阅读说明：本技术 具有自适应方向信息集合的最终运动矢量表达 (Final motion vector representation with adaptive direction information set ) 是由 C-H.孔 C-C.陈 W-J.钱 M.卡尔切维茨 于 2019-09-27 设计创作，主要内容包括：一种利用最终运动矢量表达(UMVE)对视频数据进行编解码的设备和方法。该设备从在空间上与视频数据的当前块相邻的空间相邻块集合中的一个或多个空间相邻块确定候选列表。该设备可以基于在比特流中获得的数据来确定基本候选索引、方向索引和距离索引,并且可以使用这些索引来确定基本候选、方向和距离。该设备还可以使用方向和距离来计算运动矢量差(MVD)。该设备可以使用MVD和基本候选的运动矢量来确定预测块,并且基于该预测块对当前块进行解码。(An apparatus and method for encoding and decoding video data using a final motion vector representation (UMVE). The apparatus determines a candidate list from one or more spatial neighboring blocks of a set of spatial neighboring blocks that are spatially neighboring a current block of video data. The apparatus may determine a base candidate index, a direction index, and a distance index based on data obtained in the bitstream, and may determine a base candidate, a direction, and a distance using the indices. The device may also use the direction and distance to calculate a Motion Vector Difference (MVD). The device may determine a prediction block using the MVD and the motion vector of the base candidate, and decode the current block based on the prediction block.)

1. A method of decoding video data, the method comprising:

determining a candidate list for a current block of video data from one or more spatial neighboring blocks of a set of spatial neighboring blocks that are spatially neighboring the current block of video data;

determining a base candidate index, a direction index and a distance index based on data obtained from a bitstream comprising an encoded representation of the video data;

determining a base candidate based on the base candidate index;

determining a direction based on the direction index;

determining a distance based on the distance index;

determining a motion vector difference MVD based on the direction and the distance;

determining a prediction block using the MVD and the motion vector of the base candidate; and

decoding the current block based on the prediction block.

2. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the base candidates are one or more of a middle left neighboring block in the set of spatial neighboring blocks and a middle upper neighboring block in the set of spatial neighboring blocks.

3. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the base candidates are one or more of the spatial neighboring blocks in the set of spatial neighboring blocks between a first neighboring block in the set of spatial neighboring blocks that is immediately to the left of a sample point in the upper right corner of the current block and a second neighboring block in the set of spatial neighboring blocks that is immediately to the upper left of the sample point in the upper right corner of the current block.

4. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the base candidates are one or more of the spatial neighboring blocks in the set of spatial neighboring blocks between a first neighboring block in the set of spatial neighboring blocks that is immediately to the left of a sample point in the lower left corner of the current block and a second neighboring block in the set of spatial neighboring blocks that is immediately to the upper left of a sample point in the upper right corner of the current block.

5. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the base candidates are one or more spatial neighboring blocks of the set of spatial neighboring blocks that are not adjacent to the current block.

6. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the base candidates are one or more of a neighboring block in the spatial neighboring block set that is immediately below left of a sample point in a lower left corner of the current block, a neighboring block in the spatial neighboring block set that is immediately above a sample point in an upper right corner of the current block, and a neighboring block in the spatial neighboring block set that is immediately above left of a sample point in an upper left corner of the current block.

7. The method of claim 1, wherein the direction index points to the direction in a direction table and the distance index points to the distance in a distance table, further comprising adjusting direction information in the direction table or the distance table.

8. An apparatus for decoding video data, comprising:

a memory configured to store a current block of the video data; and

one or more processors coupled to the memory, the one or more processors configured to:

determining a candidate list for a current block of the video data from a set of spatially neighboring blocks that are spatially neighboring the current block of the video data;

determining a base candidate index, a direction index and a distance index based on data obtained from a bitstream comprising an encoded representation of the video data;

determining a base candidate based on the base candidate index;

determining a direction based on the direction index;

determining a distance based on the distance index;

determining a motion vector difference MVD based on the direction and the distance;

determining a prediction block using the MVD and the motion vector of the base candidate; and

decoding the current block based on the prediction block.

9. The apparatus of claim 8, wherein the base candidate is one or more of a left-neighboring block in the set of spatial neighboring blocks and an upper-neighboring block in the set of spatial neighboring blocks.

10. The apparatus as set forth in claim 8, wherein,

wherein the base candidates are one or more of the spatial neighboring blocks in the set of spatial neighboring blocks between a first neighboring block in the set of spatial neighboring blocks that is immediately to the left of a sample point in the upper right corner of the current block and a second neighboring block in the set of spatial neighboring blocks that is immediately to the upper left of the sample point in the upper right corner of the current block.

11. The apparatus as set forth in claim 8, wherein,

wherein the base candidates are one or more of the spatial neighboring blocks in the set of spatial neighboring blocks between a first neighboring block in the set of spatial neighboring blocks that is immediately to the left of a sample point in the lower left corner of the current block and a second neighboring block in the set of spatial neighboring blocks that is immediately to the upper left of a sample point in the upper right corner of the current block.

12. The apparatus as set forth in claim 8, wherein,

wherein the base candidates are one or more spatial neighboring blocks of the set of spatial neighboring blocks that are not adjacent to the current block.

13. The apparatus as set forth in claim 8, wherein,

wherein the base candidates are one or more of a neighboring block in the spatial neighboring block set that is immediately below left of a sample point in a lower left corner of the current block, a neighboring block in the spatial neighboring block set that is immediately above a sample point in an upper right corner of the current block, and a neighboring block in the spatial neighboring block set that is immediately above left of a sample point in an upper left corner of the current block.

14. The device of claim 8, wherein the direction index points to the direction in a direction table and the distance index points to the distance in a distance table, and the one or more processors are further configured to adjust direction information in the direction table or the distance table.

15. An apparatus for encoding video data, comprising:

a memory configured to store a current block of the video data; and

one or more processors coupled to the memory, the one or more processors configured to:

determining a candidate list for a current block of the video data from a spatial neighboring block of a set of spatial neighboring blocks that is spatially neighboring the current block of the video data;

determining a base candidate for a current block of the video data;

determining a directional resolution based on the motion vectors of the one or more base candidates;

determining a distance resolution based on the motion vectors of the one or more base candidates;

determining a base candidate index, a direction index, and a distance index based on the one or more base candidates, the direction resolution, and the distance resolution;

encoding the base candidate index, the direction index, and the distance index into a bitstream;

determining a Motion Vector Difference (MVD) based on a direction and a distance associated with the direction index and the distance index;

determining a prediction block using the MVD and the motion vectors of the one or more base candidates; and

encoding the current block based on the prediction block.

16. The device of claim 15, wherein the one or more processors are configured to determine the directional resolution by determining the directional resolution from one or more of a motion vector of a left-neighboring block in the set of spatial-neighboring blocks and a motion vector of an upper-neighboring block in the set of spatial-neighboring blocks; and

wherein the one or more processors are configured to determine the distance resolution by determining the distance resolution from one or more of the motion vector of the middle left neighboring block and the motion vector of the middle upper neighboring block.

17. The apparatus as set forth in claim 15, wherein,

wherein the one or more processors are configured to determine the directional resolution by determining the directional resolution from motion vectors of one or more spatial neighboring blocks in the set of spatial neighboring blocks between a first neighboring block in the set of spatial neighboring blocks that is immediately to the left of a sample point in the top-right corner of the current block and a second neighboring block in the set of spatial neighboring blocks that is immediately to the top-left of the sample point in the top-right corner of the current block; and

wherein the one or more processors are configured to determine the distance resolution by determining the distance resolution from one or more of a motion vector of the first neighboring block and a motion vector of the second neighboring block.

18. The apparatus as set forth in claim 15, wherein,

wherein the one or more processors are configured to determine the directional resolution by determining the directional resolution from one or more of motion vectors of a spatial neighboring block in the set of spatial neighboring blocks between a first neighboring block in the set of spatial neighboring blocks that is immediately to the left of a sample point in a lower left corner of the current block and a second neighboring block in the set of spatial neighboring blocks that is immediately to the upper left of a sample point in an upper right corner of the current block; and

wherein the one or more processors are configured to determine the distance resolution by determining the distance resolution from one or more of a motion vector of the first neighboring block and a motion vector of the second neighboring block.

19. The apparatus as set forth in claim 15, wherein,

wherein the one or more processors are configured to determine the directional resolution by determining the directional resolution from motion vectors of one or more spatial neighboring blocks of the set of spatial neighboring blocks that are not adjacent to the current block; and

wherein the one or more processors are configured to determine the distance resolution by determining the distance resolution from motion vectors of one or more spatial neighboring blocks of the set of spatial neighboring blocks that are not adjacent to the current block.

20. The apparatus as set forth in claim 15, wherein,

wherein the one or more processors are configured to determine the directional resolution by determining the directional resolution from one or more of motion vectors of a neighboring block in the set of spatial neighboring blocks that is immediately below left of a sample point in a lower left corner of the current block, a neighboring block in the set of spatial neighboring blocks that is immediately above a sample point in an upper right corner of the current block, and a neighboring block in the set of spatial neighboring blocks that is immediately above left of a sample point in an upper left corner of the current block; and

wherein the one or more processors are configured to determine the distance resolution by determining the distance resolution from one or more of motion vectors of a neighboring block in the set of spatial neighboring blocks that is immediately below left of a sample point in a lower left corner of the current block, a neighboring block in the set of spatial neighboring blocks that is immediately above a sample point in an upper right corner of the current block, and a neighboring block in the set of spatial neighboring blocks that is immediately above left of a sample point in an upper left corner of the current block.

21. The apparatus of claim 15, wherein the distance is less than the distance resolution.

22. The device of claim 15, wherein the direction index points to the direction in a direction table and the distance index points to the distance in the distance table, and the one or more processors are further configured to adjust direction information in one or more of the direction table or the distance table.

23. An apparatus for decoding video data, comprising:

means for determining a candidate list of one or more spatial neighboring blocks in a set of spatial neighboring blocks that are spatially neighboring a current block of the video data.

Means for determining a base candidate, a direction index and a distance index based on data obtained from a bitstream comprising an encoded representation of the video data;

means for determining base candidates based on the base candidate index;

means for determining a direction based on the direction index;

means for determining a distance based on the distance index;

means for determining a Motion Vector Difference (MVD) based on the direction and the distance;

means for determining a prediction block using the MVD and the motion vector of the base candidate; and

means for decoding the current block based on the prediction block.

24. The apparatus of claim 23, wherein the base candidates are one or more of a left-neighboring block in the set of spatial neighboring blocks and an upper-neighboring block in the set of spatial neighboring blocks.

25. The apparatus as set forth in claim 23, wherein,

wherein the base candidates are one or more of the spatial neighboring blocks in the set of spatial neighboring blocks between a first neighboring block in the set of spatial neighboring blocks that is immediately to the left of a sample point in the upper right corner of the current block and a second neighboring block in the set of spatial neighboring blocks that is immediately to the upper left of the sample point in the upper right corner of the current block.

26. The apparatus as set forth in claim 23, wherein,

wherein the base candidates are one or more of the spatial neighboring blocks in the set of spatial neighboring blocks between a first neighboring block in the set of spatial neighboring blocks that is immediately to the left of a sample point in the lower left corner of the current block and a second neighboring block in the set of spatial neighboring blocks that is immediately to the upper left of a sample point in the upper right corner of the current block.

27. The apparatus as set forth in claim 23, wherein,

wherein the base candidates are one or more spatial neighboring blocks of the set of spatial neighboring blocks that are not adjacent to the current block.

28. The apparatus as set forth in claim 23, wherein,

wherein the base candidates are one or more of a neighboring block in the spatial neighboring block set that is immediately below left of a sample point in a lower left corner of the current block, a neighboring block in the spatial neighboring block set that is immediately above a sample point in an upper right corner of the current block, and a neighboring block in the spatial neighboring block set that is immediately above left of a sample point in an upper left corner of the current block.

29. The apparatus of claim 23, wherein the direction index points to the direction in a direction table and the distance index points to the distance in the distance table, the apparatus further comprising means for adjusting direction information in one or more of the direction table or the distance table.

Technical Field

The present disclosure relates to video encoding and video decoding.

