Simplification of sub-block transform in video coding and decoding

Abstract

The video codec may apply a sub-block transform to a block of video data. The video codec is configured to determine when to apply a sub-block transform to a block of video data based on a ratio of a width to a height (or a ratio of a height to a width) of the block. When applying a sub-block transform, the video codec may also determine when to use different transform kernels for different sub-blocks.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Patent Application No. 16 / 809,044, filed on March 4, 2020, which claims the benefit of U.S. Provisional Application No. 62 / 815,025, filed on March 7, 2019, the entire contents of each of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to video encoding and video decoding. Background Art

[0004] Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital video cameras, digital recording devices, digital media players, video game devices, video game consoles, cellular or satellite radio telephones, so-called "smart phones", video teleconferencing devices, video streaming devices, etc. Digital video devices implement video codec technologies, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4 Part 10, Advanced Video Codec (AVC), ITU-T H.265 / High Efficiency Video Codec (HEVC), and extensions of these standards. By implementing such video codec technologies, video devices can more efficiently send, receive, encode, decode and / or store digital video information.

[0005] Video coding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or eliminate redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as codec tree units (CTUs), codec units (CUs), and / or codec nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial predictions of reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial predictions of reference samples in neighboring blocks in the same picture or temporal predictions of reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames. Summary of the invention

[0006] In general, the present disclosure describes techniques for encoding and decoding video data, including techniques for applying sub-block transforms to blocks of video data. Specifically, the present disclosure describes techniques for determining when to apply sub-block transforms (e.g., horizontal and / or vertical sub-block transforms) to blocks of video data based on a ratio of width to height (or a ratio of height to width) of the block. The present disclosure also describes techniques for determining when to use different transform kernels for different sub-blocks when applying sub-block transforms. The techniques of the present disclosure can improve encoding and decoding efficiency by more efficiently determining when to apply a sub-block transform mode and how to determine which transform kernel to use.

[0007] In one example, the present disclosure describes a method of encoding and decoding video data, including determining to use a sub-block transform mode for a block based on one or more of an aspect ratio or a height-to-width ratio of the block, and applying one or more transforms to the block based on the determination to use the sub-block transform mode.

[0008] In another example, the present disclosure describes an apparatus configured to encode and decode video data, the apparatus comprising a memory configured to store a block, and one or more processors implemented in circuitry and in communication with the memory, the one or more processors configured to determine to use a sub-block transform mode for the block based on one or more of an aspect ratio or a height-to-width ratio of the block, and to apply one or more transforms to the block based on the determination to use the sub-block transform mode.

[0009] In another example, the present disclosure describes an apparatus configured to encode and decode video data, the apparatus comprising means for determining, based on one or more of an aspect ratio or a height-to-width ratio of the block, to use a sub-block transform mode for the block, and means for applying one or more transforms to the block based on the determination to use the sub-block transform mode.

[0010] In another example, the present disclosure describes a non-transitory computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device to be configured to encode and decode video data to determine, based on one or more of an aspect ratio or a height-to-width ratio of the block, to use a sub-block transform mode for the block, and to apply one or more transforms to the block based on the determination to use the sub-block transform mode.

[0011] The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure.

[0013] Figure 2Aand Figure 2B is a conceptual diagram illustrating an example quadtree binary tree (QTBT) structure and a corresponding codec tree unit (CTU).

[0014] Figure 3 is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure.

[0015] Figure 4 is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure.

[0016] Figure 5 is a conceptual diagram showing vertical and horizontal sub-block transform modes.

[0017] Figure 6 is a flow chart illustrating an example encoding method.

[0018] Figure 7 is a flow chart illustrating an example decoding method. DETAILED DESCRIPTION

[0019] Figure 1 1 is a block diagram illustrating an example video encoding and decoding system 100 that may perform the techniques of the present disclosure for applying sub-block transform modes. The techniques of the present disclosure are generally directed to encoding and decoding (encoding and / or decoding) video data. Generally, 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.

[0020] like Figure 1 As shown, in this example, system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. Specifically, source device 102 provides video data to destination device 116 via computer-readable medium 110. Source device 102 and destination device 116 may each include any of a variety of devices, including a desktop computer, a notebook (i.e., laptop) computer, a tablet computer, a set-top box, a telephone handset such as a smartphone, a television, a camera, a display device, a digital media player, a video game console, a video streaming device, etc. In some cases, source device 102 and destination device 116 may be equipped for wireless communication and, therefore, may be referred to as wireless communication devices.

[0021] exist Figure 1In the example of , source device 102 includes video source 104, memory 106, video encoder 200 and output interface 108. Destination device 116 includes input interface 122, video decoder 300, memory 120 and display device 118. According to the present disclosure, the video encoder 200 of source device 102 and the video decoder 300 of destination device 116 can be configured to apply techniques for sub-block transformation. Therefore, 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 (e.g., an external camera). Similarly, destination device 116 may interface with an external display device instead of including an integrated display device.

[0022] Figure 1 The system 100 shown is only an example. In general, any digital video encoding and / or decoding device can perform the technology for sub-block transformation. The source device 102 and the destination device 116 are only examples of such codec devices, wherein the source device 102 generates encoded video data to send to the destination device 116. The present disclosure refers to a "codec" device as a device that performs data encoding and decoding (encoding and / or decoding). Therefore, the video encoder 200 and the video decoder 300 represent examples of codec devices, specifically, video encoders and video decoders, respectively. In some examples, the devices 102, 116 can operate in a substantially symmetrical manner so that each of the devices 102, 116 includes a video encoding and decoding component. Therefore, the system 100 can support one-way or two-way video transmission between video devices 102, 116, for example, for video streaming, video playback, video broadcasting, or video telephony.

[0023] Typically, the video source 104 represents the source of video data (i.e., the original, unencoded video data) and provides a continuous series of pictures (also referred to as "frames") of the video data to the video encoder 200, which encodes the data of 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 original video, and / or a video feed interface receiving video from a video content provider. As a further alternative, the video source 104 may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. In each case, the video encoder 200 encodes the captured, pre-captured, or computer-generated video data. The video encoder 200 may rearrange the pictures from the receiving order (sometimes referred to as the "display order") into the encoding and decoding order for encoding and decoding. The video encoder 200 may generate a bitstream comprising 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 or retrieval by, for example, input interface 122 of destination device 116 .

[0024] The memory 106 of the source device 102 and the memory 120 of the destination device 116 represent general purpose memories. In some examples, the memories 106, 120 can store raw video data, for example, raw video from the video source 104 and raw, decoded video data from the video decoder 300. Additionally or alternatively, the memories 106, 120 can store software instructions that can be executed by, for example, the video encoder 200 and the video decoder 300, respectively. Although shown as separate from the video encoder 200 and the video decoder 300 in this example, it should be understood that the video encoder 200 and the video decoder 300 can also include internal memories for functionally similar or equivalent purposes. In addition, the memories 106, 120 can store, for example, encoded video data output from the video encoder 200 and input to the video decoder 300. In some examples, portions of the memories 106, 120 can be allocated as one or more video buffers, for example, to store raw, decoded and / or encoded video data.

[0025] The computer-readable medium 110 may represent any type of medium or device capable of transmitting the encoded video data from the source device 102 to the destination device 116. In one example, the computer-readable medium 110 represents a communication medium to enable the source device 102 to send the encoded video data directly to the destination device 116 in real time (e.g., via a radio frequency network or a computer-based network). The output interface 108 may modulate a transmission signal including the encoded video data, and the input interface 122 may demodulate the received transmission signal according to a communication standard such as a wireless communication protocol. 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, a switch, a base station, or any other equipment that facilitates communication from the source device 102 to the destination device 116.

[0026] 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 disc, DVD, CD-ROM, flash memory, volatile or non-volatile memory, or any other suitable digital storage medium for storing encoded video data.

[0027] In some examples, source device 102 may output the encoded video data to file server 114 or to 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 downloading. File server 114 may be any type of server device capable of storing the encoded video data and sending the encoded video data to destination device 116. File server 114 may represent a network server (e.g., for a website), a file transfer protocol (FTP) server, a content distribution 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., a digital subscriber line (DSL), a cable modem, etc.), or a combination of both suitable for accessing the 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 transmission protocol, or a combination thereof.

[0028] 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 the various IEEE 802.11 standards, or other physical components. In examples where output interface 108 and input interface 122 include wireless components, output interface 108 and input interface 122 may be configured to transmit data, such as encoded video data, according to a cellular communication standard (e.g., 4G, 4G-LTE (Long Term Evolution), LTE Advanced (LTE-A), 5G, etc.). In some examples where output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 may be configured to transmit data, such as encoded video data, according to other wireless standards (e.g., IEEE 802.11 specifications, IEEE 802.15 specifications (e.g., ZigBee TM ), Bluetooth TM Standards, etc.) to transmit data such as encoded video data. In some examples, source device 102 and / or destination device 116 may include corresponding system-on-chip (SoC) devices. For example, source device 102 may include a SoC device to perform functions belonging to video encoder 200 and / or output interface 108, and destination device 116 may include a SoC device to perform functions belonging to video decoder 300 and / or input interface 122.

[0029] The techniques disclosed herein may be applied to video encoding and decoding to support any of a variety of multimedia applications, such as over-the-air television broadcasting, cable television transmission, satellite television transmission, Internet streaming video transmission such as Dynamic Adaptive Streaming over HTTP (DASH), digital video encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0030] 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 from the computer-readable medium 110 may include signaling information defined by the video encoder 200 (e.g., syntax elements with values ​​describing characteristics and / or processing of video blocks or other codec units (e.g., slices, pictures, groups of pictures, sequences, etc.) and the signaling information is also used by the video decoder 300. The display device 118 displays the decoded pictures of the decoded video data to the user. The display device 118 may represent any of a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode display (OLED), or another type of display device.

