Signaling of sub-pictures in high level syntax for video coding

Abstract

A video decoder can be configured to decode a first syntax element indicating a size of a coding tree unit (CTU); decode, after decoding the first syntax element indicating the size of the CTU, a second syntax element indicating a width of an element of a subpicture identifier grid; decode, after decoding the first syntax element indicating the size of the CTU, a third syntax element indicating a height of the element of the subpicture identifier grid; and determine a location of a subpicture within a picture based on the first syntax element, the second syntax element, and the third syntax element.

Description

[0001] This application claims priority to U.S. Application No. 17 / 027,262 filed September 21, 2020, which claims benefit of U.S. Provisional Patent Application 62 / 904,516 filed September 23, 2019, the entire contents of each of which are incorporated herein by reference. TECHNICAL FIELD

[0002] The present disclosure relates to video encoding and video decoding. BACKGROUND

[0003] Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, tablet computers, e-book readers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio telephones, so-called “smart phones,” video teleconferencing devices, video streaming devices, and the like. Digital video devices implement video coding techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264 / MPEG-4, Part 10, Advanced Video Coding (AVC), ITU-T H.265 / High Efficiency Video Coding (HEVC), and extensions of such standards. The video devices can implement such video coding techniques to transmit, receive, encode, decode, and / or store digital video information more efficiently.

[0004] Video coding techniques include spatial (intra-picture) prediction and / or temporal (inter-picture) prediction to reduce or remove redundancy of video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) can be partitioned into video blocks, which can also be referred to as coding tree units (CTUs), coding units (CUs), and / or coding nodes. Video blocks in an intra-coded (I) slice of a picture are coded using spatial prediction of samples from reference samples in neighboring blocks within the same picture. Video blocks in an inter-coded (P or B) slice of a picture can be coded by spatial prediction of samples from reference samples in neighboring blocks within the same picture or temporal prediction of samples from reference pictures. SUMMARY

[0005] In one example of the disclosure, a video decoder can be configured to decode a first syntax element indicating a size of a coding tree unit (CTU) prior to decoding a second syntax element indicating a width of elements of a subpicture identifier grid and prior to decoding a third syntax element indicating a height of elements of the subpicture identifier grid, and then allocate memory for storing subpicture indices based on the CTU size rather than always using a grid size of 4x4. The techniques of the disclosure potentially improve operation of a video decoder by reducing an amount of memory needed to store subpicture indices. More specifically, by configuring the decoder to decode the first syntax element indicating the size of the CTU prior to decoding the second syntax element indicating the width of elements of the subpicture identifier grid and prior to decoding the third syntax element indicating the height of elements of the subpicture identifier grid, the video decoder can be configured to allocate memory for storing subpicture indices based on the CTU size rather than always using a grid size of 4x4.

[0006] In one example, the disclosure describes a method of decoding video data, the method comprising: decoding a first syntax element indicating a size of a coding tree unit (CTU); decoding, after decoding the first syntax element indicating the size of the CTU, a second syntax element indicating a width of elements of a subpicture identifier grid; decoding, after decoding the first syntax element indicating the size of the CTU, a third syntax element indicating a height of elements of the subpicture identifier grid; and determining a location of a subpicture within a picture based on the first syntax element, the second syntax element, and the third syntax element.

[0007] In another example, the disclosure describes an apparatus for decoding video data, the apparatus comprising: a memory; and one or more processors implemented in circuitry, coupled to the memory, and configured to: decode a first syntax element indicating a size of a coding tree unit (CTU); decode, after decoding the first syntax element indicating the size of the CTU, a second syntax element indicating a width of elements of a subpicture identifier grid; decode, after decoding the first syntax element indicating the size of the CTU, a third syntax element indicating a height of elements of the subpicture identifier grid; and determine a location of a subpicture within a picture based on the first syntax element, the second syntax element, and the third syntax element.

[0008] In another example, this disclosure describes a computer-readable storage medium having instructions stored thereon that, when executed, configure a processor to: decode a first syntax element indicating a size of a coding tree unit (CTU); decode, after decoding the first syntax element indicating the size of the CTU, a second syntax element indicating a width of an element of a subpicture identifier grid; decode, after decoding the first syntax element indicating the size of the CTU, a third syntax element indicating a height of the element of the subpicture identifier grid; and determine a location of a subpicture within a picture based on the first syntax element, the second syntax element, and the third syntax element.

[0009] In another example, this disclosure describes a device for decoding video data, the device comprising: means for decoding a first syntax element indicating a size of a coding tree unit (CTU); means for decoding, after decoding the first syntax element indicating the size of the CTU, a second syntax element indicating a width of an element of a subpicture identifier grid; means for decoding, after decoding the first syntax element indicating the size of the CTU, a third syntax element indicating a height of the element of the subpicture identifier grid; and means for determining a location of a subpicture within a picture based on the first syntax element, the second syntax element, and the third syntax element.

[0010] 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 detailed description, drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 FIG. 1 is a block diagram illustrating an example video encoding and decoding system that can perform the techniques of this disclosure.

[0012] FIG. 2A and FIG. 2B FIG. 2 is a conceptual diagram illustrating an example quad-tree binary-tree (QTBT) structure and corresponding coding tree units (CTUs).

[0013] FIG. 3 FIG. 3 is a block diagram illustrating an example video encoder that can perform the techniques of this disclosure.

[0014] FIG. 4 FIG. 4 is a block diagram illustrating an example video decoder that can perform the techniques of this disclosure.

[0015] FIG. 5 FIG. 5 is a flowchart illustrating an example video encoding process.

[0016] FIG. 6 FIG. 6 is a flowchart illustrating an example video decoding process.

[0017] FIG. 7 FIG. 1 is a flowchart illustrating an example video decoding process. DETAILED DESCRIPTION

[0018] Video coding (e.g., video encoding and / or video decoding) often involves predicting a block of video data from already coded video data blocks in the same picture (e.g., intra prediction) or from already coded video data blocks in different pictures (e.g., inter prediction). In some cases, a video encoder also computes residual data by comparing a predicted block to an original block. Thus, the residual data represents the difference between the samples of the predicted block and the samples of the original block. To reduce the number of bits needed to signal the residual data, the video encoder transforms and quantizes the residual data and signals the transformed and quantized residual data in an encoded bitstream. The compression achieved by the transform and quantization process can be lossy, meaning that the transform and quantization process can introduce distortion into the decoded video data.

[0019] A video decoder decodes the residual data and adds it to the predicted block to produce a reconstructed video block that more closely matches the original video block than the predicted block alone. Due to the loss introduced by the transform and quantization of the residual data, the first reconstructed block can have distortion or artifacts. To further improve the quality of the decoded video, the video decoder can perform one or more filtering operations on the reconstructed video block.

[0020] Video is coded as a series of pictures, each of which is divided into one or more slices. A slice can include an integer number of blocks, e.g., coding tree units (CTUs). In some cases, blocks within a slice can be grouped into tiles or some other such grouping. For some applications, like two-dimensional movies or television, a picture typically corresponds to a single continuous scene. For other types of applications, such as 360-degree video, one picture can include multiple sub-pictures, where a sub-picture can correspond to one continuous scene, respectively, while the entire picture does not. A sub-picture generally refers to a rectangular region composed of one or more slices within a picture. As one example use case, in some implementations, a 360-degree picture can be patched from 96 different sub-pictures. The 96 different sub-pictures can be continuous or discontinuous between boundaries. When streaming 360-degree video, a user can only receive some of the sub-pictures.

[0021] To support 360-degree video, the newly emerging Versatile Video Coding (VVC) standard supports sub-pictures. This disclosure describes signaling techniques for sub-pictures. The techniques of this disclosure can be applied to the VVC standard or other future video coding standards.

[0022] According to the techniques of this disclosure, to identify the location of sub-pictures in a picture, a video encoder and a video decoder determine a sub-picture identifier grid by dividing the picture into a series of grid elements based on a size of the picture, a number of columns in the sub-picture grid, and a number of rows in the sub-picture grid. A point on the sub-picture identifier grid or sub-picture grid corresponds to a different sample location in the picture. For each sub-picture in the picture, the video encoder signals to the video decoder a sub-picture index that identifies a grid element that includes a top-left luma sample of the sub-picture. When storing the value of the sub-picture index, the video decoder allocates memory based on a worst-case scenario, which means that the maximum potential amount of memory can be needed. The maximum potential amount of memory that can be needed is a function of the size of the grid elements used. Current implementations for sub-picture signaling utilize grid elements that are 4x4 in size. Using 4x4 grid elements, a video picture that is 8192x4320 has 2,211,840 grid elements.

[0023] In one example of the disclosure, a video decoder can be configured to decode a first syntax element that indicates a size of a coding tree unit (CTU) prior to decoding a second syntax element that indicates a width of an element of a sub-picture identifier grid and prior to decoding a third syntax element that indicates a height of the element of the sub-picture identifier grid, and then allocate memory for storing sub-picture indices based on the CTU size rather than always using a grid size of 4x4. The techniques of the disclosure potentially improve the operation of a video decoder by reducing the amount of memory needed to store sub-picture indices. More specifically, by configuring the decoder to decode a first syntax element that indicates a size of a CTU prior to decoding a second syntax element that indicates a width of an element of a sub-picture identifier grid and prior to decoding a third syntax element that indicates a height of the element of the sub-picture identifier grid, the video decoder can be configured to allocate memory for storing sub-picture indices based on the CTU size rather than always using a grid size of 4x4. By allocating memory based on the CTU size rather than always using a grid size of 4x4, the techniques of the disclosure can improve the memory usage of a device, which can improve device performance.

[0024] Additionally, according to the techniques of this disclosure, in some coding cases, by configuring a video decoder to allocate memory for storing sub-picture indices based on a maximum height value and a maximum width value of a CTU size rather than always using a grid size of 4x4, the amount of memory needed by the video decoder to store sub-picture indices can be reduced. For example, the video decoder can be configured to determine a number of columns in a sub-picture identifier grid based on the maximum width value in response to determining that a width of a CTU is less than the maximum width value, and to determine a number of rows in the sub-picture identifier grid based on the maximum height value in response to determining that a height of the CTU is less than the maximum height value.

[0025] FIG. 1 is a block diagram illustrating an example video encoding and decoding system 100 that can perform the techniques of this disclosure. The techniques of this disclosure generally relate to coding (encoding and / or decoding) video data. In general, video data includes any data used for processing video. Thus, video data can include raw, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data.

[0026] As FIG. 1 shown in FIG. 1, in this example, the system 100 includes a source device 102 that provides encoded video data to be decoded and displayed by a destination device 116. In particular, the source device 102 provides the video data to the destination device 116 via a computer-readable medium 110. The source device 102 and the destination device 116 can comprise any of a wide variety of devices, including desktop computers, notebook (i.e., laptop) computers, mobile devices, tablet computers, set-top boxes, telephone handsets such as smartphones, televisions, cameras, display devices, digital media players, video gaming consoles, video streaming devices, broadcast receiver devices, and the like. In some cases, the source device 102 and the destination device 116 can be equipped for wireless communication, and thus can be referred to as wireless communication devices.

[0027] In FIG. 1 the example of FIG. 1, the source device 102 includes a video source 104, a memory 106, a video encoder 200, and an output interface 108. The destination device 116 includes an input interface 122, a video decoder 300, a memory 120, and a display device 118. In accordance with this disclosure, the video encoder 200 of the source device 102 and the video decoder 300 of the destination device 116 can be configured to apply the techniques for subpicture signaling described herein. Thus, the source device 102 represents an example of a video encoding device, while the destination device 116 represents an example of a video decoding device. In other examples, a source device and a destination device can include other components or arrangements. For example, the source device 102 can receive video data from an external video source, such as an external camera. Also, the destination device 116 can interface with an external display device, rather than include an integrated display device.

