Patent Publication Number: US-2021195179-A1

Title: Picture header signaling for video coding

Description:
This application claims the benefit of U.S. Provisional Application No. 62/953,014, filed Dec. 23, 2019, the entire contents of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to video encoding and video decoding. 
     BACKGROUND 
     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 may transmit, receive, encode, decode, and/or store digital video information more efficiently by implementing such video coding techniques. 
     Video coding techniques include spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences. For block-based video coding, a video slice (e.g., a video picture or a portion of a video picture) may be partitioned into video blocks, which may also be referred to as coding tree units (CTUs), coding units (CUs) and/or coding nodes. Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture. Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures. Pictures may be referred to as frames, and reference pictures may be referred to as reference frames. 
     SUMMARY 
     In general, this disclosure describes techniques for signaling and parsing information in a picture header for video coding, such as signaling high level syntax (HLS) elements. For example, the disclosure describes picture order count (POC) and slice syntax elements that are signaled in the picture header. By signaling information in the picture header, rather than at other signaling levels, such as the slice header, there may be a reduction in redundant signaling which may reduce bandwidth utilization. Also, reduction in redundant signaling may reduce the amount of information that needs to be signaled and parsed, thereby reducing processing time and improving operation of a video encoder and a video decoder. 
     In one example, this disclosure describes a method of processing video data includes parsing at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header, wherein the inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted, selectively parsing at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag, and reconstructing the picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. 
     In another example, this disclosure describes a method of processing video data includes determining whether to encode a picture in accordance with at least one of a set of inter slice syntax elements of the video data and a set of intra slice syntax elements of the video data, selectively signaling at least one of the set of inter slice syntax elements, in a picture header, and the set of intra slice syntax elements, in the picture header, based on the determination, wherein the inter slice syntax elements are inter-prediction syntax elements for slices in the picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted, and signaling at least one of a first flag of the video data, in the picture header, indicative of whether the set of inter slice syntax elements are signaled in the picture header, and a second flag of the video data, in the picture header, indicative of whether the set of intra slice syntax elements are signaled in the picture header. 
     In another example, this disclosure describes a device for processing video data includes memory configured to store the video data, and processing circuitry coupled to the memory and configured to parse at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header, wherein the inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted, selectively parse at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag, and reconstruct the picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. 
     In another example, this disclosure describes a computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to: parse at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header, wherein the inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted, selectively parse at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag, and reconstruct the picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. 
     In another example, this disclosure describes a device for processing video data includes means for parsing at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header, wherein the inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted, means for selectively parsing at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag, and means for reconstructing the picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. 
     The details of one or more examples are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description, drawings, and claims. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram illustrating an example video encoding and decoding system that may perform the techniques of this disclosure. 
         FIGS. 2A and 2B  are conceptual diagrams illustrating an example quadtree binary tree (QTBT) structure, and a corresponding coding tree unit (CTU). 
         FIG. 3  is a block diagram illustrating an example video encoder that may perform the techniques of this disclosure. 
         FIG. 4  is a block diagram illustrating an example video decoder that may perform the techniques of this disclosure. 
         FIG. 5  is a flowchart illustrating an example method of processing video data. 
         FIG. 6  is a flowchart illustrating another example method of video data. 
     
    
    