[0031] although Figure 1Not shown, in some examples, the video encoder 200 and the video decoder 300 may each be integrated with an audio encoder and / or an audio decoder, and may include appropriate MUX-DEMUX units, or other hardware and / or software, to process a multiplexed stream including both audio and video in a common data stream.

[0032] The video encoder 200 and the video decoder 300 can 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 combination thereof. When these techniques are partially implemented in software, the device can store the instructions of the software in a suitable non-temporary computer-readable medium, and use one or more processors to execute the instructions in hardware to perform the techniques of the present disclosure. Each of the video encoder 200 and the video decoder 300 can be included in one or more encoders or decoders, any of which can be integrated as part of a combined encoder / decoder (codec (CODEC)) in a corresponding device. The device including the video encoder 200 and / or the video decoder 300 can include an integrated circuit, a microprocessor, and / or a wireless communication device such as a cellular phone.

[0033] The video encoder 200 and the video decoder 300 may operate according to a video codec standard (e.g., ITU-T H.265, also known as High Efficiency Video Codec (HEVC), or an extension thereof, such as a multi-view and / or scalable video codec extension). Alternatively, the video encoder 200 and the video decoder 300 may operate according to other proprietary or industry standards (e.g., Joint Exploration Test Model (JEM) ITU-T H.266 (also known as Versatile Video Codec (VCC)). The latest draft of the VVC standard is found in Bross et al., “Versatile Video Coding (Draft 4)”, Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11, 13th Meeting: Marrakech, MA, January 9-18, 2019, JVET-M1001-v5 (hereinafter referred to as “VVC Draft 4”). However, the technology of the present disclosure is not limited to any particular codec standard.

[0034] Typically, the video encoder 200 and the video decoder 300 can perform block-based picture encoding and decoding. The term "block" generally refers to a structure that includes data to be processed (e.g., to be encoded, to be decoded, or otherwise used for encoding and / or decoding processes). For example, a block may include a two-dimensional matrix of samples of luminance and / or chrominance data. Typically, the video encoder 200 and the video decoder 300 can encode and decode video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, the video encoder 200 and the video decoder 300 can encode and decode luminance and chrominance components instead of encoding and decoding red, green, and blue (RGB) data of samples of a picture, where the chrominance components may include red hue and blue hue chrominance components. In some examples, the video encoder 200 converts the received RGB format data into a YUV representation before encoding, and the video decoder 300 converts the YUV representation into an RGB format. Alternatively, a pre-processing and post-processing unit (not shown) can perform these conversions.

[0035] The present disclosure may generally refer to the encoding and decoding of a picture (e.g., encoding and decoding) to include the process of encoding or decoding the data of a picture. Similarly, the present disclosure may refer to the encoding and decoding of a block of a picture to include the process of encoding or decoding the data of the block (e.g., prediction and / or residual encoding and decoding). The encoded video bitstream generally includes a series of values ​​of syntax elements that represent codec decisions (e.g., codec mode) and the partitioning of the picture into blocks. Therefore, references to encoding and decoding a picture or block should generally be understood as encoding and decoding the values ​​of the syntax elements that form the picture or block.

[0036] HEVC defines various blocks, including codec units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video codec (e.g., video encoder 200) partitions a codec tree unit (CTU) into CUs according to a quadtree structure. That is, the video codec partitions 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 child nodes may be referred to as a "leaf node," and the CU of such a leaf node may include one or more PUs, and / or one or more TUs. The video codec may further partition the PU and TU. For example, in HEVC, a residual quadtree (RQT) represents the partitioning of a TU. In HEVC, a PU represents inter-frame prediction data, and a TU represents residual data. An intra-predicted CU includes intra-frame prediction information such as an intra-frame mode indication.

[0037] As another example, the video encoder 200 and the video decoder 300 may be configured to operate according to JEM or VVC. According to JEM or VVC, a video encoder (e.g., video encoder 200) partitions a picture into multiple codec tree units (CTUs). The video encoder 200 may partition the CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure or a multi-type tree (MTT) structure. The QTBT structure removes the concept of multiple partition types (e.g., the separation between CU, PU, ​​and TU of HEVC). The QTBT structure includes two levels: a first level for partitioning according to quadtree partitioning, and a second level for partitioning according to binary tree partitioning. The root node of the QTBT structure corresponds to the CTU. The leaf nodes of the binary tree correspond to codec units (CUs).

[0038] In the MTT partitioning structure, blocks can be partitioned using quadtree (QT) partitioning, binary tree (BT) partitioning, and one or more types of ternary tree (TT) (also known as ternary tree (TT)) partitioning. Trinary or ternary tree partitioning is a partitioning in which a block is divided into three sub-blocks. In some examples, the ternary or ternary tree partitioning divides the block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT) can be symmetric or asymmetric.

[0039] In some examples, the video encoder 200 and the video decoder 300 may use a single QTBT or MTT structure to represent each of the luma and chroma components, while in other examples, the video encoder 200 and the video decoder 300 may use two or more QTBT or MTT structures, such as one QTBT / MTT structure for the luma component and another QTBT / MTT structure for the two chroma components (or two QTBT / MTT structures for corresponding chroma components).

[0040] The video encoder 200 and the video decoder 300 may be configured to use quadtree segmentation, QTBT segmentation, MTT segmentation, or other segmentation structures in accordance with HEVC. For purposes of explanation, the description of the disclosed technology is presented with respect to QTBT segmentation. However, it should be understood that the disclosed technology may also be applied to a video codec configured to use quadtree segmentation or other types of segmentation.

[0041] Blocks (e.g., CTUs or CUs) may be grouped in a picture in various ways. As an example, a brick may refer to a rectangular area of ​​a CTU row within a particular tile in a picture. A tile may be a rectangular area of ​​a CTU within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular area of ​​a CTU having a height equal to the picture height and a width specified by a syntax element (e.g., in a picture parameter set). A tile row refers to a rectangular area of ​​a CTU having a height specified by a syntax element (e.g., in a picture parameter set) and a width equal to the width of the picture.

[0042] In some examples, a tile may be partitioned into multiple bricks, each of which may include one or more CTU rows within the tile. A tile that is not partitioned into multiple bricks may also be referred to as a brick. However, a brick that is a proper subset of a tile cannot be referred to as a tile.

[0043] Tiles in a picture can also be arranged in slices. A slice can be an integer number of tiles of a picture that can be exclusively contained in a single network abstraction layer (NAL) unit. In some examples, a slice includes a continuous sequence of multiple complete tiles or only complete tiles of one tile.

[0044] The present disclosure may use "N×N" and "N by N" interchangeably to refer to the sample dimensions of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, for example, 16×16 samples or 16 by 16 samples. Typically, a 16×16 CU has 16 samples in the vertical direction (y=16) and 16 samples in the horizontal direction (x=16). Similarly, an N×N CU typically has N samples in the vertical direction and N samples in the horizontal direction, where N represents a non-negative integer value. The samples in a CU may be arranged in rows and columns. In addition, 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.

[0045] The video encoder 200 encodes the video data of the CU representing the prediction and / or residual information and other information. The prediction information indicates how to predict the CU in order to form the prediction block of the CU. The residual information generally indicates the sample-by-sample difference between the CU sample before encoding and the prediction block.

[0046] In order to predict a CU, the video encoder 200 may typically form a prediction block of the CU by inter-frame prediction or intra-frame prediction. Inter-frame prediction generally refers to predicting a CU from data of a previously encoded picture, while intra-frame prediction generally refers to predicting a CU from previously encoded data of the same picture. In order to perform inter-frame prediction, the video encoder 200 may use one or more motion vectors to generate a prediction block. The video encoder 200 may typically perform a motion search to identify a reference block that closely matches the CU, for example, based on the difference between the CU and the reference block. The video encoder 200 may calculate a difference metric using the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean square difference (MSD), or other such difference calculations to determine whether the reference block closely matches the current CU. In some examples, the video encoder 200 may use unidirectional prediction or bidirectional prediction to predict the current CU.

[0047] Some examples of JEM and VVC also provide an affine motion compensation mode, which can be considered an inter-frame prediction mode. In the affine motion compensation mode, the video encoder 200 can determine two or more motion vectors representing non-translational motion (e.g., zooming in or out, rotation, perspective motion, or other irregular motion types).

[0048] To perform intra prediction, the video encoder 200 can select an intra prediction mode to generate a prediction block. Some examples of JEM and VVC provide sixty-seven intra prediction modes, including various directional modes, as well as a planar mode and a DC mode. Typically, the video encoder 200 selects an intra prediction mode that describes a neighboring sample of a current block (e.g., a block of a CU), where the sample of the current block is predicted from the neighboring sample. Assuming that the video encoder 200 encodes and decodes CTUs and CUs in a raster scan order (from left to right, from top to bottom), such samples can typically be above, above left, or to the left of the current block in the same picture as the current block.

[0049] The video encoder 200 encodes data representing the prediction mode of the current block. For example, for inter-frame prediction mode, the video encoder 200 may encode data representing which of the various available inter-frame prediction modes is used and the motion information of the corresponding mode. For example, for unidirectional or bidirectional inter-frame prediction, the video encoder 200 may encode the motion vector using advanced motion vector prediction (AMVP) or merge mode. The video encoder 200 may use a similar mode to encode the motion vector of the affine motion compensation mode.

[0050] After prediction, such as intra-frame prediction or inter-frame prediction of a block, the video encoder 200 can calculate residual data for the block. Residual data such as a residual block represents the sample-by-sample difference between the block and the predicted block of the block formed using the corresponding prediction mode. The video encoder 200 can apply one or more transforms to the residual block to generate transformed data in a transform domain rather than a sample domain. For example, the video encoder 200 can apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to the residual video data. Additionally, the video encoder 200 can apply a secondary transform after the primary transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), etc. In some examples, as will be described below, the video encoder 200 can apply one or more sub-block transforms. The video encoder 200 generates transform coefficients after applying one or more transforms.