Background

Digital video functionality may be integrated 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 standards defined by MPEG-2, MPEG-4, ITU-T h.263, ITU-T h.264/MPEG-4 part 10 Advanced Video Coding (AVC), High Efficiency Video Coding (HEVC) standards, ITU-T h.265/High Efficiency Video Coding (HEVC), and extensions of such standards. By implementing such video coding (coding) techniques, video devices may more efficiently transmit, receive, encode, decode, and/or store digital video information.

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 (slice) (e.g., a video picture or a portion of a video picture) may be divided 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 (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. A picture may be referred to as a frame, and a reference picture may be referred to as a reference frame.

Disclosure of Invention

In general, this disclosure describes techniques related to inter-prediction and motion vector reconstruction for coding and decoding video. For example, this disclosure describes techniques related to final motion vector representation (UMVE) with adaptive direction information sets. The techniques of this disclosure may be applied to existing video codecs, such as HEVC (high efficiency video coding), or may be applied to codec tools in future video coding standards.

In one example, the present disclosure describes a method of decoding video data, the method comprising: determining a candidate list for a current block of video data from one or more spatial neighboring blocks of a set of spatial neighboring blocks that are spatially adjacent to the current block of video data; determining a base candidate index, a direction index and a distance index based on data obtained from a bitstream comprising an encoded representation of video data; determining a base candidate based on the base candidate index; determining a direction based on the direction index; determining a distance based on the distance index; determining a Motion Vector Difference (MVD) based on the direction and the distance; determining a prediction block using the MVD and the motion vector of the base candidate; the current block is decoded based on the prediction block.

In another example, the present disclosure describes an apparatus for decoding video data, the apparatus comprising: a memory configured to store a current block of video data; and one or more processors coupled to the memory, the one or more processors configured to: determining a candidate list for a current block of video data from a set of spatially neighboring blocks that are spatially neighboring the current block of video data; determining a base candidate index, a direction index and a distance index based on data obtained from a bitstream comprising an encoded representation of video data; determining a base candidate based on the base candidate index; determining a direction based on the direction index; determining a distance based on the distance index; determining a Motion Vector Difference (MVD) based on the direction and the distance; determining a prediction block using the MVD and the motion vector of the base candidate; the current block is decoded based on the prediction block.

In another example, the present disclosure describes an apparatus for encoding video data, the apparatus comprising: a memory configured to store a current block of video data; and one or more processors coupled to the memory, the one or more processors configured to: determining a candidate list for a current block of video data from a spatial neighboring block of a set of spatial neighboring blocks that are spatially neighboring the current block of video data; determining a base candidate for a current block of video data; determining a directional resolution based on the motion vectors of the one or more base candidates; determining a distance resolution based on the motion vectors of the one or more base candidates; determining a base candidate index, a direction index, and a distance index based on one or more base candidates, a direction resolution, and a distance resolution; encoding the base candidate index, the direction index, and the distance index into a bitstream; determining a Motion Vector Difference (MVD) based on a direction and a distance associated with a direction index and a distance index; determining a prediction block using the MVD and the motion vectors of the one or more base candidates; and encoding the current block based on the prediction block. In yet another example, the present disclosure describes an apparatus for decoding video data, the apparatus comprising: means (means) for determining a candidate list of one or more spatial neighboring blocks of a set of spatial neighboring blocks that are spatially neighboring a current block of video data; means for determining a base candidate, a direction index and a distance index based on data obtained from a bitstream comprising an encoded representation of video data; means for determining base candidates based on the base candidate index; means for determining a direction based on the direction index; means for determining a distance based on the distance index; means for determining a Motion Vector Difference (MVD) based on the direction and the distance; means for determining a prediction block using the MVD and the motion vector of the base candidate; means for decoding the current block based on the prediction block. 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 and drawings, and from the claims.

Drawings

Fig. 1 is a block diagram illustrating an example video encoding and decoding system in which techniques of this disclosure may be performed.

Fig. 2A and 2B are conceptual diagrams illustrating an example binary Quadtree (QTBT) structure and corresponding Coding Tree Unit (CTU).

Fig. 3 is a block diagram illustrating an example video encoder that may perform techniques of this disclosure.

Fig. 4 is a block diagram illustrating an example video decoder that may perform techniques of this disclosure.

Fig. 5 is a flow chart illustrating an example operation of a video encoder.

Fig. 6 is a flow chart illustrating an example operation of a video decoder.

Fig. 7A to 7B are conceptual diagrams illustrating spatial neighboring motion vector candidates for a merge and Advanced Motion Vector Prediction (AMVP) mode.

Fig. 8A to 8B are conceptual diagrams illustrating Temporal Motion Vector Prediction (TMVP) candidates and motion vector scaling.

Fig. 9 is a conceptual diagram illustrating a final motion vector expression (UMVE) search process.

Fig. 10 is a conceptual diagram illustrating UMVE search points.

Fig. 11 is a conceptual diagram showing direction table selection.

Fig. 12 is a flow diagram illustrating an example method of encoding video data in accordance with the techniques of this disclosure.

Fig. 13 is a flow diagram illustrating an example method of decoding video data in accordance with the techniques of this disclosure.

FIG. 14 is a conceptual diagram illustrating spatial neighboring blocks of a current block according to the techniques of this disclosure.

Fig. 15 is a conceptual diagram illustrating non-adjacent (non-adjacent) neighboring blocks according to the techniques of this disclosure.

Detailed Description

In general, this disclosure describes techniques related to inter-prediction and motion vector reconstruction for coding and decoding video. For example, this disclosure describes techniques related to final motion vector representation (UMVE) with adaptive direction information sets. The techniques of this disclosure may be applied to existing video codecs, such as HEVC (high efficiency video codec), or may be applied to codec tools in future video coding standards. Specifically, the video encoding and decoding device determines a candidate list. The video encoding and decoding device determines a direction resolution and determines a distance resolution. The video encoding and decoding apparatus determines a basic candidate index, a direction index, and a distance index. These indices may be sent from the encoder to the decoder in the bitstream. The video encoding and decoding device determines the direction and the distance based on the information in the index. The video coding and decoding device determines the MVD. The video codec device determines a prediction block and codec the current block based on the prediction block.

Existing designs of UMVE all utilize a fixed set of directional information for motion vector expression. These fixed sets of directional information result in a large amount of information that must be coded as frequent adjustments to motion vectors, thereby degrading UMVE codec performance.

Instead of coding frequent adjustments of motion vectors, the video encoder may dynamically adjust the set of direction information used for motion vector expression (including direction resolution and distance resolution). The video codec may derive the direction resolution and distance resolution from the spatial neighboring blocks and use this information to adjust the set of direction information. This will reduce the side information sent from the encoder to the decoder, such as frequent and large adjustments to the motion vectors.

As such, the techniques of this disclosure may enable a video codec device to utilize UMVE and determine a candidate list, determine base candidates, directions, and distance indices, determine base candidates, directions, and distances, determine MVDs, determine prediction blocks, and decode based on the prediction blocks.

Fig. 1 is a block diagram illustrating an example video encoding and decoding system 100 that may perform techniques of the present disclosure. The techniques of this disclosure are generally directed to encoding (encoding and/or decoding) video data. In general, video data includes any data used to process video. Thus, video data may include original, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

As shown in fig. 1, in this example, system 100 includes a source device 102, the source device 102 providing encoded video data to be decoded and displayed by a destination device 116. In particular, source device 102 provides video data to destination device 116 via computer-readable medium 110. Source device 102 and destination device 116 may comprise any of a wide range of devices, including desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such as smart phones, televisions, cameras, display devices, digital media players, video game consoles, video streaming devices, and the like. In some cases, source device 102 and destination device 116 may be equipped for wireless communication and may therefore be referred to as wireless communication devices.

In the example of fig. 1, the source device 102 includes a video source 104, a memory 106, a video encoder 200, and an output interface 108. Destination device 116 includes input interface 122, video decoder 300, memory 120, and display device 118. In accordance with the present disclosure, the video encoder 200 of the source device 102 and the video decoder 300 of the destination device 116 may be configured to apply techniques for inter prediction and motion vector reconstruction. Thus, source device 102 represents an example of a video encoding device, and destination device 116 represents an example of a video decoding device. In other examples, the source device and the destination device may include other components or arrangements. For example, source device 102 may receive video data from an external video source, such as an external camera. Likewise, destination device 116 may interface with an external display device, rather than including an integrated display device.

The system 100 as shown in fig. 1 is merely an example. In general, any digital video encoding and/or decoding device may perform the techniques for inter prediction and motion vector reconstruction. Source device 102 and destination device 116 are merely examples of such codec devices, where source device 102 generates codec video data for transmission to destination device 116. The present disclosure refers to a "codec" device as a device that performs codec (encoding and/or decoding) of data. Accordingly, the video encoder 200 and the video decoder 300 represent examples of codec devices (particularly, a video encoder and a video decoder), respectively. In some examples, the devices 102, 116 may operate in a substantially symmetric manner such that each of the devices 102, 116 includes video encoding and decoding components. The system 100 may support one-way or two-way video transmission between the video devices 102, 116, for example, for video streaming, video playback, video broadcasting, or video telephony.

In general, video source 104 represents a source of video data (i.e., raw, unencoded video data) and provides a series of sequential pictures (also referred to as "frames") of the video data to video encoder 200, which video encoder 200 encodes the data for the pictures. The video source 104 of the 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 another alternative, video source 104 may generate computer graphics-based data as the source video, or a combination of real-time video, archived video, and computer-generated video. In each case, the video encoder 200 encodes captured, pre-captured, or computer-generated video data. The video encoder 200 may rearrange the pictures from the received order (sometimes referred to as "display order") to a codec order for codec. The video encoder 200 may generate a bitstream including the encoded video data. Source device 102 may then output the encoded video data onto computer-readable medium 110 via output interface 108 for receipt and/or retrieval by, for example, input interface 122 of destination device 116.

Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memory. In some examples, the memories 106, 120 may store raw video data, e.g., raw video from the video source 104 and raw, decoded video data from the video decoder 300. Additionally or alternatively, the memories 106, 120 may store software instructions executable by, for example, the video encoder 200 and the video decoder 300, respectively. Although the video encoder 200 and the video decoder 300 are shown separately in this example, it should be understood that the video encoder 200 and the video decoder 300 may also include internal memory for functionally similar or equivalent purposes. In addition, the memories 106, 120 may store encoded video data, e.g., output from the video encoder 200 and input to the video decoder 300. In some examples, portions of memory 106, 120 may be allocated as one or more video buffers, such as to store raw, decoded, and/or encoded video data.

Computer-readable medium 110 may represent any type of medium or device capable of transporting encoded video data from source device 102 to destination device 116. In one example, computer-readable medium 110 represents a communication medium that enables source device 102 to transmit encoded video data directly to destination device 116 in real-time, e.g., via a radio frequency network or a computer-based network. In accordance with a communication standard, such as a wireless communication protocol, output interface 108 may modulate a transmission signal including encoded video data and input interface 122 may modulate a received transmission signal. The communication medium may include 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 a router, switch, base station, or any other device that facilitates communication from source device 102 to destination device 116.

In some examples, source device 102 may output the encoded data from output interface 108 to storage device 112. Similarly, destination device 116 may access the 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 medium for storing encoded video data.

In some examples, source device 102 may output the encoded video data to file server 114 or another intermediate storage device that may store the encoded video generated by source device 102. Destination device 116 may access the 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 the encoded video data to destination device 116. The file server 114 may represent a web server (such as for a website), a File Transfer Protocol (FTP) server, a content delivery network device, or a Network Attached Storage (NAS) device. Destination device 116 may access the encoded video data from file server 114 via 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., DSL, cable modem, etc.), or a combination of both, suitable for accessing encoded video data stored on file server 114. File server 114 and input interface 122 may be configured to operate according to a streaming protocol, a download transfer protocol, or a combination thereof.

Output interface 108 and input interface 122 may represent wireless transmitters/receivers, modems, wired network 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. At the output interface 108 and the inputIn examples where the input interface 122 includes wireless components, the output interface 108 and the input interface 122 may be configured to communicate data, such as encoded video data, in accordance with a cellular communication standard, such as 4G, 4G-LTE (long term evolution), LTE-advanced, 5G, and so forth. In some examples where the output interface 108 includes a wireless transmitter, the output interface 108 and the input interface 122 may be configured according to a protocol such as the IEEE 802.11 specification, the IEEE 802.15 specification (e.g., ZigBee)^TM)、Bluetooth^TMOther wireless standards, such as standards, transmit data, such as encoded video data. In some examples, source device 102 and/or destination device 116 may include respective system on chip (SoC) devices. For example, source device 102 may include a SoC device to perform functions attributed to video encoder 200 and/or output interface 108, and destination device 116 may include a SoC device to perform functions attributed to video decoder 300 and/or input interface 122.