     DETAILED DESCRIPTION 
     In video coding, a video encoder and a video decoder partition a picture into a plurality of blocks. A slice includes one or more blocks. Video coding includes different prediction modes such as inter-prediction and intra-prediction. In both inter-prediction and intra-prediction, a video coder (e.g., a video encoder and a video decoder) determines a prediction block for predicting a current block in a picture. For inter-prediction, the prediction block is based on samples in a reference picture. For intra-prediction, the prediction block is based on samples in the same picture. 
     To perform inter-prediction or intra-prediction, the video encoder may signal and the video decoder may parse syntax elements that indicate a manner in which to perform the inter-prediction or intra-prediction. For instance, there may be a set of inter slice syntax elements and a set of intra slice syntax elements. The set of inter slice syntax elements and the set of intra slice syntax elements may provide information such as block size and the like. The inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted. 
     This disclosure describes examples for selectively signaling and parsing the set of inter slice syntax elements and the set of intra slice syntax elements. For instance, if blocks in all slices in the picture are coded in intra-prediction, then there may be no need to signal the set of inter slice syntax elements, and if blocks in all slices in the picture are coded in inter-prediction, then there may be no need to signal the set of intra slice syntax elements. 
     In accordance with one or more examples, a video encoder may signal and a video decoder may parse at least one of a first flag of the video data, in a picture header, indicative of whether the set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether the set of intra slice syntax elements are included in the picture header. The picture header is a syntax structure that includes syntax elements that apply to all slices of a coded picture. The inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted. 
     By signaling and parsing the first flag and/or the second flag in the picture header, it may be possible to selectively signal and parse the set of inter slice syntax elements and the set of intra slice syntax elements that apply to all inter or intra slices in the picture. An inter slice or intra slice refers to a slice having inter-predicted blocks or intra-predicted blocks, respectively. For instance, rather than signaling the set of inter slice syntax elements and the set of intra slice syntax elements on a slice-by-slice basis, it may be possible to signal and parse the set of inter slice syntax elements and the set of intra slice syntax elements that apply to respective inter and intra slices in the picture once in the picture header. However, if the set of inter slice syntax elements or the set of intra slice syntax elements is not needed (e.g., because there are no inter slices or intra slices in a picture), then signaling and parsing of the set of inter slice syntax elements or the set of intra slice syntax elements may be redundant and bandwidth inefficient. 
     As one example, if blocks in all slices of a picture are intra-predicted (e.g., there are only intra slices in a picture), then the video encoder may set the first flag to 0 and not signal the set of inter slice syntax elements. In this example, the video decoder may parse the first flag and determine the value of the first flag to be 0, and determine that the set of inter slice syntax elements are not present in the picture header (i.e., syntax elements in the picture header do not belong to the set of inter slice syntax elements). If there is a possibility that there is at least one slice that is inter-predicted, then the video encoder may set the first flag to 1 and signal the set of inter slice syntax elements. In this example, the video decoder may parse the first flag and determine the value of the first flag to be 1, and determine that the set of inter slice syntax elements are present in the picture header. 
     Similarly, if blocks in all slices of a picture are inter-predicted (e.g., there are only inter slices in a picture), then the video encoder may set the second flag to 0 and not signal the set of intra slice syntax elements. In this example, the video decoder may parse the second flag and determine the value of the second flag to be 0, and determine that the set of intra slice syntax elements are not present in the picture header (i.e., syntax elements in the picture header do not belong to the set of intra slice syntax elements). If there is a possibility that there is at least one slice that is intra-predicted, then the video encoder may set the second flag to 1 and signal the set of intra slice syntax elements. In this example, the video decoder may parse the second flag and determine the value of the second flag to be 1, and determine that the set of intra slice syntax elements are present in the picture header. 
     In this way, the video decoder may parse at least one of a first flag of video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header, and selectively parse at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag. The video decoder may reconstruct the picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. 
     The video encoder may determine whether to encode a picture in accordance with at least one of a set of inter slice syntax elements of the video data and a set of intra slice syntax elements of the video data. The video encoder may selectively signal at least one of the set of inter slice syntax elements, in a picture header, and the set of intra slice syntax elements, in the picture header, based on the determination, and signal at least one of a first flag of the video data, in the picture header, indicative of whether the set of inter slice syntax elements are signaled in the picture header, and a second flag of the video data, in the picture header, indicative of whether the set of intra slice syntax elements are signaled in the picture header. 
     In the above examples, the set of inter slice syntax elements and the set of intra slice syntax elements, although possible, should not be considered as necessarily including all syntax elements used for inter-prediction or intra-prediction. Rather, the set of inter slice syntax elements and the set of intra slice syntax elements may be considered as a subset of all inter slice syntax elements and the set of intra slice syntax elements, respectively. 
     This disclosure also describes examples of signaling and parsing information indicative of a picture order count (POC) value in the picture header. The information indicative of the POC value may be one or more least significant bits (LSBs) of the POC value. 
     This disclosure also describes examples of signaling and parsing information indicative of an identifier for a sequence parameter set (SPS) for reference as a first element in the SPS before other elements in the SPS. The identifier for the SPS may be sps_seq_parameter_set_id. For example, there may be plurality of SPSes used for decoding a picture. In some examples, a syntax element from a particular SPS may be needed for decoding. The particular SPS is identified by the identifier for the particular SPS. By having the identifier for the SPS as the first element, the video decoder may be able to quickly determine whether an SPS is the particular SPS of interest. For instance, if the identifier for the SPS is the Nth syntax element, then the video decoder may need to parse N-1 syntax elements of an SPS before determining the identifier for the SPS. By having the identifier for the SPS as the first element, the video decoder may not need to parse through N-1 syntax elements before determining the identifier for the SPS. 
       FIG. 1  is a block diagram illustrating an example video encoding and decoding system  100  that may perform the techniques of this disclosure. The techniques of this disclosure are generally directed to coding (encoding and/or decoding) video data. In general, video data includes any data for processing a video. Thus, video data may include raw, unencoded video, encoded video, decoded (e.g., reconstructed) video, and video metadata, such as signaling data. 
     As shown in  FIG. 1 , system  100  includes a source device  102  that provides encoded video data to be decoded and displayed by a destination device  116 , in this example. In particular, source device  102  provides the video data to destination device  116  via a computer-readable medium  110 . Source device  102  and destination device  116  may comprise any of a wide range of devices, including a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box. For example, source device  102  and destination device  116  may include desktop computers, notebook (i.e., laptop) computers, tablet computers, set-top boxes, telephone handsets such as smartphones (e.g., mobile devices), televisions, cameras, display devices, digital media players, video gaming consoles, video streaming device, or the like. In some cases, source device  102  and destination device  116  may be equipped for wireless communication, and thus may be referred to as wireless communication devices. 
     In the example of  FIG. 1 , source device  102  includes video source  104 , memory  106 , video encoder  200 , and output interface  108 . Destination device  116  includes input interface  122 , video decoder  300 , memory  120 , and display device  118 . In accordance with this disclosure, video encoder  200  of source device  102  and video decoder  300  of destination device  116  may be configured to apply the techniques for signaling and parsing information in a picture header. Thus, source device  102  represents an example of a video encoding device, while destination device  116  represents an example of a video decoding device. In other examples, a source device and a destination device may include other components or arrangements. For example, source device  102  may receive video data from an external video source, such as an external camera. Likewise, destination device  116  may interface with an external display device, rather than include an integrated display device. 
     System  100  as shown in  FIG. 1  is merely one example. In general, any digital video encoding and/or decoding device may perform techniques for signaling and parsing information in a picture header. Source device  102  and destination device  116  are merely examples of such coding devices in which source device  102  generates coded video data for transmission to destination device  116 . This disclosure refers to a “coding” device as a device that performs coding (encoding and/or decoding) of data. Thus, video encoder  200  and video decoder  300  represent examples of coding devices, in particular, a video encoder and a video decoder, respectively. In some examples, source device  102  and destination device  116  may operate in a substantially symmetrical manner such that each of source device  102  and destination device  116  includes video encoding and decoding components. Hence, system  100  may support one-way or two-way video transmission between source device  102  and destination device  116 , e.g., for video streaming, video playback, video broadcasting, or video telephony. 
     In general, video source  104  represents a source of video data (i.e., raw, unencoded video data) and provides a sequential series of pictures (also referred to as “frames”) of the video data to video encoder  200 , which encodes data for the pictures. Video source  104  of source device  102  may include a video capture device, such as a video camera, a video archive containing previously captured raw video, and/or a video feed interface to receive video from a video content provider. As a further alternative, video source  104  may generate computer graphics-based data as the source video, or a combination of live video, archived video, and computer-generated video. In each case, video encoder  200  encodes the captured, pre-captured, or computer-generated video data. Video encoder  200  may rearrange the pictures from the received order (sometimes referred to as “display order”) into a coding order for coding. Video encoder  200  may generate a bitstream including encoded video data. Source device  102  may then output the encoded video data via output interface  108  onto computer-readable medium  110  for reception and/or retrieval by, e.g., input interface  122  of destination device  116 . 
     Memory  106  of source device  102  and memory  120  of destination device  116  represent general purpose memories. In some examples, memories  106 ,  120  may store raw video data, e.g., raw video from video source  104  and raw, decoded video data from video decoder  300 . Additionally or alternatively, memories  106 ,  120  may store software instructions executable by, e.g., video encoder  200  and video decoder  300 , respectively. Although memory  106  and memory  120  are shown separately from video encoder  200  and video decoder  300  in this example, it should be understood that video encoder  200  and video decoder  300  may also include internal memories for functionally similar or equivalent purposes. Furthermore, memories  106 ,  120  may store encoded video data, e.g., output from video encoder  200  and input to video decoder  300 . In some examples, portions of memories  106 ,  120  may be allocated as one or more video buffers, e.g., to store raw, decoded, and/or encoded video data. 
     Computer-readable medium  110  may represent any type of medium or device capable of transporting the encoded video data from source device  102  to destination device  116 . In one example, computer-readable medium  110  represents a communication medium to enable source device  102  to transmit encoded video data directly to destination device  116  in real-time, e.g., via a radio frequency network or computer-based network. Output interface  108  may modulate a transmission signal including the encoded video data, and input interface  122  may demodulate the received transmission signal, according to a communication standard, such as a wireless communication protocol. The communication medium may comprise any wireless or wired communication medium, such as a radio frequency (RF) spectrum or one or more physical transmission lines. The communication medium may form part of a packet-based network, such as a local area network, a wide-area network, or a global network such as the Internet. The communication medium may include routers, switches, base stations, or any other equipment that may be useful to facilitate communication from source device  102  to destination device  116 . 
     In some examples, source device  102  may output encoded data from output interface  108  to storage device  112 . Similarly, destination device  116  may access encoded data from storage device  112  via input interface  122 . Storage device  112  may include any of a variety of distributed or locally accessed data storage media such as a hard drive, Blu-ray discs, DVDs, CD-ROMs, flash memory, volatile or non-volatile memory, or any other suitable digital storage media for storing encoded video data. 
     In some examples, source device  102  may output encoded video data to file server  114  or another intermediate storage device that may store the encoded video data generated by source device  102 . Destination device  116  may access stored video data from file server  114  via streaming or download. 
     File server  114  may be any type of server device capable of storing encoded video data and transmitting that encoded video data to the destination device  116 . File server  114  may represent a web server (e.g., for a website), a server configured to provide a file transfer protocol service (such as File Transfer Protocol (FTP) or File Delivery over Unidirectional Transport (FLUTE) protocol), a content delivery network (CDN) device, a hypertext transfer protocol (HTTP) server, a Multimedia Broadcast Multicast Service (MBMS) or Enhanced MBMS (eMBMS) server, and/or a network attached storage (NAS) device. File server  114  may, additionally or alternatively, implement one or more HTTP streaming protocols, such as Dynamic Adaptive Streaming over HTTP (DASH), HTTP Live Streaming (HLS), Real Time Streaming Protocol (RTSP), HTTP Dynamic Streaming, or the like. 
     Destination device  116  may access encoded video data from file server  114  through any standard data connection, including an Internet connection. This may include a wireless channel (e.g., a Wi-Fi connection), a wired connection (e.g., digital subscriber line (DSL), cable modem, etc.), or a combination of both that is suitable for accessing encoded video data stored on file server  114 . Input interface  122  may be configured to operate according to any one or more of the various protocols discussed above for retrieving or receiving media data from file server  114 , or other such protocols for retrieving media data. 
     Output interface  108  and input interface  122  may represent wireless transmitters/receivers, modems, wired networking components (e.g., Ethernet cards), wireless communication components that operate according to any of a variety of IEEE 802.11 standards, or other physical components. In examples where output interface  108  and input interface  122  comprise wireless components, output interface  108  and input interface  122  may be configured to transfer data, such as encoded video data, according to a cellular communication standard, such as 4G, 4G-LTE (Long-Term Evolution), LTE Advanced, 5G, or the like. In some examples where output interface  108  comprises a wireless transmitter, output interface  108  and input interface  122  may be configured to transfer data, such as encoded video data, according to other wireless standards, such as an IEEE 802.11 specification, an IEEE 802.15 specification (e.g., ZigBee™), a Bluetooth™ standard, or the like. In some examples, source device  102  and/or destination device  116  may include respective system-on-a-chip (SoC) devices. For example, source device  102  may include an SoC device to perform the functionality attributed to video encoder  200  and/or output interface  108 , and destination device  116  may include an SoC device to perform the functionality attributed to video decoder  300  and/or input interface  122 . 
     The techniques of this disclosure may be applied to video coding in support of any of a variety of multimedia applications, such as over-the-air television broadcasts, cable television transmissions, satellite television transmissions, Internet streaming video transmissions, such as dynamic adaptive streaming over HTTP (DASH), digital video that is encoded onto a data storage medium, decoding of digital video stored on a data storage medium, or other applications. 
     Input interface  122  of destination device  116  receives an encoded video bitstream from computer-readable medium  110  (e.g., a communication medium, storage device  112 , file server  114 , or the like). The encoded video bitstream may include signaling information defined by video encoder  200 , which is also used by video decoder  300 , such as syntax elements having values that describe characteristics and/or processing of video blocks or other coded units (e.g., slices, pictures, groups of pictures, sequences, or the like). Display device  118  displays decoded pictures of the decoded video data to a user. Display device  118  may represent any of a variety of display devices such as a cathode ray tube (CRT), a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device. 
     Although not shown in  FIG. 1 , in some examples, video encoder  200  and video decoder  300  may each be integrated with an audio encoder and/or audio decoder, and may include appropriate MUX-DEMUX units, or other hardware and/or software, to handle multiplexed streams including both audio and video in a common data stream. If applicable, MUX-DEMUX units may conform to the ITU H.223 multiplexer protocol, or other protocols such as the user datagram protocol (UDP). 
     Video encoder  200  and video decoder  300  each may be implemented as any of a variety of suitable encoder and/or decoder circuitry, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, software, hardware, firmware or any combinations thereof. When the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable medium and execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Each of video encoder  200  and video decoder  300  may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device. A device including video encoder  200  and/or video decoder  300  may comprise an integrated circuit, a microprocessor, and/or a wireless communication device, such as a cellular telephone. 
     One example of a video coding standard is ITU-T H.265, also referred to as High Efficiency Video Coding (HEVC), and extensions thereto, such as the multi-view and/or scalable video coding extensions. In some examples, video encoder  200  and video decoder  300  may operate according to other proprietary or industry standards, such as ITU-T H.266, also referred to as Versatile Video Coding (VVC). A draft of the VVC standard is described in Bross, et al. “Versatile Video Coding (Draft 7),” Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 16 th  Meeting: Geneva, CH, 1-11 Oct. 2019, JVET-P2001-v13 (hereinafter “VVC Draft 7”). A recent draft of the VVC standard is described in Bross, et al. “Versatile Video Coding (Draft 10),” Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 18 th  Meeting: by teleconference, 22 June-1 July 2020, JVET-S2001-vA (hereinafter “VVC Draft 10”). The techniques of this disclosure, however, are not limited to any particular coding standard. 
     In general, video encoder  200  and video decoder  300  may perform block-based coding of pictures. The term “block” generally refers to a structure including data to be processed (e.g., encoded, decoded, or otherwise used in the encoding and/or decoding process). For example, a block may include a two-dimensional matrix of samples of luminance and/or chrominance data. In general, video encoder  200  and video decoder  300  may code video data represented in a YUV (e.g., Y, Cb, Cr) format. That is, rather than coding red, green, and blue (RGB) data for samples of a picture, video encoder  200  and video decoder  300  may code luminance and chrominance components, where the chrominance components may include both red hue and blue hue chrominance components. In some examples, video encoder  200  converts received RGB formatted data to a YUV representation prior to encoding, and video decoder  300  converts the YUV representation to the RGB format. Alternatively, pre- and post-processing units (not shown) may perform these conversions. 
     This disclosure may generally refer to coding (e.g., encoding and decoding) of pictures to include the process of encoding or decoding data of the picture. Similarly, this disclosure may refer to coding of blocks of a picture to include the process of encoding or decoding data for the blocks, e.g., prediction and/or residual coding. An encoded video bitstream generally includes a series of values for syntax elements representative of coding decisions (e.g., coding modes) and partitioning of pictures into blocks. Thus, references to coding a picture or a block should generally be understood as coding values for syntax elements forming the picture or block. 
     HEVC defines various blocks, including coding units (CUs), prediction units (PUs), and transform units (TUs). According to HEVC, a video coder (such as video encoder  200 ) partitions a coding tree unit (CTU) into CUs according to a quadtree structure. That is, the video coder partitions CTUs and CUs into four equal, non-overlapping squares, and each node of the quadtree has either zero or four child nodes. Nodes without child nodes may be referred to as “leaf nodes,” and CUs of such leaf nodes may include one or more PUs and/or one or more TUs. The video coder may further partition PUs and TUs. For example, in HEVC, a residual quadtree (RQT) represents partitioning of TUs. In HEVC, PUs represent inter-prediction data, while TUs represent residual data. CUs that are intra-predicted include intra-prediction information, such as an intra-mode indication. 
     Video encoder  200  and video decoder  300  may be configured to operate according to VVC. According to VVC, a video coder (such as video encoder  200 ) partitions a picture into a plurality of coding tree units (CTUs). Video encoder  200  may partition a CTU according to a tree structure, such as a quadtree-binary tree (QTBT) structure or Multi-Type Tree (MTT) structure. The QTBT structure removes the concepts of multiple partition types, such as the separation between CUs, PUs, and TUs of HEVC. A QTBT structure includes two levels: a first level partitioned according to quadtree partitioning, and a second level partitioned according to binary tree partitioning. A root node of the QTBT structure corresponds to a CTU. Leaf nodes of the binary trees correspond to coding units (CUs). 
