CUs that are intra-predicted include intra-prediction information, such as an intra-mode indication.
As another example, video encoder 200 and video decoder 300 may be configured to operate according to VVC. According to VVC, a video coder (such as video encoder 200) partitions a picture into a plurality of coding tree units (CTUs). Video encoder 200 may partition a CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure or Multi-Type Tree (MTT) structure. The QTBT structure removes the concepts of multiple partition types, such as the separation between CUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. A root node of the QTBT structure corresponds to a CTU. Leaf nodes of the binary trees correspond to coding units (CUs).
In an MTT partitioning structure, blocks may be partitioned using a quadtree (QT) partition, a binary tree (BT) partition, and one or more types of triple tree (TT) (also called ternary tree (TT)) partitions. A triple or ternary tree partition is a partition where a block is split into three sub-blocks. In some examples, a triple or temary tree partition divides a block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT), may be symmetrical or asymmetrical.
When operating according to the AV1 codec, video encoder 200 and video decoder 300 may be configured to code video data in blocks. In AV1, the largest coding block that can be processed is called a superblock. In AV1, a superblock can be cither 128×128 luma samples or 64×64 luma samples. However, in successor video coding formats (e.g., AV2), a superblock may be defined by different (e.g., larger) luma sample sizes. In some examples, a superblock is the top level of a block quadtree. Video encoder 200 may further partition a superblock into smaller coding blocks. Video encoder 200 may partition a superblock and other coding blocks into smaller blocks using square or non-square partitioning. Non-square blocks may include N/2×N, N×N/2, N/4×N, and N×N/4 blocks. Video encoder 200 and video decoder 300 may perform separate prediction and transform processes on each of the coding blocks.
AV1 also defines a tile of video data. A tile is a rectangular array of superblocks that may be coded independently of other tiles. That is, video encoder 200 and video decoder 300 may encode and decode, respectively, coding blocks within a tile without using video data from other tiles. However, video encoder 200 and video decoder 300 may perform filtering across tile boundaries. Tiles may be uniform or non-uniform in size. Tile-based coding may enable parallel processing and/or multi-threading for encoder and decoder implementations.
In some examples, video encoder 200 and video decoder 300 may use a single QTBT or MTT structure to represent each of the luminance and chrominance components, while in other examples, video encoder 200 and video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT/MTT structure for the luminance component and another QTBT/MTT structure for both chrominance components (or two QTBT/MTT structures for respective chrominance components).
Video encoder 200 and video decoder 300 may be configured to use quadtree partitioning. QTBT partitioning. MTT partitioning, superblock partitioning, or other partitioning structures.
In some examples, a CTU includes a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples of a picture that has three sample arrays, or a CTB of samples of a monochrome picture or a picture that is coded using three separate color planes and syntax structures used to code the samples. A CTB may be an N×N block of samples for some value of N such that the division of a component into CTBs is a partitioning. A component may be an array or single sample from one of the three arrays (luma and two chroma) for a picture in 4:2:0, 4:2:2, or 4:4:4 color format, or an array or a single sample of the array for a picture in monochrome format. In some examples, a coding block is an M×N block of samples for some values of M and N such that a division of a CTB into coding blocks is a partitioning.
The blocks (e.g., CTUs or CUs) may be grouped in various ways in a picture. As one example, a brick may refer to a rectangular region of CTU rows within a particular tile in a picture. A tile may be a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements (e.g., such as in a picture parameter set). A tile row refers to a rectangular region of CTUs having a height specified by syntax elements (e.g., such as in a picture parameter set) and a width equal to the width of the picture.
In some examples, a tile may be partitioned into multiple bricks, each of which may include one or more CTU rows within the tile. A tile that is not partitioned into multiple bricks may also be referred to as a brick. However, a brick that is a true subset of a tile may not be referred to as a tile. The bricks in a picture may also be arranged in a slice. A slice may be an integer number of bricks of a picture that may be exclusively contained in a single network abstraction layer (NAL) unit. In some examples, a slice includes either a number of complete tiles or only a consecutive sequence of complete bricks of one tile.
This disclosure may use “N×N” and “N by N” interchangeably to refer to the sample dimensions of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, e.g., 16×16 samples or 16 by 16 samples. In general, a 16×16 CU will have 16 samples in a vertical direction (y=16) and 16 samples in a horizontal direction (x=16). Likewise, an N×N CU generally has N samples in a vertical direction and N samples in a horizontal direction, where N represents a nonnegative integer value. The samples in a CU may be arranged in rows and columns. Moreover, CUs need not necessarily have the same number of samples in the horizontal direction as in the vertical direction. For example, CUs may comprise N×M samples, where M is not necessarily equal to N.
Video encoder 200 encodes video data for CUs representing prediction and/or residual information, and other information. The prediction information indicates bow the CU is to be predicted in order to form a prediction block for the CU. The residual information generally represents sample-by-sample differences between samples of the CU prior to encoding and the prediction block.
To predict a CU, video encoder 200 may generally form a prediction block for the CU through inter-prediction or intra-prediction. Inter-prediction generally refers to predicting the CU from data of a previously coded picture, whereas intra-prediction generally refers to predicting the CU from previously coded data of the same picture. To perform inter-prediction, video encoder 200 may generate the prediction block using one or more motion vectors. Video encoder 200 may generally perform a motion search to identify a reference block that closely matches the CU, e.g., in terms of differences between the CU and the reference block. Video encoder 200 may calculate a difference metric using a sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or other such difference calculations to determine whether a reference block closely matches the current CU. In some examples, video encoder 200 may predict the current CU using uni-directional prediction or bi-directional prediction.
Video encoder 200 may further encode a motion vector or block vector (generally referred to as a “vector” or “vector information”) used for inter-prediction or intra-block copy (IBC) mode. Video encoder 200 may determine a search process to be used to search for an offset to be applied to a vector predictor (determined according to, e.g., merge mode) to reconstruct the vector. That is, after determining the vector (e.g., through a motion search or an intra-block copy block search), video encoder 200 may determine a merge candidate from a merge candidate list that best represents the vector (e.g., having the smallest difference relative to the vector). Video encoder 200 may then determine a search process that yields an offset that, when applied to the merge candidate (vector predictor), reconstructs the actual vector used to predict the current block.
Video encoder 200 may encode data representing the search process to be used in high level syntax (HLS), such as a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, a block header, or the like.
As an example, one of the search processes may be to perform an initial search using only integer-valued offsets, followed by a fractional-sample offset search. As another example, a search process may be to add only integer-valued offsets to a vector predictor, without performing a fractional-sample offset search (while the vector predictor may have integer or fractional sample precision). The integer search may include an exhaustive search over predefined vector predictor offsets. Alternatively, the integer search may be performed as a sequence of steps, where each step involves only candidates close to the best candidates evaluated in the previous step.
In the case that the fractional-sample search is performed, a list of fractional offsets may be used, such as {−½, ½, ¼, −¼, −¾, and ¾}. The fractional offsets may be searched together, where the best performing offset may be selected based on template matching (TM) cost. Alternatively, the fractional offset search may involve searching the ½ sample offset first, then perform a quarter-sample search around the best ½ sample candidate.
Furthermore, video encoder 200 may exclude certain candidate offset values from consideration if the candidate offset value would point to a location for which not all pixel values needed to determine a difference metric in a reference area are available. For example, to perform template matching, both the reference block and the pixels of the template(s) neighboring the reference block would need to be available in the reference area. Thus, if either the reference block or the template overlaps an unavailable area, the candidate offset value may be excluded from consideration.