[0028] As FIG. 1The system 100 illustrated in FIG. 1 is merely one example. In general, any digital video encoding and / or decoding device can perform the techniques for subpicture signaling described herein. The source device 102 and destination device 116 are merely examples of such coding devices in which the source device 102 generates coded video data for transmission to the destination device 116. This disclosure refers to “coding” devices as devices that perform coding (encoding and / or decoding) of data. Thus, video encoder 200 and video decoder 300 represent examples of coding devices, in particular, examples of video encoders and video decoders, respectively. In some examples, the source device 102 and the destination device 116 can operate in a substantially symmetrical manner such that each of the source device 102 and the destination device 116 includes video encoding and decoding components. Hence, the system 100 can support one-way or two-way video transmission between the source device 102 and the destination device 116, e.g., for video streaming, video playback, video broadcasting, or video telephony.

[0029] In general, the video source 104 represents a source of video data (i.e., raw, unencoded video) and provides a sequential series of pictures (also referred to as “frames”) of the video data to the video encoder 200, which encodes data for the pictures. The video source 104 of the source device 102 can include a video capture device, such as a video camera, a video archive containing previously captured raw video, and / or a video feed interface to receive video from a video content provider. As a further alternative, the video source 104 can 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 can rearrange the pictures from the received order (sometimes referred to as “display order”) into the coding order for coding. The video encoder 200 can generate a bitstream including encoded video data. The source device 102 can then output the encoded video data via the output interface 108 onto the computer-readable medium 110 for reception and / or retrieval by an input interface 122 of, for example, the destination device 116.

[0030] Memory 106 of source device 102 and memory 120 of destination device 116 represent general purpose memories. In some examples, memories 106, 120 can store raw video data, such as raw video from video source 104 and raw decoded video data from video decoder 300. Additionally or alternatively, memories 106, 120 can store software instructions that are executable by, for example, video encoder 200 and video decoder 300, respectively. Although memories 106 and 120 are shown as separate from video encoder 200 and video decoder 300 in this example, it should be understood that video encoder 200 and video decoder 300 can also include internal memories for similar or equivalent purposes. Furthermore, memories 106, 120 can store encoded video data that is outputted from video encoder 200 and inputted to video decoder 300, for example. In some examples, portions of memories 106, 120 can be allocated as one or more video buffers to, for example, store raw, decoded, and / or encoded video data.

[0031] Computer-readable medium 110 can represent any type of medium or device capable of transporting the encoded video data from source device 102 to destination device 116. In one example, computer-readable medium 110 represents a communication medium to enable source device 102 to transmit encoded video data directly to destination device 116 in real-time, e.g., via a wireless or computer-based network. Output interface 108 can modulate a transmission signal including the encoded video data, and input interface 122 can demodulate the received transmission signal, according to a communication standard, such as a wireless communication protocol. Communication medium can comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium can 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 can include routers, switches, base stations, or any other equipment that can be useful to facilitate communication from source device 102 to destination device 116.

[0032] In some examples, source device 102 can output encoded data from output interface 108 to storage device 112. Similarly, destination device 116 can access encoded data from storage device 112 via input interface 122. Storage device 112 can include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data.

[0033] In some examples, source device 102 can output encoded video data to a file server 114 or another intermediate storage device that can store encoded video generated by source device 102. Destination device 116 can access stored video data from file server 114 through streaming or download.

[0034] File server 114 can be any type of server device capable of storing encoded video data and transmitting that encoded video data to destination device 116. File server 114 can represent a web server (e.g., for a website), a server configured to provide file transfer protocol services (such as File Transfer Protocol (FTP) or File Delivery over Unidirectional Transport (FLUTE) protocol), a content delivery network (CDN) device, a hypertext transfer protocol (HTTP) server, a multimedia broadcast multicast service (MBMS) or enhanced MBMS (eMBMS) server, and / or a network attached storage (NAS) device. File server 114 can additionally or alternatively implement one or more HTTP streaming protocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP Dynamic Streaming, and the like.

[0035] Destination device 116 can access encoded video data from file server 114 through any standard data connection, including an Internet connection. This can include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriber line (DSL), a cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on file server 114. Input interface 122 can be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from file server 114, or other such protocols for retrieving media data.

[0036] Output interface 108 and input interface 122 can represent wireless transmitters / receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components operating according to any of a variety of IEEE 802.11 standards, or other physical components. In examples where output interface 108 and input interface 122 comprise wireless components, output interface 108 and input interface 122 can be configured to transmit data, such as encoded video data, according to a cellular communication standard, such as 4G, 4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In some examples where output interface 108 includes a wireless transmitter, output interface 108 and input interface 122 can be configured to transmit data according to other wireless standards, such as an IEEE 802.11 specification, an IEEE 802.15 specification (e.g., ZigBee), a Bluetooth standard, or the like. TM), Bluetooth TM The source device 102 and / or the destination device 116 can include respective system-on-a-chip (SoC) devices. For example, the source device 102 can include a SoC device to perform the functionality attributed to video encoder 200 and / or output interface 108, and the destination device 116 can include a SoC device to perform the functionality attributed to video decoder 300 and / or input interface 122.

[0037] The techniques of this disclosure can be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications.

[0038] Input interface 122 of destination device 116 receives an encoded video bitstream from computer- readable medium 110 (e.g., a communication medium, storage device 112, file server 114, or the like). The encoded video bitstream can include signaling information defined by video encoder 200, which is also used by video decoder 300, such as syntax elements having values

[0039] Although not shown in FIG. 1, in some examples, video encoder 200 and video decoder 300 can each be integrated with an audio encoder and / or audio decoder. The video and audio encoders can encode voice and music from audio input using audio codecs, such as AMR-NB, AMR-WB, Enhanced Voice Services (EVS), AAC, or the like. The integrated audio and video decoders can also provide decoding of voice and music from audio streams generated by the video and audio encoders, respectively. If applicable, MUX-DEMUX units can handle multiplexed streams, including by way of example, audio FIG. 1

[0040] ​Video encoder 200 and video decoder 300 each can be implemented as any of a variety of suitable encoder and / or decoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When the techniques are implemented partially in software, a device can store instructions for the software in a suitable, non- transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder 200 and video decoder 300 can be included in one or more encoders or decoders, either of which can be integrated as part of a combined video encoder / decoder (CODEC) in a respective device. A device including video encoder 200 and / or video decoder 300 can comprise an integrated circuit, a microprocessor, and / or a wireless communication device, such as a cellular telephone.

[0041] Video encoder 200 and video decoder 300 can operate according to a video coding standard, such as ITU-T H.265, also referred to as High Efficiency Video Coding (HEVC) or extensions thereof, such as the multi-view and / or scalable video coding extensions. Alternatively, video encoder 200 and video decoder 300 can operate according to other proprietary or industry standards, such as the Joint Exploration Test Model (JEM) or ITU-T H.266, also referred to as Versatile Video Coding (VVC). A recent draft of the VVC standard is described in Bross, et al. “Versatile Video Coding (Draft 6),” JVET-O2001-vl4, 15th Meeting of ITU-T SG 15 WP 3 and ISO / IEC JTC 3 / SC 29 / WG 11, Joint Video Expert Team (JVET), Gothenburg, SE, 3-12 July 2019 (hereinafter “VVC Draft 6”). The techniques of this disclosure, however, are not limited to any particular coding standard. Another draft of the VVC standard is described in Bross, et al. “Versatile Video Coding (Draft 10),” JVET-S2001-vl6, 18th Meeting of ITU-T SG 15 WP 22 and ISO / IEC JTC 3 / SC 29 / WG 11, Joint Video Expert Team (JVET), Online, 22 June - 1 July 2020 (hereinafter “VVC Draft 10”). The techniques of this disclosure, however, are not limited to any particular coding standard.

[0042] In general, video encoder 200 and video decoder 300 can perform block-based coding of pictures. The term “block” generally refers to a structure containing data to be processed (e.g., encoded, decoded, or otherwise used in the encoding and / or decoding process). For example, a block can include a two-dimensional matrix of samples of luma and / or chroma data. In general, video encoder 200 and video decoder 300 can code video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, video encoder 200 and video decoder 300 can code luma and chroma components, rather than coding red, green, and blue (RGB) data of samples of a picture. In some examples, video encoder 200 converts received RGB formatted data to a YUV representation prior to encoding, and video decoder 300 converts the YUV representation to the RGB format. Alternatively, pre- and post-processing units (not shown) can perform these conversions.

[0043] The present disclosure can generally relate to coding (e.g., encoding and decoding) pictures to include processes that encode or decode data of the pictures. Similarly, the present disclosure can relate to coding blocks of pictures to include processes that encode or decode data of the blocks, such as prediction and / or residual coding. An encoded video bitstream generally includes a series of values representing coding decisions (e.g., coding modes) and syntax elements that partition a picture into blocks. Thus, references to coding a picture or a block should generally be understood to refer to coding values of syntax elements that form the picture or block.

[0044] HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video coder, such as video encoder 200, partitions coding tree units (CTUs) into CUs according to a quadtree structure. That is, the video coder partitions CTUs and CUs into four identical, non overlapping squares, and each node of the quadtree has either zero or four child nodes. Nodes with no child nodes can be referred to as “leaf nodes,” and CUs of such leaf nodes can include one or more PUs and / or one or more TUs. The video coder can further partition PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents partitioning of TUs. In HEVC, PUs represent inter-predicted data, while TUs represent residual data. Intra-predicted CUs include intra-prediction information, such as an intra-mode indication.

[0045] As another example, video encoder 200 and video decoder 300 can be configured to operate according to VVC. According to VVC, a video coder (such as video encoder 200) partitions a picture into a plurality of coding tree units (CTUs). Video encoder 200 can partition a CTU according to a tree structure, such as a quad-tree binary tree (QTBT) structure or a multi-type tree (MTT) structure. The QTBT structure removes the concepts of multiple split types, such as the separation between CUs, PUs, and TUs of HEVC. The QTBT structure includes two levels: a first level of partitioning according to quad-tree partitioning, and a second level of partitioning according to binary tree partitioning. A root node of the QTBT structure corresponds to a CTU. Leaf nodes of the binary trees correspond to coding units (CUs).

[0046] In the MTT partitioning structure, a block can be partitioned using quad-tree (QT) splitting, binary tree (BT) splitting, and one or more types of ternary tree (TT) (also referred to as tri-tree (TT)) splitting. A ternary or tri-tree split is a split in which a block is split into three sub-blocks. In some examples, a ternary or tri-tree split divides a block into three sub-blocks without splitting the original block through a center. The split types (e.g., QT, BT, and TT) in the MTT can be symmetric or asymmetric.

[0047] In some examples, video encoder 200 and video decoder 300 can represent each of the luma and chrominance components using a single QTBT or MTT structure, while in other examples, video encoder 200 and video decoder 300 can use two or more QTBT or MTT structures, such as one QTBT / MTT structure for a luma component and another QTBT / MTT structure for two chrominance components (or two QTBT / MTT structures for respective chrominance components).

[0048] Video encoder 200 and video decoder 300 can be configured to use quad-tree partitioning according to HEVC, QTBT partitioning, MTT partitioning, or other partitioning structures. For explanatory purposes, the description of the techniques of this disclosure is presented with respect to QTBT partitioning. However, it should be understood that the techniques of this disclosure also apply to video coders configured to use quad-tree partitioning also or other types of partitioning.

[0049] In some examples, a CTU includes a coding tree block (CTB) of luma samples, two corresponding CTBs of chroma samples of a picture having three sample arrays, or one CTB of samples of a monochrome picture or a picture coded using three independent color planes and syntax structures for coding samples. A CTB can be an NxN block of samples of some N value, such that partitioning a component into CTBs is a split. A component is an array or a single sample from one of three arrays (luma and two chroma) that make up a picture in a color format of 4:2:0, 4:2:2, or 4:4:4; or a single sample of an array or an array that makes up a monochrome format picture. In some examples, a coding block is an MxN block of samples for some values of M and N, such that partitioning a CTB into coding blocks is a split.