     In an MTT partitioning structure, blocks may be partitioned using a quadtree (QT) partition, a binary tree (BT) partition, and one or more types of triple tree (TT) (also called ternary tree (TT)) partitions. A triple or ternary tree partition is a partition where a block is split into three sub-blocks. In some examples, a triple or ternary tree partition divides a block into three sub-blocks without dividing the original block through the center. The partitioning types in MTT (e.g., QT, BT, and TT), may be symmetrical or asymmetrical. 
     In some examples, video encoder  200  and video decoder  300  may use a single QTBT or MTT structure to represent each of the luminance and chrominance components, while in other examples, video encoder  200  and video decoder  300  may use two or more QTBT or MTT structures, such as one QTBT/MTT structure for the luminance component and another QTBT/MTT structure for both chrominance components (or two QTBT/MTT structures for respective chrominance components). 
     Video encoder  200  and video decoder  300  may be configured to use quadtree partitioning per HEVC, QTBT partitioning, MTT partitioning, or other partitioning structures. For purposes of explanation, 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 may also be applied to video coders configured to use quadtree partitioning, or other types of partitioning as well. 
     The blocks (e.g., CTUs or CUs) may be grouped in various ways in a picture. As one example, a brick may refer to a rectangular region of CTU rows within a particular tile in a picture. A tile may be a rectangular region of CTUs within a particular tile column and a particular tile row in a picture. A tile column refers to a rectangular region of CTUs having a height equal to the height of the picture and a width specified by syntax elements (e.g., such as in a picture parameter set). A tile row refers to a rectangular region of CTUs having a height specified by syntax elements (e.g., such as in a picture parameter set) and a width equal to the width of the picture. 
     In some examples, a tile may be partitioned into multiple bricks, each of which may include one or more CTU rows within the tile. A tile that is not partitioned into multiple bricks may also be referred to as a brick. However, a brick that is a true subset of a tile may not be referred to as a tile. 
     The bricks in a picture may also be arranged in a slice. A slice may be an integer number of bricks of a picture that may be exclusively contained in a single network abstraction layer (NAL) unit. In some examples, a slice includes either a number of complete tiles or only a consecutive sequence of complete bricks of one tile. 
     This disclosure may use “N×N” and “N by N” interchangeably to refer to the sample dimensions of a block (such as a CU or other video block) in terms of vertical and horizontal dimensions, e.g., 16×16 samples or 16 by 16 samples. In general, a 16×16 CU will have 16 samples in a vertical direction (y=16) and 16 samples in a horizontal direction (x=16). Likewise, an N×N CU generally has N samples in a vertical direction and N samples in a horizontal direction, where N represents a nonnegative integer value. The samples in a CU may be arranged in rows and columns. Moreover, CUs need not necessarily have the same number of samples in the horizontal direction as in the vertical direction. For example, CUs may comprise N×M samples, where M is not necessarily equal to N. 
     Video encoder  200  encodes video data for CUs representing prediction and/or residual information, and other information. The prediction information indicates how the CU is to be predicted in order to form a prediction block for the CU. The residual information generally represents sample-by-sample differences between samples of the CU prior to encoding and the prediction block. 
     To predict a CU, video encoder  200  may generally form a prediction block for the CU through inter-prediction or intra-prediction. Inter-prediction generally refers to predicting the CU from data of a previously coded picture, whereas intra-prediction generally refers to predicting the CU from previously coded data of the same picture. To perform inter-prediction, video encoder  200  may generate the prediction block using one or more motion vectors. Video encoder  200  may generally perform a motion search to identify a reference block that closely matches the CU, e.g., in terms of differences between the CU and the reference block. Video encoder  200  may calculate a difference metric using a sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or other such difference calculations to determine whether a reference block closely matches the current CU. In some examples, video encoder  200  may predict the current CU using uni-directional prediction (e.g., with a motion vector to samples in one reference picture) or bi-directional prediction (e.g., with two motion vectors to samples in two reference pictures). In some examples, the reference picture(s) used for uni-directional or bi-directional prediction may be identified in one or more reference picture lists (e.g., reference picture list  0  and/or reference picture list  1 ) 
     VVC may provide an affine motion compensation mode, which may be considered an inter-prediction mode. In affine motion compensation mode, video encoder  200  may determine two or more motion vectors that represent non-translational motion, such as zoom in or out, rotation, perspective motion, or other irregular motion types. 
     To perform intra-prediction, video encoder  200  may select an intra-prediction mode to generate the prediction block. VVC may provide sixty-seven intra-prediction modes, including various directional modes, as well as planar mode and DC mode. In general, video encoder  200  selects an intra-prediction mode that describes neighboring samples to a current block (e.g., a block of a CU) from which to predict samples of the current block. Such samples may generally be above, above and to the left, or to the left of the current block in the same picture as the current block, assuming video encoder  200  codes CTUs and CUs in raster scan order (left to right, top to bottom). 
     Video encoder  200  encodes data representing the prediction mode for a current block. For example, for inter-prediction modes, video encoder  200  may encode data representing which of the various available inter-prediction modes is used, as well as motion information for the corresponding mode. For uni-directional or bi-directional inter-prediction, for example, video encoder  200  may encode motion vectors using advanced motion vector prediction (AMVP) or merge mode. Video encoder  200  may use similar modes to encode motion vectors for affine motion compensation mode. 
     Following prediction, such as intra-prediction or inter-prediction of a block, video encoder  200  may calculate residual data for the block. The residual data, such as a residual block, represents sample by sample differences between the block and a prediction block for the block, formed using the corresponding prediction mode. Video encoder  200  may apply one or more transforms to the residual block, to produce transformed data in a transform domain instead of the sample domain. For example, video encoder  200  may apply a discrete cosine transform (DCT), an integer transform, a wavelet transform, or a conceptually similar transform to residual video data. Additionally, video encoder  200  may apply a secondary transform following the first transform, such as a mode-dependent non-separable secondary transform (MDNSST), a signal dependent transform, a Karhunen-Loeve transform (KLT), or the like. Video encoder  200  produces transform coefficients following application of the one or more transforms. 
     As noted above, following any transforms to produce transform coefficients, video encoder  200  may perform quantization of the transform coefficients. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression. By performing the quantization process, video encoder  200  may reduce the bit depth associated with some or all of the transform coefficients. For example, video encoder  200  may round an n-bit value down to an m-bit value during quantization, where n is greater than m. In some examples, to perform quantization, video encoder  200  may perform a bitwise right-shift of the value to be quantized. 
     Following quantization, video encoder  200  may scan the transform coefficients, producing a one-dimensional vector from the two-dimensional matrix including the quantized transform coefficients. The scan may be designed to place higher energy (and therefore lower frequency) transform coefficients at the front of the vector and to place lower energy (and therefore higher frequency) transform coefficients at the back of the vector. In some examples, video encoder  200  may utilize a predefined scan order to scan the quantized transform coefficients to produce a serialized vector, and then entropy encode the quantized transform coefficients of the vector. In other examples, video encoder  200  may perform an adaptive scan. After scanning the quantized transform coefficients to form the one-dimensional vector, video encoder  200  may entropy encode the one-dimensional vector, e.g., according to context-adaptive binary arithmetic coding (CABAC). Video encoder  200  may also entropy encode values for syntax elements describing metadata associated with the encoded video data for use by video decoder  300  in decoding the video data. 
     To perform CABAC, video encoder  200  may assign a context within a context model to a symbol to be transmitted. The context may relate to, for example, whether neighboring values of the symbol are zero-valued or not. The probability determination may be based on a context assigned to the symbol. 
     Video encoder  200  may further generate syntax data, such as block-based syntax data, picture-based syntax data, and sequence-based syntax data, to video decoder  300 , e.g., in a picture header, a block header, a slice header, or other syntax data, such as a sequence parameter set (SPS), picture parameter set (PPS), or video parameter set (VPS). Video decoder  300  may likewise decode such syntax data to determine how to decode corresponding video data. 
     In this manner, video encoder  200  may generate a bitstream including encoded video data, e.g., syntax elements describing partitioning of a picture into blocks (e.g., CUs) and prediction and/or residual information for the blocks. Ultimately, video decoder  300  may receive the bitstream and decode the encoded video data. 
     In general, video decoder  300  performs a reciprocal process to that performed by video encoder  200  to decode the encoded video data of the bitstream. For example, video decoder  300  may decode values for syntax elements of the bitstream using CABAC in a manner substantially similar to, albeit reciprocal to, the CABAC encoding process of video encoder  200 . The syntax elements may define partitioning information of a picture into CTUs, and partitioning of each CTU according to a corresponding partition structure, such as a QTBT structure, to define CUs of the CTU. The syntax elements may further define prediction and residual information for blocks (e.g., CUs) of video data. 
     The residual information may be represented by, for example, quantized transform coefficients. Video decoder  300  may inverse quantize and inverse transform the quantized transform coefficients of a block to reproduce a residual block for the block. Video decoder  300  uses a signaled prediction mode (intra- or inter-prediction) and related prediction information (e.g., motion information for inter-prediction) to form a prediction block for the block. Video decoder  300  may then combine the prediction block and the residual block (on a sample-by-sample basis) to reproduce the original block. Video decoder  300  may perform additional processing, such as performing a deblocking process to reduce visual artifacts along boundaries of the block. 
     This disclosure may generally refer to “signaling” certain information, such as syntax elements. The term “signaling” may generally refer to the communication of values for syntax elements and/or other data used to decode encoded video data. That is, video encoder  200  may signal values for syntax elements in the bitstream. In general, signaling refers to generating a value in the bitstream. As noted above, source device  102  may transport the bitstream to destination device  116  substantially in real time, or not in real time, such as might occur when storing syntax elements to storage device  112  for later retrieval by destination device  116 . 
     In the reciprocal, video decoder  300  may be configured to parse through the syntax elements in the bitstream. For instance, parsing through syntax elements includes receiving the syntax elements and determining values for the syntax elements, such as by decoding. In some examples, video decoder  300  may selectively parse through certain syntax elements. For example, the presence of some syntax elements may be conditional, and in such examples, video encoder  200  may selectively signal such syntax elements based on whether the condition is satisfied, and video decoder  300  may selectively parse such syntax elements based on whether the condition is satisfied. For instance, if the condition is satisfied, then video decoder  300  may be configured to parse certain syntax elements and if the syntax elements are not present, the bitstream may not be a conforming bitstream (e.g., there may be errors in the decoding). If the condition is not satisfied, video decoder  300  may be configured to bypass the parsing of the certain syntax elements. 
     In accordance with the techniques of this disclosure, video encoder  200  and video decoder  300  may be configured to process video data, such as syntax elements signaled and parsed in the picture header. The picture header may be a syntax structure that includes syntax elements that apply to all slices of a coded picture. 
     As one example, video encoder  200  may be configured to signal information indicative of a picture order count (POC) value in a picture header. Video decoder  300  may be configured to parse information indicative of the POC value in the picture header. The information indicative of the POC value may be information indicative of one or more least significant bits (LSBs) of the POC value. 
     As another example, video encoder  200  may be configured to signal one or more syntax elements, in a picture header, indicative of at least one of intra slice syntax elements or inter slice syntax elements, and selectively signal one or more syntax elements for intra slices or inter slices based on the one or more syntax elements indicative of at least one of intra slice syntax elements or inter slice syntax elements. Video decoder  300  may be configured to parse one or more syntax elements, in the picture header, indicative of at least one of intra slice syntax elements or inter slice syntax elements, and selectively parse one or more syntax elements for intra slices or inter slices based on the one or more syntax elements indicative of at least one of intra slice syntax elements or inter slice syntax elements. In some examples, as described in more detail below, the intra slice syntax element is a pic_intra_present_flag (also called ph_intra_slice_allowed_flag) indicative of whether intra slice syntax elements are present in the picture header, and the inter slice syntax element is a pic_inter_present_flag (also called ph_inter_slice_allowed_flag) indicative of whether inter slice syntax elements are present in the picture header. 
     For example, there may be various syntax elements that define a manner in which to perform inter-prediction or intra-prediction. In one or more examples, a set of these syntax elements may be selectively included in a picture header for a picture. 
     Examples of a set of inter slice syntax elements include one or more of ph_log2_diff_min_qt_min_cb_inter_slice, ph_max_mtt_hierarchy_depth_inter_slice, ph_log2_diff_max_bt_min_qt_inter_slice, and ph_log2_diff_max_tt_min_qt_inter_slice. The inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted. Accordingly, ph_log2_diff_min_qt_min_cb_inter_slice, ph_max_mtt_hierarchy_depth_inter_slice, ph_log2_diff_max_bt_min_qt_inter_slice, and ph_log2_diff_max_tt_min_qt_inter_slice may be inter-prediction syntax elements for slices in a picture that are inter-predicted (e.g., indicate a manner in which the inter-prediction is performed). 
     Examples of a set of intra slice syntax elements include one or more of ph_log2_diff_min_qt_min_cb_intra_slice_luma, ph_max_mtt_hierarchy_depth_intra_slice_luma, ph_log2_diff_max_bt_min_qt_intra_slice_luma, ph_log2_diff_max_tt_min_qt_intra_slice_luma, ph_log2_diff_min_qt_min_cb_intra_slice_chroma, ph_max_mtt_hierarchy_depth_intra_slice_chroma, ph_log2_diff_max_bt_min_qt_intra_slice_chroma, and ph_log2_diff_max_tt_min_qt_intra_slice_chroma. The intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted. Accordingly, ph_log2_diff_min_qt_min_cb_intra_slice_luma, ph_max_mtt_hierarchy_depth_intra_slice_luma, ph_log2_diff_max_bt_min_qt_intra_slice_luma, ph_log2_diff_max_tt_min_qt_intra_slice_luma, ph_log2_diff_min_qt_min_cb_intra_slice_chroma, ph_max_mtt_hierarchy_depth_intra_slice_chroma, ph_log2_diff_max_bt_min_qt_intra_slice_chroma, and ph_log2_diff_max_tt_min_qt_intra_slice_chroma may be intra-prediction syntax elements for slices in a picture that are intra-predicted (e.g., indicate a manner in which the intra-prediction is performed). 
     Coding information represented by each of these syntax elements is described in more detail below. There may be more or fewer syntax elements in the set of inter slice syntax elements and in the set of intra slice syntax elements than the above example. Also, the above are some examples of syntax elements used for inter-prediction or intra-prediction, and should not be considered exhaustive. It is possible for there to be other syntax elements used for inter-prediction or intra-prediction that are not signaled in the picture header and/or not selectively signaled in accordance with examples described in this disclosure. 
     However, whether video encoder  200  is to signal and whether video decoder  300  is to parse the above examples of the set of inter slice syntax elements and the set of intra slice syntax elements may be based on whether are inter slices or intra slices in a picture. According to one or more examples, video encoder  200  may signal and video decoder  300  may parse at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header. One example of the first flag is pic_inter_present_flag (also called ph_inter_slice_allowed_flag). One example of the second flag is pic_intra_present_flag (also called ph_intra_slice_allowed_flag). 
     It should be understood that the bitstream that video encoder  200  signals may include both the first flag and the second flag, or just one of the first flag or the second flag. For example, if the first flag is 0, that means that there are only intra slices in the picture (all blocks in each of the slices in the picture are intra-predicted). If the second flag is 0, that means that there are only inter slices in the picture (all blocks in each of the slices are intra-predicted). If the first flag is 1, that means there is a possibility, but not a requirement, that there is at least one inter slice. If the second flag is 1, that means there is a possibility, but not a requirement, that there is at least one intra slice. 
     A picture may include intra slices and inter slices. Therefore, it is possible for both the first flag and the second flag to be equal to 1. However, if the first flag is 0, then it may be possible to infer that the second flag is 1. Similarly, if the second flag is 0, then it may be possible to infer that the first flag is 1. 
     Accordingly, video encoder  200  signaling and video decoder  300  parsing at least one of the first flag, in the picture header, indicative of whether the set of inter slice syntax elements are included in the picture header, and the second flag, in the picture header, indicative of whether the set of intra slice syntax elements are included in the picture header may refer to video encoder  200  signaling and video decoder  300  parsing one or both of the first flag and the second flag. Again, it may be possible for the bitstream to include both the first flag and the second flag. 
     Video decoder  300  may selectively parse at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag. For example, if the first flag is 0 (e.g., only intra slices in the picture), then video decoder  300  may not parse the set of inter slice syntax elements. Rather, video decoder  300  may determine that any syntax elements that are in the picture header in locations where the set of inter slice syntax elements would belong actually belong to another syntax element. However, if the first flag is 1, then video decoder  300  may parse the set of inter slice syntax elements. 
     Similarly, if the second flag is 0 (e.g., only inter slices in the picture), then video decoder  300  may not parse the set of intra slice syntax elements. Rather, video decoder  300  may determine that any syntax elements that are in the picture header in locations where the set of intra slice syntax elements would belong actually belong to another syntax element. However, if the second flag is 1, then video decoder  300  may parse the set of intra slice syntax elements. 
     With such selective signaling and parsing of syntax elements, there may be an overall reduction in the amount of signaling and reduction in redundant signaling. For instance, rather than signaling the set of inter slice syntax elements or the set of intra slice syntax elements at a slice level (e.g., slice-by-slice), it may be possible to signal the set of inter slice syntax elements or the set of intra slice syntax elements once at the picture level (e.g., in picture header), thereby reducing signaling overhead. However, whether video encoder  200  signals and video decoder  300  parses the set of inter slice syntax elements and/or the set of intra slice syntax elements at all may be conditionally based on whether there are intra and inter slices in the picture. Therefore, by signaling and parsing the first flag indicative of whether a set of inter slice syntax elements are included in the picture header and/or the second flag indicative of whether a set of intra slice syntax elements are included in the picture header, and selectively signaling or parsing the set of inter slice syntax elements or the set of intra slice syntax elements accordingly, there may be additional reduction in the amount of information that is signaled. 
     Accordingly, video encoder  200  may determine whether to encode a picture in accordance with at least one of a set of inter slice syntax elements of the video data and a set of intra slice syntax elements of the video data. For example, video encoder  200  may determine whether to use inter-prediction or intra-prediction, what the size of the blocks should be, etc. based on rate-distortion measurements. Information about block size and other such information may be signaled as part of the set of inter slice syntax elements and/or the set of intra slice syntax elements. 
     Video encoder  200  may selectively signal at least one of the set of inter slice syntax elements, in a picture header, and the set of intra slice syntax elements, in the picture header, based on the determination. For example, if video encoder  200  determines that there are to be inter slices in the picture, then video encoder  200  may determine that the set of inter slice syntax elements is to be signaled. However, if video encoder  200  determines that there are only intra slices in the picture, then video encoder  200  may determine that the set of inter slice syntax elements is not be signaled. Similarly, if video encoder  200  determines that there are to be intra slices in the picture, then video encoder  200  may determine that the set of intra slice syntax elements is to be signaled. However, if video encoder  200  determines that there are only inter slices in the picture, then video encoder  200  may determine that the set of intra slice syntax elements is not be signaled. 
     Video encoder  200  may also signal information that video decoder  300  can use to determine whether to parse the set of inter slice syntax elements and the set of intra slice syntax elements. For example, video encoder  200  may signal at least one of a first flag of the video data, in the picture header, indicative of whether the set of inter slice syntax elements are signaled in the picture header, and a second flag of the video data, in the picture header, indicative of whether the set of intra slice syntax elements are signaled in the picture header. 