Video decoder 300 may determine the search process to be performed from the corresponding encoded syntax element. In particular, video decoder 300 may decode the syntax element, then determine the search process from the value of the decoded syntax element. Video decoder 300 may also decode a merge candidate index indicating a merge candidate to be used from a merge candidate list to determine a block predictor. Video decoder 300 may then perform the search process indicated by the syntax element, then apply an offset determined using the search process to the vector predictor to reconstruct the vector. Thus, video decoder 300 may then form a prediction block using the reconstructed vector.
Some examples of VVC also provide an affine motion compensation mode, which may be considered an inter-prediction mode. In affine motion compensation mode, video encoder 200 may determine two or more motion vectors that represent non-translational motion, such as zoom in or out, rotation, perspective motion, or other irregular motion types.
To perform intra-prediction, video encoder 200 may select an intra-prediction mode to generate the prediction block. Some examples of VVC provide sixty-seven intra-prediction modes, including various directional modes, as well as planar mode and DC mode. In general, video encoder 200 selects an intra-prediction mode that describes neighboring samples to a current block (e.g., a block of a CU) from which to predict samples of the current block. Such samples may generally be above, above and to the left, or to the left of the current block in the same picture as the current block, assuming video encoder 200 codes CTUs and CUs in raster scan order (left to right, top to bottom).
Video encoder 200 encodes data representing the prediction mode for a current block. For example, for inter-prediction modes, video encoder 200 may encode data representing which of the various available inter-prediction modes is used, as well as motion information for the corresponding mode. For uni-directional or bi-directional inter-prediction, for example, video encoder 200 may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. Video encoder 200 may use similar modes to encode motion vectors for affine motion compensation mode.
AV1 includes two general techniques for encoding and decoding a coding block of video data. The two general techniques are intra prediction (e.g., intra frame prediction or spatial prediction) and inter prediction (e.g., inter frame prediction or temporal prediction). In the context of AV1, when predicting blocks of a current frame of video data using an intra prediction mode, video encoder 200 and video decoder 300 do not use video data from other frames of video data. For most intra prediction modes, video encoder 200 encodes blocks of a current frame based on the difference between sample values in the current block and predicted values generated from reference samples in the same frame. Video encoder 200 determines predicted values generated from the reference samples based on the intra prediction mode.
Following prediction, such as intra-prediction or inter-prediction of a block, video encoder 200 may calculate residual data for the block. The residual data, such as a residual block, represents sample by sample differences between the block and a prediction block for the block, formed using the corresponding prediction mode. Video encoder 200 may apply one or more transforms to the residual block, to produce transformed data in a transform domain instead of the sample domain. For example, video encoder 200 may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to residual video data. Additionally, video encoder 200 may apply a secondary transform following the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal dependent transform, a Karhunen-Loeve transform (KLT), or the like. Video encoder 200 produces transform coefficients following application of the one or more transforms.
As noted above, following any transforms to produce transform coefficients, video encoder 200 may perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. By performing the quantization process, video encoder 200 may reduce the bit depth associated with some or all of the transform coefficients. For example, video encoder 200 may round an n-bit value down to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, video encoder 200 may perform a bitwise right-shift of the value to be quantized.
Following quantization, video encoder 200 may scan the transform coefficients, producing a one-dimensional vector from the two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place higher energy (and therefore lower frequency) transform coefficients at the front of the vector and to place lower energy (and therefore higher frequency) transform coefficients at the back of the vector. In some examples, video encoder 200 may utilize a predefined scan order to scan the quantized transform coefficients to produce a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, video encoder 200 may perform an adaptive scan. After scanning the quantized transform coefficients to form the one-dimensional vector, video encoder 200 may entropy encode the one-dimensional vector, e.g., according to context-adaptive binary arithmetic coding (CABAC). Video encoder 200 may also entropy encode values for syntax elements describing metadata associated with the encoded video data for use by video decoder 300 in decoding the video data.
To perform CABAC, video encoder 200 may assign a context within a context model to a symbol to be transmitted. The context may relate to, for example, whether neighboring values of the symbol are zero-valued or not. The probability determination may be based on a context assigned to the symbol.
Video encoder 200 may further generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, to video decoder 300. e.g., in a picture header, a block header, a slice header, or other syntax data, such as a sequence parameter set (SPS), picture parameter set (PPS), or video parameter set (VPS). Video decoder 300 may likewise decode such syntax data to determine how to decode corresponding video data.
In this manner, video encoder 200 may generate a bitstream including encoded video data, e.g., syntax elements describing partitioning of a picture into blocks (e.g., CUs) and prediction and/or residual information for the blocks. Ultimately, video decoder 300 may receive the bitstream and decode the encoded video data.
In general, video decoder 300 performs a reciprocal process to that performed by video encoder 200 to decode the encoded video data of the bitstream. For example, video decoder 300 may decode values for syntax elements of the bitstream using CABAC in a manner substantially similar to, albeit reciprocal to, the CABAC encoding process of video encoder 200. The syntax elements may define partitioning information for partitioning of a picture into CTUs. and partitioning of each CTU according to a corresponding partition structure, such as a QTBT structure, to define CUs of the CTU. The syntax elements may further define prediction and residual information for blocks (e.g., CUs) of video data.
The residual information may be represented by, for example, quantized transform coefficients. Video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of a block to reproduce a residual block for the block. Video decoder 300 uses a signaled prediction mode (intra- or inter-prediction) and related prediction information (e.g., motion information for inter-prediction) to form a prediction block for the block. Video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. Video decoder 300 may perform additional processing, such as performing a deblocking process to reduce visual artifacts along boundaries of the block.
This disclosure may generally refer to “signaling” certain information, such as syntax elements. The term “signaling” may generally refer to the communication of values for syntax elements and/or other data used to decode encoded video data. That is, video encoder 200 may signal values for syntax elements in the bitstream. In general, signaling refers to generating a value in the bitstream. As noted above, source device 102 may transport the bitstream to destination device 116 substantially in real time, or not in real time, such as might occur when storing syntax elements to storage device 112 for later retrieval by destination device 116.
A history motion vector prediction (HMVP) table size for IBC may include 25 entries. After up to 20 IBC merge candidates are derived with full pruning, a video coder (video encoder 200 or video decoder 300) may reorder the 20 IBC merge candidates. After reordering, video encoder 200 and video decoder 300 may select the first six candidates with lowest temporal matching costs as final candidates for the IBC merge list.
Rather than using zero-valued vectors to pad the IBC merge/AMVP list, a set of block vector predictor (BVP) candidates located in the IBC reference region may be used to pad the IBC merge/AMVP list. A zero-valued vector may be considered invalid as a block vector in IBC merge mode. Consequently, zero-valued vectors may be discarded as BVPs from the IBC candidate list.
Three candidates located on the nearest corners of the reference region, and three additional candidates in the middle of three sub-regions 134A, 134B, and 134C in
In the IBC-TM merge mode, the selected candidates are refined using Template Matching prior to the rate-distortion optimization (RDO) process in video encoder 200 or decoding process of video decoder 300. The IBC-TM merge mode has been put in competition with the regular IBC merge mode and a TM-merge flag is signaled.
In the IBC-TM AMVP mode, up to 3 candidates are selected from the IBC-TM merge list. Each of those 3 selected candidates are refined using the Template Matching method and sorted according to their resulting Template Matching cost. The first two candidates may then be considered in the motion estimation process.