[0051] As described above, after any transform to produce coefficients, the video encoder 200 can perform quantization of the transform coefficients. Quantization generally refers to the process of quantizing the transform coefficients to minimize the amount of data used to represent the transform coefficients, thereby providing further compression. By performing the quantization process, the video encoder 200 can reduce the bit depth associated with some or all of the transform coefficients. For example, the video encoder 200 can round down an n-bit value to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, the video encoder 200 can perform a bit-by-bit right shift on the value to be quantized.

[0052] After quantization, the video encoder 200 can scan the transform coefficients to generate a one-dimensional vector from a two-dimensional matrix including the quantized transform coefficients. The scan can be designed to place the transform coefficients of higher energy (and therefore lower frequency) in front of the vector and the transform coefficients of lower energy (and therefore higher frequency) in the back of the vector. In some examples, the video encoder 200 can scan the quantized coefficients using a predefined scan order to generate a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, the video encoder 200 can perform adaptive scanning. After scanning the quantized coefficients to form a one-dimensional vector, the video encoder 200 can entropy encode the one-dimensional vector, for example, according to context adaptive binary arithmetic coding (CABAC). The video encoder 200 can also entropy encode the values ​​of the syntax elements describing the metadata associated with the encoded video data for use by the video decoder 300 in decoding the video data.

[0053] To perform CABAC, the video encoder 200 may assign context within a context model to a symbol to be transmitted. For example, the context may relate to whether the neighboring values ​​of the symbol are zero values. The probability determination may be based on the context assigned to the symbol.

[0054] The video encoder 200 may also generate syntax data (in a picture header, a block header, a slice header), such as block-based syntax data, picture-based syntax data, and sequence-based syntax data or other syntax data, such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS) to the video decoder 300. The video decoder 300 may also decode such syntax data to determine how to decode the corresponding video data.

[0055] In this way, the video encoder 200 can generate a bitstream that includes the encoded video data, such as syntax elements describing the partitioning of a picture into blocks (e.g., CUs) and prediction and / or residual information of the blocks. Finally, the video decoder 300 can receive the bitstream and decode the encoded video data.

[0056] In general, the video decoder 300 performs a process that is the reverse of the process performed by the video encoder 200 to decode the encoded video data of the bitstream. For example, the video decoder 300 may use CABAC to decode the values ​​of the syntax elements of the bitstream in a manner substantially similar to but reverse to the CABAC encoding process of the video encoder 200. The syntax elements may define partitioning information for partitioning a picture into CTUs and partitioning each CTU according to a corresponding partitioning structure (e.g., a QTBT structure) to define CUs of the CTU. The syntax elements may also define prediction and residual information for a block (e.g., a CU) of video data.

[0057] The residual information may be represented by, for example, quantized coefficients. The video decoder 300 may inverse quantize and inverse transform the quantized transform coefficients of the block to reproduce a residual block for the block. The video decoder 300 uses the signaled prediction mode (intra-frame or inter-frame prediction) and related prediction information (e.g., motion information for inter-frame 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 performing a deblocking process to reduce visual artifacts along block boundaries.

[0058] According to the technology of the present disclosure, the video encoder 200 and the video decoder 300 can be configured to determine the use of a sub-block transform mode for the block based on one or more of the width-to-height ratio or the height-to-width ratio of the block, and apply one or more transforms to the block based on the determination of using the sub-block transform mode. In another example, the video encoder 200 and the video decoder 300 can be configured to determine a transform for a sub-block transform mode (e.g., determine whether to use a transform replacement), wherein the transform is determined from a group including at least one of DCT-8, and DCT-2 and an identity transform, and encode and decode a sub-block of the block using the sub-block transform mode and the determined transform.

[0059] The present disclosure may generally refer to "signaling" certain information such as syntax elements. The term "signaling" may generally refer to the transmission of values ​​of syntax elements and / or other data used to decode encoded video data. That is, the video encoder 200 may signal the values ​​of syntax elements in a bitstream. Generally, signaling refers to generating values ​​in a bitstream. As described above, the source device 102 may transmit the bitstream to the destination device 116 in substantially real time, or (such as may occur when storing syntax elements to the storage device 112 for later retrieval by the destination device 116) transmit the bitstream to the destination device 116 in non-real time.

[0060] Figure 2A and Figure 2B is a conceptual diagram showing an example quadtree binary tree (QTBT) structure 130 and a corresponding codec tree unit (CTU) 132. Solid lines represent quadtree partitions and dashed lines indicate binary tree partitions. At each partition (i.e., non-leaf) node of the binary tree, a flag is signaled to indicate which partition type (i.e., horizontal or vertical) is used, where 0 indicates horizontal partitioning and 1 indicates vertical partitioning in this example. For quadtree partitioning, there is no need to indicate the partition type because the quadtree node divides the block horizontally and vertically into 4 sub-blocks of equal size. Therefore, the video encoder 200 can encode syntax elements (e.g., partition information) for the regional tree level (i.e., solid line) of the QTBT structure 130 and syntax elements (e.g., partition information) for the prediction tree level (i.e., dashed line) of the QTBT structure 130, and the video decoder 300 can decode it. The video encoder 200 may encode video data (eg, prediction and transform data) of a CU represented by a terminal leaf node of the QTBT structure 130 , and the video decoder 300 may decode it.

[0061] generally, Figure 2BThe CTU 132 may be associated with parameters defining the size of blocks corresponding to nodes of the QTBT structure 130 at the first level and the second level. These parameters may include a CTU size (indicating the size of the CTU 132 in a sample), a minimum quadtree size (MinQTSize, indicating the minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, indicating the maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, indicating the maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, indicating the minimum allowed binary tree leaf node size).

[0062] The root node of the QTBT structure corresponding to the CTU may have four child nodes at the first level of the QTBT structure, and each child node may be segmented according to the quadtree segmentation. That is, the nodes at the first level are either leaf nodes (without child nodes) or have four child nodes. The example of the QTBT structure 130 represents such a node as a child node including a parent node and a solid line for branching. If the nodes at the first level are not larger than the maximum allowed binary tree root node size (MaxBTSize), the nodes may be further segmented by the corresponding binary tree. The binary tree partitioning of a node may be iterated until the node generated by the partitioning reaches the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of the QTBT structure 130 represents such a node as having a dotted line for branching. The binary tree leaf node is called a codec unit (CU), which is used for prediction (e.g., intra-picture or inter-picture prediction) and transformation without any further segmentation. As described above, a CU may also be referred to as a "video block" or "block".

[0063] In one example of a QTBT partitioning structure, the CTU size is set to 128×128 (luminance sample and two corresponding 64×64 chrominance samples), MinQTSize is set to 16×16, MaxBTSize is set to 64×64, MinBTSize (for both width and height) is set to 4, and MaxBTDepth is set to 4. Quadtree partitioning is first applied to the CTU to generate a quadtree leaf node. The quadtree leaf node can have a size from 16×16 (i.e., MinQTSize) to 128×128 (i.e., CTU size). If the quadtree leaf node is 128×128, the quadtree leaf node will not be further divided by the binary tree because its size exceeds MaxBTSize (i.e., 64×64 in this example). Otherwise, the quadtree leaf node will be further divided by the binary tree. Therefore, the quadtree leaf node is also the root node of the binary tree and has a binary tree depth of 0. When the binary tree depth reaches MaxBTDepth (4 in this case), no further splitting is allowed. A binary tree node with a width equal to MinBTSize (4 in this case) means that no further horizontal splitting is allowed. Similarly, a binary tree node with a height equal to MinBTSize means that no further vertical splitting is allowed for the binary tree node. As described above, the leaf nodes of the binary tree are called CUs and are further processed according to prediction and transformation without further segmentation.

[0064] Figure 3 is a block diagram illustrating an example video encoder 200 that may perform the disclosed techniques for sub-block transform. Figure 3 The present disclosure is provided for the purpose of explanation and should not be considered as limiting the techniques broadly illustrated and described in the present disclosure. For the purpose of explanation, the present disclosure describes the video encoder 200 in the context of video codec standards such as the HEVC video codec standard and the H.266 video codec standard under development. However, the techniques of the present disclosure are not limited to these video codec standards and are generally applicable to video encoding and decoding.

[0065] exist Figure 3In the example of , 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. Any or all of the video data memory 230, the mode selection unit 202, the residual generation unit 204, the transform processing unit 206, the quantization unit 208, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the filter unit 216, the DPB 218, and the entropy coding unit 220 may be implemented in one or more processors or processing circuits. In addition, the video encoder 200 may include additional or alternative processors or processing circuits to perform these and other functions.

[0066] The video data memory 230 may store video data to be encoded by the components of the video encoder 200. The video encoder 200 may receive video data from, for example, the video source 104 ( Figure 1 ) receives the video data stored in the video data memory 230. DPB 218 can act as a reference picture memory, which stores reference video data for use when the video encoder 200 predicts subsequent video data. Video data memory 230 and DPB 218 can be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM) (including synchronous DRAM (SDRAM)), magnetoresistive RAM (MRAM), resistive RAM (RRAM) or other types of memory devices. Video data memory 230 and DPB218 can be provided by the same memory device or a separate memory device. In various examples, as shown in the figure, video data memory 230 can be on the chip with other components of the video encoder 200, or off the chip relative to these components.

[0067] In the present disclosure, references to the video data memory 230 should not be interpreted as limited to memory internal to the video encoder 200, unless specifically described as such, or to memory external to the video encoder 200, unless specifically described as such. Instead, references to the video data memory 230 should be understood as references to memory storing video data received by the video encoder 200 for encoding (e.g., video data of a current block to be encoded). Figure 1 The memory 106 may also provide temporary storage of outputs from the various units of the video encoder 200 .

[0068] Figure 3Various units are shown to help understand the operations performed by the video encoder 200. These units can be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide specific functions and are preset on operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functions in operations that can be performed. For example, a programmable circuit can execute software or firmware so that the programmable circuit operates in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally 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 units may be integrated circuits.