     Video decoder  300  may parse at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header. For instance, video decoder  300  may utilize the first flag and the second flag to determine which additional syntax elements are in the bitstream so that when parsing the bitstream, video decoder  300  may properly determine with which syntax element a value in the bitstream is associated. The inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted 
     Video decoder  300  may selectively parse at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag. For example, video decoder  300  may determine whether a particular syntax element belongs in the bitstream or not based on the first flag and/or second flag. In this way, video decoder  300  may be able to correctly associate values in the bitstream to syntax elements. For instance, if video decoder  300  determines that the set of inter slice syntax elements are not in the bitstream (e.g., first flag is 0), then video decoder  300  may determine that values in the bitstream belong to some other syntax element that a syntax element in the set of inter slice syntax elements. Similarly, if video decoder  300  determines that the set of intra slice syntax elements are not in the bitstream (e.g., second flag is 0), then video decoder  300  may determine that values in the bitstream belong to some other syntax element that a syntax element in the set of intra slice syntax elements. 
     Video decoder  300  may reconstruct a picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. For example, video decoder  300  may utilize the set of inter slice syntax elements to perform inter-prediction on blocks in the inter slices and utilize the set of intra slice syntax elements to perform intra-prediction on blocks in the intra slices. 
     As described above, the set of inter slice syntax elements (e.g., inter-prediction syntax elements for slices in a picture that are inter-predicted) include one or more of ph_log2_diff_min_qt_min_cb_inter_slice, ph_max_mtt_hierarchy_depth_inter_slice, ph_log2_diff_max_bt_min_qt_inter_slice, and ph_log2_diff_max_tt_min_qt_inter_slice. 
     ph_log2_diff_min_qt_min_cb_inter_slice (also called pic_log2_diff_min_qt_min_cb_inter_slice) may be indicative of differences between a minimum size of luma leaf block resulting from quadtree splitting of a CTU and a minimum size of luma block that is inter-predicted (e.g., B or P slice). 
     ph_max_mtt_hierarchy_depth_inter_slice (also called pic_max_mtt_hierarchy_depth_inter_slice) may be indicative of maximum hierarchy depth of coding units resulting from multi-type tree splitting of a quadtree leaf in inter slices (e.g., B or P slices). 
     ph_log2_diff_max_bt_min_qt_inter_slice (also called pic_log2_diff_max_bt_min_qt_inter_slice) may be indicative of difference between maximum size (width or height) in luma samples of a luma coding block that can be split using binary split and minimum size (width or height) in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in inter slices (e.g., B or P slices). 
     ph_log2_diff_max_tt_min_qt_inter_slice (also called pic_log2_diff_max_tt_min_qt_inter_slice) may be indicative of a difference between maximum size (width or height) in luma samples of a luma coding block that can be split using a ternary split and the minimum size (width or height) in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in inter slices (e.g., B or P slices). 
     As descibed above, examples of a set of intra slice syntax elements (e.g., intra-prediction syntax elements for slices in a picture that are intra-predicted) include one or more of ph_log2_diff_min_qt_min_cb_intra_slice_luma, ph_max_mtt_hierarchy_depth_intra_slice_luma, ph_log2_diff_max_bt_min_qt_intra_slice_luma, ph_log2_diff_max_tt_min_qt_intra_slice_luma, ph_log2_diff_min_qt_min_cb_intra_slice_chroma, ph_max_mtt_hierarchy_depth_intra_slice_chroma, ph_log2_diff_max_bt_min_qt_intra_slice_chroma, and ph_log2_diff_max_tt_min_qt_intra_slice_chroma. 
     ph_log2_diff_min_qt_min_cb_intra_slice_luma (also called pic_log2_diff_min_qt_min_cb_intra_slice_luma) may be indicative of the difference between minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU and the minimum coding block size in luma samples for luma CUs in intra slices. 
     ph_max_mtt_hierarchy_depth_intra_slice_luma (also called pic_max_mtt_hierarchy_depth_intra_slice_luma) may be indicative of the maximum hierarchy depth for coding units resulting from multi-type tree splitting of a quadtree leaf in intra slices. 
     ph_log2_diff_max_bt_min_qt_intra_slice_luma (also called pic_log2_diff_max_bt_min_qt_intra_slice_luma) may be indicative of the difference between the maximum size (width or height) in luma samples of a luma coding block that can be split using a binary split and the minimum size (width or height) in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in intra slices. 
     ph_log2_diff_max_tt_min_qt_intra_slice_luma (also called pic_log2_diff_max_tt_min_qt_intra_slice_luma) may be indicative of difference between the maximum size (width or height) in luma samples of a luma coding block that can be split using a ternary split and the minimum size (width or height) in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in intra slices. 
     ph_log2_diff_min_qt_min_cb_intra_slice_chroma (also called pic_log2_diff_min_qt_min_cb_intra_slice_chroma) may be indicative of the difference between the minimum size in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning and the minimum coding block size in luma samples for chroma CUs with dual tree partitioning in intra slices. Dual tree partitoning may refer to the luma and chroma being partitioned differently. 
     ph_max_mtt_hierarchy_depth_intra_slice_chroma (also called pic_max_mtt_hierarchy_depth_intra_slice_chroma) may be indicative of the maximum hierarchy depth for chroma coding units resulting from multi-type tree splitting of a chroma quadtree leaf with dual tree partitioning in intra slices. 
     ph_log2_diff_max_bt_min_qt_intra_slice_chroma (also called pic_log2_diff_max_bt_min_qt_intra_slice_chroma) may be indictaive of difference between the maximum size (width or height) in luma samples of a chroma coding block that can be split using a binary split and the minimum size (width or height) in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning in intra slices. 
     ph_log2_diff_max_tt_min_qt_intra_slice_chroma (also called pic_log2_diff_max_tt_min_qt_intra_slice_chroma) may be indicative of the difference between the maximum size (width or height) in luma samples of a chroma coding block that can be split using a ternary split and the minimum size (width or height) in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning in intra slices. 
     In one or more examples, video encoder  200  may signal constant picture header parameters in a picture header. Video decoder  300  may parse the constant picture header parameters in the picture header. In some examples, the constant picture header parameters exclude values indicative of whether a flag is present that specifies that a collocated picture used for temporal motion vector prediction is derived from reference picture list  0  or reference picture list  1 . 
     Reference picture list  0  and reference picture list  1  refer to lists of reference pictures, and video encoder  200  or video decoder  300  may utilize one picture from reference picture list  0  or reference picture list  1  as a reference picture (e.g., for uni-prediction) or one picture from each of reference picture list  0  and reference picture list  1  as reference pictures (e.g., for bi-prediction) for inter-prediction. For example, video encoder  200  and video decoder  300  may determine motion vector(s) that refer to samples within a reference picture for inter-prediction. 
     In some examples, video encoder  200  may signal information indicative of an identifier for a sequence parameter set (SPS) for reference by other syntax elements as a first element in SPS syntax before other elements in the SPS. Video decoder  300  may be configured to parse information indicative of the identifier for the SPS for reference by other syntax elements as a first element in SPS syntax before other elements in the SPS. One example of the SPS is a syntax structure containing syntax elements that apply to zero or more entire coded video sequences (CVSs) as determined by the content of a syntax element found in a picture parameter set (PPS) referred to by a syntax element found in each slice header. One example of the identifier is sps_seq_parameter_set_id. By having sps_seq_parameter_set_id as the first syntax element, video decoder  300  may not need to parse multiple syntax elements before identifying the SPS. 
     As an example, assume there are four SPSes, and video encoder  200  signals a value to utlize the fourth SPS. In this example, if the identifier for the SPSes is the fifth syntax element, then video decoder  300  may need to parse four syntax elements before determining the identifier for the SPS, and in this example, may parse 20 synatx elements (e.g., five syntax elements from each of the four SPSes) until identifying the identifier for the fourth SPS. However, if the idenifier for the SPS is the first syntax element, then video decoder  300  may parse only four syntax elements (e.g., one syntax element from each of the four SPSes). 
       FIGS. 2A and 2B  are conceptual diagrams illustrating an example quadtree binary tree (QTBT) structure  130 , and a corresponding coding tree unit (CTU)  132 . The solid lines represent quadtree splitting, and dotted 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 the quadtree splitting, there is no need to indicate the splitting type, because quadtree nodes split a block horizontally and vertically into 4 sub-blocks with equal size. Accordingly, video encoder  200  may encode, and video decoder  300  may decode, syntax elements (such as splitting information) for a region tree level of QTBT structure  130  (i.e., the solid lines) and syntax elements (such as splitting information) for a prediction tree level of QTBT structure  130  (i.e., the dashed lines). Video encoder  200  may encode, and video decoder  300  may decode, video data, such as prediction and transform data, for CUs represented by terminal leaf nodes of QTBT structure  130 . 
     In general, CTU  132  of  FIG. 2B  may be associated with parameters defining sizes of blocks corresponding to nodes of QTBT structure  130  at the first and second levels. These parameters may include a CTU size (representing a size of 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 the minimum allowed binary tree leaf node size). 
     The root node of a QTBT structure corresponding to a CTU may have four child nodes at the first level of the QTBT structure, each of which may be partitioned according to quadtree partitioning. That is, nodes of the first level are either leaf nodes (having no child nodes) or have four child nodes. The example of QTBT structure  130  represents such nodes as including the parent node and child nodes having solid lines for branches. If nodes of the first level are not larger than the maximum allowed binary tree root node size (MaxBTSize), then the nodes can be further partitioned by respective binary trees. The binary tree splitting of one node can be iterated until the nodes resulting from the split reach the minimum allowed binary tree leaf node size (MinBTSize) or the maximum allowed binary tree depth (MaxBTDepth). The example of QTBT structure  130  represents such nodes as having dashed lines for branches. The binary tree leaf node is referred to as a coding unit (CU), which is used for prediction (e.g., intra-picture or inter-picture prediction) and transform, without any further partitioning. As discussed above, CUs may also be referred to as “video blocks” or “blocks.” 
     In one example of the QTBT partitioning structure, the CTU size is set as 128×128 (luma samples and two corresponding 64×64 chroma samples), the MinQTSize is set as 16×16, the MaxBTSize is set as 64×64, the MinBTSize (for both width and height) is set as 4, and the MaxBTDepth is set as 4. The quadtree partitioning is applied to the CTU first to generate quad-tree leaf nodes. The quadtree leaf nodes may have a size from 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). If the leaf quadtree node is 128×128, the leaf quadtree node will not be further split by the binary tree, because the size exceeds the MaxBTSize (i.e., 64×64, in this example). Otherwise, the leaf quadtree node will be further partitioned by the binary tree. Therefore, the quadtree leaf node is also the root node for the binary tree and has the binary tree depth as 0. When the binary tree depth reaches MaxBTDepth (4, in this example), no further splitting is permitted. When the binary tree node has a width equal to MinBTSize (4, in this example), it implies no further horizontal splitting is permitted. Similarly, a binary tree node having a height equal to MinBTSize implies no further vertical splitting is permitted for that binary tree node. As noted above, leaf nodes of the binary tree are referred to as CUs, and are further processed according to prediction and transform without further partitioning. 
     In VVC Draft 7, poc_cnt_lsb syntax element indicating picture order count (POC) least significant bits (LSB) is signalled in slice header. This syntax element indicates the POC, which is a picture level concept. For example, the POC value indicates an order in which the picture is displayed. A picture having a smaller POC value is displayed before a picture having a greater POC value. However, it is possible for a picture having a smaller POC value to be decoded later than a picture having a higher POC value. 
     In some examples, signaling of the poc_cnt_1st may be more suitable in the picture header. Also, there are intra and inter slice specific syntax elements in the picture header. There may be redundant signalling in the picture header if intra slice only or inter slice only pictures exist. In some examples, it may be more efficient to signal syntax elements that are relevant to the picture in the picture header and selectively not signal syntax elements that are not relevant, thereby removing unnecessary and in some cases redundant syntax elements. 
     This disclosure describes first example techniques for signaling and parsing POC LSB in picture header. Signaling pic_order_cnt_lsb in slice header may provide little to no additional benefit over signaling the pic_order_cnt_lsb in picture header. In some examples of the first example techniques, pic_order_cnt_lsb signaling may be moved to, i.e., signaled in, the picture header to remove potential duplicate signalling of pic_order_cnt_lsb. For example, video encoder  200  may signal information indicative of a POC value in a picture header, and video decoder  300  may receive and parse information indicative of the POC value in the picture header. The information indicative of the POC value may be pic_order_cnt_lsb (e.g., one or more least significant bits (LSBs) of the POC value). 
     This disclosure describes second example techniques for selectively signaling intra or inter slice syntax elements in the picture header. For example, two flags (e.g., first flag and second flag described above) controlling presence of intra and inter slice syntax elements may be signaled in the picture header, which may eliminate redundant syntax element signalling in the picture header when intra slice only or inter slice only pictures exists. For example, video encoder  200  may signal one or more syntax elements, in a picture header, indicative of at least one of intra slice syntax elements or inter slice syntax elements and selectively signal one or more syntax elements for intra slices or inter slices based on the one or more syntax elements indicative of at least one of intra slice syntax elements or inter slice syntax elements. Video decoder  300  may parse one or more syntax elements, in the picture header, indicative of at least one of intra slice syntax elements or inter slice syntax elements and selectively parse one or more syntax elements for intra slices or inter slices based on the one or more syntax elements indicative of at least one of intra slice syntax elements or inter slice syntax elements. As described in more detail, the intra slice syntax elements may be a pic_intra_present_flag indicative of whether intra slice syntax elements are present in the picture header, and the inter slice syntax elements may be a pic_inter_present_flag indicative of whether inter slice syntax elements are present in the picture header. 
     Stated another way, video decoder  300  may parse at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header. An example of the first flag is pic_inter_present_flag (also called ph_inter_slice_allowed_flag). Video decoder  300  may also parse a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header. An example of the second flag is pic_intra_present_flag (also called ph_intra_slice_allowed_flag). 
     Video decoder  300  may selectively parse at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag. Video decoder  300  may reconstruct a picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. 
     From the perspective of video encoder  200 , video encoder  200  may determine a manner in which to encode a picture. For example, video encoder  200  may determine whether to encode a picture in accordance with at least one of a set of inter slice syntax elements of the video data and a set of intra slice syntax elements of the video data. Video encoder  200  may selectively signal at least one of the set of inter slice syntax elements, in a picture header, and the set of intra slice syntax elements, in the picture header, based on the determination. 
     For example, if video encoder  200  determined to encode the picture in accordance with the set of inter slice syntax elements, then video encoder  200  may determine to signal the set of inter slice syntax elements. If video encoder  200  determined to encode the picture in accordance with the set of intra slice syntax elements, then video encoder  200  may determine to signal the set of intra slice syntax elements. If video encoder  200  determined to encode the picture in accordance with the set of inter slice syntax elements and the set of intra slice syntax elements, then video encoder  200  may determine to signal the set of inter slice syntax elements and the set of intra slice syntax elements. 
     Video encoder  200  may signal at least one of a first flag of the video data, in the picture header, indicative of whether the set of inter slice syntax elements are signaled in the picture header, and a second flag of the video data, in the picture header, indicative of whether the set of intra slice syntax elements are signaled in the picture header. For example, video encoder  200  may signal information to indicate to video decoder  300  whether the set of inter slice syntax elements and/or the set of intra slice syntax elements are in the bitstream, and video encoder  200  may signal such information using the first flag (e.g., pic_inter_present_flag (also called ph_inter_slice_allowed_flag)) and the second flag (e.g., pic_intra_present_flag (also called ph_intra_slice_allowed_flag)). 
     This disclosure describes third example techniques for signaling certain syntax elements that were signaled in the slice header and signaling the syntax elements in the picture header. For example, with the introduction of a picture header, constant_slice_header_params signals constant picture header elements except for pps_collocated_from_l0_idc syntax element. In some examples, pps_collocated_from_l0_idc syntax may be removed (e.g., not signaled and not parsed) from constant_slice_header_params signaling and constant_slice_header_params may be renamed from constant_slice_header_params to constant_picture_header_params. In some examples, entire constant_slice_header_params signaling may be removed completely. 
     For example, video encoder  200  may signal constant picture header parameters in a picture header. Video decoder  300  may parse the constant picture header parameters in the picture header. The constant picture header parameters may exclude values indicative of whether a flag is present that specifies that a collocated picture used for temporal motion vector prediction is derived from reference picture list  0  or reference picture list  1 . The values excluded from the picture header parameters include pps_collocated_from_l0_idc. The sytanx element pps_collocated_from_l0_idc equal to 0 specifies that the syntax element collocated_from_l0_flag is present in the slice headers of slices referring to a picture parameter set (PPS), and pps_collocated_from_l0_idc equal to 1 or 2 specifies that the syntax element collocated_from_l0_flag is not present in the slice headers of slices referring to the PPS, and the collocated_from_l0_flag equal to 1 specifies that the collocated picture used for temporal motion vector prediction is derived from reference picture list  0 , and collocated_from_l0_flag equal to 0 specifies that the collocated picture used for temporal motion vector prediction is derived from reference picture list  1 . 
     In some examples, as described in more detail below, the parameters in the constant picture header parameters include one or more of (1) pps_dep_quant_enabled_idc, wherein pps_dep_quant_enabled_idc equal to 0 specifies that the syntax element pic_dep_quant_enabled_flag is present in picture headers referring to the picture parameter set (PPS), and pps_dep_quant_enabled_idc equal to 1 or 2 specifies that the syntax element pic_dep_quant_enabled_flag is not present in picture headers referring to the PPS, (2) pps_ref_pic_list_sps_idc, wherein pps_ref_pic_list_sps_idc[ i ] equal to 0 specifies that the syntax element pic_rpl_sps_flag[ i ] is present in picture headers referring to the PPS or slice_rpl_sps_flag[ i ] is present in slice headers referring to the PPS, and pps_ref_pic_list_sps_idc[ i ] equal to 1 or 2 specifies that the syntax element pic_rpl_sps_flag[ i ] is not present in picture headers referring to the PPS and slice_rpl_sps_flag[ i ] is not present in slice headers referring to the PPS, (3) pps_mvd_l1_zero_idc, wherein pps_mvd_l1_zero_idc equal to 0 specifies that the syntax element mvd_l1_zero_flag is present in picture headers referring to the PPS, and pps_mvd_l1_zero_idc equal to 1 or 2 specifies that mvd_l1_zero_flag is not present in picture headers referring to the PPS, (4) pps_six_minus_max_num_merge_cand_plus1, wherein pps_six_minus_max_num_merge_cand_plus1 equal to 0 specifies that pic_six_minus_max_num_merge_cand is present in picture headers referring to the PPS, and pps_six_minus_max_num_merge_cand_plus1 greater than 0 specifies that pic_six_minus_max_num_merge_cand is not present in picture headers referring to the PPS, and (5) pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1, wherein pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1 equal to 0 specifies that pic_max_num_merge_cand_minus_max_num_triangle_cand is present in picture headers of slices referring to the PPS, and pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1 greater than 0 specifies that pic_max_num_merge_cand_minus_max_num_triangle_cand is not present in picture headers referring to the PPS. 
     This disclosure describes fourth example techniques for signaling sequence parameter set identification. All parameter sets except sequence parameter set (SPS) begin with their corresponding parameter_set_id. In some examples, SPS should follow the same design for easy identification of SPS parameter set id. This disclosure describes signaling sps_seq_parameter_set_id as the first element in sequence parameter set syntax. For example, video encoder  200  may signal information indicative of an identifier for a sequence parameter set (SPS) for reference by other syntax elements as first element in SPS syntax before other elements in the SPS. Video decoder  300  may parse information indicative of the identifier for the SPS for reference by other syntax elements as a first element in SPS syntax before other elements in the SPS. The identifier for the SPS may be a sps_seq_parameter_set_id. 
     The above describes first, second, third, and fourth example techniques. However, video encoder  200  and video decoder  300  may be configured to perform any one or any combination of the first, second, third, and fourth example techniques. Also, the first, second, third, and fourth example techniques are identified as such to assist with understanding and should not be considered as limiting. For instance, video encoder  200  and video decoder  300  may be configured to perform some of, all of, or more than the operations described for the first, second, third, and fourth example techniques. 
     The following describes changes to the VVC Draft 7. To ease with understanding, changes in the form of additions are shown as langauge between &lt;ADD&gt; and &lt;/ADD&gt; and changes in the form of deletions are shown as language between &lt;DELETE&gt; and &lt;/DELETE&gt;. 
     7.3.2.6 Picture Header RBSP Syntax 
       