The techniques of this disclosure may be applied to video codecs that support 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 encoded onto a data storage medium, decoding digital video stored on a data storage medium, or other applications.

The input interface 122 of the destination device 116 receives the encoded video bitstream from the computer-readable medium 110 (e.g., the storage device 112, the file server 114, etc.). The encoded video bitstream computer-readable medium 110 may include signaling information defined by the video encoder 200, also used by the video decoder 300, such as syntax elements having values that describe characteristics and/or processes of a video block or other codec unit (e.g., slice, picture, group of pictures, sequence, etc.). The display device 118 displays the decoded pictures of the decoded video data to the user. Display device 118 may represent any of a variety of display devices, such as a Cathode Ray Tube (CRT), 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 fig. 1, in some examples, video encoder 200 and video decoder 300 may be integrated with an audio encoder and/or audio decoder, respectively, and may include appropriate MUX-DEMUX units or other hardware and/or software to process multiplexed streams including audio and video in a common data stream. The MUX-DEMUX unit may conform to the ITU h.223 multiplexer protocol or other protocols, such as the User Datagram Protocol (UDP), if applicable.

Video encoder 200 and video decoder 300 may each be implemented as any of a variety of suitable encoder and/or decoder circuits, 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 in part in software, the 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 the video encoder 200 and the 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 the respective device. A device including the video encoder 200 and/or the video decoder 300 may include an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone.

The video encoder 200 and the video decoder 300 may operate according to a video coding standard, such as ITU-T h.265, also known as High Efficiency Video Coding (HEVC), or extensions thereof, such as multi-view and/or scalable video codec extensions. Alternatively, the video encoder 200 and the video decoder 300 may operate according to other proprietary or industrial codecs or standards such as joint exploration test model (JEM) or general video coding (VVC). However, the techniques of this disclosure are not limited to any particular codec standard.

In general, the video encoder 200 and the video decoder 300 may perform block-based coding of pictures. The term "block" generally refers to a structure that includes data to be processed (e.g., encoded, decoded, or otherwise used in an encoding and/or decoding process). For example, a block may comprise a two-dimensional matrix of samples of luminance data and/or chrominance data. In general, the video encoder 200 and the video decoder 300 may codec video data represented in YUV (e.g., Y, Cb, Cr) format. That is, rather than codec red, green, and blue (RGB) data of a sample point picture sample point, the video encoder 200 and the video decoder 300 may codec luminance and chrominance components, where the chrominance components may include both red-tone and blue-tone chrominance components. In some examples, the video encoder 200 converts the received RGB-format data to a YUV representation prior to encoding, and the video decoder 300 converts the YUV representation to an RGB format. Alternatively, a pre-processing unit and a post-processing unit (not shown) may perform these conversions.

The present disclosure may generally relate to a process of coding (e.g., encoding and decoding) a picture to include encoding or decoding data for the picture. Similarly, the disclosure may relate to coding of a block of a picture to include processes of encoding or decoding data of the block, e.g., prediction and/or residual coding. The encoded video bitstream typically includes a series of values for syntax elements that represent coding decisions (e.g., coding modes) and that divide the picture into blocks. Thus, references to coding a picture or block are generally to be understood as coding of syntax elements used to form the picture or block.

HEVC defines various blocks, including Coding Units (CUs), Prediction Units (PUs), and Transform Units (TUs). According to HEVC, a video codec, such as video encoder 200, partitions a Coding Tree Unit (CTU) into CUs according to a quadtree structure. That is, the video codec divides the CTU and CU into four equal, non-overlapping squares, and each node of the quadtree has zero or four child nodes. A node without a child node may be referred to as a "leaf node," and a CU of such a leaf node may include one or more PUs and/or one or more TUs. The video codec may further divide the PU and TU. For example, in HEVC, the Residual Quadtree (RQT) represents the partitioning of a TU. In HEVC, a PU represents inter prediction data and a TU represents residual data. The intra-predicted CU includes intra-prediction information, such as an intra-mode indication.

As another example, the video encoder 200 and the video decoder 300 may be configured to operate in accordance with JEM. According to JEM, a video codec, such as video encoder 200, divides a picture into a plurality of Coding Tree Units (CTUs). The video encoder 200 may partition the CTUs according to a tree structure, such as a quadtree-binary tree (QTBT) structure. The QTBT structure of JEM eliminates the concept of multiple partition types, such as the separation between CU, PU and TU of HEVC. The QTBT structure of JEM includes two levels: a first level partitioned according to a quadtree partition, and a second level partitioned according to a binary tree partition. The root node of the QTBT structure corresponds to the CTU. Leaf nodes of the binary tree correspond to Coding Units (CUs).

In some examples, the video encoder 200 and the video decoder 300 may represent each of the luma and chroma components using a single QTBT structure, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT structures, such as one QTBT structure for the luma component and another QTBT structure for the two chroma components (or two QTBT structures for the respective chroma components).

The video encoder 200 and the video decoder 300 may be configured to use quadtree partitioning according to HEVC, QTBT partitioning according to JEM, or other partitioning structures. For illustrative purposes, a description of the techniques of this disclosure is given with respect to QTBT partitioning. However, it should be understood that the techniques of this disclosure may also be applied to video codecs configured to use quadtree partitioning or other types of partitioning.

This disclosure interchangeably uses "nxn" and "N by N" to refer to the sample size of a block (such as a CU or other video block), e.g., 16 x 16 samples or 16 by 16 samples, in both the vertical and horizontal dimensions. In general, a 16 × 16CU has 16 samples (y ═ 16) in the vertical direction and 16 samples (x ═ 16) in the horizontal direction. Likewise, an nxn CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. Samples in a CU may be arranged in rows and columns. Furthermore, a CU does not necessarily have the same number of samples in the horizontal direction as in the vertical direction. For example, a CU may include N × M samples, where M is not necessarily equal to N.

Video encoder 200 encodes video data for a CU that represents prediction and/or residual information, as well as other information. The prediction information indicates how the CU is to be predicted in order to form a prediction block for the CU. The residual information typically represents the sample-by-sample difference between samples of the CU before encoding and the prediction block.

To predict a CU, video encoder 200 may typically form a prediction block for the CU through inter prediction or intra prediction. Inter prediction typically refers to predicting a CU from data of a previously coded picture, while intra prediction typically refers to predicting a CU from data of a previously coded picture of the same picture. To perform inter prediction, the video encoder 200 may generate a prediction block using one or more motion vectors. Video encoder 200 may typically perform a motion search to identify a reference block that closely matches a CU (e.g., in terms of a difference between the CU and the reference block). Video encoder 200 may calculate a difference metric using Sum of Absolute Differences (SAD), Sum of Squared Differences (SSD), Mean Absolute Differences (MAD), Mean Squared Differences (MSD), or other such difference calculations to determine whether the 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.

JEM also provides an affine motion compensation mode, which can be considered as an inter prediction mode. In affine motion compensation mode, video encoder 200 may determine two or more motion vectors representing non-translational motion, such as zoom-in or zoom-out, rotation, perspective motion, or other irregular motion types.

To perform intra-prediction, video encoder 200 may select an intra-prediction mode to generate a prediction block. JEM provides 67 intra prediction modes, including various directional modes, as well as planar and DC modes. In general, video encoder 200 selects an intra-prediction mode that describes spatially neighboring samples of a current block (e.g., a block of a CU) from which to predict samples of the current block. Assuming that the video encoder 200 encodes CTUs and CUs in raster scan order (left to right, top to bottom), such samples may typically be above, above left, or to the left of the current block in the same picture as the current block.

The video encoder 200 encodes data representing the prediction mode of the current block. For example, for an inter prediction mode, the video encoder 200 may encode data indicating which of various available inter prediction modes to use and motion information of the corresponding mode. For uni-directional or bi-directional inter prediction, for example, the video encoder 200 may encode the motion vector using an Advanced Motion Vector Prediction (AMVP) or Merge (Merge) mode. The video encoder 200 may use a similar mode to encode the motion vectors for the affine motion compensation mode.

After prediction, such as intra prediction or inter prediction, of a block, the video encoder 200 may calculate residual data for the block. Residual data, such as a residual block, represents the sample-by-sample difference between the block and a prediction block of the block formed using the corresponding prediction mode. The video encoder 200 may apply one or more transforms to the residual block to produce transformed data in the transform domain rather than the sample domain. For example, the video encoder 200 may apply a Discrete Cosine Transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. In addition, the video encoder 200 may apply a secondary transform, such as a mode dependent (dependent) inseparable secondary transform (mdsnst), a signal dependent transform, a Karhunen-Loeve transform (KLT), or the like, after the first transform. The video encoder 200 generates transform coefficients after applying one or more transforms.

As described above, video encoder 200 may perform quantization of the transform coefficients after any transform is performed to generate the transform coefficients. Quantization generally refers to the process of quantizing transform coefficients to potentially reduce the amount of data used to represent the coefficients, thereby providing further compression. By performing the quantization process, video encoder 200 may reduce the bit depth associated with some or all of the coefficients. For example, video encoder 200 may round an n-bit value 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 bit-wise right shift of the value to be quantized.

After quantization, video encoder 200 may scan the transform coefficients, thereby generating a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scanning may be designed to place higher energy (and therefore lower frequency) coefficients in front of the vector and lower energy (and therefore higher frequency) transform coefficients behind the vector. In some examples, video encoder 200 may scan the quantized transform coefficients using a predefined scan order to produce a serialized vector and then entropy encode the quantized transform coefficients of the vector. In other examples, video encoder 200 may perform adaptive scanning. After scanning the quantized transform coefficients to form a 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 of syntax elements (which describe metadata associated with the encoded video data) for use by video decoder 300 in decoding the video data.

The video encoder 200 may also generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, to the video decoder 300, for example, in a picture header (header), a block header, a slice header, or other syntax data, such as a Sequence Parameter Set (SPS), a Picture Parameter Set (PPS), or a Video Parameter Set (VPS). Video decoder 300 may similarly decode such syntax data to determine how to decode the corresponding video data.

In this way, the video encoder 200 may generate a bitstream that includes encoded video data (e.g., syntax elements describing the partitioning of a picture into blocks (e.g., CUs) and prediction and/or residual information for the blocks). Finally, the video decoder 300 may receive the bitstream and decode the encoded video data.

In general, the video decoder 300 performs reciprocal (reciprocal) processing performed by the video encoder 200 to decode encoded video data of a bitstream. For example, video decoder 300 may decode the values of syntax elements of the bitstream using CABAC in a manner substantially similar to (although reciprocal to) the CABAC encoding process of video encoder 200. The syntax elements may define partitioning information that partitions a picture into CTUs, and partitioning of each CTU according to a corresponding partitioning structure (such as a QTBT structure) to define CUs of the CTU. The syntax elements may also 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. The video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of the block to reproduce (reduce) the residual block of the block. The video decoder 300 uses the 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. The video decoder 300 may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. The video decoder 300 may perform additional processing, such as deblocking processing to reduce visual artifacts along the boundaries of the blocks.

In accordance with the techniques of this disclosure, video encoder 200 and video decoder 300 may be configured to use a final motion vector representation (UMVE).

The present disclosure may generally refer to "signaling" certain information, such as syntax elements. The term "signaling" may generally refer to the communication of value syntax elements and/or other data for decoding encoded video data. That is, the video encoder 200 may signal the value of the syntax element in the bitstream. Generally, signaling refers to generating values in a bitstream. As described above, source device 102 may transport the bitstream to destination device 116 in substantially real time or not, such as may occur when syntax elements are stored to storage device 112 for later retrieval by destination device 116.

Fig. 2A and 2B are conceptual diagrams illustrating an example binary Quadtree (QTBT) structure 130 and a corresponding Coding Tree Unit (CTU) 132. The solid line represents the quadtree split and the dashed line represents the binary tree split. In each split (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which type of split (i.e., horizontal or vertical) is used, in this example, 0 for horizontal split and 1 for vertical split. For quadtree partitioning, there is no need to indicate the partition type, since the quadtree nodes partition a block horizontally and vertically into 4 sub-blocks of equal size. Accordingly, the video encoder 200 and the video decoder 300 may encode syntax elements (e.g., partition information) of the region tree level (i.e., solid line) of the QTBT structure 130 and syntax elements (e.g., partition information) of the prediction tree level (i.e., dotted line) of the QTBT structure 130, and the video decoder 300 may decode them. The video encoder 200 may be used to encode video data (such as prediction and transform data) of a CU represented by the terminal leaf node of the QTBT structure 130, and the video decoder 300 may decode it.