[0050] Blocks (e.g., CTUs or CUs) can be grouped in various ways in a picture. As one example, a brick can refer to a rectangular region of CTU rows within a particular tile in a brick. A tile can be a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular region of CTUs having a height equal to a picture height and a width specified by a syntax element (e.g., such as in a picture parameter set). A tile row refers to a rectangular region of CTUs having a height specified by a syntax element (e.g., such as in a picture parameter set) and a width equal to a picture width.

[0051] In some examples, a tile can be partitioned into multiple bricks, each of which can include one or more CTU rows within the tile. A tile that is not partitioned into multiple bricks can also be referred to as a brick. However, a brick that is a true subset of a tile cannot be referred to as a tile.

[0052] Bricks in a picture can also be arranged in the form of slices. A slice can be an integer number of bricks of a picture, which can be exclusively contained in a single network abstraction layer (NAL) unit. In some examples, a slice includes a contiguous sequence of consecutive bricks of multiple complete tiles or only one tile.

[0053] The disclosure interchangeably uses "NxN" and "N by N" to refer to the sample size of a block (such as a CU or other video block) with respect to vertical and horizontal dimensions, e.g., 16x16 samples or 16 by 16 samples. In general, a 16x16 CU will have 16 samples in the vertical direction (y = 16) and 16 samples in the horizontal direction (x = 16). Likewise, an NxN CU generally 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 can be arranged in columns and rows. Moreover, a CU need not have the same number of samples in the horizontal direction and the vertical direction. For example, a CU can comprise NxM samples, where M need not equal N.

[0054] Video encoder 200 encodes video data for a CU, including prediction and / or residual information and other information. Prediction information indicates how the CU is to be predicted in order to form a prediction block for the CU. Residual information generally represents sample-by-sample differences between the CU prior to encoding and the prediction block.

[0055] To predict a CU, video encoder 200 can generally form a prediction block for the CU via inter prediction or intra prediction. Inter prediction generally refers to predicting the CU from data of a previously coded picture, whereas intra prediction generally refers to predicting the CU from previously coded data of the same picture. To perform inter prediction, video encoder 200 can use one or more motion vectors to produce the prediction block. Video encoder 200 can generally perform a motion search to identify a reference block that closely matches the CU, e.g., in terms of differences between the CU and the reference block. Video encoder 200 can calculate a difference metric using a sum of absolute difference (SAD), sum of squared difference (SSD), mean absolute difference (MAD), mean squared difference (MSD), or other such difference calculations to determine whether a reference block closely matches a current CU. In some examples, video encoder 200 can use uni -prediction or bi-prediction to predict a current CU.

[0056] Some examples of VVC also provide an affine motion compensation mode, which can be considered an inter prediction mode. In the affine motion compensation mode, video encoder 200 can determine two or more motion vectors that represent non-translational motion, such as scaling or zooming, rotation, perspective motion, or other irregular types of motion.

[0057] To perform intra prediction, video encoder 200 can select an intra prediction mode to generate the prediction block. Some examples of VVC provide sixty-seven intra prediction modes, including various directional modes as well as a planar mode and a DC mode. In general, video encoder 200 selects an intra prediction mode from which to predict samples of a current block that describes samples neighboring the current block (e.g., a block of a CU). Assuming that video encoder 200 is coding CTUs and CUs in a raster scan order (left-to-right, top-to-bottom), such samples can generally be above, above-and-to-the-left of, or to the left of the current block in the same picture as the current block.

[0058] Video encoder 200 encodes data representing the prediction mode of the current block. For example, for inter prediction modes, video encoder 200 can encode data representing which of various available inter prediction modes to use and motion information for the corresponding mode. For example, for uni- or bi-prediction, video encoder 200 can use advanced motion vector prediction (AMVP) or merge mode to encode motion vectors. Video encoder 200 can use similar modes to encode motion vectors for affine motion compensation modes.

[0059] Following prediction of a block, such as intra prediction or inter prediction, video encoder 200 can calculate residual data for the block. Residual data, such as a residual block, represents sample-by-sample differences between the block and a prediction block formed using the corresponding prediction mode. Video encoder 200 can apply one or more transforms to the residual block to produce transformed data in a transform domain rather than the sample domain. For example, video encoder 200 can apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform. In addition, video encoder 200 can apply a second transform following a first transform, such as a mode-dependent non-separable second transform (MDNSST), a signal-dependent transform, a Karhunen-Loeve transform (KLT), or the like. Video encoder 200 produces transform coefficients following application of the one or more transforms.

[0060] As noted above, following any transforms to produce transform coefficients, video encoder 200 can perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. By performing the quantization process, video encoder 200 can reduce the bit depth of some or all of the transform coefficients. For example, video encoder 200 can round n-bit values to m-bit values during quantization, where n is greater than m. In some examples, to perform quantization, video encoder 200 can perform a bitwise right-shift of the values to be quantized.

[0061] After quantization, video encoder 200 can scan the transform coefficients, producing a one-dimensional vector from the two-dimensional matrix comprising the quantized transform coefficients. The scan can be designed to place higher energy (and hence less frequent) transform coefficients at the front of the vector, and lower energy (and hence more frequent) transform coefficients at the end of the vector. In some examples, video encoder 200 can utilize a pre-defined scan order to scan the quantized transform coefficients to produce a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, video encoder 200 can perform an adaptive scan. After scanning the quantized transform coefficients to form a one-dimensional vector, video encoder 200 can entropy encode the one-dimensional vector, e.g., according to context-adaptive binary arithmetic coding (CABAC). Video encoder 200 can also entropy encode values for syntax elements describing metadata associated with the encoded video data for use in decoding the video data by video decoder 300.

[0062] To perform CABAC, video encoder 200 can assign a context within a context model to a symbol to be transmitted. The context can relate to, for example, whether neighboring values of the symbol are zero-valued or not. The probability determination can be based on the context assigned to the symbol.

[0063] Video encoder 200 can further generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, e.g., in a picture header, a block header, a slice header, or other syntax data such as a sequence parameter set (SPS), a picture parameter set (PPS), or a video parameter set (VPS), to video decoder 300. Video decoder 300 can likewise decode such syntax data to determine how to decode corresponding video data.

[0064] As such, video encoder 200 can generate a bitstream including encoded video data, e.g., syntax elements describing partitioning of a picture into blocks (e.g., CUs) and prediction and / or residual information for the blocks. Ultimately, video decoder 300 can receive the bitstream and decode the encoded video data.

[0065] In general, video decoder 300 performs a reciprocal of the process that video encoder 200 performs to encode the video data of the bitstream. For example, video decoder 300 can decode values for syntax elements of the bitstream using CABAC in a manner substantially similar to, but reciprocal of, the CABAC encoding process used by video encoder 200. The syntax elements can define partitioning information for partitioning a picture into CTUs, and partitioning of each CTU according to a corresponding partition structure, such as a QTBT structure, to define CUs of the CTU. The syntax elements can further define prediction and residual information for blocks (e.g., CUs) of the video data.

[0066] The residual information can be represented by, for example, quantized transform coefficients. Video decoder 300 can inverse quantize and inverse transform the quantized transform coefficients of a block to reproduce a residual block for the block. Video decoder 300 uses the signaled prediction mode (intra or inter prediction) and related prediction information (e.g., motion information for inter prediction) to form a prediction block for the block. Video decoder 300 can then (sample-wise) combine the prediction block and the residual block to reproduce the original block. Video decoder 300 can perform additional processing such as performing a deblocking procedure to reduce visual artifacts along block boundaries.

[0067] This disclosure can generally refer to “signaling” certain information, such as syntax elements. The term “signaling” can generally refer to communicating values for syntax elements and / or other data used to decode encoded video data. That is, video encoder 200 can signal values for syntax elements in a bitstream. In general, signaling refers to producing values in a bitstream. As mentioned above, source device 102 can transmit the bitstream to destination device 116 in substantially real time, or not in real time, such as can occur when syntax elements are stored to storage device 112 for later retrieval by destination device 116.

[0068] FIG. 2A and FIG. 2B FIG. 1 is a conceptual diagram illustrating an example quadtree-binary tree (QTBT) structure 130 and a corresponding coding tree unit (CTU) 132. Solid lines represent quadtree splitting, while dashed lines indicate binary tree splitting. In each split (i.e., non-leaf) node of the binary tree, one flag is signaled to indicate which splitting type (i.e., horizontal or vertical) is used, where 0 indicates horizontal splitting and 1 indicates vertical splitting in this example. For quadtree splitting, the splitting type does not need to be indicated because a quadtree node splits one block horizontally and vertically into 4 equally-sized sub-blocks. Thus, video encoder 200 can encode and video decoder 300 can decode syntax elements, such as splitting information, for a region tree hierarchy (i.e., solid lines) of QTBT structure 130 and syntax elements, such as splitting information, for a prediction tree hierarchy (i.e., dashed lines) of QTBT structure 130. For a CU represented by a terminal leaf node of QTBT structure 130, video encoder 200 can encode and video decoder 300 can decode video data, such as prediction data and transform data.

[0069] In general, FIG. 2BA CTU 132 can be associated with parameters defining sizes of blocks corresponding to nodes of the QTBT structure 130 at the first and second levels. These parameters can include a CTU size (representing a size of the CTU 132 in samples), a minimum quadtree size (MinQTSize, representing a minimum allowed quadtree leaf node size), a maximum binary tree size (MaxBTSize, representing a maximum allowed binary tree root node size), a maximum binary tree depth (MaxBTDepth, representing a maximum allowed binary tree depth), and a minimum binary tree size (MinBTSize, representing a minimum allowed binary tree leaf node size).

[0070] A root node of a QTBT structure corresponding to a CTU can have four child nodes at the first level of the QTBT structure, each of which can be split according to quadtree partitioning. That is, a node at the first level is either a leaf node (having no child nodes) or has four child nodes. The example of the QTBT structure 130 represents such nodes as including parent and child nodes represented by branches in solid lines. If a node at the first level is not larger than the maximum allowed binary tree root node size (MaxBTSize), the node can be further partitioned by a corresponding binary tree. Binary tree splitting of a node can iterate until nodes resulting from the splitting reach 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 nodes as including parent and child nodes represented by branches in dashed lines. Binary tree leaf nodes are referred to as coding units (CUs), which are used for prediction (e.g., intra-picture or inter-picture prediction) and transform without any further partitioning. As discussed above, a CU can also be referred to as a “video block” or “block.”

[0071] In one example of the QTBT segmentation structure, the CTU size is set to 128x128 (luma samples and two corresponding 64x64 chroma samples), the MinQTSize is set to 16x16, the MaxBTSize is set to 64x64, the MinBTSize (for both width and height) is set to 4, and the MaxBTDepth is set to 4. Quadtree partitioning is first applied to the CTU to generate a quadtree leaf node. The size of the quadtree leaf node can be from 16x16 (i.e., MinQTSize) to 128x128 (i.e., CTU size). If the leaf quadtree node is 128x128, the leaf quadtree node will not be further split by the binary tree because the size exceeds the MaxBTSize (i.e., 64x64 in this example). Otherwise, the quadtree leaf node will be further split by the binary tree. Thus, the quadtree leaf node is also the root node of the binary tree and its binary tree depth is 0. When the binary tree depth reaches the MaxBTDepth (4 in this example example), no further splitting is allowed. A binary tree node with a width equal to the MinBTSize (4 in this example) implies that no further vertical splitting (i.e., width partitioning) is allowed for that binary tree node. Similarly, a binary tree node with a height equal to the MinBTSize implies that no further horizontal splitting (i.e., height partitioning) is allowed for that binary tree node. As described above, the leaf nodes of the binary tree are referred to as CUs and are further processed according to prediction and transform without further segmentation.