[0069] The video encoder 200 may include an arithmetic logic unit (ALU), an elementary function unit (EFU), a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video encoder 200 is performed using software executed by a programmable circuit, the memory 106 ( Figure 1 ) may store object code for software received and executed by the video encoder 200, or another memory (not shown) within the video encoder 200 may store such instructions.

[0070] The video data memory 230 is configured to store the received video data. The video encoder 200 may retrieve the picture of the 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 the video data memory 230 may be the original video data to be encoded.

[0071] The mode selection unit 202 includes a motion estimation unit 222, a motion compensation unit 224, and an intra prediction unit 226. The mode selection unit 202 may include additional functional units to perform video prediction according to other prediction modes. As an example, the mode selection unit 202 may include a palette unit, an 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, etc.

[0072] The mode selection unit 202 typically coordinates multiple encoding passes to test combinations of encoding parameters and rate-distortion values ​​of the results of such combinations. The encoding parameters may include the partitioning of CTUs into CUs, the prediction mode of the CUs, the transform type of the residual data of the CUs, the quantization parameter of the residual data of the CUs, etc. The mode selection unit 202 may ultimately select a combination of encoding parameters that has a better rate-distortion value than other tested combinations.

[0073] The video encoder 200 may partition the picture retrieved from the video data memory 230 into a series of CTUs and encapsulate one or more CTUs in a slice. The mode selection unit 202 may partition the CTUs of the picture according to a tree structure (e.g., the QTBT structure or quadtree structure of HEVC described above). As described above, the video encoder 200 may form one or more CUs from the partitioned CTUs according to the tree structure. Such CUs may also be generally referred to as "video blocks" or "blocks".

[0074] Typically, the mode selection unit 202 also controls its components (e.g., the motion estimation unit 222, the motion compensation unit 224, and the intra prediction unit 226) to generate a prediction block for the current block (e.g., the current CU, or in HEVC, the overlapping portion of the PU and TU). For inter prediction of the current block, the motion estimation unit 222 can 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 encoded pictures stored in the DPB 218). Specifically, the motion estimation unit 222 can calculate a value indicating how similar the potential reference block is to the current block, for example, based on the sum of absolute differences (SAD), the sum of squared differences (SSD), the mean absolute difference (MAD), the mean squared difference (MSD), etc. The motion estimation unit 222 can generally perform these calculations using the sample-by-sample difference between the current block and the reference block under consideration. The motion estimation unit 222 can identify the reference block having the lowest value obtained from these calculations, which indicates the reference block that most closely matches the current block.

[0075] The 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 the position of a current block in a current picture. The motion estimation unit 222 may then provide the motion vectors to the motion compensation unit 224. For example, for unidirectional inter prediction, the motion estimation unit 222 may provide a single motion vector, and for bidirectional inter prediction, the motion estimation unit 222 may provide two motion vectors. The motion compensation unit 224 may then use the motion vectors to generate a prediction block. For example, the motion compensation unit 224 may use the motion vectors to retrieve data for the reference block. As another example, if the motion vectors have fractional sample precision, the motion compensation unit 224 may interpolate the values ​​of the prediction block according to one or more interpolation filters. In addition, for bidirectional inter prediction, the motion compensation unit 224 may retrieve data for two reference blocks identified by the corresponding motion vectors and combine the retrieved data by, for example, sample-by-sample averaging or weighted averaging.

[0076] As another example, for intra prediction or intra prediction codec, the intra prediction unit 226 can generate a prediction block from samples adjacent to the current block. For example, for directional mode, the intra prediction unit 226 can generally mathematically combine the values ​​of the adjacent 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 can calculate the average of the adjacent samples of the current block and generate a prediction block to include the resulting average for each sample of the prediction block.

[0077] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives the original, uncoded version of the current block from the video data memory 230 and receives the prediction block from the mode selection unit 202. The residual generation unit 204 calculates the sample-by-sample difference between the current block and the prediction block. The resulting sample-by-sample difference defines a residual block for the current block. In some examples, the residual generation unit 204 may also determine the difference between the sample values ​​in the residual block to generate the residual block using residual differential pulse code modulation (RDPCM). In some examples, the residual generation unit 204 may be formed using one or more subtractor circuits that perform binary subtraction.

[0078] In the example where the mode selection unit 202 partitions the 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 of various sizes. As described above, the size of the CU may refer to the size of the luma codec block of the CU, and the size of the PU may refer to the size of the luma prediction unit of the PU. Assuming that the size of a particular CU is 2N×2N, the video encoder 200 may support PU sizes of 2N×2N or N×N for intra-frame prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N or the like for inter-frame prediction. The video encoder 200 and the video decoder 300 may also support asymmetric partitioning of PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter-frame prediction.

[0079] In an example where the mode selection unit 202 does not further partition 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 300 may support a CU size of 2N×2N, 2N×N, or N×2N.

[0080] 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, the mode selection unit 202 generates a prediction block for the current block being encoded via a corresponding unit associated with the codec technique. In some examples, such as palette mode codec, the mode selection unit 202 may not generate a prediction block, but instead generate syntax elements indicating how to reconstruct the block based on the selected palette. In this mode, the mode selection unit 202 may provide these syntax elements to the entropy coding unit 220 for encoding.

[0081] As described above, the residual generation unit 204 receives video data of a current block and a 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 the sample-by-sample difference between the prediction block and the current block.

[0082] The 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"). The transform processing unit 206 can apply various transforms to the residual block to form the transform coefficient block. For example, the transform processing unit 206 can apply a discrete cosine transform (DCT), a directional transform, a Karl-Lof transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 can perform multiple transforms on the residual block, such as a primary transform and a secondary transform (e.g., a rotation transform). In some examples, the transform processing unit 206 does not apply a transform to the residual block.

[0083] As will be described in more detail below, the transform processing unit 206 may apply one or more transforms to the residual block using a sub-block transform mode. In the sub-block transform mode, the transform processing unit 206 may divide the residual block into two sub-blocks. In one example, for the vertical sub-block transform mode, the transform processing unit 206 divides the residual block into two vertical sub-blocks. In some examples, the two vertical sub-blocks have a width of 1 / 2 the width of the residual block. In other examples, the two vertical sub-blocks have a width of 1 / 4 the width of the residual block and a width of 3 / 4 the width of the residual block, respectively. In other examples, different divisions of the residual block into sub-blocks may be used. The transform processing unit 206 may then apply one or more transforms to the vertical sub-blocks.

[0084] In other examples, for the horizontal sub-block transform mode, the transform processing unit 206 divides the residual block into two horizontal sub-blocks. In some examples, the two horizontal sub-blocks have a height of 1 / 2 the height of the residual block. In other examples, the two horizontal sub-blocks have a height of 1 / 4 the height of the residual block and 3 / 4 the height of the residual block, respectively. In other examples, different divisions of the residual block into sub-blocks can be used. The transform processing unit 206 can then apply one or more transforms to the horizontal sub-blocks.

[0085] According to the technology of the present disclosure, the transform processing unit 206 may be configured to determine whether to apply a sub-block transform mode to the residual block based on the width and height of the residual block. For example, the transform processing unit 206 may be configured to determine whether to use a sub-block transform mode for the block based on one or more of the aspect ratio or the height-to-width ratio of the block, and apply one or more transforms to the block based on the determination of using the sub-block transform mode. For the vertical sub-block transform mode (vertical sub-block transform mode, SBT-V), the transform processing unit 206 may be configured to determine not to use the vertical sub-block transform mode (SBT-V) when the aspect ratio of the block is less than a first threshold. In this case, the transform processing unit 206 may apply one or more transforms to the entire residual block. When the aspect ratio of the block is greater than or equal to the first threshold, the transform processing unit 206 may divide the block into two vertical sub-blocks and apply one or more transforms to the sub-blocks.

[0086] Similarly, for the horizontal sub-block transform mode (SBT-H), the transform processing unit 206 may be configured to determine not to use the horizontal sub-block transform mode (SBT-H) when the aspect ratio of the block is less than the second threshold. In this case, the transform processing unit 206 may apply one or more transforms to the entire residual block. When the aspect ratio of the block is greater than or equal to the second threshold, the transform processing unit 206 may divide the block into two horizontal sub-blocks and apply one or more transforms to the sub-blocks.

[0087] The quantization unit 208 may quantize the transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 may quantize the transform coefficients in the transform coefficient block according to a quantization parameter (QP) value associated with the current block. The video encoder 200 (e.g., via the mode selection unit 202) may adjust the degree of quantization applied to the coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce information loss, and therefore, the quantized transform coefficients may have lower precision than the original transform coefficients produced by the transform processing unit 206.

[0088] The inverse quantization unit 210 and the inverse transform processing unit 212 may apply inverse quantization and inverse transform to the quantized transform coefficient block, respectively, 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 it may have a certain 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 of the prediction block generated by the free mode selection unit 202 to generate a reconstructed block.

[0089] Filter unit 216 may perform one or more filtering operations on the reconstructed blocks. For example, filter unit 216 may perform a deblocking operation to reduce blocking artifacts along CU edges. In some examples, the operations of filter unit 216 may be skipped.

[0090] The video encoder 200 stores the reconstructed block in the DPB 218. For example, in an example where the operation of the filter unit 216 is not performed, the reconstruction unit 214 can store the reconstructed block to the DPB 218. In an example where the operation of the filter unit 216 is performed, the filter unit 216 can store the filtered reconstructed block to the DPB 218. The motion estimation unit 222 and the motion compensation unit 224 can retrieve a reference picture from the DPB 218, which is formed by the reconstructed (and possibly filtered) block to perform inter-frame prediction on a block of a subsequently encoded picture. In addition, the intra-frame prediction unit 226 can use the reconstructed block of the current picture in the DPB 218 to intra-frame predict other blocks in the current picture.