IBC motion vectors may be constrained (i) to be integer valued and (ii) to be within a reference region as shown in
An initial merge candidate list is first constructed according to given checking order, such as spatial, TMVPs, non-adjacent, HMVPs, pairwise, virtual merge candidates. Then the candidates in the initial list may be divided into several subgroups. For the template matching (TM) merge mode, adaptive DMVR mode, each merge candidate in the initial list may first be refined by using TM/multi-pass DMVR. Merge candidates in each subgroup may be reordered to generate a reordered merge candidate list according to cost values based on template matching. The index of a selected merge candidate in the reordered merge candidate list may be signalled by video encoder 200 to video decoder 300. For simplification, merge candidates in the last but not the first subgroup need not be reordered. All the zero candidates from the ARMC reordering process may be excluded during the construction of Merge motion vector candidates list. The subgroup size may be set to 5 for regular merge mode and TM merge mode. The subgroup size may be set to 3 for affine merge mode.
The template matching cost of a merge candidate during the reordering process may be measured by the sum of absolute difference (SAD) between samples of a template of current block 160 and their corresponding reference samples. Other cost calculation methods, such as sum of squared difference (SSD), mean absolute difference (MAD), or mean squared difference (MSD), may be used instead. The template may include a set of reconstructed samples neighboring to current block 160. Reference samples of the template may be located by the motion information of the merge candidate. When a merge candidate utilizes bi-directional prediction, the reference samples of the template of the merge candidate are also generated by bi-prediction, as shown in
When multi-pass DMVR is used to derive the refined motion to the initial merge candidate list, the first pass (i.e., PU level) of multi-pass DMVR may be applied in reordering. When template matching is used to derive the refined motion, the template size is set equal to 1. The above or left template may be used during the motion refinement of TM when the block is flat with block width greater than 2 times of height or narrow with height greater than 2 times of width. TM may be extended to perform 1/16-pel MVD precision. The first four merge candidates may be reordered with the refined motion in TM merge mode.
In particular, in this example, reference picture 180 includes collocated block 182, which is at the same position of reference picture 180 as the position of current block 172 in current picture 170. Thus, collocated block 182 includes collocated sub-blocks 184A-184G. The template information of above template 176 and left template 178 may be used to determine reference sub-blocks 186A-186G using above or left sub-templates neighboring sub-blocks 186A-186G.
In the reordering process, a candidate may be considered redundant if the cost difference between the candidate and its predecessor is inferior to a lambda value, e.g., |D1-D2|<λ, where D1 and D2 are the costs obtained during the first ARMC ordering and λ is the Lagrangian parameter used in the RD criterion by video encoder 200.
The reordering algorithm may be as follows:
Video coders may apply this algorithm to the Regular, TM, BM, and Affine merge modes. A similar algorithm is applied to the Merge MMVD and sign MVD prediction methods which also use ARMC for the reordering.
The value of λ may be set equal to the % of the rate distortion criterion used to select the best merge candidate at the encoder side for low delay configuration and to the value λ corresponding to a another QP for Random Access configuration. A set of λ values corresponding to each signaled QP offset is provided in the SPS or in the Slice Header for the QP offsets which are not present in the SPS.
The ARMC design is also applicable to the AMVP mode wherein the AMVP candidates are reordered according to the TM cost. For the template matching for advanced motion vector prediction (TM-AMVP) mode, an initial AMVP candidate list is constructed, followed by a refinement from TM to construct a refined AMVP candidate list. In addition, an MVP candidate with a TM cost greater than a threshold, which is equal to five times of the cost of the first MVP candidate, may be skipped.
When wrap around motion compensation is enabled, the MV candidate may be clipped with wrap around offset taken into consideration.
The first N motion candidates in the candidate list before being reordered are utilized as the base candidates for MMVD and affine MMVD. N is equal to 3 for MMVD, and [1, 3] depending on the neighboring block affine flags for affine MMVD. Two ways of adding MMVD offsets are allowed, including the ‘two-side’ and ‘one-side’, depending on whether the offset of the other reference picture list is mirrored or directly set to zero. Which way is applied to one block is dependent on the TM cost.
Geometric partition mode (GPM) in ITU-T H.266/Versatile Video Coding (VVC) may be extended by applying motion vector refinement on top of the existing GPM uni-directional MVs. A flag may first be signalled for a GPM CU, to specify whether this mode is used. If the mode is used, each geometric partition of a GPM CU can further decide whether to signal MVD or not. If MVD is signalled for a geometric partition, after a GPM merge candidate is selected, the motion of the partition is further refined by the signalled MVDs information. All other procedures are kept the same as in GPM.
The MVD may be signaled as a pair of distance and direction, similar as in MMVD. There are nine candidate distances (¼-pel, ½-pel, 1-pel, 2-pel. 3-pel, 4-pel, 6-pel, 8-pel, 16-pel), and eight candidate directions (four horizontal/vertical directions and four diagonal directions) involved in GPM with MMVD (GPM-MMVD). In addition, when pic_fpel_mmvd_enabled_flag is equal to 1, the MVD is left shifted by 2 as in MMVD.
The MVD may be signaled as a pair of distance and direction, similar as in MMVD. There are nine candidate distances (¼-pel. ½-pel, 1-pel. 2-pel, 3-pel. 4-pel, 6-pel, 8-pel, 16-pel), and eight candidate directions (four horizontal/vertical directions and four diagonal directions) involved in GPM with MMVD (GPM-MMVD). In addition, when pic_fpel_mmvd_enabled_flag is equal to 1, the MVD is left shifted by 2 as in MMVD.
A Reconstruction-Reordered IBC (RR-IBC) mode is allowed for IBC coded blocks. When RR-IBC is applied, the samples in a reconstruction block are flipped according to a flip type of the current block. At video encoder 200, the original block is flipped before motion search and residual calculation, while the prediction block is derived without flipping. At video decoder 300, the reconstruction block is flipped back to restore the original block.
Two flip methods, horizontal flip (as shown in
To better utilize the symmetry property, a flip-aware BV adjustment approach is applied to refine the block vector candidate. For example, as shown in
Affine-MMVD and GPM-MMVD have been adopted to ECM as an extension of regular MMVD mode. It is natural to extend the MMVD mode to the IBC merge mode.
In IBC-MBVD, the distance set is {1-pel, 2-pel, 4-pel, 8-pel, 12-pel, 16-pel, 24-pel, 32-pel, 40-pel, 48-pel, 56-pel. 64-pel, 72-pel. 80-pel, 88-pel. 96-pel, 104-pel, 112-pel. 120-pel, 128-pel}, and the BVD directions are two horizontal and two vertical directions.
The base candidates may be selected from the first five candidates in the reordered IBC merge list. And based on the SAD cost between the template (one row above and one column left to the current block) and its reference for each refinement position, all the possible MBVD refinement positions (20×4) for each base candidate may be reordered. Finally, the top 8 refinement positions with the lowest template SAD costs are kept as available positions, consequently for MBVD index coding. The MBVD index may be binarized using rice code with the parameter equal to 1.
An IBC-MBVD coded block does not inherit flip type from a RR-IBC coded neighbor block.
Table I below depicts values used to code various BVD values:
In current ECM, IBC merge mode with block vector differences (IBC-MBVD) mode derives a BVD candidates list of 8 candidates for each block vector predictor (BVP) by using template matching to reorder 80 candidates. Wherein, the 80 candidates have a distance to a BVP from a distance set of {1-pel, 2-pel, 4-pel, 8-pel, 12-pel, 16-pel. 24-pel, 32-pel, 40-pel, 48-pel. 56-pel, 64-pel. 72-pel, 80-pel. 88-pel, 96-pel, 104-pel, 112-pel, 120-pel. 128-pel}, and in two horizontal and two vertical directions.
This disclosure recognizes that in the current ECM implementation, enabling MBVD and MMVD at slice-level is only possible after enabling Merge and IBC Merge, correspondingly. However, separate use of MBVD and MMVD without enabling Merge and IBC Merge may be beneficial.