In general, the CTUs 132 of fig. 2B may be associated with parameters that define the size of the blocks corresponding to the nodes of the QTBT structure 130 at the first level and the second level. These parameters may include CTU size (representing the size of CTU 132 in the sample point), minimum quadtree size (MinQTSize, representing the minimum allowed quadtree leaf node size), maximum binary tree size (MaxBTSize, representing the maximum allowed binary tree root node size), maximum binary tree depth (MaxBTDepth, representing the maximum allowed binary tree depth), and minimum binary tree size (MinBTSize, representing the minimum allowed binary tree leaf node size).

The root node of the QTBT structure corresponding to the CTU may have four child nodes at the first level of the QTBT structure, each of which may be partitioned according to a quadtree partition. That is, the first level node is a leaf node (no child node) or has four child nodes. The example of the QTBT structure 130 represents such nodes as including parent and child nodes with solid lines for branching. If the nodes of the first level are not larger than the maximum allowed binary tree root node size (MaxBTSize), they may be further partitioned by the corresponding binary tree. The binary tree partitioning of a node may be iteratively performed until the partitioning results in a node that reaches a minimum allowed binary tree leaf node size (MinBTSize) or a maximum allowed binary tree depth (MaxBTDepth). An example of a QTBT structure 130 is represented as such a node with a dashed line for branching. Binary tree leaf nodes are called Coding Units (CUs) and are used for prediction (e.g. intra-picture or inter-picture prediction) and transformation without any further partitioning. As described above, a CU may also be referred to as a "video block" or "block.

In one example of the QTBT partition structure, the CTU size is set to 128 × 128 (luma samples and two corresponding 64 × 64 chroma samples), MinQTSize is set to 16 × 16, MaxBTSize is set to 64 × 64, MinBTSize (for width and height) is set to 4, and MaxBTDepth is set to 4. Quadtree partitioning is first applied to CTUs to generate quadtree leaf nodes. The sizes of the leaf nodes of the quadtree may range from 16 × 16 (i.e., MinQTSize) to 128 × 128 (i.e., CTU size). If the quad tree leaf nodes are 128 x 128, then there is no further partitioning through the binary tree because the size exceeds MaxBTSize (i.e., 64 x 64 in this example). Otherwise, the quadtree leaf nodes will be further partitioned by the binary tree. Thus, the leaf nodes of the quadtree are also the root nodes of the binary tree, and their binary tree depth is 0. When the binary tree depth reaches MaxBTDepth (4 in this example), no further partitioning is allowed. When the width of the binary tree node is equal to MinBTSize (4 in this example), it means that no further horizontal splitting is allowed. Similarly, the height of a binary tree node equal to MinBTSize means that the binary tree node does not allow further vertical partitioning. As described above, the leaf nodes of the binary tree are referred to as CUs and are further processed according to prediction and transformation without further partitioning.

Fig. 3 is a block diagram illustrating an example video encoder 200 that may perform techniques of this disclosure. Fig. 3 is provided for purposes of explanation and should not be considered a limitation of the technology broadly illustrated and described in this disclosure. For purposes of illustration, the present disclosure describes video encoder 200 in the context of a video coding standard, such as the HEVC video coding standard and the h.266 video coding standard under development. However, the techniques of this disclosure are not limited to these video encoding standards and are generally applicable to video encoding and decoding.

In the example of fig. 3, the video encoder 200 includes a video data memory 230, a mode selection unit 202, a residual generation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a filter unit 216, a Decoded Picture Buffer (DPB)218, and an entropy coding unit 220.

Video data memory 230 may store video data to be encoded by components of video encoder 200. Video encoder 200 may receive video data stored in video data storage 230 from, for example, video source 104 (fig. 1). DPB 218 may be used as a reference picture memory that stores reference video data for use by video encoder 200 in predicting subsequent video data. Video data memory 230 and DPB 218 may be formed from any of a variety of memory devices, such as Dynamic Random Access Memory (DRAM), including synchronous DRAM (sdram), magnetoresistive ram (mram), resistive ram (rram), or other types of memory devices. Video data memory 230 and DPB 218 may be provided by the same memory device or separate memory devices. In various examples, video data memory 230 may be on-chip with other components of video encoder 200, as shown, or off-chip with respect to those components.

In this disclosure, references to video data memory 230 should not be construed as 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). Conversely, references to the video data memory 230 should be understood as reference memory that stores video data received by the video encoder 200 for encoding (e.g., video data for a current block to be encoded). The memory 106 of fig. 1 may also provide temporary storage of the outputs from the various units of the video encoder 200.

The various elements of fig. 3 are shown to aid in understanding the operations performed by video encoder 200. These units may be implemented as fixed function circuits, programmable circuits, or a combination thereof. These units may be implemented as one or more circuits or logic elements, as part of a hardware circuit, or as part of a processor, ASIC, or FPGA. Fixed function circuitry refers to circuitry that provides a particular function and is preset in operations that can be performed. Programmable circuitry refers to circuitry that can be programmed to perform various tasks and provide flexible functionality in the operations that can be performed. For example, a programmable circuit may execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed function circuitry may execute software instructions (e.g., to receive parameters or output parameters), but the type of operations performed by the fixed function circuitry is typically immutable. In some examples, one or more of the units may be different circuit blocks (fixed function or programmable), and in some examples, one or more of the units may be integrated circuits.

The video encoder 200 may include an Arithmetic Logic Unit (ALU), a basic function unit (EFU), digital circuitry, analog circuitry, and/or a programmable core formed from programmable circuitry. In examples where the operations of video encoder 200 are performed using software executed by programmable circuitry, memory 106 (fig. 1) may store object code of the software received and executed by video encoder 200, or another memory (not shown) within video encoder 200 may store such instructions.

The video data memory 230 is configured to store the received video data. The video encoder 200 may retrieve pictures of video data from the video data memory 230 and provide the video data to the residual generation unit 204 and the mode selection unit 202. The video data in video data memory 230 may be the original video data to be encoded.

Mode selection unit 202 includes motion estimation unit 222, motion compensation unit 224, and intra prediction unit 226. The mode selection unit 202 may comprise additional functional units to perform video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette (palette) unit, an intra-block (intra-block) copy unit (which may be part of the motion estimation unit 222 and/or the motion compensation unit 224), an affine unit, a Linear Model (LM) unit, and/or the like.

In some examples, motion estimation unit 222 may include UMVE unit 228. Although UMVE unit 228 is shown in motion estimation unit 222, in some examples it may be in motion compensation unit 224. In other examples, the UMVE 228 unit may be split or duplicated between the motion estimation unit 222 and the motion compensation unit 224. Motion estimation unit 222 may determine a candidate list of a current block of one or more spatial neighboring blocks in a set of spatial neighboring blocks that are spatially neighboring the current block of video data. The motion estimation unit 222 may determine the base candidate in the candidate list. The base candidate may be denoted as MVbase. Motion estimation unit 222 or UMVE unit 228 may determine the directional resolution, for example, based on one or more base candidate motion vectors. In addition, motion estimation unit 222 or UMVE unit 228 may determine the distance resolution, for example, based on one or more base candidate motion vectors.

UMVE unit 228 may determine a set of Motion Vector Differences (MVDs). UMVE unit 228 may determine each MVD as a combination of a direction having a determined direction resolution and a distance having a determined distance resolution. For each MVD, UMVE unit 228 may determine a rate-distortion (RD) cost associated with the MVD. The RD cost associated with the MVD may be an RD cost associated with encoding the current block using a motion vector obtained by adding the MVD to a base candidate (MVbase). The UMVE unit 228 may repeat this process for each MVD.

UMVE unit 228 may select an MVD having the smallest RD cost and add the selected MVD to a base candidate (MVbase) to determine a final motion vector. The final motion vector may be denoted MVfinal. MCU 224 may then use the final motion vector to determine a prediction block. The video encoder 200 may encode the current block based on the prediction block. For example, to encode a current block based on a prediction block, video encoder 200 (e.g., residual generation unit 204 of video encoder 200) may determine residual data that indicates a difference between samples in the prediction block and samples in the current block. The video encoder 200 may then process the residual data as described elsewhere in this disclosure. For example, the transform processing unit 206, the quantization unit 208, and the entropy encoding unit 220 may process the residual data.

The video encoder 200 may signal data indicating the base candidates, the direction index of the selected MVD, and the distance index of the selected MVD in a bitstream comprising an encoded representation of the video data. The base candidate index may indicate the base candidates defined in the candidate list. The direction index may indicate directions defined in a direction table that may closely correspond to the determined direction resolution. The distance index may indicate distances defined in a distance table that may closely correspond to the determined distance resolution.

The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and resulting rate-distortion values for such combinations. The encoding parameters may include a partitioning of the CTUs into CUs, a prediction mode for the CUs, a transform type of residual data for the CUs, a quantization parameter of the residual data for the CUs, and so on. The mode selection unit 202 may finally select a combination of encoding parameters having a better rate-distortion value than other tested combinations.

Video encoder 200 may divide the pictures retrieved from video data memory 230 into a series of CTUs and encapsulate one or more CTUs within a stripe. The mode selection unit 202 may divide the CTUs of a picture according to a tree structure, such as the QTBT structure of HEVC or a quadtree structure described above. As described above, the video encoder 200 may form one or more CUs by dividing CTUs according to a tree structure. Such CUs may also be commonly referred to as "video blocks" or "blocks".

Typically, mode select unit 202 also controls its components (e.g., motion estimation unit 222, motion compensation unit 224, intra prediction unit 226) to generate a prediction block for a current block (e.g., the current CU, or overlapping portions of a PU and a TU in HEVC). For inter prediction of a current block, the 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 the DPB 218). In particular, the motion estimation unit 222 may calculate a value representing how similar the potential reference block is to the current block, e.g., from a Sum of Absolute Differences (SAD), a Sum of Squared Differences (SSD), a Mean Absolute Difference (MAD), a Mean Squared Difference (MSD), etc. The motion estimation unit 222 may typically perform these calculations using the sample-by-sample point difference between the current block and the reference block under consideration. The motion estimation unit 222 may identify the reference block having the lowest value resulting from these calculations, which indicates the reference block that most closely matches the current block.

Motion estimation unit 222 may form one or more Motion Vectors (MVs) that define the position of a reference block in a reference picture relative to a current block in a current picture. One or more motion vectors may be used in UMVE unit 228 to determine a Motion Vector Difference (MVD) by combining direction and distance.

The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, for uni-directional inter prediction, motion estimation unit 222 may provide a single motion vector, while for bi-directional inter prediction, motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate the prediction block.

For example, the motion compensation unit 224 may use the motion vectors to retrieve data of the reference block. As another example, if the motion vector has fractional sample precision, the motion compensation unit 224 may interpolate the prediction block according to one or more interpolation filters. Further, for bi-directional inter prediction, the motion compensation unit 224 may retrieve data for two reference blocks identified by the respective motion vectors and combine the retrieved data, e.g., by a sample-wise average or a weighted average.

As another example, for intra-prediction or intra-prediction encoding, the intra-prediction unit 226 may generate a prediction block from samples spatially adjacent to the current block. For example, for directional modes, the intra-prediction unit 226 may generally mathematically combine values of spatially neighboring samples and pad these calculated values in a defined direction across the current block to produce a prediction block. As another example, for DC mode, the intra prediction unit 226 may calculate an average of spatially neighboring samples to the current block and generate the prediction block to include the resulting average for each sample of the prediction block.

The mode selection unit 202 supplies the prediction block determined by the motion compensation unit 224 to the residual generation unit 204. The residual generation unit 204 receives the original, unencoded version of the current block from the video data memory 230 and the original, unencoded version of the prediction block from the mode selection unit 202. The residual generation unit 204 calculates a sample-by-sample point difference between the current block and the prediction block. The resulting sample-wise point difference defines a residual block for the current block. In some examples, the residual generation unit 204 may also determine differences between sample values in the residual block to generate the 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 an example where mode selection unit 202 divides a CU into PUs, each PU may be associated with a luma prediction unit and a corresponding chroma prediction unit. The video encoder 200 and the video decoder 300 may support PUs having various sizes. As described above, the size of a CU may refer to the size of a 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 2 nx 2N, video encoder 200 may support 2 nx 2N or N × N PU sizes for intra prediction, and 2 nx 2N, 2 nx N, N × 2N, N × N or similar symmetric PU sizes for inter prediction. Video encoder 20 and video decoder 30 may also support asymmetric partitioning of PU sizes of 2 nxnu, 2 nxnd, nlx 2N, and nR x 2N for inter prediction.