[0091] In general, the entropy coding unit 220 may entropy encode syntax elements received from other functional components of the video encoder 200. For example, the entropy coding unit 220 may entropy encode the quantized transform coefficient blocks from the quantization unit 208. As another example, the entropy coding unit 220 may entropy encode the prediction syntax elements (e.g., motion information for inter prediction or intra mode information for intra prediction) from the mode selection unit 202. The entropy coding unit 220 may perform one or more entropy coding operations on the syntax elements as another example of video data to generate entropy-encoded data. For example, the entropy coding 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 coding operation on the data. In some examples, entropy encoding unit 220 may operate in a bypass mode, where syntax elements are not entropy encoded.

[0092] The video encoder 200 may output a bitstream including entropy-encoded syntax elements required to reconstruct a block of a slice or a picture. Specifically, the entropy encoding unit 220 may output a bitstream.

[0093] The operations described above are described with respect to blocks. Such descriptions should be understood as operations for luma codec blocks and / or chroma codec blocks. As described above, in some examples, the luma codec blocks and chroma codec blocks are the luma and chroma components of a CU. In some examples, the luma codec blocks and chroma codec blocks are the luma and chroma components of a PU.

[0094] In some examples, operations performed on luma codec blocks need not be repeated for chroma codec blocks. As an example, operations to identify motion vectors (MVs) and reference pictures for luma codec blocks need not be repeated for identifying MVs and reference pictures for chroma blocks. Instead, the MVs of luma codec blocks may be scaled to determine the MVs of chroma blocks, and the reference pictures may be the same. As another example, the intra prediction process may be the same for luma codec blocks and chroma codec blocks.

[0095] The video encoder 200 represents an example of a device configured to encode video data, the device including a memory configured to store the video data, and one or more processing units implemented in circuitry and configured to determine a transform for a sub-block transform mode (e.g., determine whether to use a transform alternative), wherein the transform is determined from a group including DCT-8, and at least one of DCT-2 and an identity transform, and encode and decode sub-blocks of a block using the sub-block transform mode and the determined transform. In other examples, the video encoder 200 may be configured to determine to use a sub-block transform mode for a block based on one or more of an aspect ratio or a height-to-width ratio of the block, and to apply one or more transforms to the block based on the determination to use the sub-block transform mode.

[0096] Figure 4 is a block diagram illustrating an example video decoder 300 that may perform the disclosed techniques for sub-block transforms. Figure 4 The present disclosure is provided for the purpose of explanation and does not limit the techniques widely illustrated and described in the present disclosure. For the purpose of explanation, the present disclosure describes a video decoder 300 according to the technical descriptions of JEM, VVC, and HEVC. However, the techniques of the present disclosure can be performed by video codec devices configured to other video codec standards.

[0097] exist Figure 4In the example of , 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. Any or all of the CPB memory 320, the entropy decoding unit 302, the prediction processing unit 304, the inverse quantization unit 306, the inverse transform processing unit 308, the reconstruction unit 310, the filter unit 312, and the DPB 314 may be implemented in one or more processors or processing circuits. In addition, the video decoder 300 may include additional or alternative processors or processing circuits to perform these and other functions.

[0098] The prediction processing unit 304 includes a motion compensation unit 316 and an intra prediction unit 318. The prediction processing unit 304 may include additional units to perform predictions 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, etc. In other examples, the video decoder 300 may include more, fewer, or different functional components.

[0099] The CPB memory 320 may store video data, such as an encoded video bitstream, to be decoded by components of the video decoder 300. For example, the video data stored in the CPB memory 320 may be, for example, from the computer readable medium 110 ( Figure 1 ). The CPB memory 320 may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. In addition, the CPB memory 320 may store video data other than syntax elements of encoded and decoded pictures, such as temporary data representing outputs from various units of the video decoder 300. The DPB 314 typically stores decoded pictures, which may be output and / or used as reference video data when the video decoder 300 decodes subsequent data or pictures of the encoded video bitstream. The CPB memory 320 and the DPB 314 may be formed by any of a variety of memory devices, such as DRAM (including SDRAM), MRAM, RRAM, or other types of memory devices. The CPB memory 320 and the DPB 314 may be provided by the same memory device or by 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 relative to these components.

[0100] Additionally or alternatively, in some examples, video decoder 300 may retrieve the video from memory 120 ( Figure 1) retrieves the encoded and decoded video data. That is, the memory 120 may utilize the CPB memory 320 to store data as described above. Similarly, when some or all of the functions of the video decoder 300 are implemented in software to be executed by the processing circuitry of the video decoder 300, the memory 120 may store instructions to be executed by the video decoder 300.

[0101] Figure 4 The various units shown 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. Figure 3 , fixed-function circuits refer to circuits that provide specific functions and are preset on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functions in the operations that can be performed. For example, a programmable circuit can execute software or firmware so that the programmable circuit operates in a manner defined by the instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., receive parameters or output parameters), but the type of operation performed by the fixed-function circuit is generally 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 units may be integrated circuits.

[0102] The video decoder 300 may include an ALU, an EFU, a digital circuit, an analog circuit, and / or a programmable core formed by a programmable circuit. In an example where the operation of the video decoder 300 is performed by software executed on a programmable circuit, an on-chip or off-chip memory may store instructions (e.g., object code) of the software received and executed by the video decoder 300.

[0103] The entropy decoding unit 302 may receive the encoded video data from the CPB and entropy decode the video data to reproduce the syntax elements. 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 the syntax elements extracted from the bitstream.

[0104] Typically, the video decoder 300 reconstructs a picture on a block-by-block basis. The video decoder 300 may perform a reconstruction operation on each block individually (where the block currently being reconstructed (ie, decoded) may be referred to as a "current block").

[0105] The entropy decoding unit 302 may entropy decode syntax elements defining quantized transform coefficients of the quantized transform coefficient block, and transform information, such as a quantization parameter (QP) and / or (multiple) transform mode indications. The inverse quantization unit 306 may use the QP associated with the quantized transform coefficient block to determine a degree of quantization, and similarly, determine a degree of inverse quantization to be applied by the inverse quantization unit 306. For example, the inverse quantization unit 306 may perform a bitwise left shift operation to inverse quantize the quantized transform coefficients. The inverse quantization unit 306 may thereby form a transform coefficient block including the transform coefficients.

[0106] After the inverse quantization unit 306 forms the transform coefficient block, the 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 Karl-Lof transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the coefficient block.

[0107] As will be described in more detail below, the inverse transform processing unit 308 may apply one or more transforms (e.g., inverse transforms) to the transform coefficient block using a sub-block transform mode. In the sub-block transform mode, the inverse transform processing unit 308 may divide the transform coefficient block into two sub-blocks. In one example, for the vertical sub-block transform mode, the inverse transform processing unit 308 divides the transform coefficient block into two vertical sub-blocks. In some examples, the two vertical sub-blocks have a width of 1 / 2 the width of the transform coefficient block. In other examples, the two vertical sub-blocks have a width of 1 / 4 the width of the transform coefficient block and a width of 3 / 4 the width of the transform coefficient block, respectively. In other examples, different partitions of the transform coefficient block into sub-blocks may be used. The inverse transform processing unit 308 may then apply one or more inverse transforms to the vertical sub-blocks.

[0108] In other examples, for the horizontal sub-block transform mode, the inverse transform processing unit 308 divides the transform coefficient block into two horizontal sub-blocks. In some examples, the two horizontal sub-blocks have a height of 1 / 2 the height of the transform coefficient block. In other examples, the two horizontal sub-blocks have a height of 1 / 4 the height of the transform coefficient block and 3 / 4 the height of the transform coefficient block, respectively. In other examples, different divisions of the transform coefficient block into sub-blocks may be used. The inverse transform processing unit 308 may then apply one or more inverse transforms to the horizontal sub-blocks.

[0109] According to the techniques of this disclosure, inverse transform processing unit 308 may be configured to determine whether to apply a sub-block transform mode to a transform coefficient block based on the width and height of the transform coefficient block. For example, inverse transform processing unit 308 may be configured to determine to use a sub-block transform mode for a block based on one or more of an aspect ratio or a height-to-width ratio of the block, and to apply one or more transforms to the block based on the determination to use the sub-block transform mode.

[0110] For the vertical sub-block transform mode (SBT-V), the inverse transform processing unit 308 may be configured to determine not to use the vertical sub-block transform mode (SBT-V) when the aspect ratio of the block is less than a first threshold. In this case, the inverse transform processing unit 308 may apply one or more transforms to the entire transform coefficient block. When the aspect ratio of the block is greater than or equal to the first threshold, the inverse transform processing unit 308 may divide the block into two vertical sub-blocks and apply one or more inverse transforms to the sub-blocks.

[0111] Similarly, for the horizontal sub-block transform mode (SBT-H), the inverse transform processing unit 308 can be configured to determine not to use the horizontal sub-block transform mode (SBT-H) when the aspect ratio of the block is less than the second threshold. In this case, the inverse transform processing unit 308 can apply one or more transforms to the entire transform coefficient block. When the aspect ratio of the block is greater than or equal to the second threshold, the inverse transform processing unit 308 can divide the block into two horizontal sub-blocks and apply one or more inverse transforms to the sub-blocks.

[0112] In addition, prediction processing unit 304 generates a prediction block based on the prediction information syntax element entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax element indicates that the current block is inter-predicted, motion compensation unit 316 can generate the prediction block. In this case, the prediction information syntax element can indicate a reference picture in DPB 314 from which the reference block is retrieved, and a motion vector that identifies the position of the reference block in the reference picture relative to the position of the current block in the current picture. Motion compensation unit 316 can generally generate a prediction block in a manner substantially similar to that described with respect to motion compensation unit 224 ( Figure 3 ) describes the method to perform the inter-frame prediction process.

[0113] As another example, if the prediction information syntax element indicates that the current block is intra-predicted, the intra-prediction unit 318 can generate a prediction block according to the intra-prediction mode indicated by the prediction information syntax element. Likewise, the intra-prediction unit 318 can generally generate a prediction block in a manner substantially similar to that described with respect to the intra-prediction unit 226 ( Figure 3 The intra prediction process is performed in the manner described in ). The intra prediction unit 318 can retrieve the data of the neighboring samples of the current block from the DPB 314.