This disclosure further recognizes that increasing the granularity of distance set and increasing the number of the directions may improve the compression efficiency. However, reordering all candidates to derive the final BVD candidate list of 8 candidates may require additional complexity at both encoder and decoder sides. For example, a distance set of 128 values: {1-pel, 2-pel, 3-pel, 4-pel, . . . 127-pel, 128-pel} with 4 directions requires 512 template matching SAD calculations for each BVP, compared to 80 template matching SAD calculation of the current ECM.
The current ECM supports IBC search range to be 2 times of min (CTU size, 128), which means that the maximum offset of BVD set may be increased to 256-pel. The current ECM supports quarter-pel IBC BV, meaning that the number of positions (BVP+MVD offset) in one direction reaches 1024. The above example requires 4096 template matching SAD calculation for each BVP, while the current ECM needs only 80.
Thus, this disclosure describes various techniques for deriving a candidate list for prediction, e.g., BVP or an MVP candidate list. Video encoder 200 and video decoder 300 may be configured to perform any of the various techniques of this disclosure, alone or in combination. Initially, video encoder 200 or video decoder 300 may derive a BVD or an MVD candidates list and code data indicating MBVD or MMVD mode usage to achieve a good trade-off in term of coding performance and coding time. In the following paragraphs, BVP, MBVD, BV, IBC Merge are used to describe the techniques of this disclosure. These techniques may be applied to other modes that use motion vector candidates and offsets for prediction, for example, MMVD. In this example, BVP, MBVD, or BV used in the description should be understood to apply to MVP, MMVD, or MV.
In some examples, video encoder 200 and video decoder 300 may be configured to perform independent MBVD mode signaling. An SPS flag may be coded to indicate that IBC-MBVD or MMVD techniques are enabled. This SPS flag may be signaled independently (separately) from a flag enabling IBC Merge or regular merge, respectively. In some examples, IBC-MBVD can be enabled for a slice when IBC Merge is disabled.
In some examples, video encoder 200 and video decoder 300 may be configured to code data indicating a search process choice. The disclosed MBVD or MMVD techniques may have different search strategies as to how to find the best offset. Therefore, a choice of the search strategy may be signaled, e.g., using a value for a syntax element. The signaling can be done at high level, for example in SPS, PPS, picture header, slice header or at a block level, for example CTU, CU, or PU.
When the choice is signaled at a high level, the choice signaling may be conditional and be signaled only if MBVD or MMVD tool is enabled. For example, a search process choice in SPS may be conditionally signaled only of MBVD or MMVD tool SPS flag is enabled. In another example, the search process choice data is signaled if a merge tool is enabled.
In some examples, the several search processes may include using the existed search process, for example that used in ECM-9.0, and the second choice may be one of this disclosure.
The choice signaling may be represented by a flag if only 2 choices are used, or as an index if more choices are available.
Video encoder 200 and video decoder 300 may be configured to perform a template search procedure for a fractional pixel (pel) case. Block vectors (BVs) in IBC may have integer and fractional pel accuracy. Thus, when BV search is performed, i.e., to find what BV is used for prediction, such search may be performed in both integer and fractional pel domains. In such case, the complexity may significantly increase, since integer and fractional pel BVs should be considered. In some examples, the search may be performed in a brute force manner where all BV candidates may be checked.
To lower the complexity, BV search may be represented in multiple stages, an initial BV search may be performed using only integer BVs following by a fractional BV refinement search step which may be performed for a certain subset of all integer BVs identified as the best candidates.
In MBVD techniques, a BV candidate may be represented by a BVP and an added MVBD offset. There may be several different MBVD offsets added to the same BVP, referred to as base, and there may be multiple bases that can be used.
Following the described techniques, video encoder 200 and video decoder 300 may perform the initial integer search by adding only integer MVBD offsets to a BVP, while BVP may have integer or fractional pel. If integer MVBD is added to fractional BVP, the resulted BV=BVP+MVBD is fractional, so in another alternative to lower the complexity further the initial BVPs, if fractional, may be rounded to integer pel such that the initial BVs will be all integer vectors. It should be noted that integer BVs do not require interpolation, while interpolation is used for fractional BVs to derive the prediction. Integer MBVD offsets may be represented by a list of integer offsets, for example already used in MBVD method {1-pel, 2-pel. 4-pel, 8-pel. 12-pel, 16-pel. 24-pel, 32-pel, 40-pel, 48-pel, 56-pel, 64-pel. 72-pel, 80-pel. 88-pel, 96-pel. 104-pel, 112-pel, 120-pel, 128-pel}, in another example the list may consist of or all possible integer values in a range of [1, 128]. However, any other list of offsets may be used in the described method and should be considered within the scope of this disclosure.
After the initial integer search, several best BVs, having the smallest cost, may be selected. In one example, the cost may be SAD between the current and a reference block templates, where the template is a set of the neighboring reconstructed samples of the current block or a reference block. This cost derivation may be denoted as a template matching (TM) cost.
This integer search may be implemented as one step executing an exhaustive search over the predefined MBVD offsets set. In another alternative, it may be implemented as a sequence of steps, where each next step involves only candidates close to the best candidates chosen at the previous step. Such approach may reduce the total number of candidates to consider. For example, precision of MBVD may be increased within 3 steps: first 4-pel precision, second 2-pel precision and third 1-pel precision.
For an identified list of best BV candidates after the initial search, a fraction pel BV refinement may be performed. In this refinement, a fractional MBVD offset is added to a candidate. In one example, a list of MBVD fractional offsets may be used {−½, ½, ¼, −¼, −¾, ¾}, offsets of ¾ and −¾ may be optional since they are closer to the next integer candidate. However, any other list of offsets may be used in the described method and should be considered within the scope of this invention.
Those fractional offsets (½ and ¼) may be searched together, and the best offset is identified by TM cost. In another alternative, the search may be split to perform half-pel (½) search first and perform quarter-pel (¼) search around the best half-pel precision candidates.
Another advantage of the method is that all BV searches in each step may be performed in parallel, e.g., all TM costs are calculated in parallel for all candidates. It is possible since there is no dependency between the candidates in each step.
In some examples, when checking availability of a fractional pel BV, i.e., having a non-integer horizontal or vertical component, the prediction block itself and all samples required for the interpolation may be required to be located inside the search range.
For example, a BV with non-integer horizontal and integer vertical components, the leftmost and rightmost samples required by filtering to interpolate the extended reference block are required to be available, meanwhile the rows above the top row and below the bottom row of the extended reference block are not required to be available, as shown in
In the example of
Video data memory 230 may store video data to be encoded by the components of video encoder 200. Video encoder 200 may receive the video data stored in video data memory 230 from, for example, video source 104 (
In this disclosure, reference to video data memory 230 should not be interpreted as being limited to memory internal to video encoder 200, unless specifically described as such, or memory external to video encoder 200, unless specifically described as such. Rather, reference to video data memory 230 should be understood as reference memory that stores video data that video encoder 200 receives for encoding (e.g., video data for a current block that is to be encoded). Memory 106 of
The various units of
Video encoder 200 may include arithmetic logic units (ALUs), elementary function units (EFUs), digital circuits, analog circuits, and/or programmable cores, formed from programmable circuits. In examples where the operations of video encoder 200 are performed using software executed by the programmable circuits, memory 106 (
Video data memory 230 is configured to store received video data. Video encoder 200 may retrieve a picture of the video data from video data memory 230 and provide the video data to residual generation unit 204 and mode selection unit 202. Video data in video data memory 230 may be raw video data that is to be encoded.
Mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra-prediction unit 226. Mode selection unit 202 may include additional functional units to perform video prediction in accordance with other prediction modes. As examples, mode selection unit 202 may include a palette unit, an intra-block copy unit (which may be part of motion estimation unit 222 and/or motion compensation unit 224), an affine unit, a linear model (LM) unit, or the like.
Mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and resulting rate-distortion values for such combinations. The encoding parameters may include partitioning of CTUs into CUs, prediction modes for the CUs, transform types for residual data of the CUs, quantization parameters for residual data of the CUS, and so on. Mode selection unit 202 may ultimately select the combination of encoding parameters having rate-distortion values that are better than the other tested combinations.
Video encoder 200 may partition a picture retrieved from video data memory 230 into a series of CTUs. and encapsulate one or more CTUs within a slice. Mode selection unit 202 may partition a CTU of the picture in accordance with a tree structure, such as the MTT structure, QTBT structure, superblock structure, or the quad-tree structure described above. As described above, video encoder 200 may form one or more CUs from partitioning a CTU according to the tree structure. Such a CU may also be referred to generally as a “video block” or “block.”
In general, mode selection unit 202 also controls the components thereof (e.g., motion estimation unit 222, motion compensation unit 224, and intra-prediction unit 226) to generate a prediction block for a current block (e.g., a current CU, or in HEVC, the overlapping portion of a PU and a TU). For inter-prediction of a current block, motion estimation unit 222 may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in DPB 218). In particular, motion estimation unit 222 may calculate a value representative of how similar a potential reference block is to the current block, e.g., according to sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or the like. Motion estimation unit 222 may generally perform these calculations using sample-by-sample differences between the current block and the reference block being considered. Motion estimation unit 222 may identify a reference block having a lowest value resulting from these calculations, indicating a reference block that most closely matches the current block.
Motion estimation unit 222 may form one or more motion vectors (MVs) that defines the positions of the reference blocks in the reference pictures relative to the position of the current block in a current picture. Motion estimation unit 222 may then provide the motion vectors to motion compensation unit 224. For example, for uni-directional inter-prediction, motion estimation unit 222 may provide a single motion vector, whereas for bi-directional inter-prediction, motion estimation unit 222 may provide two motion vectors. Motion compensation unit 224 may then generate a prediction block using the motion vectors. For example, motion compensation unit 224 may retrieve data of the reference block using the motion vector. As another example, if the motion vector has fractional sample precision, motion compensation unit 224 may interpolate values for the prediction block according to one or more interpolation filters. Moreover, for bi-directional inter-prediction, motion compensation unit 224 may retrieve data for two reference blocks identified by respective motion vectors and combine the retrieved data. e.g., through sample-by-sample averaging or weighted averaging.
When operating according to the AV1 video coding format, motion estimation unit 222 and motion compensation unit 224 may be configured to encode coding blocks of video data (e.g., both Juma and chroma coding blocks) using translational motion compensation, affine motion compensation, overlapped block motion compensation (OBMC), and/or compound inter-intra prediction.
As another example, for intra-prediction, or intra-prediction coding, intra-prediction unit 226 may generate the prediction block from samples neighboring the current block. For example, for directional modes, intra-prediction unit 226 may generally mathematically combine values of neighboring samples and populate these calculated values in the defined direction across the current block to produce the prediction block. As another example, for DC mode, intra-prediction unit 226 may calculate an average of the neighboring samples to the current block and generate the prediction block to include this resulting average for each sample of the prediction block.
As still another example, intra-prediction unit 226 may use intra-block copy (IBC) mode to predict the current block. IBC mode generally involves predicting the current block relative to a reference block of the current picture identified by a block vector.
Assuming either inter-prediction or IBC mode is used to predict the current block, mode selection unit 202 may encode the vector (motion vector or block vector) using merge mode with motion vector difference or block vector difference (MMVD or MBVD). Such techniques may further include decoder-side vector refinement, which may include using template matching (TM) to determine an offset to be applied to the vector predictor. Mode selection unit 202 may select a search process to be used to perform TM. Furthermore, mode selection unit 202 may provide a value for a syntax element indicative of the search process to entropy encoding unit 220 to be encoded, e.g., in a sequence parameter set (SPS), picture parameter set (PPS), slice header, block header, or the like.
As discussed above, one of the search processes may be to perform an initial search using only integer-valued offsets, followed by a fractional-sample offset search. As another example, a search process may be to add only integer-valued offsets to a vector predictor, without performing a fractional-sample offset search (while the vector predictor may have integer or fractional sample precision). The integer search may include an exhaustive search over predefined vector predictor offsets. Alternatively, the integer search may be performed as a sequence of steps, where each step involves only candidates close to the best candidates evaluated in the previous step.
In the case that the fractional-sample search is performed, a list of fractional offsets may be used, such as {−½, ½, ¼, −¼, −¾, and ¾}. The fractional offsets may be searched together, where the best performing offset may be selected based on template matching (TM) cost. Alternatively, the fractional offset search may involve searching the ½ sample offset first, then perform a quarter-sample search around the best ½ sample candidate.
Furthermore, certain candidate offset values may be excluded from consideration if the candidate offset value would point to a location for which not all pixel values needed to determine a difference metric in a reference area are available. For example, to perform template matching, both the reference block and the pixels of the template(s) neighboring the reference block would need to be available in the reference area. Thus, if either the reference block or the template overlaps an unavailable area, the candidate offset value may be excluded from consideration.
When operating according to the AV1 video coding format, intra prediction unit 226 may be configured to encode coding blocks of video data (e.g., both luma and chroma coding blocks) using directional intra prediction, non-directional intra prediction, recursive filter intra prediction, chroma-from-luma (CFL) prediction, intra block copy (IBC), and/or color palette mode. Mode selection unit 202 may include additional functional units to perform video prediction in accordance with other prediction modes.
Mode selection unit 202 provides the prediction block to residual generation unit 204. Residual generation unit 204 receives a raw, uncoded version of the current block from video data memory 230 and the prediction block from mode selection unit 202. Residual generation unit 204 calculates sample-by-sample differences between the current block and the prediction block. The resulting sample-by-sample differences define a residual block for the current block. In some examples, residual generation unit 204 may also determine differences between sample values in the residual block to generate a residual block using residual differential pulse code modulation (RDPCM). In some examples, residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.
In examples where mode selection unit 202 partitions CUs into PUs, each PU may be associated with a luma prediction unit and corresponding chroma prediction units. Video encoder 200 and video decoder 300 may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size of a luma prediction unit of the PU. Assuming that the size of a particular CU is 2N×2N, video encoder 200 may support PU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder 200 and video decoder 300 may also support asymmetric partitioning for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N for inter prediction.
In examples where mode selection unit 202 does not further partition a CU into PUs, each CU may be associated with a luma coding block and corresponding chroma coding blocks. As above, the size of a CU may refer to the size of the luma coding block of the CU. The video encoder 200 and video decoder 300 may support CU sizes of 2N×2N. 2N×N. or N×2N.
For other video coding techniques such as an intra-block copy mode coding, an affine-mode coding, and linear model (LM) mode coding, as some examples, mode selection unit 202, via respective units associated with the coding techniques, generates a prediction block for the current block being encoded. In some examples, such as palette mode coding, mode selection unit 202 may not generate a prediction block, and instead generate syntax elements that indicate the manner in which to reconstruct the block based on a selected palette. In such modes, mode selection unit 202 may provide these syntax elements to entropy encoding unit 220 to be encoded.
As described above, residual generation unit 204 receives the video data for the current block and the corresponding prediction block. Residual generation unit 204 then generates a residual block for the current block. To generate the residual block, residual generation unit 204 calculates sample-by-sample differences between the prediction block and the current block.