[0072] According to techniques of this disclosure, video decoder 300 can be configured to decode a first syntax element that indicates a size of a CTU. The first syntax element can be, for example, log2_ctu_size_minus5, which is described in more detail below. After decoding the first syntax element that indicates the size of the CTU, video decoder 300 can decode a second syntax element that indicates a width of an element of a subpicture identifier grid. The second syntax element can be, for example, subpic_grid_col_width_minusl, which is described in more detail below. After decoding the first syntax element that indicates the size of the CTU, video decoder 300 can decode a third syntax element that indicates a height of an element of the subpicture identifier grid. The third syntax element can be, for example, subpic_grid_row_height_minusl, which is described in more detail below. Video decoder 300 can determine a location of a subpicture within a picture based on the first syntax element, the second syntax element, and the third syntax element.

[0073] To determine the position of the subpicture within the picture based on the first syntax element, the second syntax element, and the third syntax element, video decoder 300 can be configured to determine a number of columns in the subpicture identifier grid based on the second syntax element and a width of the picture, determine a number of rows in the subpicture identifier grid based on the third syntax element and a height of the picture, and determine the position of the subpicture within the picture based on the number of columns in the subpicture identifier grid and the number of rows in the subpicture identifier grid. The number of columns in the subpicture identifier grid is shown below as variable NumSubPicGridCols, while the width of the picture is shown below as variable pic width max in luma samples. The number of rows in the subpicture identifier grid is represented below by variable NumSubPicGridRows, while the height of the picture is represented below by variable pic height max in luma samples.

[0074] To determine the number of columns in the subpicture identifier grid based on the second syntax element and the width of the picture, video decoder 300 can be configured to determine whether a width of the CTU is less than a maximum width value, and in response to determining that the width of the CTU is less than the maximum width value, determine the number of columns in the subpicture identifier grid based on the maximum width value. Video decoder 300 can also be configured to determine whether a height of the CTU is less than a maximum height value, and in response to determining that the height of the CTU is less than the maximum height value, determine the number of rows in the subpicture identifier grid based on the maximum height value.

[0075] To determine the position of the subpicture within the picture based on the first syntax element, the second syntax element, and the third syntax element, video decoder 300 can receive a fourth syntax element and identify one of the element identifiers in the subpicture identifier grid based on a value of the fourth syntax element, the number of columns in the subpicture identifier grid, and the number of rows in the subpicture identifier grid, and determine the position of the subpicture within the picture based on the identified element. The fourth syntax element can be, for example, subpic_grid_idx[i][j] described in more detail below. To determine the position of the subpicture within the picture based on the identified element, video decoder 300 can determine a top-left luma sample of the subpicture based on the identified element. The top-left luma sample is represented below by SubPicTop and SubPicLeft.

[0076] A portion of the improved VVC Draft 6, 14th edition, in this disclosure is copied below:

[0077] Section 7.3.2.3 in VVC Draft 6, 14th edition:

[0078]

[0079]

[0080] Section 7.4.3.3 in VVC Draft 6 version 14:

[0081] subpics_present_flag equal to 1 specifies that subpicture parameters are present in the SPS RBSP syntax. subpics_present_flag equal to 0 specifies that subpicture parameters are not present in the SPS RBSP syntax.

[0082] NOTE 2 - When the bitstream is the result of a sub-bitstream extraction process and contains only a subset of the subpictures of the input bitstream of the sub-bitstream extraction process, it can be necessary to set the value of subpics_present_flag to equal 1 in the RBSP of the SPS.

[0083] max_subpics_minus1 plus 1 specifies the maximum number of subpictures that can be present in the CVS. The range of max_subpics_minus1 shall be in the range of 0 to 254. The value 255 is reserved for future use by ITU-T | ISO / IEC.

[0084] subpic_grid_col_width_minus1 plus 1 specifies, in units of 4 samples, the width of each element of the subpicture identifier grid. The length of the syntax element is Ceil( Log2( pic_width_max_in_luma_samples / 4 ) ) bits.

[0085] The variable NumSubPicGridCols is derived as follows:

[0086] NumSubPicGridCols = ( pic_width_max_in_luma_samples + subpic_grid_col_width_minus1 * 4 + 3 ) / ( subpic_grid_col_width_minus1 * 4 + 4 ) (7-5)

[0087] subpic_grid_row_height_minus1 plus 1 specifies, in units of 4 samples, the height of each element of the subpicture identifier grid. The length of the syntax element is Ceil( Log2( pic_height_max_in_luma_samples / 4 ) ) bits.

[0088] The variable NumSubPicGridRows is derived as follows:

[0089] NumSubPicGridRows = ( pic height max in luma samples + subpic grid row height minusl * 4 + 3 ) / ( subpic grid row height minusl * 4 + 4 ) (7-6)

[0090] subpic_grid_idx[ i ][ j ] specifies the subpicture index of grid location ( i, j ). The length of the syntax element is Ceil( Log2( max subpics minusl + 1 ) ) bits.

[0091] The variables SubPicTop[ subpic_grid_idx[ i ][ j ] ], SubPicLeft[ subpic_grid_idx[ i ][ j ] ], SubPicWidth[ subpic_grid_idx[ i ][ j ] ], SubPicHeight[ subpic_grid_idx[ i ][ j ] ], and NumSubPics are derived as follows:

[0092]

[0093] subpic_treated_as_pic_flag[ i ] equal to 1 specifies that the i-th subpicture of each coded picture in the CVS is treated as a picture in the decoding process that does not include the in-loop filtering operation. subpic_treated_as_pic_flag[ i ] equal to 0 specifies that the i-th subpicture of each coded picture in the CVS is not treated as a picture in the decoding process that does not include the in-loop filtering operation. If not present, the value of subpic_treated_as_pic_flag[ i ] is inferred to be equal to 0.

[0094] loop_filter_across_subpic_enabled_flag[ i ] equal to 1 specifies that the in-loop filtering operation can be performed across the boundaries of the i-th subpicture in each coded picture in the CVS. loop_filter_across_subpic_enabled_flag[ i ] equal to 0 specifies that the in-loop filtering operation is not performed across the boundaries of the i-th subpicture in each coded picture in the CVS. If not present, the value of loop_filter_across_subpic_enabled_pic_flag[ i ] is inferred to be equal to 1.

[0095] The following constraints are required for bitstream conformance:

[0096] - For any two sub-pictures subpicA and subpicB, any coded NAL unit of subPicA shall follow any coded NAL unit of subPicB in decoding order when the index of subpicA is less than the index of subpicB.

[0097] The shape of a sub-picture shall be such that each sub-picture, when decoded, shall have its entire left and top boundaries consist of picture boundaries or consist of boundaries of previously decoded sub-pictures.

[0098] The sub-picture signaling implemented in VVC Draft 6 version 14 only allows the presence of one sub-picture while subpics_present_flag is enabled. Since subpics_present_flag is meaningfully enabled only when there are at least two or more sub-pictures, this signaling can be ambiguous by allowing one sub-picture when subpics_present_flag is equal to 1. This problem can occur when subpic_grid_col_width_minus1 and subpic_grid_row_height_minus1 are both equal to 0 and when max_subpics_minus1 is equal to 0. The present disclosure also describes additional techniques that can solve other problems related to grid size. The techniques of the present disclosure potentially solve these drawbacks.

[0099] The present disclosure describes several techniques for improving sub-picture signaling in SPS, PPS, and slice headers. The disclosed techniques can be used individually or in combination. The techniques will be described with respect to changes to VVC Draft 6 version 14. The suggested changes are shown below.

[0100] When subpics_present_flag is enabled, the subpicture signaling implemented in VVC Draft 6 version 14 allows only one subpicture to exist. Since subpics_present_flag is only meaningfully enabled when there are at least 2 or more subpictures, this signaling can create ambiguity by allowing one subpicture when subpics_present_flag is equal to 1. This problem can occur when subpic_grid_col_width_minus1 and subpic_grid_row_height_minus1 are both equal to 0 and when max_subpics_minus1 is equal to 0. According to one example, the present disclosure describes techniques to replace max_subpics_minus1 with max_subpics_minus2 to start the number of subpictures from 2. The present disclosure also describes techniques to not allow subpic_grid_col_width_minus1 and subpic_grid_row_height_minus1 to both be equal to 0. The following table shows the syntax changes to VVC Draft 6 version 14, where the text between <add> and < / add> corresponds to additions, and the text between <del> and < / del> corresponds to deletions.

[0101] Section 7.3.2.3 in VVC Draft 6 version 14:

[0102]

[0103] Section 7.4.3.3 in VVC Draft 6 version 14:

[0104] subpics_present_flag equal to 1 specifies that subpicture parameters are present in the SPS RBSP syntax. subpics_present_flag equal to 0 specifies that subpicture parameters are not present in the SPS RBSP syntax.

[0105] NOTE 2 - When the bitstream is the result of a sub-bitstream extraction process and contains only a subset of the subpictures of the input bitstream of the sub-bitstream extraction process, it can be necessary to set the value of subpics_present_flag to equal 1 in the RBSP of the SPS.

[0106] <del>max subpics minusl plus 1 specifies the maximum number of subpictures that can be present in a CVS. The range of max subpics minusl shall be in the range of 0 to 254. The value 255 is reserved for future use by ITU-T | ISO / IEC.< / del>

[0107] <add>max_subpics_minus2 plus 2 specifies the maximum number of subpictures that can be present in the CVS. The range of max_subpics_minus2 shall be in the range of 0 to N. The value N + b is reserved for future use by ITU-T | ISO / IEC.

[0108] Note that N and b are positive integers, N can be any positive number less than 256, and b can be any positive number such as 1 and 2.

[0109] subpic_grid_col_width_minus1 plus 1 specifies the width of each element of the subpicture identifier grid in units of 4 samples. The length of the syntax element is Ceil( Log2( pic_width_max_in_luma_samples / 4 ) ) bits.

[0110] The variable NumSubPicGridCols is derived as follows:

[0111] NumSubPicGridCols = ( pic_width_max_in_luma_samples + subpic_grid_col_width_minus1 * 4 + 3 ) / ( subpic_grid_col_width_minus1 * 4 + 4 ) (7-5)

[0112] ( subpic_grid_col_width_minus1 * 4 + 4 ) (7-5)

[0113] subpic_grid_row_height_minus1 plus 1 specifies the height of each element of the subpicture identifier grid in units of 4 samples. The length of the syntax element is Ceil( Log2( pic_height_max_in_luma_samples / 4 ) ) bits.

[0114] The variable NumSubPicGridRows is derived as follows:

[0115] NumSubPicGridRows = ( pic_height_max_in_luma_samples + subpic_grid_row_height_minus1 * 4 + 3 ) / ( subpic_grid_row_height_minus1 * 4 + 4 ) (7-6)

[0116] <add>The bitstream conformance requirement is that a single subpicture is not allowed to exist.

[0117] The bitstream conformance requirement is that NumSubPicGridCols = 1 and NumSubPicGridRows = 1 are not allowed.< / add>

[0118] subpic_grid_idx[ i ][ j ] specifies the subpicture index for grid location ( i, j ). The length of the syntax element is Ceil( Log2( max_subpics_minus1 + 1 ) ) bits.

[0119] The variables SubPicTop[ subpic_grid_idx[ i ][ j ] ], SubPicLeft[ subpic_grid_idx[ i ][ j ] ], SubPicWidth[ subpic_grid_idx[ i ][ j ] ], SubPicHeight[ subpic_grid_idx[ i ][ j ] ], and NumSubPics are derived as follows:

[0120]

[0121]

[0122] subpic_treated_as_pic_flag[ i ] equal to 1 specifies that the i-th subpicture of each coded picture in the CVS is treated as a picture in the decoding process that does not include the in-loop filtering operation. subpic_treated_as_pic_flag[ i ] equal to 0 specifies that the i-th subpicture of each coded picture in the CVS is not treated as a picture in the decoding process that does not include the in-loop filtering operation. If not present, the value of subpic_treated_as_pic_flag[ i ] is inferred to be equal to 0.