In examples where the mode selection unit no longer divides the CU into PUs, each CU may be associated with a luma codec block and a corresponding chroma codec block. As described above, the size of a CU may refer to the size of the luma codec block of the CU. The video encoder 200 and the video decoder 120 may support CU sizes of 2N × 2N, 2N × N, or N × 2N.

For other video codec techniques, such as intra block copy mode codec, affine mode codec, and Linear Model (LM) mode codec, as a few examples, mode selection unit 202 generates a prediction block for the current block being encoded via various units associated with the codec technique. In some examples, such as palette mode coding, mode selection unit 202 may not generate a prediction block using UMVE 228, but rather generate a syntax element that indicates the manner in which a block is reconstructed based on the selected palette. In this mode, mode selection unit 202 may provide these syntax elements to entropy encoding unit 220 for encoding.

As described above, the residual generation unit 204 receives video data of the current block and the corresponding prediction block. The residual generation unit 204 then generates a residual block for the current block. To generate the residual block, the residual generation unit 204 calculates a sample-by-sample point difference 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 the residual block to form a block of transform coefficients. For example, the transform processing unit 206 may apply Discrete Cosine Transform (DCT), directional transform, Karhunen-Loeve transform (KLT), or conceptually similar transform to the residual block. In some examples, transform processing unit 206 may perform a plurality of transforms on the 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 the transform to the residual block.

The quantization unit 208 may quantize transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The 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 coefficient blocks associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce a loss of information and, therefore, the precision of the quantized transform coefficients may be lower than the precision of the original transform coefficients produced by the transform processing unit 206.

The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform, respectively, to the quantized transform coefficient block to reconstruct a residual block from the transform coefficient block. The reconstruction unit 214 may generate a reconstructed block corresponding to the current block (although possibly with some degree of distortion) based on the reconstructed residual block and the prediction block generated by the mode selection unit 202. For example, the reconstruction unit 214 may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by the motion compensation unit in the mode selection unit 202 to produce a reconstructed block.

The filter unit 216 may perform one or more filter operations on the reconstructed block. For example, filter unit 216 may perform deblocking operations to reduce blocking artifacts along the edges of the CU. In some examples, the operation of the filter unit 216 may be skipped.

The video encoder 200 stores the reconstructed block in the DPB 218. For example, in an example of an operation that does not require the filter unit 216, the reconstruction unit 214 may store the reconstruction block to the DPB 218. In examples where operation of filter unit 216 is desired, filter unit 216 may store the filtered reconstructed block to DPB 218. The motion estimation unit 222 and the motion compensation unit 224 may retrieve reference pictures formed of reconstructed (and possibly filtered) blocks from the DPB 218 for inter-prediction of blocks of subsequently encoded pictures. In addition, the intra prediction unit 226 may intra predict other blocks in the current picture using reconstructed blocks in the DPB 218 of 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 the quantized transform coefficient block from quantization unit 208. As another example, entropy encoding unit 220 may entropy encode the 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 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 coding operation, or another type of entropy encoding operation on the data. In some examples, entropy encoding unit 220 may operate in a bypass mode in which syntax elements are not entropy encoded.

The video encoder 200 may output a bitstream including entropy-encoded syntax elements required to reconstruct blocks of slices or pictures. In particular, the entropy encoding unit 220 may output a bitstream

The above operations are described with respect to blocks. This description should be understood as an operation for the luma codec block and/or the chroma codec block. As described above, in some examples, the luma and chroma coding blocks are luma and chroma components of a CU. In some examples, the luma codec block and the chroma codec block are luma and chroma components of the PU.

In some examples, the operations performed for the luma codec block need not be repeated for the chroma codec block. As one example, the operations of identifying Motion Vectors (MVs) and reference pictures for luma coded blocks need not be repeated to identify MVs and reference pictures for chroma blocks. Conversely, the MVs for the luma codec blocks may be scaled to determine MVs for chroma blocks, and the reference pictures may be the same. As another example, the intra prediction process may be the same for luma and chroma codec blocks.

Video encoder 200 represents an example of a device configured to encode video data, the device including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to perform the improved UMVE techniques of this disclosure.

Fig. 4 is a block diagram illustrating an example video decoder 300 that may perform techniques of this disclosure. Fig. 4 is provided for purposes of explanation and does not limit the techniques broadly illustrated and described in this disclosure. For purposes of illustration, this disclosure describes a video decoder 300 described in accordance with the techniques of JEM and HEVC. However, the techniques of this disclosure may be performed by video codec devices configured to implement other video codec standards.

In the example of fig. 4, the video decoder 300 includes a Coded Picture Buffer (CPB) memory 320, an entropy decoding unit 302, a prediction processing unit 304, an inverse quantization unit 306, an inverse transform processing unit 308, a reconstruction unit 310, a filter unit 312, and a Decoded Picture Buffer (DPB) 314. The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The motion compensation unit may comprise a UMVE unit 322. As described below, UMVE unit 322 may determine the MVD. The prediction processing unit 304 may include an addition unit to perform prediction according to other prediction modes. As an example, the prediction processing unit 304 may include a palette unit, an intra block copy unit (which may form part of the motion compensation unit 316), an affine unit, a Linear Model (LM) unit, and the like. In other examples, video decoder 300 may include more, fewer, or different functional components.

The CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by the components of the video decoder 300. The video data stored in the CPB memory 320 may be obtained, for example, from the computer-readable medium 110 (fig. 1). The CPB memory 320 may include CPBs that store encoded video data (e.g., syntax elements) from an encoded video bitstream. Also, the CPB memory 320 may store video data other than syntax elements of the codec picture, such as temporary data representing outputs from the respective units of the video decoder 300. The DPB 314 typically stores decoded pictures, which the video decoder 300 may output and/or use as reference video data when decoding subsequent data or pictures of the encoded video bitstream. The CPB memory 320 and DPB 314 may be formed from any of a variety of memory devices, such as Dynamic Random Access Memory (DRAM), including synchronous DRAM (sdram), magnetoresistive ram (mram), resistive ram (rram), or other types of memory devices. The CPB memory 320 and DPB 314 may be provided by the same memory device or separate memory devices. In various examples, the CPB memory 320 may be on-chip with other components of the video decoder 300 or off-chip with respect to those components.

Additionally or alternatively, in some examples, video decoder 300 may retrieve the coded video data from memory 120 (fig. 1). That is, the memory 120 may store data as discussed above with the CPB memory 320. Also, when some or all of the functionality of the video decoder 300 is implemented in software for execution by the processing circuitry of the video decoder 300, the memory 120 may store instructions to be executed by the video decoder 300.

The various elements shown in fig. 4 are shown to aid in understanding the operations performed by the video decoder 300. These units may be implemented as fixed function circuits, programmable circuits, or a combination thereof. These units may be implemented as one or more circuits or logic elements, as part of a hardware circuit, or as part of a processor, ASIC, or FPGA. Similar to fig. 3, a fixed function circuit refers to a circuit that provides a specific function and is preset in operation that can be performed. Programmable circuitry refers to circuitry that can be programmed to perform various tasks and provide flexible functionality in the operations that can be performed. For example, a programmable circuit may execute software or firmware that causes the programmable circuit to operate in a manner defined by the instructions of the software or firmware. Fixed function circuitry may execute software instructions (e.g., to receive parameters or output parameters), but the type of operations performed by the fixed function circuitry is typically immutable. In some examples, one or more of the units may be different circuit blocks (fixed function or programmable), and in some examples, one or more of the units may be integrated circuits.

The video decoder 300 may include an ALU, an EFU, digital circuitry, analog circuitry, and/or a programmable core formed from programmable circuitry. In examples where the operations of video decoder 300 are performed by software executing on programmable circuitry, on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by video decoder 300.

The entropy decoding unit 302 may receive the encoded video data from the CPB and entropy decode the video data to reproduce the syntax element. The prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, and the filter unit 312 may generate decoded video data based on syntax elements extracted from the bitstream.

Typically, the video decoder 300 reconstructs pictures on a block-by-block basis. The video decoder 300 may perform a reconstruction operation on each block separately (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 that define quantized transform coefficients of a quantized transform coefficient block and transform information such as 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 application by inverse quantization unit 306. The inverse quantization unit 306 may, for example, perform a bit-wise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thus form a transform coefficient block comprising 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, the inverse transform processing unit 308 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotation transform, an inverse direction transform, or another inverse transform to the coefficient block.

Also, the prediction processing unit 304 may generate a prediction block according to the prediction information syntax element entropy-decoded by the entropy decoding unit 302. For example, if the prediction information syntax element indicates that the current block is inter-predicted, the motion compensation unit 316 may generate a prediction block. In this case, the prediction information syntax element may indicate the reference picture in the DPB 314 from which the reference block is retrieved, and the motion vector that identifies the location of the reference block in the reference picture relative to the location of the current block in the current picture. The prediction processing unit may include a motion compensation unit 316. Motion compensation unit 316 may include a UMVE unit 322. The motion compensation unit 316 may generally perform the inter prediction process in a manner substantially similar to that described with respect to the motion compensation unit 224 (fig. 3).

Motion compensation unit 316 may comprise UMVE unit 332. In some examples, motion compensation unit 316 may determine a candidate list of one or more spatially neighboring blocks that are spatially neighboring a current block of video data. The video decoder 300 may receive data representing the base candidate index, the direction index, and the distance index in a bitstream representing video data (e.g., the encoded video bitstream of fig. 4). The base candidate index may indicate a base candidate defined in the candidate list, the direction index may indicate a direction defined in the direction table, and the distance index may indicate a distance defined in the distance table. Motion compensation unit 316 or UMVE unit 332 may determine the base candidate(s) based on the base candidate index. Motion compensation unit 316 or UMVE 332 may determine the direction based on the direction index. The motion compensation unit 316 or UMVE unit 332 may also determine the distance based on the distance index. UMVE unit 332 may determine the MVD based on the direction and distance. The motion compensation unit 316 may determine a prediction block using the MVD and the motion vector of the base candidate. The video decoder 300 (e.g., the entropy decoding unit 302, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the decoding buffer unit 314) may then decode the current block based on the prediction block. For example, to decode the current block based on the prediction block, the video decoder 300 (e.g., reconstruction unit 310) may add samples of the prediction block (e.g., from prediction processing unit 304) to corresponding residual samples (e.g., from inverse transform processing unit 308) to obtain reconstructed samples of the current block. Although UMVE unit 332 is shown in motion compensation unit 316, in some examples, UMVE unit 332 may be located elsewhere in video decoder 300 or may be split between motion compensation unit 316 and other portions of video decoder 300.

As another example, if the prediction information syntax element indicates that the current block is intra-predicted, the intra prediction unit 318 may generate the prediction block according to the intra prediction mode indicated by the prediction information syntax element. Again, intra-prediction unit 318 may generally perform the intra-prediction process in a manner substantially similar to that described with respect to intra-prediction unit 226 (fig. 3). The intra-prediction unit 318 may retrieve data of spatially neighboring samples from the DPB 314 to the current block.

The reconstruction unit 310 may reconstruct the current block using the prediction block and the residual block. For example, the reconstruction unit 310 may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

The filter unit 312 may perform one or more filter operations on the reconstructed block. For example, the filter unit 312 may perform deblocking operations to reduce blocking artifacts along the edges of the reconstructed block. The operation of the filter unit 312 is not necessarily performed in all examples.

The video decoder 300 may store the reconstructed block in the DPB 314. As described above, the 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 the prediction processing unit 304. In addition, video decoder 300 may output decoded pictures from DPB 314 for subsequent presentation on a display device, such as display device 118 of fig. 1.

In this manner, video decoder 300 represents an example of a video decoding device that includes a memory configured to store video data and one or more processing units implemented in circuitry and configured to perform the UMVE techniques of this disclosure.