     
       
         
           
               
               
             
               
                   
               
               
                 picture_header_rbsp( ) { 
                 Descriptor 
               
               
                   
               
             
            
               
                  non_reference_picture_flag 
                 u(1) 
               
               
                  gdr_pic_flag 
                 u(1) 
               
               
                  &lt;ADD&gt;pic_order_cnt_lsb 
                 u(v) 
               
               
                  if( sps_poc_msb_flag ) { 
                   
               
               
                   ph_poc_msb_present_flag 
                 u(1) 
               
               
                   if( ph_poc_msb_present_flag ) 
                   
               
               
                    poc_msb_val 
                 u(v) 
               
               
                  }&lt;/ADD&gt; 
                   
               
               
                  no_output_of_prior_pics_flag 
                 u(1) 
               
               
                  if( gdr_pic_flag ) 
                   
               
               
                   recovery_poc_cnt 
                 ue (v) 
               
               
                  ph_pic_parameter_set_id 
                 ue(v) 
               
               
                 &lt;DELETE&gt; if( sps_poc_msb_flag ) { 
                   
               
               
                   ph_poc_msb_present_flag 
                 u(1) 
               
               
                   if( ph_poc_msb_present_flag ) 
                   
               
               
                    poc_msb_val 
                 u(v) 
               
               
                  }&lt;/DELETE&gt; 
                   
               
               
                  if( sps_subpic_id_present_flag &amp;&amp; !sps_subpic_id_signalling_flag ) { 
                   
               
               
                   ph_subpic_id_signalling_present_flag 
                 u(1) 
               
               
                   if( ph_subpics_id_signalling_present_flag ) { 
                   
               
               
                    ph_subpic_id_len_minus1 
                 ue(v) 
               
               
                    for( i = 0; i &lt;= sps_num_subpics_minus1; i++) 
                   
               
               
                      ph_subpic_id[ i ] 
                 u(v) 
               
               
                   } 
                   
               
               
                  } 
                   
               
               
                  if( !sps_loop_filter_across_virtual_boundaries_disabled_present_flag ) { 
                   
               
               
                   ph_loop_filter_across_virtual_boundaries_disabled_present_flag 
                 u(1) 
               
               
                   if( ph_loop_filter_across_virtual_boundaries_disabled_present_flag ) { 
                   
               
               
                    ph_num_ver_virtual_boundaries 
                 u(2) 
               
               
                    for( i = 0; i &lt; ph_num_ver_virtual_boundaries; i++ ) 
                   
               
               
                     ph_virtual_boundaries_pos_x[ i ] 
                 u(13) 
               
               
                    ph_num_hor_virtual_boundaries 
                 u(2) 
               
               
                    for( i = 0; i &lt; ph_num_hor_virtual_boundaries; i++ ) 
                   
               
               
                     ph_virtual_boundaries_pos_y[ i ] 
                 u(13) 
               
               
                   } 
                   
               
               
                  } 
                   
               
               
                  if( separate_colour_plane_flag = = 1 ) 
                   
               
               
                   colour_plane_id 
                 u(2) 
               
               
                  if( output_flag_present_flag ) 
                   
               
               
                   pic_output_flag 
                 u(1) 
               
               
                  pic_rpl_present_flag 
                 u(1) 
               
               
                  if( pic_rpl_present_flag ) { 
                   
               
               
                   for( i = 0; i &lt; 2; i++ ) { 
                   
               
               
                    if( num_ref_pic_lists_in_sps[ i ] &gt; 0 &amp;&amp; !pps_ref_pic_list_sps_idc[ i ] &amp;&amp; 
                   
               
               
                      ( i = = 0 | | ( i = = 1 &amp;&amp; rpl1_idx_present_flag ) ) ) 
                   
               
               
                     pic_rpl_sps_flag [ i ] 
                 u(1) 
               
               
                    if( pic_rpl_sps_flag[ i ] ) { 
                   
               
               
                     if( num_ref_pic_lists_in_sps [ i ] &gt; 1 &amp;&amp; 
                   
               
               
                       ( i = = 0 | | ( i = = 1 &amp;&amp; rpl1_idx_present_flag ) ) ) 
                   
               
               
                    pic_rpl_idx[ i ] 
                 u(v) 
               
               
                    } else 
                   
               
               
                     ref_pic_list_struct( i, num_ref_pic_lists_in_sps[ i ] ) 
                   
               
               
                    for( j = 0; j &lt; NumLtrpEntries[ i ][ RplsIdx[ i ] ]; j++ ) { 
                   
               
               
                     if( ltrp_in_slice_header_flag[ i ][ RplsIdx[ i ] ] ) 
                   
               
               
                      pic_poc_lsb_lt[ i ][ j ] 
                 u(v) 
               
               
                     pic_delta_poc_msb_present_flag[ i ][ j ] 
                 u(1) 
               
               
                     if( pic_delta_poc_msb_present_flag[ i ][ j ] ) 
                   
               
               
                      pic_delta_poc_msb_cycle_lt[ i ][ j ] 
                 ue(v) 
               
               
                    } 
                   
               
               
                   } 
                   
               
               
                  } 
                   
               
               
                 &lt;ADD&gt; pic_intra_present_flag 
                 u(1) 
               
               
                  pic_inter_present_flag 
                 u(1) 
               
               
                   
                 &lt;/ADD&gt; 
               
               
                  if( partition_constraints_override_enabled_flag ) { 
                   
               
               
                   partition_constraints_override_flag 
                 u(1) 
               
               
                   if( partition_constraints_override_flag ) { 
                   
               
               
                    &lt;ADD&gt; if( pic_intra_present_flag ) { &lt;/ADD&gt; 
                   
               
               
                     pic_log2_diff_min_qt_min_cb_intra_slice_luma 
                 ue(v) 
               
               
                     pic_max_mtt_hierarchy_depth_intra_slice_luma 
                 ue(v) 
               
               
                     if( pic_max_mtt_hierarchy_depth_intra_slice_luma != 0 ) { 
                   
               
               
                      pic_log2_diff_max_bt_min_qt_intra_slice_luma 
                 ue(v) 
               
               
                      pic_log2_diff_max_tt_min_qt_intra_slice_luma 
                 ue(v) 
               
               
                     } 
                   
               
               
                     if( qtbtt_dual_tree_intra_flag ) { 
                   
               
               
                      pic_log2_diff_min_qt_min_cb_intra_slice_chroma 
                 ue(v) 
               
               
                      pic_max_mtt_hierarchy_depth_intra_slice_chroma 
                 ue(v) 
               
               
                      if( pic_max_mtt_hierarchy_depth_intra_slice_chroma != 0 ) { 
                   
               
               
                       pic_log2_diff_max_bt_min_qt_intra_slice_chroma 
                 ue(v) 
               
               
                       pic_log2_diff_max_tt_min_qt_intra_slice_chroma 
                 ue(v) 
               
               
                     } 
                   
               
               
                    } 
                   
               
               
                  &lt;ADD&gt; }&lt;/ADD&gt; 
                   
               
               
                   &lt;ADD&gt; if( pic_inter_present_flag ) { &lt;/ADD&gt; 
                   
               
               
                    pic_log2_diff_min_qt_min_cb_inter_slice 
                 ue(v) 
               
               
                    pic_max_mtt_hierarchy_depth_inter_slice 
                 ue(v) 
               
               
                    if( pic_max_mtt_hierarchy_depth_inter_slice != 0 ) { 
                   
               
               
                      pic_log2_diff_max_bt_min_qt_inter_slice 
                 ue(v) 
               
               
                     pic_1og2_diff_max_tt_min_qt_inter_slice 
                 ue(v) 
               
               
                    } 
                   
               
               
                    &lt;ADD&gt;}&lt;/ADD&gt; 
                   
               
               
                   } 
                   
               
               
                  } 
                   
               
               
                 &lt;ADD&gt; if (pic_intra_present_flag ) { &lt;/ADD&gt; 
                   
               
               
                   if( cu_qp_delta_enabled_flag ) 
                   
               
               
                   pic_cu_qp_delta_subdiv_intra_slice 
                 ue(v) 
               
               
                   if( pps_cu_chroma_qp_offset_list_enabled_flag ) 
                   
               
               
                    pic_cu_chroma_qp_offset_subdiv_intra_slice 
                 ue(v) 
               
               
                  &lt;ADD&gt;}&lt;/ADD&gt; 
                   
               
               
                  &lt;ADD&gt;if( pic_inter_present_flag ) {&lt;/ADD&gt; 
                   
               
               
                   if( cu_qp_delta_enabled_flag ) 
                   
               
               
                    pic_cu_qp_delta_subdiv_inter_slice 
                 ue(v) 
               
               
                   if( pps_cu_chroma_qp_offset_list_enabled_flag ) 
                   
               
               
                    pic_cu_chroma_qp_offset_subdiv_inter_slice 
                 ue(v) 
               
               
                   if( sps_temporal_mvp_enabled_flag ) 
                   
               
               
                    pic_temporal_mvp_enabled_flag 
                 u(1) 
               
               
                   if(!pps_mvd_l1_zero_idc ) 
                   
               
               
                    mvd_l1_zero_flag 
                 u(1) 
               
               
                   if( !pps_six_minus_max_num_merge_cand_plus1 ) 
                   
               
               
                    pic_six_minus_max_num_merge_cand 
                 ue(v) 
               
               
                   if( sps_affine_enabled_flag ) 
                   
               
               
                    pic_five_minus_max_num_subblock_merge_cand 
                 ue(v) 
               
               
                   if( sps_fpel_mmvd_enabled_flag ) 
                   
               
               
                    pic_fpel_mmvd_enabled_flag 
                 u(1) 
               
               
                   if( sps_bdof_pic_present_flag ) 
                   
               
               
                    pic_disable_bdof_flag 
                 u(1) 
               
               
                   if( sps_dmvr_pic_present_flag ) 
                   
               
               
                    pic_disable_dmvr_flag 
                 u(1) 
               
               
                   if( sps_prof_pic_present_flag ) 
                   
               
               
                    pic_disable_prof_flag 
                 u(1) 
               
               
                   if( sps_triangle_enabled_flag &amp;&amp; MaxNumMergeCand &gt;= 2 &amp;&amp; 
                   
               
               
                    !pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1 ) 
                   
               
               
                    pic_max_num_merge_cand_minus_max_num_triangle_cand 
                 ue(v) 
               
               
                  &lt;ADD&gt;}&lt;/ADD&gt; 
                   
               
               
                  if ( sps_ibc_enabled_flag ) 
                   
               
               
                   pic_six_minus_max_num_ibc_merge_cand 
                 ue(v) 
               
               
                  if( sps joint_cbcr_enabled_flag ) 
                   
               
               
                   pic joint_cbcr_sign_flag 
                 u(1) 
               
               
                  if( sps_sao_enabled_flag ) { 
                   
               
               
                   pic_sao_enabled_present_flag 
                 u(1) 
               
               
                   if( pic_sao_enabled_present_flag ) { 
                   
               
               
                    pic_sao_luma_enabled_flag 
                 u(1) 
               
               
                    if(ChromaArrayType != 0 ) 
                   
               
               
                     pic_sao_chroma_enabled_flag 
                 u(1) 
               
               
                   } 
                   
               
               
                  } 
                   
               
               
                  ... 
               