Transform processing unit 206 applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a “transform coefficient block”). Transform processing unit 206 may apply various transforms to a residual block to form the transform coefficient block. For example, transform processing unit 206 may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to a residual block. In some examples, transform processing unit 206 may perform multiple transforms to a residual block, e.g., a primary transform and a secondary transform, such as a rotational transform. In some examples, transform processing unit 206 does not apply transforms to a residual block.
When operating according to AV1, transform processing unit 206 may apply one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a “transform coefficient block”). Transform processing unit 206 may apply various transforms to a residual block to form the transform coefficient block. For example, transform processing unit 206 may apply a horizontal/vertical transform combination that may include a discrete cosine transform (DCT), an asymmetric discrete sine transform (ADST), a flipped ADST (e.g., an ADST in reverse order), and an identity transform (IDTX). When using an identity transform, the transform is skipped in one of the vertical or horizontal directions. In some examples, transform processing may be skipped.
Quantization unit 208 may quantize the transform coefficients in a transform coefficient block, to produce a quantized transform coefficient block. Quantization unit 208 may quantize transform coefficients of a transform coefficient block according to a quantization parameter (QP) value associated with the current block. Video encoder 200 (e.g., via mode selection unit 202) may adjust the degree of quantization applied to the transform coefficient blocks associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce loss of information, and thus, quantized transform coefficients may have lower precision than the original transform coefficients produced by transform processing unit 206.
Inverse quantization unit 210 and inverse transform processing unit 212 may apply inverse quantization and inverse transforms to a quantized transform coefficient block, respectively, to reconstruct a residual block from the transform coefficient block. Reconstruction unit 214 may produce a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and a prediction block generated by mode selection unit 202. For example, reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by mode selection unit 202 to produce the reconstructed block.
Filter unit 216 may perform one or more filter operations on reconstructed blocks. For example, filter unit 216 may perform deblocking operations to reduce blockiness artifacts along edges of CUs. Operations of filter unit 216 may be skipped, in some examples.
When operating according to AV1, filter unit 216 may perform one or more filter operations on reconstructed blocks. For example, filter unit 216 may perform deblocking operations to reduce blockiness artifacts along edges of CUs. In other examples, filter unit 216 may apply a constrained directional enhancement filter (CDEF), which may be applied after deblocking, and may include the application of non-separable, non-linear, low-pass directional filters based on estimated edge directions. Filter unit 216 may also include a loop restoration filter, which is applied after CDEF, and may include a separable symmetric normalized Wiener filter or a dual self-guided filter.
Video encoder 200 stores reconstructed blocks in DPB 218. For instance, in examples where operations of filter unit 216 are not performed, reconstruction unit 214 may store reconstructed blocks to DPB 218. In examples where operations of filter unit 216 are performed, filter unit 216 may store the filtered reconstructed blocks to DPB 218. Motion estimation unit 222 and motion compensation unit 224 may retrieve a reference picture from DPB 218, formed from the reconstructed (and potentially filtered) blocks, to inter-predict blocks of subsequently encoded pictures. In addition, intra-prediction unit 226 may use reconstructed blocks in DPB 218 of a current picture to intra-predict other blocks in the current picture.
In general, entropy encoding unit 220 may entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy encoding unit 220 may entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy encoding unit 220 may entropy encode prediction syntax elements (e.g., motion information for inter-prediction or intra-mode information for intra-prediction) from mode selection unit 202. Entropy encoding unit 220 may perform one or more entropy encoding operations on the syntax elements, which are another example of video data, to generate entropy-encoded data. For example, entropy encoding unit 220 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, an Exponential-Golomb encoding operation, or another type of entropy encoding operation on the data. In some examples, entropy encoding unit 220 may operate in bypass mode where syntax elements are not entropy encoded.
Video encoder 200 may output a bitstream that includes the entropy encoded syntax elements needed to reconstruct blocks of a slice or picture. In particular, entropy encoding unit 220 may output the bitstream.
In accordance with AV1, entropy encoding unit 220 may be configured as a symbol-to-symbol adaptive multi-symbol arithmetic coder. A syntax element in AV1 includes an alphabet of N elements, and a context (e.g., probability model) includes a set of N probabilities. Entropy encoding unit 220 may store the probabilities as n-bit (e.g., 15-bit) cumulative distribution functions (CDFs). Entropy encoding unit 22 may perform recursive scaling, with an update factor based on the alphabet size, to update the contexts.
The operations described above are described with respect to a block. Such description should be understood as being operations for a luma coding block and/or chroma coding blocks. As described above, in some examples, the luma coding block and chroma coding blocks are luma and chroma components of a CU. In some examples, the luma coding block and the chroma coding blocks are luma and chroma components of a PU.
In some examples, operations performed with respect to a luma coding block need not be repeated for the chroma coding blocks. As one example, operations to identify a motion vector (MV) and reference picture for a luma coding block need not be repeated for identifying a MV and reference picture for the chroma blocks. Rather, the MV for the luma coding block may be scaled to determine the MV for the chroma blocks, and the reference picture may be the same. As another example, the intra-prediction process may be the same for the luma coding block and the chroma coding blocks.
In the example of
Prediction processing unit 304 includes motion compensation unit 316 and intra-prediction unit 318. Prediction processing unit 304 may include additional units to perform prediction in accordance with other prediction modes. As examples, prediction processing unit 304 may include a palette unit, an intra-block copy unit (which may form part of motion compensation unit 316), an affine unit, a linear model (LM) unit, or the like. In other examples, video decoder 300 may include more, fewer, or different functional components.
When operating according to AV1, motion compensation unit 316 may be configured to decode coding blocks of video data (e.g., both luma and chroma coding blocks) using translational motion compensation, affine motion compensation, OBMC, and/or compound inter-intra prediction, as described above. Intra prediction unit 318 may be configured to decode coding blocks of video data (e.g., both luma and chroma coding blocks) using directional intra prediction, non-directional intra prediction, recursive filter intra prediction, CFL, intra block copy (IBC), and/or color palette mode, as described above.
CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by the components of video decoder 300. The video data stored in CPB memory 320 may be obtained, for example, from computer-readable medium 110 (
Additionally or alternatively, in some examples, video decoder 300 may retrieve coded video data from memory 120 (
The various units shown in
Video decoder 300 may include ALUs, EFUs, digital circuits, analog circuits, and/or programmable cores formed from programmable circuits. In examples where the operations of video decoder 300 are performed by software executing on the programmable circuits, on-chip or off-chip memory may store instructions (e.g., object code) of the software that video decoder 300 receives and executes.
Entropy decoding unit 302 may receive encoded video data from the CPB and entropy decode the video data to reproduce syntax elements. Prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, and filter unit 312 may generate decoded video data based on the syntax elements extracted from the bitstream.
In general, video decoder 300 reconstructs a picture on a block-by-block basis. Video decoder 300 may perform a reconstruction operation on each block individually (where the block currently being reconstructed, i.e., decoded, may be referred to as a “current block”).
Entropy decoding unit 302 may entropy decode syntax elements defining quantized transform coefficients of a quantized transform coefficient block, as well as transform information, such as a quantization parameter (QP) and/or transform mode indication(s). Inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 306 to apply Inverse quantization unit 306 may, for example, perform a bitwise left-shift operation to inverse quantize the quantized transform coefficients. Inverse quantization unit 306 may thereby form a transform coefficient block including transform coefficients.
After inverse quantization unit 306 forms the transform coefficient block, inverse transform processing unit 308 may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.