Video encoder 200 and video decoder 300 may encode and decode video data using UMVE in accordance with the techniques of this disclosure. It may be helpful to describe the encoding and decoding processes. FIG. 5 is a flow diagram illustrating an example method for encoding a current block. The current block may include a current CU. Although described with respect to video encoder 200 (fig. 1 and 2), it should be understood that other devices may be configured to perform methods similar to those of fig. 5.

In this example, the video encoder 200 initially predicts the current block (350). For example, the video encoder 200 may form a prediction block for the current block. The video encoder 200 may then calculate a residual block for the current block (352). To calculate the residual block, the video encoder 200 may calculate the difference between the original, non-coded block and the prediction block of the current block. The video encoder 200 may then transform and quantize the coefficients of the residual block (354). Next, video encoder 200 may scan the quantized transform coefficients of the residual block (356). During or after scanning, video encoder 200 may entropy encode the coefficients (358). For example, video encoder 200 may encode the coefficients using CAVLC or CABAC. The video encoder 200 may then output entropy encoded data for the block (360).

FIG. 6 is a flow diagram illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although described with respect to video decoder 300 (fig. 1 and 3), it should be understood that other devices may be configured to perform methods similar to those of fig. 6.

The video decoder 300 may receive entropy-encoded data for the current block, such as entropy-encoded prediction information and entropy-encoded data for coefficients of a residual block corresponding to the current block (370). The video decoder 300 may entropy decode the entropy-encoded data to determine prediction information of the current block and regenerate coefficients of the residual block (372). The video decoder 300 may predict the current block, e.g., using an intra or inter prediction mode as indicated by the prediction information for the current block (374), to calculate a prediction block for the current block. The video decoder 300 may then inverse scan the regenerated coefficients (376) to create a block of quantized transform coefficients. The video decoder 300 may then inverse quantize and inverse transform the coefficients to produce a residual block (378). The video decoder 300 may finally decode the current block by combining the prediction block and the residual block (380).

ITU-T VCEG (Q6/16) and ISO/IEC MPEG (JTC 1/SC 29/WG 11) are now studying the potential requirements for future video codec technology standardization with compression capabilities that will significantly exceed the current HEVC standard, including its current and recent extensions for screen content codecs and high dynamic range codecs. These groups collectively address this exploratory activity in a joint collaboration called joint video exploration team (jfet) to evaluate compression technique designs proposed by experts in this field. Jvt meets for the first time in 2015, 10 months, 19 days to 21 days. "Algorithm Description of Joint Exploration Test Model 7" by J.Chen, E.Alshina, G.J.Sullivan, J. -R.ohm, J.Boyce (JVET-G1001, 7.2017) is an algorithmic Description of Joint Exploration Test Model 7 (JEM-7). Jfet is currently developing a universal video coding (VVC) standard based on JEM. The Joint Video Experts Team (JVET) of Bross et al, "Versatile Video Coding (Draft 2)", ITU-T SG 16WP 3 and ISO/IEC JTC1/SC 29/WG 11, at Lumburgia (Ljubljana, SI) meeting 11 at 7/10 to 18 days 2018, document JVET-K1001 (hereinafter "JVET-K") is a Draft of the VVC standard.

In HEVC, the largest codec unit in a slice is referred to as a Codec Tree Block (CTB) or a Codec Tree Unit (CTU). The CTB includes a quad tree whose nodes are codec units. In the HEVC main profile (profile), the size of the CTB may be in the range of 16 × 16 to 64 × 64 (although 8 × 8 CTB sizes may be technically supported). The size of a CU may be the same as a CTB, although a CU may be as small as 8 × 8. Furthermore, each CU is coded in one mode (i.e., inter-coded or intra-coded). A CU may be further partitioned into 2 or 4 PUs when the CU is inter coded, or become only one PU when no further partitioning is applied. When two PUs are present in one CU, the two PUs may be a half-size rectangle or two rectangle sizes of 1/4 or 3/4 of the size of the CU. When a CU is inter-coded, there is one set of motion information for each PU. In addition, each PU is coded with a unique inter prediction mode to derive a set of motion information.

In HEVC, for PU, there are two inter prediction modes, named merge mode (special case where skip is considered as merge mode) and Advanced Motion Vector Prediction (AMVP) mode, respectively. In AMVP or merge mode, a Motion Vector (MV) candidate list will be maintained for multiple motion vector predictors (predictors). The motion vector of the current PU and the reference index in merge mode are generated by selecting one candidate from the MV candidate list. The MV candidate list contains a maximum of 5 candidates for the merge mode and only two candidates are used for the AMVP mode. The merge candidates may contain a set of motion information, e.g., a motion vector and a reference index corresponding to two reference picture lists (list 0 and list 1). If a merge candidate is identified by the merge index, the reference picture will be used for prediction of the current block and associated motion vector. However, in AMVP mode, for each potential prediction direction from list 0 or list 1, the reference index and MV predictor (MVP) index need to be explicitly signaled to the MV candidate list since the AMVP candidate contains only motion vectors. In AMVP mode, the predicted motion vector can be further refined. As can be seen from the above, the merge candidate corresponds to the complete motion information set, whereas the AMVP candidate only contains one motion vector and reference index for a particular prediction direction. Candidates for both modes are similarly derived from the same spatial and temporal neighboring blocks.

For a particular PU (PU)₀) The spatial MV candidates are derived from the neighboring blocks shown in fig. 7A and 7B, although the method for generating candidates from the blocks is different for the merge and AMVP modes.

In the merge mode, a maximum of four spatial MV candidates can be derived in the order shown in fig. 7A. Specifically, the sequence is as follows: left side (0), top (1), upper right (2), lower left (3) and upper left (4).

In AMVP mode, spatial neighboring blocks are divided into two groups. The first group is the left group consisting of blocks 0 and 1. The second group is the upper group consisting of blocks 2, 3 and 4, as shown in fig. 7B. For each group, a potential candidate in a spatially neighboring block that references the same reference picture as indicated by the signaled reference index has the highest priority to be selected to form the final candidate for the group. It is possible that none of the spatial neighboring blocks contain a motion vector pointing to the same reference picture. Thus, if no such candidate is found, the first available candidate will be scaled to form the final candidate, so that the temporal distance difference can be compensated for.

Fig. 8A and 8B are conceptual diagrams illustrating Temporal Motion Vector Prediction (TMVP) candidates. Fig. 8A shows an example of a TMVP candidate. If the TMVP candidate is enabled and available, it is added to the MV candidate list after the spatial motion vector candidate. The motion vector derivation process for the TMVP candidate is the same for the merge and AMVP modes, but the target reference index of the TMVP candidate is always set to 0 in the merge mode.

The primary (primary) block location for TMVP candidate derivation is the lower right block outside the collocated (collocated) PU, shown as block "T" in fig. 8A, to compensate for deviations to the blocks above and to the left for generating spatially neighboring candidates. However, if the block is outside the current CTB row or motion information is not available, the block is replaced with the central block of the PU.

The motion vector of the TMVP candidate is derived from the collocated PU of the collocated picture indicated at the slice level. The motion vector of the collocated PU is called collocated MV.

Fig. 8B shows an example of MV scaling. In order to derive the TMVP candidate motion vector, the collocated MV needs to be scaled to compensate for the temporal distance difference, as shown in fig. 8B.

Several other aspects of the merge mode and AMVP mode are worth mentioning below. For example, the video encoder 200 and the video decoder 300 may perform motion vector scaling. It is assumed that the value of the motion vector is proportional to the distance of the picture in the presentation time. The motion vector associates two pictures: reference pictures and pictures that contain motion vectors (i.e., contain pictures). When a motion vector is used to predict another motion vector, the distance between the included picture and the reference picture is calculated based on a Picture Order Count (POC) value.

For a motion vector to be predicted, its associated containing picture and reference picture may be different. Therefore, a new distance (based on POC) will be calculated. Video encoder 200 and video decoder 300 may scale the motion vector based on these two POC distances. For spatial neighboring candidates, the included pictures for the two motion vectors are the same, while the reference pictures are different. In HEVC, motion vector scaling applies to both TMVP and AMVP for spatial and temporal neighbor candidates.

In another example, the video encoder 200 and the video decoder 300 may perform artificial motion vector candidate generation. If the motion vector candidate list is not complete, an artificial motion vector candidate may be generated and inserted at the end of the list until the list will have all candidates.

In merge mode, there are two types of artificial MV candidates: a combination candidate derived only for B slices and a zero candidate used only if the first type does not provide enough artificial candidates. The zero candidate is a candidate of a motion vector designated to have a magnitude of 0. For each pair of candidates that are already in the candidate list and have the necessary motion information, a bi-directional combined motion vector candidate is derived by combining the motion vector of the first candidate of a picture in reference list 0 and the motion vector of the second candidate of a picture in reference list 1.

In another example, the video encoder 200 and the video decoder 300 may perform a pruning process for candidate insertions. The candidates from different blocks may happen to be the same, which reduces the efficiency of merging/AMVP candidate lists. A pruning process may be applied to address this problem. The pruning process compares one candidate with the other candidates in the current candidate list to avoid inserting the same candidate to some extent. To reduce complexity, the pruning process is applied to a limited number of candidates, rather than comparing each potential candidate to all other candidates.

As specified in HEVC, when use _ integer _ mv _ flag is equal to 0 in the slice header, the video encoder 200 may signal a Motion Vector Difference (MVD) (between the motion vector of the PU and the predicted motion vector) in units of quarter luma samples (pixels). Alternatively, the video encoder 200 may signal MVDs in units of quarter luma samples, integer luma samples, or four luma samples, as specified in JEM. The MVD resolution may be controlled at the CU level and the MVD resolution flag is signaled conditionally for each CU with at least one non-zero MVD component.

For CUs having at least one non-zero MVD component, video encoder 200 may signal a first flag to indicate whether quarter-luma sample MV precision is used in the CU. A first flag equal to 1 indicates that quarter-luma sample MV precision is not used, while another flag is set to indicate whether integer-luma sample MV precision or four-luma sample MV precision is used.

The video encoder 200 and the video decoder 300 use the quarter-luma sample MV resolution for a CU when the first MVD resolution flag of the CU is zero or the CU is not coded (meaning all MVDs in the CU are zero). When the video encoder 200 and the video decoder 300 use integer-luma sample MV precision or four-luma sample MV precision for a CU, the video encoder 200 and the video decoder 300 round MVPs in the AMVP candidate list to the corresponding precision.

The video encoder 200 and the video decoder 300 may use CU-level Rate Distortion (RD) checking to determine which MVD resolution is to be used for a CU. That is, the CU level RD check is performed 3 times for each MVD resolution. To speed up the video encoder 200, the coding schemes labeled (1) and (2) in the following paragraphs may be applied in JEM.

(1) During the RD check of a CU with a conventional quarter luma sample MVD resolution, video encoder 200 stores motion information (integer luma sample precision) of the current CU. During the RD check on the same CU with integer luma samples and 4 luma sample MVD resolution, the stored motion information (after rounding) is used as a starting point for further small-range motion vector refinement, so that the time-consuming motion estimation process is not repeated three times.

(2) Video encoder 200 and video decoder 300 may conditionally invoke RD checking for CUs with a 4 luma sample MVD resolution. For a CU, RD checking for a 4 luma sample MVD resolution of the CU may be skipped when the RD cost for the integer luma sample MVD resolution is much greater than the RD cost for the quarter luma sample MVD resolution.

The final motion vector expression (UMVE) is described in "CE 4 Ultimate motion vector expression in JVT-J0024 (Test 4.2.9)" of S.Jeong et al (JVOT-K0115, 7.2018) (hereinafter "JVOT-J0024"), and "CE 4 Ultimate motion vector expression (Test 4.5.4)" of S.Jeong et al (JVOT-L0054, 10.2018) (hereinafter "JVOT 35ET-L0054"). UMVE can be used in either skip mode or merge mode with the proposed motion vector expression method. The video encoder 200 and the video decoder 300 may reuse the merge candidates. In merging the candidates, the candidates may be selected and further expanded by the proposed motion vector expression method. UMVE provides motion vector representation using simplified signaling. The expression method comprises a starting point, a motion amplitude and a motion direction.

UMVE uses the merge candidate list as the merge candidate list described in HEVC. However, extensions to UMVE only consider candidates for a DEFAULT merge TYPE (e.g., MRG _ TYPE _ DEFAULT _ N).