               
                   
               
            
           
         
       
     
     7.3.7.1 General Slice Header Syntax 
       
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 slice_header( ) { 
                 Descriptor 
               
               
                   
                   
               
             
            
               
                   
                 &lt;DELETE&gt; slice_pic_order_cnt_lsb 
                 u(v) 
               
               
                   
                   
                 &lt;/DELETE&gt; 
               
               
                   
                  if( subpics_present_flag ) 
                   
               
               
                   
                   slice_subpic_id 
                 u(v) 
               
               
                   
                  if( rect_slice_flag | | NumTilesInPic &gt; 1 ) 
                   
               
               
                   
                   slice_address 
                 u(v) 
               
               
                   
                   
               
            
           
         
       
     
     7.4.3.6 Picture Header RBSP Semantics 
     &lt;ADD&gt; pic_order_cnt_lsb specifies the picture order count modulo MaxPicOrderCntLsb for the current picture. The length of the pic_order_cnt_lsb syntax element is log2_max_pic_order_cnt_lsb_minus4 +4 bits. The value of the pic_order_cnt_lsb shall be in the range of 0 to MaxPicOrderCntLsb −1, inclusive. 
     pic_intra_present_flag equal to 1 specifies intra slice syntax elements are present in the picture header. 
     pic_inter_present_flag equal to 1 specifies inter slice syntax elements are present in the PH.&lt;/ADD&gt; 
     7.4.8.1 General Slice Header Semantics 
     &lt;DELETE&gt; When present, the value of the slice header syntax element slice_pic_order_cnt_lsb shall be the same in all slice headers of a coded picture.&lt;/DELETE&gt; &lt;ADD&gt; The slice_pic_order_cnt_lsb of a slice is equal to the pic_order_cnt_lsb of the associated PH of the slice.&lt;/ADD&gt; 
     7.3.2.4 Picture Parameter Set RBSP Syntax 
       
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 ... 
                   
               
               
                  constant_&lt;DELETE&gt;slice&lt;/DELETE&gt; &lt;ADD&gt; 
                 u(1) 
               
               
                 picture&lt;/ADD&gt;_header_params_enabled_flag 
                   
               
               
                  if( constant_&lt;DELETE&gt;slice&lt;/DELETE&gt; &lt;ADD&gt; 
                   
               
               
                 picture&lt;/ADD&gt;_header_params_enabled_flag ) { 
                   
               
               
                   pps_dep_quant_enabled_idc 
                 u(2) 
               
               
                   for( i = 0; i &lt; 2; i++ ) 
                   
               
               
                    pps_ref_pic_list_sps_idc[ i ] 
                 u(2) 
               
               
                   pps_mvd_l1_zero_idc 
                 u(2) 
               
               
                   &lt;DELETE&gt; pps_collocated_from_l0_idc 
                 u(2) 
               
               
                   
                 &lt;/DELETE&gt; 
               
               
                   pps_six_minus_max_num_merge_cand_plus1 
                 ue(v) 
               
               
                   pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1 
                 ue(v) 
               
               
                 } 
               
               
                   
               
            
           
         
       
     
     7.3.7.1 General Slice Header Syntax 
       
     
       
         
           
               
               
             
               
                   
               
             
            
               
                 ... 
                   
               
               
                  if( cabac_init_present_flag ) 
                   
               
               
                   cabac_init_flag 
                 u(1) 
               
               
                  if( pic_temporal_mvp_enabled_flag ) { 
                   
               
               
                   if( slice_type = = B &lt;DELETE&gt; &amp;&amp; !pps_collocated_from_l0_idc &lt;/DELETE&gt;) 
                   
               
               
                    collocated_from_l0_flag 
                 u(1) 
               
               
                  if( ( collocated_from_l0_flag &amp;&amp; NumRefIdxActive[ 0 ] &gt; 1 ) | | 
                   
               
               
                   ( !collocated_from_l0_flag &amp;&amp; NumRefIdxActive[ 1 ] &gt; 1 ) ) 
                   
               
               
                   collocated_ref_idx 
                 ue(v) 
               
               
                 } 
               
               
                   
               
            
           
         
       
     
     constant_&lt;DELETE&gt;slice&lt;/DELETE&gt; &lt;ADD&gt; picture&lt;/ADD&gt;_header_params_enabled_flag equal to 0 specifies that pps_dep_quant_enabled_idc, pps_ref_pic_list_sps_idc[ i ], pps_mvd_l1_zero_idc, &lt;DELETE&gt; pps_collocated_from_l0_idc, &lt;/DELETE&gt;, pps_six_minus_max_num_merge_cand_plus1, and pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1 are inferred to be equal to 0. constant_&lt;DELETE&gt;slice&lt;/DELETE&gt;&lt;ADD&gt;picture&lt;/ADD&gt;_header_params_enabled_flag equal to 1 specifies that these syntax elements are present in the PPS. 
     7.3.2.3 Sequence Parameter Set RBSP Syntax 
       
     
       
         
           
               
               
             
               
                   
               
               
                 seq_parameter_set_rbsp( ) { 
                 Descriptor 
               
               
                   
               
             
            
               
                  &lt;ADD&gt; sps_seq_parameter_set_id 
                 u(4) 
               
               
                   
                 &lt;/ADD&gt; 
               
               
                  sps_decoding_parameter_set_id 
                 u(4) 
               
               
                  sps_video_parameter_set_id 
                 u(4) 
               
               
                  sps_max_sublayers_minus1 
                 u(3) 
               
               
                  sps_reserved_zero_4bits 
                 u(4) 
               
               
                  sps_ptl_dpb_hrd_params_present_flag 
                 u(1) 
               
               
                  if( sps_ptl_dpb_hrd_params_present_flag ) 
                   
               
               
                   profile_tier_level( 1, sps_max_sublayers_minus1 ) 
                   
               
               
                  gdr_enabled_flag 
                 u(1) 
               
               
                  &lt;DELETE&gt; sps_seq_parameter_set_id 
                 u(4) 
               
               
                   
                 &lt;/DELETE&gt; 
               
               
                  chroma_format_idc 
                 u(2) 
               
               
                  if( chroma_format_idc = = 3 ) 
                   
               
               
                   separate_colour_plane_flag 
                 u(1) 
               
               
                 ... 
                 u(1) 
               
               
                   
               
            
           
         
       
     