[0123] loop_filter_across_subpic_enabled_flag[ i ] equal to 1 specifies that the in- loop filtering operation can be performed across the boundaries of the i-th subpicture in each coded picture in the CVS. loop_filter_across_subpic_enabled_flag[ i ] equal to 0 specifies that the in-loop filtering operation is not performed across the boundaries of the i-th subpicture in each coded picture in the CVS. If not present, the value of loop_filter_across_subpic_enabled_pic_flag[ i ] is inferred to be equal to 1.

[0124] The following constraints are required for bitstream conformance:

[0125] - For any two subpictures subpicA and subpicB, when the index of subpicA is less than the index of subpicB, any coded NAL unit of subPicA shall follow any coded NAL unit of subPicB in decoding order.

[0126] - The shape of a subpicture shall be such that, when decoded, each subpicture shall have its entire left and top boundaries consisting of picture boundaries or of boundaries of previously decoded subpictures.

[0127] Implementing subpicture signaling in VVC Draft 6 version 14 can require a large amount of memory to store data of subpicture indices (e.g., subpic_grid_idx[i][j]) because the 4x4 grid size is too small. Using a picture of an 8192x4320 video as an example, storing values of subpicture indices requires 2.21 megabytes in the worst case according to the 4x4 grid size. Accordingly, the present disclosure describes techniques for expanding the grid size and thus reducing the amount of memory required to store subpicture indices. Several examples are described as follows.

[0128] According to a first example, expanding the grid size can depend on the CTU size. Video decoder 300 can assign an amount of memory to store subpicture indices, for example, based on the size of the CTU. Using a picture of an 8192x4320 video as an example, storing subpicture indices requires 34 kilobytes for a 32x32 grid size.

[0129] According to a second example, video decoder 300 can be configured to assign memory for storing subpicture indices according to the CTU size but not smaller than a minimum value (such as 64x64). Using a picture of an 8192x4320 video as an example, if the minimum grid size is 64x64, storing subpicture indices requires 8.6 kilobytes in the worst case.

[0130] To implement the first and second examples above, the signaling of the CTU size, log2_ctu_size_minus5, can be moved forward and precede the syntax elements subpic_grid_idx[i][j]. For example, video decoder 300 can be configured to receive a first syntax element (e.g., log2_ctu_size_minus5), a second syntax element (e.g., subpic_grid_col_width_minus1), and a third syntax element (e.g., subpic_grid_row_height_minus1) in a SPS of the video data, the first syntax element being included in the SPS prior to the second syntax element and the third syntax element.

[0131] The following shows exemplary syntax changes to VVC Draft 6 version 14, where text between <add> and < / add> corresponds to additions, and text between <del> and < / del> corresponds to deletions.

[0132] Section 7.3.2.3 in VVC Draft 6 version 14:

[0133]

[0134]

[0135] Section 7.4.3.3 in VVC Draft 6 version 14:

[0136] log2_ctu_size_minus5 plus 5 specifies the luma coding tree block size of each CTU. The bitstream conformance requirement is that the value of log2_ctu_size_minus5 is less than or equal to 2.

[0137] CtbLog2SizeY = log2_ctu_size_minus5 + 5 (7-15)

[0138] CtbSizeY = 1 « CtbLog2SizeY (7-16)

[0139] subpic_grid_col_width_minus1 plus 1 specifies the width of each element of the subpicture identifier grid in units of <add>CtbSizeY< / add> samples. The length of the syntax element is Ceil( Log2( pic_width_max_in_luma_samples / <add>CtbSizeY< / add> ) ) bits.

[0140] The variable NumSubPicGridCols is derived as follows:

[0141] NumSubPicGridCols = ( pic_width_max_in_luma_samples + subpic_grid_col_width_minus1 * <add>CtbSizeY + CtbSizeY - 1< / add> ) / 64

[0142] ( subpic_grid_col_width_minus1 * <add>CtbSizeY + CtbSizeY< / add> )

[0143] (7-5)

[0144] subpic_grid_row_height_minus1 plus 1 specifies the height of each element of the subpicture identifier grid in units of <add>CtbSizeY< / add> samples. The length of the syntax element is Ceil( Log2( pic_height_max_in_luma_samples / <add>CtbSizeY< / add> ) ) bits.

[0145] The variable NumSubPicGridRows is derived as follows:

[0146] NumSubPicGridRows = ( pic_height_max_in_luma_samples + subpic_grid_row_height_minus1 * <add>CtbSizeY + CtbSizeY - 1< / add> ) /

[0147] ( subpic_grid_row_height_minus1 * <add>CtbSizeY + CtbSizeY< / add> )

[0148] (7-6)

[0149] The following shows exemplary syntax changes to implement the second example above for VVC Draft 6 version 14, where text between <add> and < / add> corresponds to additions, and text between <del> and < / del> corresponds to deletions.

[0150] Section 7.3.2.3 in VVC Draft 6 version 14:

[0151]

[0152] Section 7.4.3.3 in VVC Draft 6 version 14:

[0153] log2_ctu_size_minus5 plus 5 specifies the luma coding tree block size of each CTU. Bitstream conformance requires that the value of log2_ctu_size_minus5 is less than or equal to 2.

[0154] CtbLog2SizeY = log2_ctu_size_minus5 + 5 (7-15)

[0155] CtbSizeY = 1 << CtbLog2SizeY (7-16)

[0156] subpic_grid_col_width_minus1 plus 1 specifies the width of each element of the subpicture identifier grid in <add>max(64, CtbSizeY)< / add> samples. The length of the syntax element is Ceil( Log2( pic_width_max_in_luma_samples / max( 64, CtbSizeY ) ) ) bits.

[0157] The variable NumSubPicGridCols is derived as follows:

[0158] NumSubPicGridCols = ( pic_width_max_in_luma_samples + subpic_grid_col_width_minus1 *<add>max(64, CtbSizeY) + max(64, CtbSizeY) - 1 <add>) / (subpic_grid_col_width_minus1* <add>max(64, CtbSizeY) + max(64, CtbSizeY)< / add> ) (7-5)

[0159] subpic_grid_row_height_minus1 plus 1 to <add>max(64, CtbSizeY)< / add> The height of each element of the sub-picture identifier grid is specified in units of samples. The length of the syntax element is Ceil(Log2(pic_height_max_in_luma_samples / <add>max(64, CtbSizeY)< / add> ))bits.

[0160] The variable NumSubPicGridRows is derived as follows:

[0161] NumSubPicGridRows=(pic_height_max_in_luma_samples+subpic_grid_row_height_minus1* <add>max(64, CtbSizeY) + max(64, CtbSizeY) - 1< / add> ) /

[0162] (subpic_grid_row_height_minus1* <add>max(64, CtbSizeY) + max(64, CtbSizeY))< / add> (7-6)

[0163] FIG. 3 is a block diagram illustrating an example video encoder 200 that may perform the techniques of this disclosure. FIG. 3 This is provided for illustrative purposes and should not be considered limiting of the techniques broadly exemplified and described in this disclosure. For illustrative purposes, this disclosure describes the video encoder 200 in the context of video codec standards such as the ITU-T H.265 (HEVC) video codec standard and the ITU-T H.266 (VVC) video codec standard under development. However, the techniques of this disclosure are not limited to these video codec standards and are generally applicable to video encoding and decoding.

[0164] exist FIG. 3 In the example of FIG. 2, video encoder 200 includes video data memory 230, mode select unit 202, residual generation unit 204, transform processing unit 206, quantization unit 208, inverse quantization unit 210, inverse transform processing unit 212, reconstruction unit 214, filter unit 216, decoded picture buffer (DPB) 218, and entropy encoding unit 220. Any or all of video data memory 230, mode select unit 202, residual generation unit 204, transform processing unit 206, quantization unit 208, inverse quantization unit 210, inverse transform processing unit 212, reconstruction unit 214, filter unit 216, DPB 218, and entropy encoding unit 220 can be implemented in one or more processors or in processing circuitry. Additionally, video encoder 200 can include additional or alternative processors or processing circuitry to perform these and other functions.

[0165] Video data memory 230 can store video data to be encoded by the components of video encoder 200. Video encoder 200 can receive the video data stored in video data memory 230 from, for example, video source 104 FIG. 1 DPB 218 can function as a reference picture memory that stores reference video data for use in encoding by video encoder 200 of 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 DPB 218 can be provided by the same memory device or separate memory devices. In various examples, video data memory 230 can be on-chip with other components of video encoder 200, as illustrated, or off-chip relative to those components.

[0166] In this disclosure, reference to video data memory 230 should not be construed as being limited to memory that is internal to video encoder 200, unless specifically so described, or memory that is external to video encoder 200, unless specifically so described. Rather, reference to video data memory 230 should be understood as a reference to a memory that stores video data that video encoder 200 receives for encoding (e.g., video data of a current block that is to be encoded). FIG. 1 Memory 106 of video encoder 200 can also provide temporary storage of the outputs from the various units of video encoder 200.

[0167] FIG. 3 The various units of video encoder 200 are shown to assist with understanding the operations performed by video encoder 200. The units can be implemented as fixed- function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide particular functionality, and default operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexible functionality in the operations that can be performed. For example, programmable circuits can execute software or firmware that cause the programmable circuits to operate in ways defined by instructions of the software or firmware. Fixed-function circuits can execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. In some examples, one or more of the units can be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units can be integrated circuits.

[0168] Video encoder 200 can include arithmetic logic units (ALUs), elementary function units (EFUs), digital circuits, analog circuits, and / or programmable cores formed from programmable circuits. In examples where the operations of video encoder 200 are performed using software executed by the programmable circuits, memory 106 FIG. 1 ) can store instructions (e.g., object code) of the software that video encoder 200 receives and executes, or another memory within video encoder 200 (not shown) can store such instructions.

[0169] Video data memory 230 is configured to store received video data. Video encoder 200 can retrieve pictures of the video data from video data memory 230 and provide the video data to residual generation unit 204 and mode selection unit 202. Video data in video data memory 230 can be raw video data that is to be encoded.

[0170] Mode selection unit 202 includes motion estimation unit 222, motion compensation unit 224, and intra-prediction unit 226. Mode selection unit 202 can include additional functional units to conduct video prediction according to other prediction modes. As examples, mode selection unit 202 can include a palette unit, an intra-block copy unit (which can be part of motion estimation unit 222 and / or motion compensation unit 224), an affine unit, a linear model (LM) unit, etc.

[0171] Mode selection unit 202 generally coordinates multiple encoding passes to test combinations of encoding parameters and resulting rate-distortion values for such combinations. The encoding parameters can include partitioning of CTUs into CUs, prediction modes for CUs, transform types for residual data of CUs, quantization parameters for residual data of CUs, and so forth. Mode selection unit 202 can ultimately select the combination of encoding parameters that has the best rate- distortion value, of the combinations that were tested.

[0172] Video encoder 200 can partition a picture retrieved from video data memory 230 into a series of CTUs, and encapsulate one or more CTUs within a slice. Mode select unit 202 can partition a CTU of a picture according to a tree structure, such as the QTBT structure described above or the quad-tree structure of HEVC. As described above, video encoder 200 can form one or more CUs from partitioning a CTU according to the tree structure. The CU can also be referred to generally as a "video block" or a "block."

[0173] In general, mode select unit 202 also controls its components (e.g., motion estimation unit 222, motion compensation unit 224, and intra prediction unit 226) to generate a prediction block for a current block (e.g., a current CU, or a portion of a PU and TU that overlap in HEVC). For inter prediction of a current block, 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 coded pictures stored in DPB 218). Specifically, motion estimation unit 222 can calculate a value that represents a degree of similarity of a potential reference block to the current block, e.g., according to a sum of absolute difference (SAD), a sum of squared difference (SSD), a mean absolute difference (MAD), a mean squared difference (MSD), etc. Motion estimation unit 222 can generally perform these calculations using sample-by-sample differences between the current block and a considered reference block. Motion estimation unit 222 can identify the reference block with the smallest value resulting from these calculations, indicating the reference block that most closely matches the current block.