Fig. 9 is a conceptual diagram illustrating a UMVE search process, and fig. 10 is a conceptual diagram illustrating UMVE search points. For example, video encoder 200 may search for blocks in one or more reference pictures that are similar to the current block. In fig. 9, the current block in the current frame is depicted between the L0 reference picture and the L1 reference picture. The prediction direction information indicates a prediction direction among L0, L1, L0, and L1 predictions. In the B slice, the video encoder 200 and the video decoder 300 may generate bidirectional prediction candidates from the merge candidates having unidirectional prediction by using a mirroring technique as shown in fig. 9 and 10. For example, a prediction in the direction of one pixel to the right in L0 (black circle in fig. 10) would be mirrored to one pixel to the left in L1 (also black circle in fig. 10). In another example, a prediction in the direction of two pixels up in L0 (empty circle in fig. 10) would be mirrored in two pixels down in L1 (also empty circle in fig. 10).

In B-slice, the video encoder 200 and the video decoder 300 may intra-predict, uni-directionally inter-predict, or bi-directionally inter-predict a block. For example, if the merging candidate is uni-directionally predicted using L1, the reference index of L0 is decided by searching for a reference picture in list 0 that mirrors the reference picture of list 1. If there is no corresponding picture, the reference picture closest to the current picture is used. The MV of L0 is derived by scaling the MV of L1. The scaling factor is calculated from the POC distance.

The video encoder 200 may signal the UMVE prediction direction index for the block. The prediction direction index may have one bit or two bits. If the prediction direction of the UMVE candidate is the same as one of the original merge candidates, the value of the first (and only) bit of the prediction direction index is 0. However, if the prediction direction of the UMVE candidate is not the same as some of the original merge candidates, the first bit of the prediction direction index has a value of 1. After sending the first bit of the UMVE prediction direction index, video encoder 200 may signal the second bit of the UMVE prediction direction index. The second bit of the UMVE prediction direction index indicates the prediction direction of the UMVE candidate. The prediction directions of the UMVE candidates may be signaled based on a predefined priority order of UMVE prediction directions.

The priority order of the UMVE prediction directions is L0/L1 prediction, L0 prediction and L1 prediction. For example, if the prediction direction of the merge candidate is L1, the video encoder 200 signals "0" as a UMVE prediction direction index to indicate that the prediction direction of the UMVE candidate is L1. In this example, video encoder 200 may signal "10" as a UMVE prediction direction index to indicate that the prediction directions of the UMVE candidates are L0 and L1. Further, in this example, the video encoder 200 may signal "11" as a UMVE prediction direction index to indicate that the prediction direction of the UMVE candidate is L0. Thus, if the prediction direction of the UMVE candidate matches the prediction direction of the merge candidate, the UMVE prediction direction index has only 1 bit. If the L0 and L1 prediction lists are the same, the video encoder 200 does not signal the UMVE prediction direction information.

The base candidate index in table 1 defines a starting point for selecting candidates for MVP. The base candidate index indicates the best candidate among the candidates in the list. The video encoder 200 may signal the base candidate index to indicate to the video decoder 300 which base candidate is the best candidate. For example, if the best candidate is the first MVP, video encoder 200 may signal 0. If the number of basic candidates is equal to 1, the basic candidate index (i.e., the basic candidate IDX) is not signaled.

TABLE 1 basic candidate IDX

The distance index in table 2 is motion amplitude information. The distance index indicates a predefined distance from the starting point (base candidate). The video encoder 200 can signal the distance index to indicate the distance of the MV. For example, if the distance of the MV is 4 pixels, the video encoder 200 may signal 4.

TABLE 2 distance IDX

The direction index in table 3 indicates the direction of the MVD with respect to the starting point. The direction index may represent four directions, i.e., up, down, left, and right. The video encoder 200 may signal the direction index to indicate the direction of the MV to the video decoder 300. For example, if the direction is upward, the video encoder may signal 10.

TABLE 3 Direction IDX

Direction IDX	00	01	10	11
					X axis	+	-	N/A	N/A
y axis	N/A	N/A	+	–

A flag is used in video codec to signal to video decoder 300 that video encoder 200 has encoded a block of video data using a particular mode. For example, if the video encoder 200 is using skip mode for a block, it may signal a skip flag indicating that the block is encoded using skip mode. If the video encoder 200 is using the merge mode for a block, the video encoder 200 may signal a merge flag indicating that the block is encoded using the merge mode. If video encoder 200 is using UMVE for a block, video encoder 200 may signal a UMVE flag indicating that the block is encoded using UMVE. If video encoder 200 is using an affine mode for a block, video encoder 200 may signal an affine flag indicating that the block is encoded using an affine mode.

The video encoder 200 may signal the UMVE flag immediately after sending the skip flag and the merge flag. If the skip flag and merge flag are true, the video decoder 300 parses the UMVE flag. If the UMVE flag is equal to 1, it indicates that UMVE is being used and the UMVE syntax is parsed. If the UMVE flag is not equal to 1, the video decoder 300 parses the AFFINE flag. An AFFINE flag equal to 1 indicates AFFINE mode. If AFFINE flag is not equal to 1, the skip/merge index is parsed for the skip/merge mode of the VTM.

Due to the UMVE candidates, no additional line buffers are needed, since the skip/merge candidates are directly used as base candidates. Using the input UMVE index, any adjustments to the MV are decided prior to motion compensation. Therefore, a long line buffer may not be required.

An Enhanced version of UMVE described in "Non-CE 4: Enhanced optimal motion vector expression," (hereinafter "jvt-L0355") by hashimoto et al (jvt-L0355, month 10 2018), provides two changes to extend the original UMVE (described in jvt-L0054), as follows: 1) increase the number of directions from 4 to 8, as shown in table 4 below; 2) a plurality of distance lists are used as shown in tables 5 and 6 below.

TABLE 4 moving directions

Direction IDX	000	001	010	011	100	101	110	111
									X axis	+1	-1	0	0	+1/2	-1/2	-1/2	+1/2
y axis	0	0	+1	-1	+1/2	-1/2	+1/2	-1/2

The direction index in table 4 indicates 8 directions. It can be seen that the values of the x-axis and the y-axis in the diagonal direction are half the values in the horizontal direction and the vertical direction, respectively.

jfet-L0355 describes two distance lists, considering that the amount of distance (motion difference) will be different from the region and sequence features. The selection flags of the list may be context-coded by the video encoder 200 for optimal application. For example, if the distance of the MV is less than 1 pixel, the video encoder 200 may signal a selection flag for the first distance list. In another example, if the distance of the MV is 2 pixels or greater, the video encoder 200 may signal a selection flag for the second distance list.

TABLE 5 first distance List

TABLE 6 second distance List

Li, R. — L.Liao, C.S.Lim (JFET-L0408, month 10 2018) "Ce 4-related: Improvement on estimate motion vector expression" (hereinafter "JFET-L0408") provides three changes to extend the original UMVE of JFET-L0054 as follows: 1) as shown in tables 7 and 8, the number of directions was increased from 4 to 8; 2) providing 2 adaptive distance tables as shown in tables 9 and 10; 3) full-pixel search points are provided for large distance values.

Table 7: UMVE direction table of JFET-L0054

Direction IDX	00	01	10	11
					X axis	+	-	N/A	N/A
y axis	N/A	N/A	+	-

Table 8: additional direction information table

Direction IDX	00	01	10	11
					X axis	+	-	+	-
y axis	+	-	-	+

The additional directions in Table 8 that support the diagonal direction are added to the original UMVE in the JFET-L0054 direction table in Table 7. The video encoder 200 may select one of two direction tables (i.e., table 7 or table 8) based on the angle of the base motion vector candidate. If the angle of the base motion vector candidate is within [22.5 °, 67.5 ° ], [112.5 °, 157.5 ° ], [202.5 °, 247.5 ° ] or [292.5 °, 337.5 ° ] the video encoder 200 selects the diagonal direction table in table 8. Otherwise, the video encoder 200 selects the horizontal/vertical direction table in table 7. A diagram of the direction table selection is shown in fig. 11. Fig. 11 depicts a circle divided into a plurality of sections (sections) based on angle. Each of these segments (segments) corresponds to one of the possible directions from the direction table 7 and the additional direction information table 8. For example, if the base motion vector candidate is within 22.5 degrees and 67.5 degrees, the video encoder 200 may select the additional direction information table 8, signal the additional direction information table 8 to the video decoder 300, and signal that the direction index is 00. If the base motion vector candidate is between 67.5 degrees and 112.5 degrees, the video encoder 200 may select direction table 7, signal the direction table 7 to the video decoder, and signal a direction index of 00.

The UMVE implementation in JFET-L0054 has a fixed distance table (Table 9) for generating UMVE search points. The enhanced implementation of UMVE in jfet-L0408 uses an additional adaptive distance table shown in table 10 based on image resolution, as described below. The adaptive distance table may be adjusted based on the frequency of use for a given distance.

TABLE 9, CE4.5.4UMVE distance table

TABLE 10 additional UMVE distance Table set forth in JVET-L0408

If the picture resolution is not greater than 2K (i.e., 1920 × 1080), the video encoder 200 may select table 9 as the base distance table. Otherwise, the video encoder 200 may select table 10 as the base distance table.

The video encoder 200 and the video decoder 300 may reorder the distance indices according to the use of each distance index in previously coded pictures ranked from high to low. For example, assuming that table 9 is used as the basic distance table and 2 pixels are used most in the previously coded picture, the 2-pixel distance may be assigned to index 0 instead of index 3.

To reduce complexity, the enhanced UMVE candidate values may be modified such that a CU in UMVE mode has a full-pixel motion vector instead of a sub-pixel motion vector if the UMVE distance is greater than a threshold. In the present embodiment, a 16-pixel distance is used as the threshold value.

Previous UMVEs described in JVET-L0054, JVET-L0355, and JVET-L0408 all employ a fixed set for Motion Vector (MV) expression. Enhanced UMVE for jfet-L0355 and jfet-L0408 extends the set of directional information. Enhanced UMVE for jfet-L0355 and jfet-L0408 may also adaptively select 1 aggregation table from 2 fixed aggregation tables during codec. However, having a fixed set of direction information results in a large amount of side information (such as frequent and large adjustments to motion vectors) to be encoded and decoded. The large amount of codec side information may degrade the UMVE codec performance of the video encoder 200 and the video decoder 300. This disclosure describes techniques for addressing a reduction in the amount of side information that is coded, thereby reducing a reduction in UMVE codec performance.

The video encoder 200 and the video decoder 300 may apply any of the following techniques, including any combination thereof.

Fig. 12 is a flow diagram illustrating a technique for encoding video data in accordance with the present disclosure. In the example of fig. 12, the motion estimation unit 222 of the video encoder 200 may derive direction information including a distance resolution and a direction resolution from spatially neighboring blocks. The motion estimation unit 222 of the video encoder 200 may determine a candidate list for the current block from the spatial neighboring blocks and the base candidates (382). The motion estimation unit 222 or the UMVE unit 228 of the video encoder 200 may then determine a directional resolution based on the motion vectors of one or more spatial neighboring blocks of the set of spatial neighboring blocks that are spatially neighboring the current block of video data (384). For example, motion estimation unit 222 or UMVE unit 228 of video encoder 200 may examine one or more spatial neighboring blocks having motion vectors and set the directional resolution of the current block based on the motion vectors of the spatial neighboring block(s). Motion estimation unit 222 or UMVE unit 228 of video encoder 200 may also determine a distance resolution based on motion vectors of one or more spatial neighboring blocks (386). For example, motion estimation unit or UMVE unit 228 of video encoder 200 may examine one or more spatial neighboring blocks having motion vectors associated therewith and set the distance resolution to the distance resolution of the current block based on the motion vectors of the spatial neighboring block(s). UMVE unit 228 (e.g., motion estimation unit 222) of video encoder 200 may also determine 388 a base candidate index, a direction index, and a distance index. For example, UMVE unit 228 may look up the base candidates in a base candidate list and select an index associated with the selected base candidate. UMVE unit 228 may also look up the directional resolution in the directional table and determine which directional index is closest to the directional resolution. Similarly, UMVE unit 228 may look up the range resolution in the range table and determine which range index is closest to the range resolution in the range table. The video encoder 200 may encode the direction index and the distance index into a bitstream to be decoded by the video decoder 300 (390). The direction index and the distance index may be stored in a direction table and a distance table, respectively, in memories in the video encoder 200 (e.g., the video data memory 230) and the video decoder 300 (e.g., the CPB memory 320). The direction table and distance table may be fixed prior to codec and modified by video encoder 200 (e.g., motion estimation unit 222) based on direction information from spatial neighboring blocks and modified by video decoder 300 (e.g., motion compensation unit 316) based on direction information from spatial neighboring blocks during codec. For example, UMVE unit 228 of video encoder 200 may determine that the current direction resolution in the direction table and/or the current distance resolution in the distance table is not optimal. For example, the distance table may only contain distance resolutions shorter than many distances of the motion vectors of the spatially neighboring blocks. In this example, UMVE unit 228 may update the distance table with the new distance resolution or resolutions and signal in the bitstream how the distance table has been updated so that UMVE unit 332 of video decoder 300 may similarly update its distance table. If the directional resolution(s) is not optimal, UMVE unit 228 may similarly update the directional resolution(s) contained in the directional table and signal in the bitstream how the directional table has been updated so that UMVE unit 332 of video decoder 300 may update its directional table.