[0114] 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.

[0115] The filter unit 312 may perform one or more filtering operations on the reconstructed block. For example, the filter unit 312 may perform a deblocking operation to reduce blocking artifacts along the edges of the reconstructed block. The operations of the filter unit 312 need not be performed in all examples.

[0116] The video decoder 300 may store the reconstructed blocks in the DPB 314. As described above, the DPB 314 may provide reference information to the prediction processing unit 304, such as samples of the current image for intra-frame prediction and previously decoded pictures for subsequent motion compensation. In addition, the video decoder 300 may output decoded images from the DPB for subsequent display on a display device (e.g., Figure 1 The display device 118) is presented.

[0117] In this manner, the 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 determine a transform for a sub-block transform mode (e.g., determine whether to use a transform alternative), wherein the transform is determined from a group including DCT-8, and at least one of DCT-2 and an identity transform, and to encode and decode a sub-block of a block using the sub-block transform mode and the determined transform. In other examples, the video decoder 300 may be configured to determine to use a sub-block transform mode for a block based on one or more of an aspect ratio or a height-to-width ratio of the block, and to apply one or more transforms to the block based on the determination to use the sub-block transform mode.

[0118] In VVC Test Model 4 (VTM4) and VVC Draft 4, the sub-block transform (SBT) mode is adopted to improve codec efficiency. An example of the SBT mode is described in Y. Zhao et al., "CE6: Sub-block transform for inter blocks (CE6.4.1)", Joint Video Experts Group (JVET) of ITU-T SG 16WP 3 and ISO / IEC JTC 1 / SC 29 / WG 11, 13th Meeting, Massachusetts, MA, January 9-18, 2019, JVET-M0140.

[0119] For an inter-predicted block (e.g., CU) with the codec block flag (cu_cbf_flag) equal to 1, a sub-block transform flag (cu_sbt_flag) may be signaled to indicate whether the entire residual block or a sub-portion of the residual block is decoded. cu_cbf_flag equal to 1 indicates that the block includes non-zero transform coefficients. cu_sbt_flag indicates whether SBT mode is used. For example, a value of cu_sbt_flag equal to 1 specifies that for the current block (e.g., codec unit), sub-block transform mode is used. A value of cu_sbt_flag equal to 0 specifies that for the current block (e.g., codec unit), sub-block transform mode is not used.

[0120] Figure 5 is a conceptual diagram showing sub-block transform modes SBT-V (vertical sub-block transform mode) and SBT-H (horizontal sub-block transform mode). Figure 5 As shown, there are two SBT types (vertical and horizontal) and two SBT positions (e.g., two SBT sub-blocks at position 0 and position 1). For SBT-V (or SBT-H), the TU width (or height) can be equal to half of the CU width (or height) or 1 / 4 of the CU width (or height), signaled by another flag. This results in a 2:2 partition or a 1:3 / 3:1 partition. The 2:2 partition is like a binary tree (BT) partition, while the 1:3 / 3:1 partition is like an asymmetric binary tree (ABT) partition.

[0121] Figure 5 Blocks 500, 510, 520, and 530 are shown for various SBT types and locations. In the context of video encoding, blocks 500, 510, 520, and 530 are residual blocks created after inter-frame prediction. In the context of video decoding, blocks 500, 510, 520, and 530 are transform coefficient blocks to which inverse transforms are applied to reconstruct the residual blocks. The residual blocks are then decoded using inter-frame prediction.

[0122] exist Figure 5 , block 500 is an inter-predicted block encoded and decoded using SBT-V mode at position 0. Block 500 has a width w. Sub-block 502 is an SBT-V sub-block located at position 0. Sub-block 502 has a sub-block width of w1, where w1 is half (1 / 2) or one quarter (1 / 4) of the width of block 500. Sub-block 504 has a sub-block width of (w-w1). In one example, the video encoder 200 may apply horizontal DCT-8 and vertical DST-7 to sub-block 502. Similarly, the video decoder 300 may apply inverse horizontal DCT-8 and inverse vertical DST-7 to sub-block 502. The video encoder 200 and the video decoder 300 do not apply a transform to sub-block 504. Typically, an unencoded sub-block (i.e., a sub-block to which a transform is not applied) does not include any non-zero transform coefficients.

[0123] Block 510 is an inter-predicted block encoded and decoded using SBT-V mode at position 1. Block 510 has a width w. Subblock 512 is an SBT-V subblock at position 1. Subblock 512 has a subblock width of w1, where w1 is half (1 / 2) or one quarter (1 / 4) of the width of block 510. Subblock 514 has a subblock width of (w-w1). In one example, the video encoder 200 may apply horizontal DST-7 and vertical DST-7 to subblock 512. Similarly, the video decoder 300 may apply inverse horizontal DST-7 and inverse vertical DST-7 to subblock 512. The video encoder 200 and the video decoder 300 do not apply a transform to subblock 514.

[0124] Block 520 is an inter-predicted block encoded and decoded using SBT-H mode at position 0. Block 520 has a height h. Sub-block 522 is an SBT-H sub-block located at position 0. Sub-block 522 has a sub-block height of h1, where h1 is half (1 / 2) or one quarter (1 / 4) of the height of block 520. Sub-block 524 has a sub-block height of (h-h1). In one example, the video encoder 200 may apply horizontal DST-7 and vertical DCT-8 to sub-block 522. Similarly, the video decoder 300 may apply inverse horizontal DST-7 and inverse vertical DCT-8 to sub-block 522. The video encoder 200 and the video decoder 300 do not apply a transform to sub-block 524.

[0125] Block 530 is an inter-predicted block encoded and decoded using SBT-H mode at position 1. Block 530 has a height h. Sub-block 532 is an SBT-H sub-block at position 1. Sub-block 532 has a sub-block height of h1, where h1 is half (1 / 2) or one quarter (1 / 4) of the height of block 530. Sub-block 534 has a sub-block height of (h-h1). In one example, the video encoder 200 may apply horizontal DST-7 and vertical DST-7 to sub-block 532. Similarly, the video decoder 300 may apply inverse horizontal DST-7 and inverse vertical DST-7 to sub-block 532. The video encoder 200 and the video decoder 300 do not apply a transform to sub-block 534.

[0126] like Figure 5 As shown, the video encoder 200 and the video decoder 300 can apply position-dependent transforms to the luma transform block in SBT-V mode and SBT-H mode. In some examples, the video encoder 200 and the video decoder 300 use DCT-2 transforms for chroma components. The two positions (e.g., position 0 and position 1) of SBT-H and SBT-V are associated with different core transforms. More specifically, Figure 5The horizontal and vertical transforms for each SBT position are specified in . For example, the horizontal and vertical transforms for SBT-V position 0 are DCT-8 and DST-7, respectively. In some examples, when one side of the residual TU is greater than 32, the corresponding transform is set to DCT-2.

[0127] The present disclosure describes the following techniques for applying the SBT mode to blocks of video data. The techniques of the present disclosure are not limited to blocks of interframe prediction, but can be used together with blocks encoded and decoded with any prediction technique in which the SBT mode is desired to be applied. The following techniques can improve coding efficiency and / or can simplify encoder and decoder implementations. The following techniques can be applied alone or in any combination.

[0128] In one example, the present disclosure proposes to replace DCT-8 with other transform kernels in SBT-V and / or SBT-H modes. For example, the video encoder 200 and the video decoder 300 may be configured to use an identity transform (IDT) or DCT-2 instead of DCT-8 for one or more SBT types and / or SBT positions. In one example, the video encoder 200 and the video decoder 300 may replace DCT-8 with another transform (e.g., IDT or DCT-2) only for SBT-V or only for SBT-H. In another example, the video encoder 200 and the video decoder 300 may replace DCT-8 with another transform (e.g., IDT or DCT-2) for both SBT-V and SBT-H.

[0129] In one example, the video encoder 200 and the video decoder 300 may encode and decode (i.e., encode and decode) one or more of a sequence level flag, a picture level flag, a slice level flag, and / or a tile group level flag to indicate and determine whether an alternative transform (e.g., an IDT transform or DCT-2) is applied.

[0130] In another example, the video encoder 200 and the video decoder 300 may apply an alternative transform (eg, IDT or DCT-2) to blocks matching certain conditions (eg, the size and / or number of non-zero quantized transform coefficients).

[0131] In another example of the present disclosure, for each block and / or vertical transform or horizontal transform, the video encoder 200 can be configured to signal which transform kernel (e.g., DST-7, DCT-8, DCT-2, IDT, etc.) is applied. In one example, the video encoder 200 can signal the transform kernel using syntax for signaling inter-frame multiple transform sets (MTS) and transform skips (TS). The video decoder 300 can be configured to receive such syntax and determine the transform kernel to use.

[0132] In another example of the present disclosure, the video encoder 200 and the video decoder 300 are configured to not apply SBT-V (2:2 and / or 1:3 SBT-V) when the aspect ratio of the block is less than a threshold. The threshold may be a fixed value or signaled at one or more levels of the sequence / picture / slice / tile group level.

[0133] In another example of the present disclosure, the video encoder 200 and the video decoder 300 are configured to not apply SBT-H (2:2 and / or 1:3 SBT-H) when the aspect ratio of the block is less than a threshold. The threshold may be a fixed value or may be signaled at one or more levels of the sequence / picture / slice / tile group level.

[0134] Therefore, in one example of the present disclosure, the video encoder 200 and the video decoder 300 are configured to determine to use a sub-block transform mode (e.g., SBT-V and / or SBT-H) for a block based on one or more of an aspect ratio or a height-to-width ratio of the block, and to apply one or more transforms to the block based on the determination to use the sub-block transform mode.