[0174] Motion estimation unit 222 can form one or more motion vectors (MVs) that define the position of a reference block in a reference picture relative to the position of the current block in the current picture. Motion estimation unit 222 can then provide the motion vector(s) to motion compensation unit 224. For example, for single prediction, motion estimation unit 222 can provide a single motion vector, while for bi-prediction, motion estimation unit 222 can provide two motion vectors. Motion compensation unit 224 can then use the motion vector(s) to generate the prediction block. For example, motion compensation unit 224 can use the motion vector(s) to retrieve data for the reference block(s). As another example, if the motion vector(s) have fractional sample precision, motion compensation unit 224 can interpolate values for the prediction block according to one or more interpolation filters. Further, for bi-prediction, motion compensation unit 224 can retrieve data for two reference blocks identified by the respective motion vectors, and combine the retrieved data, e.g., via sample-by-sample averaging or weighted averaging.

[0175] As another example, for intra prediction or intra prediction coding, the intra prediction unit 226 can generate a prediction block from samples neighboring the current block. For example, for directional modes, the intra prediction unit 226 can mathematically combine values of the neighboring samples and interpolate these calculated values across a defined direction across the current block to generate the prediction block. As another example, for a DC mode, the intra prediction unit 226 can calculate an average of the values of the samples neighboring the current block and generate the prediction block to include this resulting average for each sample of the prediction block.

[0176] The mode selection unit 202 provides the prediction block to the residual generation unit 204. The residual generation unit 204 receives the original, unencoded version of the current block from the video data memory 230 and the original, unencoded version of the prediction block from the mode selection unit 202. The residual generation unit 204 calculates 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 can also determine the difference between 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 can be formed using one or more subtractor circuits that perform binary subtraction.

[0177] In examples in which the mode selection unit 202 partitions the CU into PUs, each PU can be associated with a luma prediction unit and corresponding chroma prediction units. Video encoder 200 and video decoder 300 can support PUs having various sizes. As indicated above, the size of a CU can refer to the size of the CU’s luma coding block, while the size of a PU can refer to the size of the PU’s luma prediction unit. Assuming that a particular CU has a size of 2Nx2N, video encoder 200 can support 2Nx2N or NxN PU sizes for intra prediction, and 2Nx2N, 2NxN, Nx2N, NxN, or similar symmetric PU sizes for inter prediction. Video encoder 200 and video decoder 300 can also support non-symmetric partitioning for inter prediction for PU sizes of 2NxnU, 2NxnD, nLx2N, and nRx2N.

[0178] In examples in which the mode selection unit 202 does not partition the CU into PUs, each CU can be associated with a luma coding block and corresponding chroma coding blocks. As shown above, the size of a CU can refer to the size of the CU’s luma coding block. Video encoder 200 and video decoder 300 can support CU sizes of 2N x 2N, 2N x N, or N x 2N.

[0179] For other video coding techniques such as intra block copy mode coding, affine mode coding, and linear model (LM) mode coding, to name a few examples, the mode selection unit 202 generates a prediction block for the positively encoded current block via a respective unit associated with the coding technique. In some examples, such as palette mode coding, the mode selection unit 202 can not generate a prediction block, but rather generate syntax elements indicative of a way to reconstruct the block based on a selected palette. In such modes, the mode selection unit 202 can provide these syntax elements to the entropy encoding unit 220 to be encoded.

[0180] As described above, the residual generation unit 204 receives video data for the 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 computes a sample-by-sample difference between the prediction block and the current block.

[0181] The transform processing unit 206 applies one or more transforms to the residual block to produce 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 Karhunen-Loeve transform (KLT), or a conceptually similar transform to the residual block. In some examples, the transform processing unit 206 can perform multiple transforms, e.g., a primary transform and a secondary transform such as a rotational transform, on the residual block. In some examples, the transform processing unit 206 does not apply a transform to the residual block.

[0182] The quantization unit 208 can quantize transform coefficients in the transform coefficient block to produce a quantized transform coefficient block. The quantization unit 208 can quantize transform coefficients of 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) can adjust the degree of quantization applied to the transform coefficient block associated with the current block by adjusting the QP value associated with the CU. Quantization can introduce loss of information, and thus, quantized transform coefficients can have lower precision than the original transform coefficients produced by the transform processing unit 206.

[0183] Inverse quantization unit 210 and inverse transform processing unit 212 can apply inverse quantization and inverse transforms, respectively, to the quantized transform coefficient blocks to reconstruct residual blocks from the transform coefficient blocks. Reconstruction unit 214 can generate a reconstructed block corresponding to the current block based on the reconstructed residual block and the prediction block generated by mode selection unit 202, although possibly with some degree of distortion. For example, reconstruction unit 214 can add samples of the reconstructed residual block to corresponding samples from the prediction block generated by mode selection unit 202 to produce the reconstructed block.

[0184] Filter unit 216 can perform one or more filtering operations on the reconstructed block. For example, filter unit 216 can perform a deblocking operation to reduce blocking artifacts along the edges of the CU. In some examples, the operations of filter unit 216 can be skipped.

[0185] Video encoder 200 stores the reconstructed block in DPB 218. For example, in examples in which the operations of filter unit 216 are not performed, reconstruction unit 214 can store the reconstructed block to DPB 218. In examples in which the operations of filter unit 216 are performed, filter unit 216 can store the filtered reconstructed block to DPB 218. Motion estimation unit 222 and motion compensation unit 224 can retrieve reference pictures formed from reconstructed (and possibly filtered) blocks from DPB 218 to inter-predict blocks of a subsequently encoded picture. In addition, intra-prediction unit 226 can use reconstructed blocks of the current picture in DPB 218 to intra-predict other blocks in the current picture.

[0186] In general, entropy encoding unit 220 can entropy encode syntax elements received from other functional components of video encoder 200. For example, entropy encoding unit 220 can entropy encode quantized transform coefficient blocks from quantization unit 208. As another example, entropy encoding unit 220 can entropy encode prediction syntax elements (e.g., motion information for inter-prediction or intra-mode information for intra-prediction) from mode selection unit 202. Entropy encoding unit 220 can perform one or more entropy encoding operations on the syntax elements, which are another example of video data, to produce entropy encoded data. For example, entropy encoding unit 220 can 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 index Columb coding operation, or another type of entropy coding operation. In some examples, entropy encoding unit 220 can operate in a bypass mode where the syntax elements are not entropy encoded.

[0187] Video encoder 200 can output a bitstream that includes the entropy encoded syntax elements needed to reconstruct blocks of a slice or picture. In particular, entropy encoding unit 220 can output the bitstream.

[0188] The operations described above are described in terms of blocks. This description should be understood to be operations for a luma coded block and / or a chroma coded block. As described above, in some examples, the luma coded block and the chroma coded block are luma and chroma components of a CU. In some examples, the luma coded block and the chroma coded block are luma and chroma components of a PU.

[0189] In some examples, operations performed with respect to a luma coded block need not be repeated for a chroma coded block. As one example, the operations to identify a motion vector (MV) and a reference picture for a luma coded block need not be repeated to identify an MV and a reference picture for a chroma block. More specifically, the MV of the luma coded block can be scaled to determine the MV of the chroma block, and the reference picture can be the same. As another example, the intra prediction procedure can be the same for luma and chroma coded blocks.

[0190] As such, video encoder 200 represents an example of a video encoding device including a memory configured to store video data and one or more processing units implemented in circuitry and configured to encode a first syntax element, where a value for the first syntax element plus 2 indicates a maximum number of subpictures that can be present in a coded video sequence (CVS).

[0191] Video encoder 200 also represents an example of a video encoding device including a memory configured to store video data and one or more processing units implemented in circuitry and configured to encode video data according to a restriction where neither a first syntax element nor a second syntax element can be equal to 0 at the same time, where a value for the first syntax element plus 1 specifies a width of each element of a subpicture identifier grid in units of N samples, and a value for the second syntax element plus 1 specifies a height of each element of the subpicture identifier grid in units of N samples, where N is an integer value.

[0192] Video encoder 200 also represents an example of a video encoding device including a memory configured to store video data and one or more processing units implemented in circuitry and configured to encode syntax elements indicating a size of a coding tree unit and, after encoding the syntax elements indicating the size of the coding tree unit, encode a first syntax element and a second syntax element, where a value of the first syntax element plus one specifies a width of each element of a subpicture identifier grid in units of N samples and a value of the second syntax element plus one specifies a height of each element of the subpicture identifier grid in units of N samples, where N is an integer value.

[0193] Video encoder 200 also represents an example of a video encoding device including a memory configured to store video data and one or more processing units implemented in circuitry and configured to encode syntax elements indicating a size of a coding tree unit and, after encoding the syntax elements indicating the size of the coding tree unit, encode a first syntax element and a second syntax element, where a value of the first syntax element plus one specifies a width of each element of a subpicture identifier grid in units of a maximum(64, CtbSizeY) samples and the second syntax element specifies a height of each element of the subpicture identifier grid in units of a maximum(64, CtbSizeY) samples. In this example or any of the above examples, the syntax elements may, for example, be included in an SPS.

[0194] FIG. 4 FIG. 3 is a block diagram illustrating an example video decoder 300 that can perform the techniques of this disclosure. FIG. 4 The techniques of this disclosure are not limited to video decoder 300 as illustrated in FIG. 3. Other devices can perform the techniques of this disclosure, including video encoding devices. Video decoder 300 is illustrated and described for purposes of explanation and as an example of a device that can implement the techniques of this disclosure. Although video decoder 300 is described as performing the techniques of this disclosure, other devices can perform the techniques of this disclosure, including video encoding devices.

[0195] In FIG. 4 In the example of FIG. 3, video decoder 300 includes coded picture buffer (CPB) memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and decoded picture buffer (DPB) 314. Any or all of CPB memory 320, entropy decoding unit 302, prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, filter unit 312, and DPB 314 can be implemented in one or more processors or in processing circuitry. Moreover, video decoder 300 can include additional or alternative processors or processing circuitry to perform these and other functions.

[0196] Prediction processing unit 304 includes motion compensation unit 316 and intra-prediction unit 318. Prediction processing unit 304 can include additional units to perform prediction from other prediction modes. As examples, prediction processing unit 304 can include a palette unit, an intra-block copy unit (which can form a part of motion compensation unit 316), an affine unit, a linear model (LM) unit, or the like. In other examples, video decoder 300 can include more, less, or different functional components.

[0197] CPB memory 320 can store video data, such as encoded video bitstreams, to be decoded by the components of video decoder 300. The video data stored in CPB memory 320 can be obtained, for example, from computer- readable medium 110( FIG. 1 ). CPB memory 320 can include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. Also, memory 320 can store video data other than syntax elements of encoded pictures, such as temporary data representing outputs from the various units of video decoder 300. DPB 314 generally stores decoded pictures that video decoder 300 can output and / or use as reference video data when decoding subsequent data or pictures of an encoded video bitstream. CPB memory 320 and DPB 314 can be formed by any of a variety of memory devices, including DRAM, such as SDRAM, MRAM, RRAM, or other types of memory devices. CPB memory 320 and DPB 314 can be provided by the same memory devices or by separate memory devices. In various examples, CPB memory 320 can be on-chip with other components of video decoder 300 or off-chip relative to those components.

[0198] Additionally or alternatively, in some examples, video decoder 300 can obtain video data from memory 120( FIG. 1 ) retrieve the coded video data. That is, memory 120 can store the data as discussed above through CPB memory 320. Likewise, when some or all of the functionality of video decoder 300 is implemented in software executed by processing circuitry of video decoder 300, memory 120 can store the instructions to be executed by video decoder 300.