Video encoder 200 may determine the MVD based on the direction and distance associated with the direction and distance index (392). For example, UMVE unit 228 of video encoder 200 may look up a direction and distance index in a direction and distance table and calculate an MVD by combining the direction and distance indicated by the direction and distance index. The video encoder 200 may then determine a prediction block using the MVD and the motion vector(s) of the base candidate (394). For example, the video encoder 200 (e.g., the mode selection unit 202) may select a prediction block by adding the MVD to the motion vector(s) of the base candidate(s). The video encoder 200 may then encode the current block based on the prediction block (396).

Fig. 13 is a flow diagram illustrating a technique for decoding video data in accordance with the present disclosure. In the example of fig. 13, UMVE unit 332 of video decoder 300 may derive the direction information from the spatial neighboring blocks. In particular, in the example of fig. 13, the motion compensation unit 316 of the video decoder 300 may determine a candidate list for the current block from, for example, spatially neighboring blocks (402). Motion compensation unit 316 or UMVE unit 332 of video decoder 300 may determine a base candidate index, a direction index, and a distance index (404). The base candidate index, the direction index, and the distance index may be encoded in a bitstream by the video encoder 200 and decoded by the video decoder 300. The base candidate index, the direction index, and the distance index may be stored in a base candidate list, a direction table, and a distance table, respectively, in memories in the video encoder 200 (e.g., the video data memory 230) and the video decoder 300 (e.g., the CPB memory 320). As described above, the direction table and distance table may be fixed prior to codec, and may be modified by the video encoder 200 during codec based on direction information from spatially neighboring blocks, and may be modified by the video decoder 300 based on direction information from spatially neighboring blocks.

Motion compensation unit 316 or UMVE unit 332 of video decoder 300 may determine base candidate(s) based on the base candidate index (406) by looking up the base candidate index in a base candidate list. UMVE unit 332 of video decoder 300 may determine the direction based on the direction index by looking up the direction index in a direction index table (408). UMVE unit 332 of video decoder 300 may determine the distance based on the distance index by looking up the distance index in a distance index table (410).

UMVE unit 332 of video decoder 300 may determine the MVD based on the direction and distance (412). For example, the UMVE unit 332 of the video decoder 300 may look up a direction and distance index in a direction and distance table and calculate an MVD by combining the direction and distance indicated by the direction and distance index. The motion compensation unit 316 of the video decoder 300 may determine a prediction block using the MVD and the motion vector of the base candidate (414). For example, the video decoder 300 (e.g., the prediction processing unit 304) may select a prediction block by adding an MVD to a motion vector of a base candidate. The video decoder 300 (e.g., the entropy decoding unit 302, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the decoding buffer unit 314) may then decode the current block based on the prediction block (416).

Fig. 14 is a conceptual diagram illustrating spatial neighboring blocks of a current block. The current block is spatially adjacent to blocks a0, a1, L, B2, T, B1, B0, RT, RB, and LB. The current block also has a collocated time block CT. In some examples, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution from MVs of spatially neighboring blocks. For example, the UMVE unit 228 of the video encoder 200 and the UMVE unit 332 of the video decoder 300 may determine the directional resolution and/or the distance resolution from the MVs of the neighboring blocks (a0) immediately below and to the left of the sample point in the lower left corner of the current block in the set of spatial neighboring blocks, the neighboring block (a1) immediately to the left of the sample point in the lower left corner of the current block in the set of spatial neighboring blocks, the neighboring block (B0) immediately above the sample point in the upper right corner of the current block in the set of spatial neighboring blocks, the neighboring block (B1) immediately above the sample point in the upper right corner of the current block in the set of spatial neighboring blocks, and the neighboring block (B2) immediately above and to the left of the sample point in the upper left corner of the current block in the set of spatial neighboring blocks, if available (e.g., the spatial neighboring blocks have been encoded or decoded). For example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by averaging the directional resolutions and/or the distance resolutions of the available spatial neighboring blocks a0, a1, B0, B1, and B2. In another example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by obtaining a first available directional resolution and/or distance resolution from spatially neighboring blocks a0, a1, B0, B1, and B2. In some examples, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution from the MVs of the middle left (L) neighboring block in the set of spatial neighboring blocks and the middle upper (T) neighboring block in the set of spatial neighboring blocks in fig. 14, if available. For example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by averaging the directional resolutions and/or the distance resolutions of the available spatial neighboring blocks L and T. In another example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by obtaining a first available directional resolution and/or distance resolution from spatially neighboring blocks L and T.

In still other examples, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution from MVs of neighboring blocks between a first neighboring block in the set of spatially neighboring blocks and a second neighboring block in the set of spatially neighboring blocks, if available, where in fig. 14 the first neighboring block (B1) is immediately to the left of a sample point in the top right corner of the current block and the second neighboring block (B2) is immediately to the top left of a sample point in the top right corner of the current block. For example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by averaging the directional resolution and/or the distance resolution of the available spatial neighboring blocks between B1 and B2. In another example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by obtaining a first available directional resolution and/or distance resolution from a spatial neighboring block between B1 and B2.

In another example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution from MVs of neighboring blocks between a first neighboring block in the set of spatially neighboring blocks and a second neighboring block in the set of spatially neighboring blocks, if available, where in fig. 14 the first neighboring block (a1) is immediately to the left of a sample point in the lower left corner of the current block and the second neighboring block (B2) is immediately to the upper left of a sample point in the upper right corner of the current block. For example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by averaging the directional resolution and/or the distance resolution of the available spatial neighboring blocks between a1 and B2. In another example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by obtaining a first available directional resolution and/or distance resolution from a spatial neighboring block between a1 and B2.

Fig. 15 is a conceptual diagram illustrating non-adjacent spatial neighboring blocks. FIG. 15 depicts a current block, adjacent spatially neighboring blocks 1-5, and non-adjacent spatially neighboring blocks 6-49. In some examples, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution from MVs of one or more spatially neighboring blocks that are not adjacent to the current block, such as any of blocks 6-49 (if available). For example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by averaging the directional resolution and/or the distance resolution of, for example, available non-adjacent spatial neighboring blocks 6-10. In another example, UMVE unit 228 of video encoder 200 and UMVE unit 332 of video decoder 300 may determine the directional resolution and/or the distance resolution by obtaining a first available directional resolution and/or distance resolution from, for example, non-adjacent spatially neighboring blocks 6-10.

The determined directional information may include a flexible range resolution number and a flexible directional resolution coding number. That is, the determined direction information may be used to dynamically adjust the direction table and/or the distance table such that a given direction index and/or a given distance index will point to a different distance and/or direction in the distance and/or direction table after the table is adjusted.

The available neighboring blocks may contain their motion vector resolution information. For example, a neighboring block may have been encoded by video encoder 200 or decoded by video decoder 300, and the motion vector associated with the neighboring block may be known and available. The distance resolution may be determined based on the known available neighboring motion vector resolution. For a block coded in merge mode, its best prediction block will likely be located near the position pointed to by the original merge MV. Thus, a smaller UMVE distance may help locate the best prediction block. Accordingly, the video encoder 200 and the video decoder 300 may limit the determined UMVE distance to a distance less than the neighboring motion vector resolution. For example, if the neighboring motion vector resolution is 1 pixel, the determined UMVE distance may include 1/2 pixels, 1/4 pixels, or other values less than 1 pixel. If the neighboring motion vector resolution is 4 pixels, the determined UMVE resolution will include 2 pixels, 1 pixel, or other values less than 4 pixels. Thus, the distance may be less than the distance resolution.

Alternatively, the video encoder 200 and the video decoder 300 may limit the determined UMVE distance to a distance equal to or slightly greater than the available neighboring motion vector resolution, e.g., no greater than twice the size of the neighboring motion vector resolution. For example, if the neighboring motion vector resolution is 1 pixel, the determined UMVE distance may include 1 pixel and 2 pixels, or other values greater than or equal to 1 pixel. If the neighboring motion vector resolution is 4 pixels, the determined UMVE resolution may include 4 pixels, 8 pixels, or other values greater than or equal to 4 pixels.

The determined distance resolution number may be less than the distance resolution numbers disclosed in JFET-K0115, JFET-L0054, JFET-L0355, and JFET-L0408, and thus less bits may be used for encoding and decoding. In accordance with the techniques of this disclosure, the determined UMVE directional resolutions are shown in table 11.

TABLE 11 possible determined UMVE directional resolutions

Direction IDX	000	001	010	011	100	101	110	111
									X axis	+1	-1	0	0	+1	-1	-1	+1
y axis	0	0	+1	-1	+1	-1	+1	-1

The available neighboring blocks may contain their motion vector direction information. In other words, an available neighboring block may have been encoded by video encoder 200 or decoded by video decoder 300, and the motion vector associated with the available neighboring block may be known. UMVE unit 228 of video encoder 200 may determine the directional resolution of UMVE based on available neighboring motion vector direction information. If the adjacent motion direction is within [67.5 °, 112.5 ° ] in fig. 11, the determined directional resolution may be 010, as shown in table 11. If the adjacent motion directions are within [67.5 °, 112.5 ° ] and [22.5 °, 67.5 ° ] the determined directional resolutions would be 010 and 100, respectively, as shown in table 11.

Alternatively, UMVE unit 228 of video encoder 200 may determine the UMVE direction resolution to include directions near adjacent motion vector directions. For example, if the adjacent motion directions are within [67.5 °, 112.5 ° ] in fig. 11, the determined directional resolutions may be 010, 100, and 110, as shown in table 11.

The determined directional resolution number may be less than the directional resolution numbers in JFET-K0115, JFET-L0054, JFET-L0355, and JFET-L0408, and the codec may be performed with fewer bits.

The original UMVE in JFET-K0115, JFET-L0054, JFET-L0355, and JFET-L0408 provides a fixed amount of direction and distance resolution. In accordance with the techniques of this disclosure, the determined direction information may include a flexible distance resolution number and a flexible direction resolution number. That is, the determined direction information may be used to dynamically adjust entries in the direction table and distance table. The number of determined UMVE distances may be decided based on the motion vector resolutions of the neighboring blocks. The number of determined UMVE directions may be decided based on the motion vector directions of the neighboring blocks.

The techniques of this disclosure may reduce the amount of signaling side information (such as large and frequent MVDs) and may provide better codec performance.

It will be recognized that, according to an example, certain acts or events of any of the techniques described herein can be performed in a different order, may be added, merged, or omitted entirely (e.g., not all described acts or events are necessary for technical practice). Further, in some examples, actions 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. The computer readable medium may comprise a computer readable storage medium corresponding to a tangible medium, such as a data storage medium, or a communication medium, including any medium that facilitates transfer of a computer program from one place to another, for example, according to a communication protocol. In this manner, the computer-readable medium may generally correspond to (1) a non-transitory tangible computer-readable storage medium or (2) a communication medium such as a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures to implement the techniques described in this disclosure. The 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 the 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 definition of medium includes coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are 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.

The instructions may be executed by one or more processors, such as one or more Digital Signal Processors (DSPs), general purpose microprocessors, an Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Thus, as used herein, the term "processor" may refer to any of the foregoing structure or any other structure suitable for implementing 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 may be fully implemented in one or more circuits or logic elements.

The techniques of this disclosure may be implemented in a wide range of devices or apparatuses including a wireless handset, an Integrated Circuit (IC), or a set of ICs (e.g., a chipset). 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 implementation by different hardware units. Rather, as noted above, the 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.