[0135] In the context of the present disclosure, for video encoding, a block is a residual block generated by a prediction process (e.g., inter, intra, or other). For video decoding, a block is a transform coefficient block (e.g., transform coefficients associated with the block) to be reconstructed using a prediction process (e.g., inter, intra, or other).

[0136] In one example, the video encoder 200 and the video decoder 300 may be configured to determine the use of a vertical sub-block transform mode (SBT-V) based on the aspect ratio of the block. The video encoder 200 and the video decoder 300 may be configured to determine not to use a vertical sub-block transform mode (SBT-V) when the aspect ratio of the block is less than a first threshold. In this case, the video encoder 200 and the video decoder 300 may apply one or more transforms to the entire block. Conversely, the video encoder 200 and the video decoder 300 may be configured to determine the use of a vertical sub-block transform mode (SBT-V) when the aspect ratio of the block is greater than or equal to a first threshold. In this case, as described above, the video encoder 200 and the video decoder 300 may apply one or more transforms to a sub-block of the block (e.g., at position 0 or position 1). The video encoder 200 and the video decoder 300 may be configured to encode and decode the first threshold at one or more levels of a sequence level, a picture level, a slice level, or a tile group level.

[0137] In another example, the video encoder 200 and the video decoder 300 may be configured to determine the use of a horizontal sub-block transform mode (SBT-H) based on the aspect ratio of the block. The video encoder 200 and the video decoder 300 may be configured to determine not to use the horizontal sub-block transform mode (SBT-H) when the aspect ratio of the block is less than a second threshold. In this case, the video encoder 200 and the video decoder 300 may apply one or more transforms to the entire block. Conversely, the video encoder 200 and the video decoder 300 may be configured to determine the use of a horizontal sub-block transform mode (SBT-H) when the height-to-width ratio of the block is greater than or equal to the second threshold. In this case, as described above, the video encoder 200 and the video decoder 300 may apply one or more transforms to a sub-block of the block (e.g., at position 0 or position 1). The video encoder 200 and the video decoder 300 may be configured to encode and decode the second threshold at one or more levels of a sequence level, a picture level, a slice level, or a tile group level.

[0138] As described above, in the context of the present disclosure, for video encoding, a block is a residual block generated by a prediction process. For video decoding, a block is a transform coefficient block (e.g., a transform coefficient associated with the block) to be reconstructed using a prediction process. Therefore, for video encoding, the video encoder 200 can be configured to encode the block using a prediction process to create a residual block, and apply one or more transforms to the residual block based on a determination using a sub-block transform mode. Similarly, for video decoding, the video decoder 300 can be configured to apply one or more inverse transforms to the transform coefficients associated with the block based on a determination using a sub-block transform mode to create a residual block, and perform a prediction process on the residual block to reconstruct the block.

[0139] In other examples, the video encoder 200 and the video decoder 300 may be configured to determine a transform for a sub-block transform mode (e.g., determine whether to use transform substitution), wherein the transform is determined from a group including DCT-8, and at least one of DCT-2 and an identity transform, and encode and decode a sub-block of a block using the sub-block transform mode and the determined transform.

[0140] In one example, the sub-block transform mode is a vertical sub-block transform mode, and determining the transform includes always determining a DCT-2 or identity transform.

[0141] In another example, the sub-block transform mode is a horizontal sub-block transform mode, and determining the transform includes always determining a DCT-2 or identity transform.

[0142] In another example, the sub-block transform mode is a horizontal sub-block transform mode or a vertical sub-block transform mode, and determining the transform includes always determining a DCT-2 or an identity transform.

[0143] In another example, determining the transform includes determining the transform based on a syntax element.

[0144] In another example, determining the transform includes determining the transform based on one or more of a size of the block or a number of non-zero quantized coefficients associated with the block.

[0145] Figure 6 2 is a flowchart illustrating an example method for encoding a current block. The current block may include a current CU. Although with respect to the video encoder 200 ( Figure 1 and Figure 3 It should be understood that other devices may be configured to perform similar Figure 6 method.

[0146] In this example, the video encoder 200 initially predicts (e.g., using a prediction process) a current block (350). For example, the video encoder 200 may use inter-prediction or intra-prediction to form a prediction block for the current block. The video encoder 200 may then calculate a residual block for the block (352). To calculate the residual block, the video encoder 200 may calculate the difference between the original, unencoded block and the prediction block for the current block. The video encoder 200 may then determine to use a sub-block transform mode for the residual block based on one or more of the aspect ratio or width ratio of the block (354).

[0147] The video decoder 300 may then apply one or more transforms to the residual block based on the determination of using the sub-block transform mode (356). The video encoder 200 may also quantize the resulting transform coefficients of the residual block. Next, the video encoder 200 may scan the quantized transform coefficients of the residual block (358). During or after the scan, the video encoder 200 may entropy encode the coefficients (360). For example, the video encoder 200 may encode the coefficients using CAVLC or CABAC. The video encoder 200 may then output the entropy-encoded data of the block (362).

[0148] Figure 7 is a flowchart illustrating an example method for decoding a current block of video data. The current block may include a current CU. Although with respect to the video decoder 300 ( Figure 1 and 4 ), but it should be understood that other devices may be configured to perform similar Figure 7 method.

[0149] The video decoder 300 may receive entropy-coded data for a current block, such as entropy-coded prediction information and entropy-coded data corresponding to coefficients of a residual block of the current block (370). The video decoder 300 may entropy decode the entropy-coded data to determine prediction information for the current block and reproduce a block of coefficients (372). The video decoder 300 may then inverse scan the reproduced block of coefficients (374) to create a block of quantized transform coefficients. The video decoder 300 may determine to use a sub-block transform mode for the block of coefficients based on one or more of an aspect ratio or a height-to-width ratio of the block (376). The video decoder 300 may then apply one or more inverse transforms to the block of coefficients based on the determination to use a sub-block transform mode to produce a residual block (378). The video decoder 300 may also inverse quantize the coefficients / the video decoder 300 may predict the current block (380), such as calculating a prediction block for the current block using intra-frame prediction, inter-frame prediction, or other modes indicated by the prediction information of the current block. The video decoder 300 may finally decode the current block by combining the prediction block and the residual block ( 382 ).

[0150] Additional illustrative examples of the present disclosure are described below.

[0151] Example 1: A method for encoding and decoding video data, the method comprising: determining a transform for a sub-block transform mode, wherein the transform is determined from a group including DCT-8, and at least one of DCT-2 and an identity transform; and using the sub-block transform mode and the determined transform to encode and decode a sub-block of an inter-frame predicted block.

[0152] Example 2: The method of Example 1, wherein the sub-block transform mode is a vertical sub-block transform mode, and wherein determining the transform comprises: always determining a DCT-2 or an identity transform.

[0153] Example 3: The method of Example 1, wherein the sub-block transform mode is a horizontal sub-block transform mode, and wherein determining the transform comprises: always determining a DCT-2 or an identity transform.

[0154] Example 4: The method of Example 1, wherein the sub-block transform mode is a horizontal sub-block transform mode or a vertical sub-block transform mode, and wherein determining the transform comprises: always determining DCT-2 or an identity transform.

[0155] Example 5: The method of Example 1, wherein determining the transformation comprises: determining the transformation based on a syntax element.

[0156] Example 6: The method of Example 1, wherein determining the transform comprises determining the transform based on one or more of a size of the inter-predicted block or a number of non-zero quantization coefficients associated with the inter-predicted block.

[0157] Example 7: A method of encoding and decoding video data, comprising: determining to use a sub-block transform mode for an inter-frame predicted block based on one or more of an aspect ratio or a height-to-width ratio of the block.

[0158] Example 8: The method of any one of Examples 1-7, wherein encoding and decoding includes decoding.

[0159] Example 9: The method of any one of Examples 1-7, wherein encoding and decoding includes encoding.

[0160] Example 10: A device for encoding and decoding video data, the device comprising one or more components for performing the method of any one of Examples 1-9.

[0161] Example 11: The device of Example 10, wherein the one or more components include one or more processors implemented in circuitry.

[0162] Example 12: The apparatus of any of Examples 10 and 11, further comprising a memory for storing video data.

[0163] Example 13: The apparatus of any of Examples 10-12, further comprising a display configured to display the decoded video data.

[0164] Example 14: The device of any of Examples 10-13, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0165] Example 15: The device of any of Examples 10-14, wherein the device comprises a video decoder.

[0166] Example 16: The device of any of Examples 10-15, wherein the device comprises a video encoder.

[0167] Example 17: A computer-readable storage medium having instructions stored thereon, which when executed cause one or more processors to perform the method of any of Examples 1-9.

[0168] It should be appreciated that, depending on the examples, certain actions or events of any of the techniques described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., not all described actions or events are necessary for the practice of the techniques). In addition, in some examples, actions or events may be performed simultaneously, e.g., by multithreading, interrupt handling, or multiple processors, rather than being performed sequentially.

[0169] 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 through a computer-readable medium as one or more instructions or codes and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media corresponding to tangible media such as data storage media, or communication media including any media that facilitates (e.g., according to a communication protocol) transferring a computer program from one place to another. In this manner, computer-readable media may generally correspond to (1) non-temporary tangible computer-readable storage media, or (2) communication media such as signals or carrier waves. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, codes, and / or data structures to implement the techniques described in the present disclosure. A computer program product may include a computer-readable medium.

[0170] As an example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store the desired program code in the form of an instruction or data structure and can be accessed by a computer. In addition, any connection is properly referred to as a computer-readable medium. For example, if a coaxial cable, optical fiber cable, twisted pair, digital subscriber line (DSL) or wireless technology (such as infrared, radio and microwave) is used to send instructions from a website, server or other remote source, then the coaxial cable, optical fiber cable, twisted pair, DSL or wireless technology (such as infrared, radio and microwave) is included in the definition of the medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other temporary media, but are directed to non-temporary tangible storage media. The disk and optical disk used herein include compact disc (CD), laser optical disc, optical optical disc, digital versatile disc (DVD), floppy disk and blue-ray disc, wherein the disk usually reproduces data magnetically, and the optical disc reproduces data optically with a laser. The above combination should also be included in the scope of computer-readable media.