Furthermore, prediction processing unit 304 generates a prediction block according to prediction information syntax elements that were entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax elements indicate that the current block is inter-predicted, motion compensation unit 316 may generate the prediction block. In this case, the prediction information syntax elements may indicate a reference picture in DPB 314 from which to retrieve a reference block, as well as a motion vector identifying a location of the reference block in the reference picture relative to the location of the current block in the current picture. Motion compensation unit 316 may generally perform the inter-prediction process in a manner that is substantially similar to that described with respect to motion compensation unit 224 (
As another example, if the prediction information syntax elements indicate that the current block is intra-predicted, intra-prediction unit 318 may generate the prediction block according to an intra-prediction mode indicated by the prediction information syntax elements. Again, intra-prediction unit 318 may generally perform the intra-prediction process in a manner that is substantially similar to that described with respect to intra-prediction unit 226 (
In the case that the current block is inter-predicted or predicted according to intra-block copy (IBC), prediction processing unit 304 may initially determine whether merge with motion vector difference (MMVD) or merge with block vector difference (MBVD) is enabled for the current block. If so, entropy decoding unit 302 may decode a value for a syntax element indicating a search process to be performed during a TM process used to reconstruct the vector (motion vector for inter-prediction or block vector for IBC). Prediction processing unit 304 may receive a merge index representing a merge candidate in a merge candidate list indicating a vector predictor. Prediction processing unit 304 may then perform the search process indicated by the value of the syntax element to determine an offset to be applied to the vector predictor to reconstruct the vector. This vector may then be used to generate the prediction block for the current block, as discussed above.
In some examples, one of the search processes may be to perform an initial search using only integer-valued offsets, followed by a fractional-sample offset search. As another example, a search process may be to add only integer-valued offsets to a vector predictor, without performing a fractional-sample offset search (while the vector predictor may have integer or fractional sample precision). The integer search may include an exhaustive search over predefined vector predictor offsets. Alternatively, the integer search may be performed as a sequence of steps, where each step involves only candidates close to the best candidates evaluated in the previous step.
In the case that the fractional-sample search is performed, a list of fractional offsets may be used, such as {−½, ½, ¼, −¼, −¾, and ¾}. The fractional offsets may be searched together, where the best performing offset may be selected based on template matching (TM) cost. Alternatively, the fractional offset search may involve searching the ½ sample offset first, then perform a quarter-sample search around the best ½ sample candidate.
Furthermore, certain candidate offset values may be excluded from consideration if the candidate offset value would point to a location for which not all pixel values needed to determine a difference metric in a reference area are available. For example, to perform template matching, both the reference block and the pixels of the template(s) neighboring the reference block would need to be available in the reference area. Thus, if either the reference block or the template overlaps an unavailable area, the candidate offset value may be excluded from consideration.
Reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.
Filter unit 312 may perform one or more filter operations on reconstructed blocks. For example, filter unit 312 may perform deblocking operations to reduce blockiness artifacts along edges of the reconstructed blocks. Operations of filter unit 312 are not necessarily performed in all examples.
Video decoder 300 may store the reconstructed blocks in DPB 314. For instance, in examples where operations of filter unit 312 are not performed, reconstruction unit 310 may store reconstructed blocks to DPB 314. In examples where operations of filter unit 312 are performed, filter unit 312 may store the filtered reconstructed blocks to DPB 314. As discussed above, DPB 314 may provide reference information, such as samples of a current picture for intra-prediction and previously decoded pictures for subsequent motion compensation, to prediction processing unit 304. Moreover, video decoder 300 may output decoded pictures (e.g., decoded video) from DPB 314 for subsequent presentation on a display device, such as display device 118 of
In this example, video encoder 200 initially predicts the current block (350). For example, video encoder 200 may form a prediction block for the current block. Video encoder 200 may then calculate a residual block for the current block (352). To calculate the residual block, video encoder 200 may calculate a difference between the original, uncoded block and the prediction block for the current block. Video encoder 200 may then transform the residual block and quantize transform coefficients of the residual block (354). Next, video encoder 200 may scan the quantized transform coefficients of the residual block (356). During the scan, or following the scan, video encoder 200 may entropy encode the transform coefficients (358). For example, video encoder 200 may encode the transform coefficients using CAVLC or CABAC. Video encoder 200 may then output the entropy encoded data of the block (360).
Video encoder 200 may also decode the current block after encoding the current block, to use the decoded version of the current block as reference data for subsequently coded data (e.g., in inter- or intra-prediction modes). Thus, video encoder 200 may inverse quantize and inverse transform the coefficients to reproduce the residual block (362). Video encoder 200 may combine the residual block with the prediction block to form a decoded block (364). Video encoder 200 may then store the decoded block in DPB 218 (366).
Video decoder 300 may receive entropy encoded data for the current block, such as entropy encoded prediction information and entropy encoded data for transform coefficients of a residual block corresponding to the current block (370). Video decoder 300 may entropy decode the entropy encoded data to determine prediction information for the current block and to reproduce transform coefficients of the residual block (372). Video decoder 300 may predict the current block (374), e.g., using an intra- or inter-prediction mode as indicated by the prediction information for the current block, to calculate a prediction block for the current block. Video decoder 300 may then inverse scan the reproduced transform coefficients (376), to create a block of quantized transform coefficients. Video decoder 300 may then inverse quantize the transform coefficients and apply an inverse transform to the transform coefficients to produce a residual block (378). Video decoder 300 may ultimately decode the current block by combining the prediction block and the residual block (380).
Initially, video decoder 300 may determine that merge with motion vector difference (MMVD) or merge with block vector difference (MBVD) is enabled for a current block of video data (400). Furthermore, video decoder 300 may decode data indicating a search process to be performed when reconstructing a vector for the current block (402), e.g., during template matching (TM). Video decoder 300 may also decode a merge index (404), representing a merge candidate in a merge candidate list. Although not shown in
Video decoder 300 may then perform the search process as indicated by the syntax element discussed above to determine an offset (408). As an example, one of the search processes may be to perform an initial search using only integer-valued offsets, followed by a fractional-sample offset search. As another example, a search process may be to add only integer-valued offsets to a vector predictor, without performing a fractional-sample offset search (while the vector predictor may have integer or fractional sample precision). The integer search may include an exhaustive search over predefined vector predictor offsets. Alternatively, the integer search may be performed as a sequence of steps, where each step involves only candidates close to the best candidates evaluated in the previous step. Any of the other various search processes discussed herein, or other such search processes, may also be used or considered.
After determining the offset using the search process, video decoder 300 may apply the offset to the vector predictor to reconstruct a final vector for the current block (410). Video decoder 300 may then form a prediction block for the current block using the final vector (412). Video decoder 300 may ultimately decode the current block using the prediction block, as discussed above.
Various examples of the techniques of this disclosure are summarized in the following clauses:
Clause 1: A method of decoding video data, the method comprising: determining that vector information for a current block of video data is to be coded using a merge with vector difference mode: determining a search process to be used to determine a vector difference for the vector information; selecting a merge candidate from a merge candidate list to determine a vector predictor for the vector information; performing the search process to determine the vector difference: applying the vector difference to the vector predictor to form a final vector; and forming a prediction block for the current block using the final vector.
Clause 2: The method of clause 1, wherein determining the search process comprises decoding data indicative of the search process.
Clause 3: The method of clause 2, wherein decoding the data indicative of the search process comprises decoding at least one of a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, or a block header including the data indicative of the search process.
Clause 4: The method of clause 2, wherein decoding the data indicative of the search process comprises decoding the data indicative of the search process in response to determining that the merge with vector difference mode is enabled for the current block.
Clause 5: The method of clause 4, wherein determining that the merge with vector difference mode is enabled for the current block comprises coding data of a sequence parameter set (SPS) or a picture parameter set (PPS) indicating that the merge with vector difference mode is enabled for the current block.