[0199] FIG. 4 The various units shown in FIG. 3 are shown as being part of video decoder 300. The units can be implemented as fixed function circuitry, programmable circuitry, or as a combination of both fixed function and programmable circuitry. Similar to FIG. 3 , fixed function circuitry refers to circuitry that provides specific functionality, and defaults to a particular operation for that functionality. Programmable circuitry refers to circuitry that can be programmed to perform various tasks, and provides flexible functionality in the operations that can be performed. For example, programmable circuitry can execute software or firmware instructions using a central processing unit or microprocessor, which access instructions fixed in memory to perform a particular task. In some examples, one or more of the units shown in FIG. 3 can be different circuit blocks (fixed or programmable), and in some examples, one or more of the units shown in FIG. 3 can be integrated circuitry.

[0200] Video decoder 300 can include ALUs, EFUs, digital circuits, analog circuits, and / or programmable cores formed from programmable circuitry. In examples where operations of video decoder 300 are performed by software executing on programmable circuitry, on-chip or off-chip memory can store instructions (e.g., object code) of the software that video decoder 300 receives and executes.

[0201] Entropy decoding unit 302 can receive encoded video data from the CPB memory and entropy decode the video data to reproduce syntax elements. Prediction processing unit 304, inverse quantization unit 306, inverse transform processing unit 308, reconstruction unit 310, and filter unit 312 can generate decoded video data based on the syntax elements extracted from the bitstream.

[0202] In general, video decoder 300 reconstructs a picture on a block-by-block basis. Video decoder 300 can perform the reconstruction operation separately for each block, where the currently reconstructed (i.e., decoded) block can be referred to as the "current block."

[0203] Entropy decoding unit 302 can entropy decode syntax elements defining quantized transform coefficients of a quantized transform coefficient block, as well as transform information such as a quantization parameter (QP) and / or an indication of a transform mode. Inverse quantization unit 306 can use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 306 to apply. Inverse quantization unit 306 may, for example, perform a bitshift operation to inverse quantize the quantized transform coefficients. Inverse quantization unit 306 can thereby form a transform coefficient block comprising transform coefficients.

[0204] After inverse quantization unit 306 forms the transform coefficient block, inverse transform processing unit 308 can apply one or more inverse transforms to the transform coefficient block to produce a residual block associated with the current block. For example, inverse transform processing unit 308 can apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve Transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block.

[0205] Further, prediction processing unit 304 generates a prediction block from the prediction information syntax elements entropy decoded by entropy decoding unit 302. For example, if the prediction information syntax elements indicate that the current block is inter predicted, motion compensation unit 316 can generate the prediction block. In that case, the prediction information syntax elements can indicate a reference picture in DPB 314 from which to retrieve the reference block, as well as a motion vector that identifies a location of the reference block in the reference picture relative to a location of the current block in the current picture. Motion compensation unit 316 can generally perform the inter prediction process substantially similar to the manner described with respect to motion compensation unit 224 FIG. 3 ) described above.

[0206] As another example, if the prediction information syntax elements indicate that the current block is intra predicted, intra prediction unit 318 can generate the prediction block according to an intra prediction mode indicated by the prediction information syntax elements. Also, intra prediction unit 318 can generally perform the intra prediction process substantially similar to the manner described with respect to intra prediction unit 226 FIG. 3 ) described above. Intra prediction unit 318 can retrieve data of neighboring samples from DPB 314 to the current block.

[0207] Reconstruction unit 310 can use the prediction block and the residual block to reconstruct the current block. For example, reconstruction unit 310 can add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block.

[0208] Filter unit 312 can perform one or more filtering operations on the reconstructed block. For example, filter unit 312 can perform a deblocking operation to reduce blocking artifacts along the edges of the reconstructed block. The operations of filter unit 312 are not necessarily performed in all examples.

[0209] Video decoder 300 can store the reconstructed blocks in DPB 314. For instance, in examples in which operations of filter unit 312 are not performed, reconstructed unit 310 can store the reconstructed blocks to DPB 314. In examples in which operations of filter unit 312 are performed, filter unit 312 can store the filtered reconstructed blocks to DPB 314. As discussed above, DPB 314 can provide reference information, such as samples of previously decoded pictures for inter prediction and current pictures for subsequent motion compensation, to prediction processing unit 304. In addition, video decoder 300 can output decoded pictures (e.g., a decoded video) from DPB 314 for subsequent presentation on a display device, such as display device 118 of FIG. 1. FIG. 1

[0210] As such, video decoder 300 represents an example of a video decoding device including a memory configured to store video data and one or more processing units implemented in circuitry and configured to decode a first syntax element, where a value for the first syntax element plus 2 indicates a maximum number of subpictures that can be present in a coded video sequence.

[0211] Video decoder 300 also represents an example of a video decoding device including a memory configured to store video data and one or more processing units implemented in circuitry and configured to decode video data according to a restriction in which neither a first syntax element nor a second syntax element can be equal to 0 at the same time, where a value for the first syntax element plus 1 specifies a width of each element of a subpicture identifier grid in units of N samples, and a value for the second syntax element plus 1 specifies a height of each element of the subpicture identifier grid in units of N samples, where N is an integer value.

[0212] Video decoder 300 also represents an example of a video decoding device including a memory configured to store video data and one or more processing units implemented in circuitry and configured to decode a syntax element indicating a size of a coding tree unit and, after the syntax element indicating the size of the coding tree unit is decoded, decode a first syntax element and a second syntax element, where a value for the first syntax element plus 1 specifies a width of each element of a subpicture identifier grid in units of N samples, and a value for the second syntax element plus 1 specifies a height of each element of the subpicture identifier grid in units of N samples, where N is an integer value.

[0213] ​Video decoder 300 also represents an example of a video decoding device including a memory configured to store video data and one or more processing units implemented in circuitry and configured to decode syntax elements indicating a size of a coding tree unit and, after the syntax elements indicating the size of the coding tree unit are coded, decode a first syntax element and a second syntax element, where a value of the first syntax element plus one specifies a width of each element of a subpicture identifier grid in units of max(64, CtbSizeY) samples, and the second syntax element specifies a height of each element in the subpicture identifier grid in units of max(64, CtbSizeY) samples. In this or any of the above examples, the syntax elements may, for example, be included in an SPS.

[0214] FIG. 5 is a flowchart illustrating an example process for encoding a current block. The current block can include a current CU. Although described with respect to video encoder 200 FIG. 1 and FIG. 3 ), it should be understood that other devices can be configured to perform methods similar to the method of FIG. 5 .

[0215] In this example, video encoder 200 first predicts the current block (350). For example, video encoder 200 can form a prediction block for the current block. Video encoder 200 can then calculate a residual block for the current block (352). To calculate the residual block, video encoder 200 can calculate a difference between an original, unencoded block of the current block and the prediction block. Video encoder 200 can then transform and quantize coefficients of the residual block (354). Next, video encoder 200 can scan the quantized transform coefficients of the residual block (356). During the scan or after the scan, video encoder 200 can entropy encode the transform coefficients (358). For example, video encoder 200 can encode the transform coefficients using CAVLC or CABAC. Video encoder 200 can then output the entropy encoded data for the block (360).

[0216] FIG. 6 is a flowchart illustrating an example process for decoding a current block of video data. The current block can include a current CU. Although described with respect to video decoder 300 FIG. 1 and FIG. 4 ), it should be understood that other devices can be configured to perform methods similar to the method of FIG. 6 .

[0217] Video decoder 300 can receive entropy encoded data for the current block, such as entropy encoded prediction information and entropy encoded data corresponding to the coefficients of the residual block for the current block (370). Video decoder 300 can entropy decode the entropy encoded data to determine prediction information for the current block and to reproduce the coefficients of the residual block (372). Video decoder 300 can predict the current block (374), e.g., using intra- or inter-prediction as indicated by the prediction information for the current block, to calculate a prediction block for the current block. Video decoder 300 can then inverse scan the reproduced coefficients (376) to produce a block of quantized transform coefficients. Video decoder 300 can then inverse quantize and inverse transform the transform coefficients to produce a residual block (378). Video decoder 300 can finally decode the current block by combining the prediction block with the residual block (380).

[0218] FIG. 7 is a flowchart illustrating an exemplary process for decoding a block of a picture of video data. Although described with respect to video decoder 300 FIG. 1 and FIG. 4 ), it should be understood that other devices can be configured to perform methods similar to the method of FIG. 7 .

[0219] In the example of FIG. 7 , video decoder 300 decodes a first syntax element that indicates a size of a CTU (400). After decoding the first syntax element that indicates the size of the CTU, video decoder 300 decodes a second syntax element that indicates a width of an element of a subpicture identifier grid (402). After decoding the first syntax element that indicates the size of the CTU, video decoder 300 decodes a third syntax element that indicates a height of an element of the subpicture identifier grid (404). Video decoder 300 may, for example, receive the first syntax element, the second syntax element, and the third syntax element in a sequence parameter set of the video data. The first syntax element can be included in the sequence parameter set of the video data prior to the second syntax element and the third syntax element.

[0220] Video decoder 300 determines a position of a subpicture within a picture based on the first syntax element, the second syntax element, and the third syntax element (406). To determine the position of the subpicture within the picture based on the first syntax element, the second syntax element, and the third syntax element, video decoder 300 can be configured to determine a number of columns in the subpicture identifier grid based on the first syntax element, the second syntax element, and a width of the picture; determine a number of rows in the subpicture identifier grid based on the first syntax element, the third syntax element, and a height of the picture; and determine the position of the subpicture within the picture based on the number of columns in the subpicture identifier grid and the number of rows in the subpicture identifier grid.

[0221] To determine the number of columns in the subpicture identifier grid based on the second syntax element and a width of the picture, video decoder 300 can be configured to determine whether a width of the CTU is less than a maximum width value, and in response to determining that the width of the CTU is less than the maximum width value, determine the number of columns in the subpicture identifier grid based on the maximum width value. To determine the number of rows in the subpicture identifier grid based on the third syntax element and a height of the picture, video decoder 300 can be configured to determine whether a height of the CTU is less than a maximum height value, and in response to determining that the height of the CTU is less than the maximum height value, determine the number of rows in the subpicture identifier grid based on the maximum height value.

[0222] To determine a position of the subpicture within the picture based on the first syntax element, the second syntax element, and the third syntax element, video decoder 300 can be configured to receive a fourth syntax element, identify an element of the elements of the subpicture identifier grid based on a value of the fourth syntax element, the number of columns in the subpicture identifier grid, and the number of rows in the subpicture identifier grid, and determine the position of the subpicture within the picture based on the identified element. To determine the position of the subpicture within the picture based on the identified element, video decoder 300 can be configured to determine a top-left luma sample of the subpicture based on the identified element. Video decoder 300 can allocate an amount of memory to store the value of the fourth syntax element based on a size of the CTU.

[0223] Video decoder 300 can decode the subpicture based on the determined position. As part of the decoding, video decoder 300 can, for example, extract the subpicture from the picture or move the subpicture relative to other subpictures in the picture.

[0224] The following examples describe techniques that can be performed by one or both of video encoder 200 and video decoder 300.

[0225] Example 1 : A method of coding video data includes coding a first syntax element, where a value of the first syntax element plus 2 indicates a maximum number of subpictures that can be present in a coded video sequence.

[0226] Example 2: A method of coding video data includes coding the video data according to a restriction where neither a first syntax element nor a second syntax element can both be equal to 0, where a value of the first syntax element plus 1 specifies a width of each element of a subpicture identifier grid in units of N samples, and a value of the second syntax element plus 1 specifies a height of each element of the subpicture identifier grid in units of N samples, where N is an integer value.

[0227] Example 3: A method of coding video data comprises coding a syntax element indicating a size of a coding tree unit; coding, after coding the syntax element indicating the size of the coding tree unit, a first syntax element and a second syntax element, wherein a value of the first syntax element plus 1 specifies a width of each element of a subpicture identifier grid in units of N samples, and a value of the second syntax element plus 1 specifies a height of each element of the subpicture identifier grid in units of N samples, where N is an integer value.