[0171] Instructions may be executed by one or more processors, such as one or more DSPs, general-purpose microprocessors, ASICs, FPGAs, or other equivalent integrated or discrete logic circuits. Therefore, the terms "processor" and "processing circuit" used herein may refer to any of the aforementioned structures or any other structure suitable for implementing the techniques described herein. In addition, in some aspects, the functions described herein may be provided in dedicated hardware and / or software modules configured for encoding and decoding, or incorporated into a combined codec. In addition, these techniques may be fully implemented in one or more circuits or logic elements.

[0172] The techniques of the present disclosure may be implemented in a variety of devices or apparatuses, including wireless handsets, integrated circuits (ICs), or sets of ICs (e.g., chipsets). Various components, modules, or units are described in the present disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily need to be implemented by different hardware units. Instead, as described above, the various units may be combined in a codec hardware unit, or provided by a collection of interoperable hardware units including one or more processors as described above in combination with appropriate software and / or firmware.

[0173] Various examples have been described. These and other examples are within the scope of the following claims.

Claims

1. A method for decoding video data, comprising: Determine to use a vertical sub-block transform mode SBT-V for the block based on an aspect ratio of the block being greater than or equal to a first threshold, and determine not to use the SBT-V mode based on an aspect ratio of the block being less than the first threshold; Determine to use a horizontal subblock transform mode SBT-H for the block based on the aspect ratio of the block being greater than a second threshold, and determine not to use the SBT-H mode if the aspect ratio of the block is less than the second threshold; and Applying the determined subblock transform mode to produce a residual block by applying at least one inverse transform to a first subblock of a transform coefficient block and not applying an inverse transform to a second subblock of the transform coefficient block, wherein the second subblock does not include any non-zero transform coefficients, wherein each of the first subblock and the second subblock is encoded using inter-frame prediction, wherein the subblock transform determined for a luma subblock depends on a position of the luma subblock; and An inter-frame prediction process is performed on the residual block to generate a reconstructed block.

2. The method according to claim 1, further comprising: The first threshold is decoded at one or more of a sequence level, a picture level, a slice level, or a tile group level.

3. The method according to claim 1, further comprising: The second threshold is decoded at one or more of a sequence level, a picture level, a slice level, or a tile group level.

4. The method according to claim 1, further comprising: A picture including the block is displayed.

5. A method for encoding video data, comprising: Determine to use a vertical sub-block transform mode SBT-V for the block based on an aspect ratio of the block being greater than or equal to a first threshold, and determine not to use the SBT-V mode based on an aspect ratio of the block being less than the first threshold; Determine to use a horizontal sub-block transform mode SBT-H for the block based on the aspect ratio of the block being greater than a second threshold, and determine not to use the SBT-H mode when the aspect ratio of the block is less than the second threshold; encoding the block using inter prediction to create a residual block; as well as The determined sub-block transform mode is applied by applying at least one inverse transform to a first sub-block of the residual block and not applying an inverse transform to a second sub-block of the residual block, wherein the second sub-block does not include any non-zero transform coefficients, wherein the sub-block transform determined for a luma sub-block depends on a position of the luma sub-block.

6. The method according to claim 5, further comprising: The first threshold is encoded at one or more of a sequence level, a picture level, a slice level, or a tile group level.

7. The method according to claim 5, further comprising: The second threshold is encoded at one or more of a sequence level, a picture level, a slice level, or a tile group level.

8. The method according to claim 5, further comprising: A picture including the block is captured.

9. An apparatus configured to decode video data, the apparatus comprising: A memory configured as a memory block; as well as one or more processors implemented in circuitry and in communication with the memory, the one or more processors being configured to: Determine to use a vertical sub-block transform mode SBT-V for the block based on an aspect ratio of the block being greater than or equal to a first threshold, and determine not to use the SBT-V mode based on an aspect ratio of the block being less than the first threshold; Determine to use a horizontal subblock transform mode SBT-H for the block based on the aspect ratio of the block being greater than a second threshold, and determine not to use the SBT-H mode if the aspect ratio of the block is less than the second threshold; and Applying the determined subblock transform mode to produce a residual block by applying at least one inverse transform to a first subblock of a transform coefficient block and not applying an inverse transform to a second subblock of the transform coefficient block, wherein the second subblock does not include any non-zero transform coefficients, wherein each of the first subblock and the second subblock is encoded using inter-frame prediction, wherein the subblock transform determined for a luma subblock depends on a position of the luma subblock; and An inter-frame prediction process is performed on the residual block to generate a reconstructed block.

10. The device according to claim 9, wherein: The one or more processors are further configured to: The first threshold is decoded at one or more of a sequence level, a picture level, a slice level, or a tile group level.

11. The device according to claim 9, wherein: The one or more processors are further configured to: The second threshold is decoded at one or more of a sequence level, a picture level, a slice level, or a tile group level.

12. The device according to claim 9, further comprising: A display is configured to display a picture including the block.

13. An apparatus configured to encode video data, the apparatus comprising: A memory configured as a memory block; as well as one or more processors implemented in circuitry and in communication with the memory, the one or more processors being configured to: Determine to use a vertical sub-block transform mode SBT-V for the block based on an aspect ratio of the block being greater than or equal to a first threshold, and determine not to use the SBT-V mode based on an aspect ratio of the block being less than the first threshold; Determine to use a horizontal sub-block transform mode SBT-H for the block based on the aspect ratio of the block being greater than a second threshold, and determine not to use the SBT-H mode when the aspect ratio of the block is less than the second threshold; encoding the block using inter prediction to create a residual block; as well as The determined sub-block transform mode is applied by applying at least one inverse transform to a first sub-block of the residual block and not applying an inverse transform to a second sub-block of the residual block, wherein the second sub-block does not include any non-zero transform coefficients, wherein the sub-block transform determined for a luma sub-block depends on a position of the luma sub-block.

14. The device according to claim 13, wherein: The one or more processors are further configured to: The first threshold is encoded at one or more of a sequence level, a picture level, a slice level, or a tile group level.

15. The device according to claim 13, wherein: The one or more processors are further configured to: The second threshold is encoded at one or more of a sequence level, a picture level, a slice level, or a tile group level.

16. The apparatus according to claim 13, further comprising: A camera is configured to capture a picture including the block.

17. An apparatus configured to decode video data, the apparatus comprising: means for determining to use a vertical sub-block transform mode SBT-V for the block based on an aspect ratio of the block being greater than or equal to a first threshold, and determining not to use the SBT-V mode based on an aspect ratio of the block being less than the first threshold; means for determining to use a horizontal sub-block transform mode SBT-H for the block based on the aspect ratio of the block being greater than a second threshold, and determining not to use the SBT-H mode when the aspect ratio of the block is less than the second threshold; as well as means for applying the determined subblock transform mode to produce a residual block by applying at least one inverse transform to a first subblock of a transform coefficient block and not applying an inverse transform to a second subblock of the transform coefficient block, wherein the second subblock does not include any non-zero transform coefficients, wherein each of the first subblock and the second subblock is encoded using inter-frame prediction, wherein the subblock transform determined for a luma subblock depends on a position of the luma subblock; and means for performing an inter-frame prediction process on the residual block to generate a reconstructed block.

18. An apparatus configured to encode video data, the apparatus comprising: means for determining to use a vertical sub-block transform mode SBT-V for the block based on an aspect ratio of the block being greater than or equal to a first threshold, and determining not to use the SBT-V mode based on an aspect ratio of the block being less than the first threshold; means for determining to use a horizontal sub-block transform mode SBT-H for the block based on the aspect ratio of the block being greater than a second threshold, and determining not to use the SBT-H mode when the aspect ratio of the block is less than the second threshold; means for encoding the block using inter prediction to create a residual block; as well as Means for applying the determined sub-block transform mode by applying at least one inverse transform to a first sub-block of the residual block and not applying an inverse transform to a second sub-block of the residual block, wherein the second sub-block does not include any non-zero transform coefficients, wherein the sub-block transform determined for a luma sub-block depends on a position of the luma sub-block.

19. A non-transitory computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device to be configured to decode video data to: Determine to use a vertical sub-block transform mode SBT-V for the block based on an aspect ratio of the block being greater than or equal to a first threshold, and determine not to use the SBT-V mode based on an aspect ratio of the block being less than the first threshold; Determine to use a horizontal subblock transform mode SBT-H for the block based on the aspect ratio of the block being greater than a second threshold, and determine not to use the SBT-H mode if the aspect ratio of the block is less than the second threshold; and Applying the determined subblock transform mode to produce a residual block by applying at least one inverse transform to a first subblock of a transform coefficient block and not applying an inverse transform to a second subblock of the transform coefficient block, wherein the second subblock does not include any non-zero transform coefficients, wherein each of the first subblock and the second subblock is encoded using inter-frame prediction, wherein the subblock transform determined for a luma subblock depends on a position of the luma subblock; and An inter-frame prediction process is performed on the residual block to generate a reconstructed block.

20. A non-transitory computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device to be configured to encode video data to: Determine to use a vertical sub-block transform mode SBT-V for the block based on an aspect ratio of the block being greater than or equal to a first threshold, and determine not to use the SBT-V mode based on an aspect ratio of the block being less than the first threshold; Determine to use a horizontal sub-block transform mode SBT-H for the block based on the aspect ratio of the block being greater than a second threshold, and determine not to use the SBT-H mode when the aspect ratio of the block is less than the second threshold; encoding the block using inter prediction to create a residual block; as well as The determined sub-block transform mode is applied by applying at least one inverse transform to a first sub-block of the residual block and not applying an inverse transform to a second sub-block of the residual block, wherein the second sub-block does not include any non-zero transform coefficients, wherein the sub-block transform determined for a luma sub-block depends on a position of the luma sub-block.

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