       FIG. 3  is a block diagram illustrating an example video encoder  200  that may perform the techniques of this disclosure.  FIG. 3  is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video encoder  200  in the context of video coding standards such as VVC and HEVC. However, the techniques of this disclosure are not limited to these video coding standards, and are applicable generally to video encoding and decoding. 
     In the example of  FIG. 3 , video encoder  200  includes video data memory  230 , mode selection 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 selection 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  may be implemented in one or more processors or in processing circuitry. For instance, the units of video encoder  200  may be implemented as one or more circuits or logic elements as part of hardware circuitry, or as part of a processor, ASIC, of FPGA. Moreover, video encoder  200  may include additional or alternative processors or processing circuitry to perform these and other functions. 
     Video data memory  230  may store video data to be encoded by the components of video encoder  200 . Video encoder  200  may receive the video data stored in video data memory  230  from, for example, video source  104  ( FIG. 1 ). DPB  218  may act as a reference picture memory that stores reference video data for use in prediction of subsequent video data by video encoder  200 . Video data memory  230  and DPB  218  may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Video data memory  230  and DPB  218  may be provided by the same memory device or separate memory devices. In various examples, video data memory  230  may be on-chip with other components of video encoder  200 , as illustrated, or off-chip relative to those components. 
     In this disclosure, reference to video data memory  230  should not be interpreted as being limited to memory internal to video encoder  200 , unless specifically described as such, or memory external to video encoder  200 , unless specifically described as such. Rather, reference to video data memory  230  should be understood as reference memory that stores video data that video encoder  200  receives for encoding (e.g., video data for a current block that is to be encoded). Memory  106  of  FIG. 1  may also provide temporary storage of outputs from the various units of video encoder  200 . 
     The various units of  FIG. 3  are illustrated to assist with understanding the operations performed by video encoder  200 . The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may 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 may be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits. 
     Video encoder  200  may include arithmetic logic units (ALUs), elementary function units (EFUs), digital circuits, analog circuits, and/or programmable cores, formed from programmable circuits. In examples where the operations of video encoder  200  are performed using software executed by the programmable circuits, memory  106  ( FIG. 1 ) may store the instructions (e.g., object code) of the software that video encoder  200  receives and executes, or another memory within video encoder  200  (not shown) may store such instructions. 
     Video data memory  230  is configured to store received video data. Video encoder  200  may retrieve a picture of the video data from video data memory  230  and provide the video data to residual generation unit  204  and mode selection unit  202 . Video data in video data memory  230  may be raw video data that is to be encoded. 
     Mode selection unit  202  includes a motion estimation unit  222 , motion compensation unit  224 , and an intra-prediction unit  226 . Mode selection unit  202  may include additional functional units to perform video prediction in accordance with other prediction modes. As examples, mode selection unit  202  may include a palette unit, an intra-block copy unit (which may be part of motion estimation unit  222  and/or motion compensation unit  224 ), an affine unit, a linear model (LM) unit, or the like. 
     Mode selection unit  202  generally coordinates multiple encoding passes to test combinations of encoding parameters and resulting rate-distortion values for such combinations. The encoding parameters may include partitioning of CTUs into CUs, prediction modes for the CUs, transform types for residual data of the CUs, quantization parameters for residual data of the CUs, and so on. Mode selection unit  202  may ultimately select the combination of encoding parameters having rate-distortion values that are better than the other tested combinations. 
     Video encoder  200  may partition a picture retrieved from video data memory  230  into a series of CTUs, and encapsulate one or more CTUs within a slice. Mode selection unit  202  may partition a CTU of the picture in accordance with a tree structure, such as the QTBT structure or the quad-tree structure of HEVC described above. As described above, video encoder  200  may form one or more CUs from partitioning a CTU according to the tree structure. Such a CU may also be referred to generally as a “video block” or “block.” 
     In general, mode selection unit  202  also controls the components thereof (e.g., motion estimation unit  222 , motion compensation unit  224 , and intra-prediction unit  226 ) to generate a prediction block for a current block (e.g., a current CU, or in HEVC, the overlapping portion of a PU and a TU). For inter-prediction of a current block, motion estimation unit  222  may perform a motion search to identify one or more closely matching reference blocks in one or more reference pictures (e.g., one or more previously coded pictures stored in DPB  218 ). In particular, motion estimation unit  222  may calculate a value representative of how similar a potential reference block is to the current block, e.g., according to sum of absolute difference (SAD), sum of squared differences (SSD), mean absolute difference (MAD), mean squared differences (MSD), or the like. Motion estimation unit  222  may generally perform these calculations using sample-by-sample differences between the current block and the reference block being considered. Motion estimation unit  222  may identify a reference block having a lowest value resulting from these calculations, indicating a reference block that most closely matches the current block. 
     Motion estimation unit  222  may form one or more motion vectors (MVs) that defines the positions of the reference blocks in the reference pictures relative to the position of the current block in a current picture. Motion estimation unit  222  may then provide the motion vectors to motion compensation unit  224 . For example, for uni-directional inter-prediction, motion estimation unit  222  may provide a single motion vector, whereas for bi-directional inter-prediction, motion estimation unit  222  may provide two motion vectors. Motion compensation unit  224  may then generate a prediction block using the motion vectors. For example, motion compensation unit  224  may retrieve data of the reference block using the motion vector. As another example, if the motion vector has fractional sample precision, motion compensation unit  224  may interpolate values for the prediction block according to one or more interpolation filters. Moreover, for bi-directional inter-prediction, motion compensation unit  224  may retrieve data for two reference blocks identified by respective motion vectors and combine the retrieved data, e.g., through sample-by-sample averaging or weighted averaging. 
     As another example, for intra-prediction, or intra-prediction coding, intra-prediction unit  226  may generate the prediction block from samples neighboring the current block. For example, for directional modes, intra-prediction unit  226  may generally mathematically combine values of neighboring samples and populate these calculated values in the defined direction across the current block to produce the prediction block. As another example, for DC mode, intra-prediction unit  226  may calculate an average of the neighboring samples to the current block and generate the prediction block to include this resulting average for each sample of the prediction block. 
     Mode selection unit  202  provides the prediction block to residual generation unit  204 . Residual generation unit  204  receives a raw, unencoded version of the current block from video data memory  230  and the prediction block from mode selection unit  202 . Residual generation unit  204  calculates sample-by-sample differences between the current block and the prediction block. The resulting sample-by-sample differences define a residual block for the current block. In some examples, residual generation unit  204  may also determine differences between sample values in the residual block to generate a residual block using residual differential pulse code modulation (RDPCM). In some examples, residual generation unit  204  may be formed using one or more subtractor circuits that perform binary subtraction. 
     In examples where mode selection unit  202  partitions CUs into PUs, each PU may be associated with a luma prediction unit and corresponding chroma prediction units. Video encoder  200  and video decoder  300  may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size of a luma prediction unit of the PU. Assuming that the size of a particular CU is 2N×2N, video encoder  200  may support PU sizes of 2N×2N or N×N for intra prediction, and symmetric PU sizes of 2N×2N, 2N×N, N×2N, N×N, or similar for inter prediction. Video encoder  200  and video decoder  300  may also support asymmetric partitioning for PU sizes of 2N×nU, 2N×nD, nL×2N, and nR×2N for inter prediction. 
     In examples where mode selection unit  202  does not further partition a CU into PUs, each CU may be associated with a luma coding block and corresponding chroma coding blocks. As above, the size of a CU may refer to the size of the luma coding block of the CU. The video encoder  200  and video decoder  300  may support CU sizes of 2N×2N, 2N×N, or N×2N. 
     For other video coding techniques such as an intra-block copy mode coding, an affine-mode coding, and linear model (LM) mode coding, as few examples, mode selection unit  202 , via respective units associated with the coding techniques, generates a prediction block for the current block being encoded. In some examples, such as palette mode coding, mode selection unit  202  may not generate a prediction block, and instead generate syntax elements that indicate the manner in which to reconstruct the block based on a selected palette. In such modes, mode selection unit  202  may provide these syntax elements to entropy encoding unit  220  to be encoded. 
     As described above, residual generation unit  204  receives the video data for the current block and the corresponding prediction block. Residual generation unit  204  then generates a residual block for the current block. To generate the residual block, residual generation unit  204  calculates sample-by-sample differences between the prediction block and the current block. 
     Transform processing unit  206  applies one or more transforms to the residual block to generate a block of transform coefficients (referred to herein as a “transform coefficient block”). Transform processing unit  206  may apply various transforms to a residual block to form the transform coefficient block. For example, transform processing unit  206  may apply a discrete cosine transform (DCT), a directional transform, a Karhunen-Loeve transform (KLT), or a conceptually similar transform to a residual block. In some examples, transform processing unit  206  may perform multiple transforms to a residual block, e.g., a primary transform and a secondary transform, such as a rotational transform. In some examples, transform processing unit  206  does not apply transforms to a residual block. 
     Quantization unit  208  may quantize the transform coefficients in a transform coefficient block, to produce a quantized transform coefficient block. Quantization unit  208  may quantize transform coefficients of a transform coefficient block according to a quantization parameter (QP) value associated with the current block. Video encoder  200  (e.g., via mode selection unit  202 ) may adjust the degree of quantization applied to the transform coefficient blocks associated with the current block by adjusting the QP value associated with the CU. Quantization may introduce loss of information, and thus, quantized transform coefficients may have lower precision than the original transform coefficients produced by transform processing unit  206 . 
     Inverse quantization unit  210  and inverse transform processing unit  212  may apply inverse quantization and inverse transforms to a quantized transform coefficient block, respectively, to reconstruct a residual block from the transform coefficient block. Reconstruction unit  214  may produce a reconstructed block corresponding to the current block (albeit potentially with some degree of distortion) based on the reconstructed residual block and a prediction block generated by mode selection unit  202 . For example, reconstruction unit  214  may add samples of the reconstructed residual block to corresponding samples from the prediction block generated by mode selection unit  202  to produce the reconstructed block. 
     Filter unit  216  may perform one or more filter operations on reconstructed blocks. For example, filter unit  216  may perform deblocking operations to reduce blockiness artifacts along edges of CUs. Operations of filter unit  216  may be skipped, in some examples. 
     Video encoder  200  stores reconstructed blocks in DPB  218 . For instance, in examples where operations of filter unit  216  are not needed, reconstruction unit  214  may store reconstructed blocks to DPB  218 . In examples where operations of filter unit  216  are needed, filter unit  216  may store the filtered reconstructed blocks to DPB  218 . Motion estimation unit  222  and motion compensation unit  224  may retrieve a reference picture from DPB  218 , formed from the reconstructed (and potentially filtered) blocks, to inter-predict blocks of subsequently encoded pictures. In addition, intra-prediction unit  226  may use reconstructed blocks in DPB  218  of a current picture to intra-predict other blocks in the current picture. 
     In general, entropy encoding unit  220  may entropy encode syntax elements received from other functional components of video encoder  200 . For example, entropy encoding unit  220  may entropy encode quantized transform coefficient blocks from quantization unit  208 . As another example, entropy encoding unit  220  may entropy encode prediction syntax elements (e.g., motion information for inter-prediction or intra-mode information for intra-prediction) from mode selection unit  202 . Entropy encoding unit  220  may perform one or more entropy encoding operations on the syntax elements, which are another example of video data, to generate entropy-encoded data. For example, entropy encoding unit  220  may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, an Exponential-Golomb encoding operation, or another type of entropy encoding operation on the data. In some examples, entropy encoding unit  220  may operate in bypass mode where syntax elements are not entropy encoded. 
     Video encoder  200  may output a bitstream that includes the entropy encoded syntax elements needed to reconstruct blocks of a slice or picture. In particular, entropy encoding unit  220  may output the bitstream. 
     The operations described above are described with respect to a block. Such description should be understood as being operations for a luma coding block and/or chroma coding blocks. As described above, in some examples, the luma coding block and chroma coding blocks are luma and chroma components of a CU. In some examples, the luma coding block and the chroma coding blocks are luma and chroma components of a PU. 
     In some examples, operations performed with respect to a luma coding block need not be repeated for the chroma coding blocks. As one example, operations to identify a motion vector (MV) and reference picture for a luma coding block need not be repeated for identifying a MV and reference picture for the chroma blocks. Rather, the MV for the luma coding block may be scaled to determine the MV for the chroma blocks, and the reference picture may be the same. As another example, the intra-prediction process may be the same for the luma coding block and the chroma coding blocks. 
     Video encoder  200  represents an example of a device configured to encode video data including a memory configured to store video data, and one or more processing units implemented in circuitry and configured to signal information indicative of a picture order count (POC) value in a picture header. The one or more processing units may be configured to signal one or more syntax elements, in a picture header, indicative of at least one of intra slice syntax elements or inter slice syntax elements, and selectively signal one or more syntax elements for intra slices or inter slices based on the one or more syntax elements indicative of at least one of intra slice syntax elements or inter slice syntax elements. The one or more processing units may be configured to signal constant picture header parameters in the picture header, wherein the constant picture header parameters exclude values indicative of whether a flag is present that specifies that a collocated picture used for temporal motion vector prediction is derived from reference picture list  0  or reference picture list  1 . The one or more processing units may be configured to signal information indicative of an identifier for the SPS for reference by other syntax elements as a first element in SPS syntax before other elements in the SPS. 
     In some examples, mode selection unit  202  may determine whether to encode a picture in accordance with at least one of a set of inter slice syntax elements of the video data and a set of intra slice syntax elements of the video data. Mode selection unit  202  may selectively signal at least one of the set of inter slice syntax elements, in a picture header, and the set of intra slice syntax elements, in the picture header, based on the determination. Mode selection unit  202  may also signal at least one of a first flag of the video data, in the picture header, indicative of whether the set of inter slice syntax elements are signaled in the picture header, and a second flag of the video data, in the picture header, indicative of whether the set of intra slice syntax elements are signaled in the picture header. The picture header may be a syntax structure that includes syntax elements that apply to all slices of the picture. 
     In some examples, mode selection unit  202  may signal information indicative of a picture order count (POC) value in a picture header. The information indicative of the POC value comprises information indicative of one or more least significant bits (LSBs) of the POC value. In some examples, mode selection unit  202  may signal information indicative of an identifier for a sequence parameter set (SPS) for reference as first element in the SPS before other elements in the SPS. The identifier for the SPS may be a sps_seq_parameter_set_id. 
       FIG. 4  is a block diagram illustrating an example video decoder  300  that may perform the techniques of this disclosure.  FIG. 4  is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure. For purposes of explanation, this disclosure describes video decoder  300  according to the techniques of VVC and HEVC. However, the techniques of this disclosure may be performed by video coding devices that are configured to other video coding standards. 
     In the example of  FIG. 4 , 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  may be implemented in one or more processors or in processing circuitry. For instance, the units of video decoder  300  may be implemented as one or more circuits or logic elements as part of hardware circuitry, or as part of a processor, ASIC, of FPGA. Moreover, video decoder  300  may include additional or alternative processors or processing circuitry to perform these and other functions. 
     Prediction processing unit  304  includes motion compensation unit  316  and intra-prediction unit  318 . Prediction processing unit  304  may include additional units to perform prediction in accordance with other prediction modes. As examples, prediction processing unit  304  may include a palette unit, an intra-block copy unit (which may form part of motion compensation unit  316 ), an affine unit, a linear model (LM) unit, or the like. In other examples, video decoder  300  may include more, fewer, or different functional components. 
     CPB memory  320  may store video data, such as an encoded video bitstream, to be decoded by the components of video decoder  300 . The video data stored in CPB memory  320  may be obtained, for example, from computer-readable medium  110  ( FIG. 1 ). CPB memory  320  may include a CPB that stores encoded video data (e.g., syntax elements) from an encoded video bitstream. Also, CPB memory  320  may store video data other than syntax elements of a coded picture, such as temporary data representing outputs from the various units of video decoder  300 . DPB  314  generally stores decoded pictures, which video decoder  300  may output and/or use as reference video data when decoding subsequent data or pictures of the encoded video bitstream. CPB memory  320  and DPB  314  may be formed by any of a variety of memory devices, such as DRAM, including SDRAM, MRAM, RRAM, or other types of memory devices. CPB memory  320  and DPB  314  may be provided by the same memory device or separate memory devices. In various examples, CPB memory  320  may be on-chip with other components of video decoder  300 , or off-chip relative to those components. 
     Additionally or alternatively, in some examples, video decoder  300  may retrieve coded video data from memory  120  ( FIG. 1 ). That is, memory  120  may store data as discussed above with CPB memory  320 . Likewise, memory  120  may store instructions to be executed by video decoder  300 , when some or all of the functionality of video decoder  300  is implemented in software to be executed by processing circuitry of video decoder  300 . 