[0228] Example 4: A method of coding video data comprises coding a syntax element indicating a size of a coding tree unit; coding, after coding the syntax element indicating the size of the coding tree unit, a first syntax element and a second syntax element, wherein a value of the first syntax element plus 1 specifies a width of each element of a subpicture identifier grid in units of max(64, CtbSizeY) samples, and the second syntax element specifies a height of each element of the subpicture identifier grid in units of max(64, CtbSizeY) samples.

[0229] Example 5: The method of any of examples 1-4, wherein the syntax element is included in a sequence parameter set.

[0230] Example 6: The method of any of examples 1-5, wherein coding comprises decoding.

[0231] Example 7: The method of any of examples 1-5, wherein coding comprises encoding.

[0232] Example 8: An apparatus for coding video data, the apparatus comprising one or more means for performing the method of any of examples 1-5.

[0233] Example 9: The apparatus of example 8, wherein the one or more means comprise one or more processors implemented in circuitry.

[0234] Example 10: The apparatus of any of examples 8 or 9, further comprising a memory for storing video data.

[0235] Example 11: The apparatus of any of examples 8-10, further comprising a display configured to display decoded video data.

[0236] Example 12: The apparatus of any of examples 8-11, wherein the apparatus comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box.

[0237] Example 13: The device of any of examples 8-12, wherein the device comprises a video decoder.

[0238] Example 14: The device of any of examples 8-13, wherein the device comprises a video encoder.

[0239] Example 15: A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to perform the method of any of examples 1-7.

[0240] It is recognized that depending on the example, certain acts or events of any of the techniques described herein can be performed in a different sequence, can be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the techniques). Moreover, in certain examples, acts or events can be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.

[0241] In one or more examples, the functions described can be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions can be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media can include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer- readable media generally can correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media can be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and / or data structures for implementation of the techniques described in this disclosure. A computer program product can include a computer-readable medium.

[0242] By way of example, and not limitation, such computer-readable storage media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other storage medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transient media, but are instead directed to non-transient, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0243] Instructions can be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the term "processor," as used herein can refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein can be provided within dedicated hardware and / or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be embodied in one or more circuits or logic elements.

[0244] The techniques of this disclosure can be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described herein as being configured to perform a particular function or task. Unless otherwise specified, the particular function or task can be performed by one or more circuits or logic elements. For example, various components, modules, or units can be implemented by one or more circuits or logic elements, which can include portions of the circuit or logic elements coupled with one or more processors. In some aspects, one or more of the components, modules, or units can be implemented by one or more processors executing instructions as described herein.

[0245] Various examples have been described. These and other examples are within the scope of the following claims.< / add> < / add>

Claims

1. A method for decoding video data, the method comprising: decoding a first syntax element indicating a size of a codec tree unit (CTU); After decoding the first syntax element indicating the size of the CTU, decoding a second syntax element indicating a width of an element of a sub-picture identifier grid; After decoding the first syntax element indicating the size of the CTU, decoding a third syntax element indicating the height of an element of a sub-picture identifier grid; After decoding the first syntax element indicating the size of the CTU, decoding a fourth syntax element indicating a grid index of a sub-picture; determining a maximum value between a size of a CTU and a predetermined value; wherein the predetermined value is a value indicating a predetermined size of a sub-picture identifier grid; wherein the second syntax element indicates the width of the element of the sub-picture identifier grid in units of the maximum value; wherein the third syntax element indicates the height of the element of the sub-picture identifier grid in units of the maximum value; responsive to determining the maximum value, determining a number of columns in the sub-picture identifier grid based on the maximum value, an image width in luma samples, and a sub-picture identifier grid column width; In response to determining the maximum value, determining a number of rows in the sub-picture identifier grid based on the maximum value, a picture height in luma samples, and a sub-picture identifier grid row width; determining a position of the sub-picture within a picture based on the grid index, the determined number of columns, and the determined number of rows; and The sub-picture is decoded based on the determined position.

2. The method according to claim 1, wherein Determining a position of the sub-picture within the picture based on the grid index, the determined number of columns, and the determined number of rows further comprises: identifying one of the elements of the sub-picture identifier grid based on the value of the fourth syntax element, the determined number of columns in the sub-picture identifier grid, and the determined number of rows in the sub-picture identifier grid; and The position of the sub-picture within the picture is determined based on the identified element.

3. The method according to claim 2, wherein: Determining a position of the sub-picture within a picture based on the identified element includes determining a top left luma sample of the sub-picture based on the identified element.

4. The method according to claim 2, further comprising: An amount of memory is allocated based on the size of the CTU to store the value of the fourth syntax element.

5. The method according to claim 1, further comprising: The first syntax element, the second syntax element, and the third syntax element in a sequence parameter set for the video data are received.

6. The method according to claim 5, wherein: The sequence parameter set includes the first syntax element, the second syntax element, and the third syntax element, and in the sequence parameter set, the first syntax element precedes the second syntax element and the third syntax element.

7. A device for decoding video data, the device comprising: Memory; as well as one or more processors implemented in circuitry, the one or more processors coupled to the memory and configured to: decoding a first syntax element indicating a size of a codec tree unit (CTU); After decoding a first syntax element indicating a size of the CTU, decoding a second syntax element indicating a width of an element of a sub-picture identifier grid; After decoding a first syntax element indicating a size of the CTU, decoding a third syntax element indicating a height of an element of a sub-picture identifier grid; After decoding a first syntax element indicating a size of the CTU, decoding a fourth syntax element indicating a grid index of a sub-picture; determining a maximum value between a size of a CTU and a predetermined value; wherein the predetermined value is a value indicating a predetermined size of a sub-picture identifier grid; wherein the second syntax element indicates the width of the element of the sub-picture identifier grid in units of the maximum value; wherein the third syntax element indicates the height of the element of the sub-picture identifier grid in units of the maximum value; responsive to determining the maximum value, determining a number of columns in the sub-picture identifier grid based on the maximum value, an image width in luma samples, and a sub-picture identifier grid column width; In response to determining the maximum value, determining a number of rows in the sub-picture identifier grid based on the maximum value, a picture height in luma samples, and a sub-picture identifier grid row width; determining a position of the sub-picture within a picture based on the grid index, the determined number of columns, and the determined number of rows; and The sub-picture is decoded based on the determined position.

8. The apparatus according to claim 7, wherein To determine a position of the sub-picture within the picture based on the grid index, the determined number of columns, and the determined number of rows, the one or more processors are further configured to: identifying one of the elements of the sub-picture identifier grid based on a value of the fourth syntax element, a determined number of columns in the sub-picture identifier grid, and a determined number of rows in the sub-picture identifier grid; as well as The position of the sub-picture within the picture is determined based on the identified element.

9. The apparatus according to claim 8, wherein To determine the position of the sub-picture within the picture based on the identified element, the one or more processors are further configured to determine a top left luma sample of the sub-picture based on the identified element.

10. The apparatus according to claim 8, wherein The one or more processors are further configured to: An amount of memory is allocated based on the size of the CTU to store the value of the fourth syntax element.

11. The apparatus according to claim 7, wherein The one or more processors are further configured to: The first syntax element, the second syntax element, and the third syntax element in a sequence parameter set for the video data are received.

12. The apparatus according to claim 11, wherein The sequence parameter set includes the first syntax element, the second syntax element, and the third syntax element, and in the sequence parameter set, the first syntax element precedes the second syntax element and the third syntax element.

13. The apparatus of claim 10, further comprising: A display is configured to display the decoded sub-picture.

14. A computer-readable storage medium having stored thereon instructions that, when executed, configure a processor to: decoding a first syntax element indicating a size of a codec tree unit (CTU); After decoding a first syntax element indicating a size of the CTU, decoding a second syntax element indicating a width of an element of a sub-picture identifier grid; After decoding a first syntax element indicating a size of the CTU, decoding a third syntax element indicating a height of an element of a sub-picture identifier grid; After decoding a first syntax element indicating a size of the CTU, decoding a fourth syntax element indicating a grid index of a sub-picture; determining a maximum value between a size of a CTU and a predetermined value; wherein the predetermined value is a value indicating a predetermined size of a sub-picture identifier grid; wherein the second syntax element indicates the width of the element of the sub-picture identifier grid in units of the maximum value; wherein the third syntax element indicates the height of the element of the sub-picture identifier grid in units of the maximum value; responsive to determining the maximum value, determining a number of columns in the sub-picture identifier grid based on the maximum value, an image width in luma samples, and a sub-picture identifier grid column width; In response to determining the maximum value, determining a number of rows in the sub-picture identifier grid based on the maximum value, a picture height in luma samples, and a sub-picture identifier grid row width; determining a position of the sub-picture within a picture based on the grid index, the determined number of columns, and the determined number of rows; and The sub-picture is decoded based on the determined position.

15. The computer-readable storage medium of claim 14, wherein: The instructions configure the processor to: identifying one of the elements of the sub-picture identifier grid based on a value of the fourth syntax element, a determined number of columns in the sub-picture identifier grid, and a determined number of rows in the sub-picture identifier grid; as well as The position of the sub-picture within the picture is determined based on the identified element.

16. The computer-readable storage medium of claim 15, wherein: The instructions configure the processor to determine a top left luma sample of the sub-picture based on the identified element.

17. The computer-readable storage medium of claim 14, wherein: The instructions configure the processor to allocate an amount of memory based on a size of the CTU to store a value of the fourth syntax element.

18. The computer-readable storage medium of claim 14, wherein: The instructions configure the processor to: The first syntax element, the second syntax element, and the third syntax element in a sequence parameter set for video data are received.

19. The computer-readable storage medium of claim 18, wherein: The sequence parameter set includes the first syntax element, the second syntax element, and the third syntax element, and in the sequence parameter set, the first syntax element precedes the second syntax element and the third syntax element.

20. A device for decoding video data, the device comprising: means for decoding a first syntax element indicating a size of a codec tree unit (CTU); means for decoding a second syntax element indicating a width of an element of a sub-picture identifier grid after decoding said first syntax element indicating a size of a CTU; means for decoding a third syntax element indicating a height of an element of a sub-picture identifier grid after decoding said first syntax element indicating a size of a CTU; means for decoding, after decoding the first syntax element indicating the size of the CTU, a fourth syntax element indicating a grid index of a sub-picture; means for determining a maximum value between a size of a CTU and a predetermined value; wherein the predetermined value is a value indicating a predetermined size of a sub-picture identifier grid; wherein the second syntax element indicates the width of the element of the sub-picture identifier grid in units of the maximum value; and wherein the third syntax element indicates the height of the element of the sub-picture identifier grid in units of the maximum value; means for determining, in response to determining the maximum value, a number of columns in the sub-picture identifier grid based on the maximum value, an image width in luma samples, and a sub-picture identifier grid column width; means for determining, in response to determining the maximum value, a number of rows in the sub-picture identifier grid based on the maximum value, a picture height in luma samples, and a sub-picture identifier grid row width; means for determining a position of the sub-picture within the picture based on the grid index, the determined number of columns, and the determined number of rows; and Means for decoding the sub-picture based on the determined position.

21. The apparatus according to claim 20, wherein The means for determining a position of the sub-picture within the picture based on the grid index, the determined number of columns and the determined number of rows further comprises: means for identifying one of the elements of the sub-picture identifier grid based on a value of the fourth syntax element, the determined number of columns in the sub-picture identifier grid, and the determined number of rows in the sub-picture identifier grid; and Means for determining a position of the sub-picture within the picture based on the identified element.

22. The apparatus of claim 20, further comprising: means for allocating an amount of memory to store a value of the fourth syntax element based on a size of the CTU.

23. A computer program product comprising computer readable instructions which, when executed by a processor, cause the processor to perform the method of any one of claims 1 to 6.

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