Clause 6: The method of clause 1, wherein selecting the merge candidate comprises decoding a merge candidate index indicative of the merge candidate in the merge candidate list.
Clause 7: The method of clause 1, wherein performing the search process comprises performing a first search in an integer pixel domain and performing a second search in a fractional pixel domain.
Clause 8: The method of clause 7, wherein performing the first search comprises performing the first search as a first search phase, and wherein performing the second search comprises performing the second search as a second search phase following the first search phase and starting at a result of the first search phase.
Clause 9: The method of clause 7, wherein performing the first search comprises testing a plurality of integer value offsets relative to the vector predictor.
Clause 10: The method of clause 1, wherein performing the search process comprises searching only potential vector differences that, when applied to the vector information, refer to a reference block for which all pixels needed for calculating a difference metric are available in a reference area.
Clause 11: The method of clause 10, wherein the pixels needed for calculating the difference metric comprise at least one of pixels needed for performing interpolation or pixels needed for performing template matching refinement.
Clause 12: The method of clause 1, further comprising decoding the current block using the prediction block.
Clause 13: The method of clause 1, further comprising encoding the current block prior to decoding the current block.
Clause 14: A device for decoding video data, the device comprising: a memory configured to store video data; and a processing system comprising one or more processors implemented in circuitry, the processing system being configured to: determine that vector information for a current block of video data is to be coded using a merge with vector difference mode: determine a search process to be used to determine a vector difference for the vector information: select a merge candidate from a merge candidate list to determine a vector predictor for the vector information; perform the search process to determine the vector difference: apply the vector difference to the vector predictor to form a final vector; and form a prediction block for the current block using the final vector.
Clause 15: The device of clause 14, wherein to determine the search process, the processing system is configured to decode data indicative of the search process.
Clause 16: The device of clause 14, wherein to select the merge candidate, the processing system is configured to decode a merge candidate index indicative of the merge candidate in the merge candidate list.
Clause 17: The device of clause 14, wherein to perform the search process, the processing system is configured to perform a first search in an integer pixel domain and perform a second search in a fractional pixel domain.
Clause 18: The device of clause 14, wherein to perform the search process, the processing system is configured to search only potential vector differences that, when applied to the vector information, refer to a reference block for which all pixels needed for determining a difference metric are available in a reference area.
Clause 19: The device of clause 14, further comprising a display configured to display the decoded video data.
Clause 20: The device of clause 14, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.
Clause 21: A method of decoding video data, the method comprising: determining that vector information for a current block of video data is to be coded using a merge with vector difference mode: determining a search process to be used to determine a vector difference for the vector information: selecting a merge candidate from a merge candidate list to determine a vector predictor for the vector information; performing the search process to determine the vector difference: applying the vector difference to the vector predictor to form a final vector; and forming a prediction block for the current block using the final vector.
Clause 22: The method of clause 21, wherein determining the search process comprises decoding data indicative of the search process.
Clause 23: The method of clause 22, wherein decoding the data indicative of the search process comprises decoding at least one of a sequence parameter set (SPS), a picture parameter set (PPS), a slice header, or a block header including the data indicative of the search process.
Clause 24: The method of any of clauses 22 and 23, wherein decoding the data indicative of the search process comprises decoding the data indicative of the search process in response to determining that the merge with vector difference mode is enabled for the current block.
Clause 25: The method of clause 24, wherein determining that the merge with vector difference mode is enabled for the current block comprises coding data of a sequence parameter set (SPS) or a picture parameter set (PPS) indicating that the merge with vector difference mode is enabled for the current block.
Clause 26: The method of any of clauses 21-25, wherein selecting the merge candidate comprises decoding a merge candidate index indicative of the merge candidate in the merge candidate list.
Clause 27: The method of any of clauses 21-26, wherein performing the search process comprises performing a first search in an integer pixel domain and performing a second search in a fractional pixel domain.
Clause 28: The method of clause 27, wherein performing the first search comprises performing the first search as a first search phase, and wherein performing the second search comprises performing the second search as a second search phase following the first search phase and starting at a result of the first search phase.
Clause 29: The method of clause any of clauses 27 and 28, wherein performing the first search comprises testing a plurality of integer value offsets relative to the vector predictor.
Clause 30: The method of any of clauses 21-29, wherein performing the search process comprises searching only potential vector differences that, when applied to the vector information, refer to a reference block for which all pixels needed for calculating a difference metric are available in a reference area.
Clause 31: The method of clause 30, wherein the pixels needed for calculating the difference metric comprise at least one of pixels needed for performing interpolation or pixels needed for performing template matching refinement.
Clause 32: The method of any of clauses 21-31, further comprising decoding the current block using the prediction block.
Clause 33: The method of any of clauses 21-32, further comprising encoding the current block prior to decoding the current block.
Clause 34: A device for decoding video data, the device comprising: a memory configured to store video data; and a processing system comprising one or more processors implemented in circuitry, the processing system being configured to: determine that vector information for a current block of video data is to be coded using a merge with vector difference mode: determine a search process to be used to determine a vector difference for the vector information: select a merge candidate from a merge candidate list to determine a vector predictor for the vector information; perform the search process to determine the vector difference; apply the vector difference to the vector predictor to form a final vector; and form a prediction block for the current block using the final vector.
Clause 35: The device of clause 34, wherein to determine the search process, the processing system is configured to decode data indicative of the search process.
Clause 36: The device of any of clauses 34 and 35, wherein to select the merge candidate, the processing system is configured to decode a merge candidate index indicative of the merge candidate in the merge candidate list.
Clause 37: The device of any of clauses 34-36, wherein to perform the search process, the processing system is configured to perform a first search in an integer pixel domain and perform a second search in a fractional pixel domain.
Clause 38: The device of any of clauses 34-37, wherein to perform the search process, the processing system is configured to search only potential vector differences that, when applied to the vector information, refer to a reference block for which all pixels needed for determining a difference metric are available in a reference area.
Clause 39: The device of any of clauses 34-38, further comprising a display configured to display the decoded video data.
Clause 40: The device of any of clauses 34-39, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.
Clause 41: A computer-readable storage medium having stored thereon instructions that, when executed, cause a processor to: determine that vector information for a current block of video data is to be coded using a merge with vector difference mode; determine a search process to be used to determine a vector difference for the vector information: select a merge candidate from a merge candidate list to determine a vector predictor for the vector information; perform the search process to determine the vector difference: apply the vector difference to the vector predictor to form a final vector; and form a prediction block for the current block using the final vector.
Clause 42: A device for decoding video data, the device comprising: means for determining that vector information for a current block of video data is to be coded using a merge with vector difference mode: means for determining a search process to be used to determine a vector difference for the vector information: means for selecting a merge candidate from a merge candidate list to determine a vector predictor for the vector information: means for performing the search process to determine the vector difference; means for applying the vector difference to the vector predictor to form a final vector; and means for forming a prediction block for the current block using the final vector.
In this manner, the method of
It is to be recognized that depending on the example, certain acts or events of any of the techniques described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the techniques). Moreover, in certain examples, acts or events may be performed concurrently. e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.
In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.
By way of example, and not limitation, such computer-readable storage media can comprise RAM. ROM. EEPROM. CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the terms “processor” and “processing circuitry,” as used herein may refer to any of the foregoing structures or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.
The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.
Various examples have been described. These and other examples are within the scope of the following claims.
This application claims the benefit of U.S. Provisional Application No. 63/510,607, filed Jun. 27, 2023, the entire contents of which are hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63510607 | Jun 2023 | US |