     The various units shown in  FIG. 4  are illustrated to assist with understanding the operations performed by video decoder  300 . The units may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Similar to  FIG. 3 , fixed-function circuits refer to circuits that provide particular functionality, and are preset on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks, and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may 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 may be distinct circuit blocks (fixed-function or programmable), and in some examples, one or more of the units may be integrated circuits. 
     Video decoder  300  may include ALUs, EFUs, digital circuits, analog circuits, and/or programmable cores formed from programmable circuits. In examples where the operations of video decoder  300  are performed by software executing on the programmable circuits, on-chip or off-chip memory may store instructions (e.g., object code) of the software that video decoder  300  receives and executes. 
     Entropy decoding unit  302  may receive encoded video data from the CPB and entropy decode the video data to reproduce syntax elements. Prediction processing unit  304 , inverse quantization unit  306 , inverse transform processing unit  308 , reconstruction unit  310 , and filter unit  312  may generate decoded video data based on the syntax elements extracted from the bitstream. 
     In general, video decoder  300  reconstructs a picture on a block-by-block basis. Video decoder  300  may perform a reconstruction operation on each block individually (where the block currently being reconstructed, i.e., decoded, may be referred to as a “current block”). 
     Entropy decoding unit  302  may entropy decode syntax elements defining quantized transform coefficients of a quantized transform coefficient block, as well as transform information, such as a quantization parameter (QP) and/or transform mode indication(s). Inverse quantization unit  306  may use the QP associated with the quantized transform coefficient block to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit  306  to apply. Inverse quantization unit  306  may, for example, perform a bitwise left-shift operation to inverse quantize the quantized transform coefficients. Inverse quantization unit  306  may thereby form a transform coefficient block including transform coefficients. 
     After inverse quantization unit  306  forms the transform coefficient block, inverse transform processing unit  308  may apply one or more inverse transforms to the transform coefficient block to generate a residual block associated with the current block. For example, inverse transform processing unit  308  may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the transform coefficient block. 
     Furthermore, prediction processing unit  304  generates a prediction block according to prediction information syntax elements that were entropy decoded by entropy decoding unit  302 . For example, if the prediction information syntax elements indicate that the current block is inter-predicted, motion compensation unit  316  may generate the prediction block. In this case, the prediction information syntax elements may indicate a reference picture in DPB  314  from which to retrieve a reference block, as well as a motion vector identifying a location of the reference block in the reference picture relative to the location of the current block in the current picture. Motion compensation unit  316  may generally perform the inter-prediction process in a manner that is substantially similar to that described with respect to motion compensation unit  224  ( FIG. 3 ). 
     As another example, if the prediction information syntax elements indicate that the current block is intra-predicted, intra-prediction unit  318  may generate the prediction block according to an intra-prediction mode indicated by the prediction information syntax elements. Again, intra-prediction unit  318  may generally perform the intra-prediction process in a manner that is substantially similar to that described with respect to intra-prediction unit  226  ( FIG. 3 ). Intra-prediction unit  318  may retrieve data of neighboring samples to the current block from DPB  314 . 
     Reconstruction unit  310  may reconstruct the current block using the prediction block and the residual block. For example, reconstruction unit  310  may add samples of the residual block to corresponding samples of the prediction block to reconstruct the current block. 
     Filter unit  312  may perform one or more filter operations on reconstructed blocks. For example, filter unit  312  may perform deblocking operations to reduce blockiness artifacts along edges of the reconstructed blocks. Operations of filter unit  312  are not necessarily performed in all examples. 
     Video decoder  300  may store the reconstructed blocks in DPB  314 . For instance, in examples where operations of filter unit  312  are not performed, reconstruction unit  310  may store reconstructed blocks to DPB  314 . In examples where operations of filter unit  312  are performed, filter unit  312  may store the filtered reconstructed blocks to DPB  314 . As discussed above, DPB  314  may provide reference information, such as samples of a current picture for intra-prediction and previously decoded pictures for subsequent motion compensation, to prediction processing unit  304 . Moreover, video decoder  300  may output decoded pictures (e.g., decoded video) from DPB  314  for subsequent presentation on a display device, such as display device  118  of  FIG. 1 . 
     In this manner, 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 parse information indicative of the POC value in the picture header. The one or more processing units may be configured to parse one or more syntax elements, in the picture header, indicative of at least one of intra slice syntax elements or inter slice syntax elements, and selectively parse one or more syntax elements for intra slices or inter slices based on the one or more syntax elements indicative of at least one of intra slice syntax elements or inter slice syntax elements. The one or more processing units may be configured to parse the constant picture header parameters in the picture header, wherein the constant picture header parameters exclude values indicative of whether a flag is present that specifies that a collocated picture used for temporal motion vector prediction is derived from reference picture list  0  or reference picture list  1 . The processing units may be configured to parse information indicative of the identifier for the SPS for reference by other syntax elements as a first element in SPS syntax befor other elements in the SPS. 
     As one example, prediction processing unit  304  may parse at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header. An example of the first flag is pic_inter_present_flag (also called ph_inter_slice_allowed_flag). An example of the second flag is pic_intra_present_flag (also called ph_intra_slice_allowed_flag). 
     Prediction processing unit  304  may selectively parse at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag. For example, if pic_inter_present_flag is false (e.g., 0), then prediction processing unit  304  may determine that the set of inter slice syntax elements is not parsed. If pic_inter_present_flag is true (e.g., 1), then prediction processing unit  304  may determine that the set of inter slice syntax elements is parsed. If pic_intra_present_flag is false (e.g., 0), then prediction processing unit  304  may determine that the set of intra slice syntax elements is not parsed. If pic_inter_present_flag is true (e.g., 1), then prediction processing unit  304  may determine that the set of intra slice syntax elements is not parsed. 
     Video decoder  300  may reconstruct a picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. For example, prediction processing unit  304  may instruct motion compensation unit  316  and/or intra-prediction unit  318  to generate prediction blocks for blocks in the picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements. Reconstruction unit  310  may add the prediction blocks with respective residual blocks to reconstruct blocks of the picture, and thereby reconstruct the picture. 
       FIG. 5  is a flowchart illustrating an example method for encoding a current block. The current block may comprise a current CU. Although described with respect to video encoder  200  ( FIGS. 1 and 3 ), it should be understood that other devices may be configured to perform a method similar to that of  FIG. 5 . 
     Video encoder  200  may determine whether to encode a picture in accordance with at least one of a set of inter slice syntax elements of the video data and a set of intra slice syntax elements of the video data ( 500 ). For example, based on rate distortion determinations, video encoder  200  may determine that some slices in the picture should be inter slices (e.g., blocks with inter slices are inter-predicted), and that some slices in the picture should be intra slices (e.g., blocks with intra slices are intra-predicted). In some examples, video encoder  200  may determine no slice should be inter-predicted or no slice should be intra-predicted. The set of inter slice syntax elements and the set of intra slice syntax elements may be define size and depth hierarchy, etc. of the slices that are determined to be inter slices and intra slices, respectively. For example, the inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted 
     Video encoder  200  may selectively signal at least one of the set of inter slice syntax elements, in a picture header, and the set of intra slice syntax elements, in the picture header, based on the determination ( 502 ). For example, if video encoder  200  determined that there are one or more inter slices in the picture, then video encoder  200  may signal the set of inter slice syntax elements. If video encoder  200  determined that there are one or more intra slices in the picture, then video encoder  200  may signal the set of intra slice syntax elements. However, if there are no inter slices, then video encoder  200  may not signal the set of inter slice syntax elements, and if there are no intra slices, then video encoder  200  may not signal the set of intra slice syntax elements. 
     Video encoder  200  may signal at least one of a first flag of the video data, in the picture header, indicative of whether the set of inter slice syntax elements are signaled in the picture header, and a second flag of the video data, in the picture header, indicative of whether the set of intra slice syntax elements are signaled in the picture header ( 504 ). For example, video encoder  200  may need to indicate to video decoder  300  whether the set of inter slice syntax elements are signaled or not, and whether the set of intra slice syntax elements are signaled or not. Video encoder  200  may provide such information with the first flag and the second flag. An example of the first flag is pic_inter_present_flag (also called ph_inter_slice_allowed_flag). An example of the second flag is pic_intra_present_flag (also called ph_intra_slice_allowed_flag). 
     The set of inter slice syntax elements include one or more of the following: a first syntax element indicative of differences between a minimum size of luma leaf block resulting from quadtree splitting of a coding tree unit (CTU) and a minimum size of luma block that is inter-predicted (e.g., ph_log2_diff_min_qt_min_cb_inter_slice (also called pic_log2_diff_min_qt_min_cb_inter_slice)), a second syntax element indicative of maximum hierarchy depth of coding units resulting from multi-type tree splitting of a quadtree leaf in inter slices (e.g., ph_max_mtt_hierarchy_depth_inter_slice (also called pic_max_mtt_hierarchy_depth_inter_slice)), a third syntax element indicative of difference between maximum size in luma samples of a luma coding block that can be split using binary split and minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in inter slices (e.g., ph_log2_diff_max_bt_min_qt_inter_slice (also called pic_log2_diff_max_bt_min_qt_inter_slice)), and a fourth syntax element indicative of a difference between maximum size in luma samples of a luma coding block that can be split using a ternary split and the minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in inter slices (e.g., ph_log2_diff_max_tt_min_qt_inter_slice (also called pic_log2_diff_max_tt_min_qt_inter_slice)). 
     The set of intra slice syntax elements include one or more of the following: a first syntax element indicative of difference between minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a coding tree unit (CTU) and the minimum coding block size in luma samples for luma coding units (CUs) in intra slices (e.g., ph_log2_diff_min_qt_min_cb_intra_slice_luma (also called pic_log2_diff_min_qt_min_cb_intra_slice_luma)), a second syntax element indicative of maximum hierarchy depth for coding units resulting from multi-type tree splitting of a quadtree leaf in intra slices (e.g., ph_max_mtt_hierarchy_depth_intra_slice_luma (also called pic_max_mtt_hierarchy_depth_intra_slice_luma)), a third syntax element indicative of difference between the maximum size in luma samples of a luma coding block that can be split using a binary split and the minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in intra slices (e.g., ph_log2_diff_max_bt_min_qt_intra_slice_luma (also called pic_log2_diff_max_bt_min_qt_intra_slice_luma)), a fourth syntax element indicative of difference between the maximum size in luma samples of a luma coding block that can be split using a ternary split and the minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in intra slices (e.g., ph_log2_diff_max_tt_min_qt_intra_slice_luma (also called pic_log2_diff_max_tt_min_qt_intra_slice_luma)), a fifth syntax element indicative of difference between the minimum size in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning and the minimum coding block size in luma samples for chroma CUs with dual tree partitioning in intra slices (e.g., ph_log2_diff_min_qt_min_cb_intra_slice_chroma (also called pic_log2_diff_min_qt_min_cb_intra_slice_chroma), a sixth syntax element indicative of maximum hierarchy depth for chroma coding units resulting from multi-type tree splitting of a chroma quadtree leaf with dual tree partitioning in intra slices (e.g., ph_max_mtt_hierarchy_depth_intra_slice_chroma (also called pic_max_mtt_hierarchy_depth_intra_slice_chroma)), a seventh syntax element indicative of difference between the maximum size in luma samples of a chroma coding block that can be split using a binary split and the minimum size in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning in intra slices (e.g., ph_log2_diff_max_bt_min_qt_intra_slice_chroma (also called pic_log2_diff_max_bt_min_qt_intra_slice_chroma)), and an eighth syntax element indicative of difference between the maximum size in luma samples of a chroma coding block that can be split using a ternary split and the minimum size in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning in intra slices (e.g., ph_log2_diff_max_tt_min_qt_intra_slice_chroma (also called pic_log2_diff_max_tt_min_qt_intra_slice_chroma)). 
       FIG. 6  is a flowchart illustrating an example method for decoding a current block of video data. The current block may comprise a current CU. Although described with respect to video decoder  300  ( FIGS. 1 and 4 ), it should be understood that other devices may be configured to perform a method similar to that of  FIG. 6 . 
     Video decoder  300  may be configured to parse at least one of a first flag of the video data, in a picture header, indicative of whether a set of inter slice syntax elements are included in the picture header, and a second flag of the video data, in the picture header, indicative of whether a set of intra slice syntax elements are included in the picture header ( 600 ). The inter slice syntax elements are inter-prediction syntax elements for slices in a picture that are inter-predicted, and the intra slice syntax elements are intra-prediction syntax elements for slices in the picture that are intra-predicted. An example of the first flag is pic_inter_present_flag (also called ph_inter_slice_allowed_flag). An example of the second flag is pic_intra_present_flag (also called ph_intra_slice_allowed_flag). 
     The first flag and the second flag may be binary with a value of 0 or 1. The first flag and the second flag may not be NAL unit types. The bitstream that video decoder  300  parses may include both the first flag and the second flag, or one of the first flag and the second flag. 
     Video decoder  300  may selectively parse at least one of the set of inter slice syntax elements, in the picture header, based on the first flag and the set of intra slice syntax elements, in the picture header, based on the second flag ( 602 ). For example, if the first flag is false (e.g., 0), then video decoder  300  may not parse the set of inter slice syntax elements. If the first flag is true (e.g., 1), then video decoder  300  may parse the set of inter slice syntax elements. If the second flag is false (e.g., 0), then video decoder  300  may not parse the set of intra slice syntax elements. If the second flag is true (e.g., 1), then video decoder  300  may parse the set of inter slice syntax elements. 
     It may be possible for the bitstream to include both the set of inter slice syntax elements and the set of intra slice syntax elements. For instance, the picture may include both inter slices and intra slices. However, in some examples, there may be no inter slices (e.g., the first flag is 0) in the picture. In some examples, there may be no intra slices (e.g., the second flag is 0) in the picture. 
     Video decoder  300  may reconstruct a picture based on at least one of the set of inter slice syntax elements and the set of intra slice syntax elements ( 604 ). For example, video decoder  300  may utilize the set of inter slice syntax elements to determine how to inter-predict blocks in the inter slices and utilize the set of intra slice syntax elements to determine how to intra-predict blocks in the intra slices. However, there is a possibility that there are no inter slices, and therefore, there would be no inter slice syntax elements. Also, there is a possibility that there are no intra slices, and therefore, there would be not intra slice syntax elements. 
     The set of inter slice syntax elements include one or more of the following: a first syntax element indicative of differences between a minimum size of luma leaf block resulting from quadtree splitting of a coding tree unit (CTU) and a minimum size of luma block that is inter-predicted (e.g., ph_log2_diff_min_qt_min_cb_inter_slice (also called pic_log2_diff_min_qt_min_cb_inter_slice)), a second syntax element indicative of maximum hierarchy depth of coding units resulting from multi-type tree splitting of a quadtree leaf in inter slices (e.g., ph_max_mtt_hierarchy_depth_inter_slice (also called pic_max_mtt_hierarchy_depth_inter_slice)), a third syntax element indicative of difference between maximum size in luma samples of a luma coding block that can be split using binary split and minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in inter slices (e.g., ph_log2_diff_max_bt_min_qt_inter_slice (also called pic_log2_diff_max_bt_min_qt_inter_slice)), and a fourth syntax element indicative of a difference between maximum size in luma samples of a luma coding block that can be split using a ternary split and the minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in inter slices (e.g., ph_log2_diff_max_tt_min_qt_inter_slice (also called pic_log2_diff_max_tt_min_qt_inter_slice)). 
     The set of intra slice syntax elements include one or more of the following: a first syntax element indicative of difference between minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a coding tree unit (CTU) and the minimum coding block size in luma samples for luma coding units (CUs) in intra slices (e.g., ph_log2_diff_min_qt_min_cb_intra_slice_luma (also called pic_log2_diff_min_qt_min_cb_intra_slice_luma)), a second syntax element indicative of maximum hierarchy depth for coding units resulting from multi-type tree splitting of a quadtree leaf in intra slices (e.g., ph_max_mtt_hierarchy_depth_intra_slice_luma (also called pic_max_mtt_hierarchy_depth_intra_slice_luma)), a third syntax element indicative of difference between the maximum size in luma samples of a luma coding block that can be split using a binary split and the minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in intra slices (e.g., ph_log2_diff_max_bt_min_qt_intra_slice_luma (also called pic_log2_diff_max_bt_min_qt_intra_slice_luma)), a fourth syntax element indicative of difference between the maximum size in luma samples of a luma coding block that can be split using a ternary split and the minimum size in luma samples of a luma leaf block resulting from quadtree splitting of a CTU in intra slices (e.g., ph_log2_diff_max_tt_min_qt_intra_slice_luma (also called pic_log2_diff_max_tt_min_qt_intra_slice_luma)), a fifth syntax element indicative of difference between the minimum size in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning and the minimum coding block size in luma samples for chroma CUs with dual tree partitioning in intra slices (e.g., ph_log2_diff_min_qt_min_cb_intra_slice_chroma (also called pic_log2_diff_min_qt_min_cb_intra_slice_chroma), a sixth syntax element indicative of maximum hierarchy depth for chroma coding units resulting from multi-type tree splitting of a chroma quadtree leaf with dual tree partitioning in intra slices (e.g., ph_max_mtt_hierarchy_depth_intra_slice_chroma (also called pic_max_mtt_hierarchy_depth_intra_slice_chroma)), a seventh syntax element indicative of difference between the maximum size in luma samples of a chroma coding block that can be split using a binary split and the minimum size in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning in intra slices (e.g., ph_log2_diff_max_bt_min_qt_intra_slice_chroma (also called pic_log2_diff_max_bt_min_qt_intra_slice_chroma)), and an eighth syntax element indicative of difference between the maximum size in luma samples of a chroma coding block that can be split using a ternary split and the minimum size in luma samples of a chroma leaf block resulting from quadtree splitting of a chroma CTU with dual tree partitioning in intra slices (e.g., ph_log2_diff_max_tt_min_qt_intra_slice_chroma (also called pic_log2_diff_max_tt_min_qt_intra_slice_chroma)). 
     The following are some example techniques that may be applied alone or in combination. 
     Clause 1. A method of processing video data, the method comprising signaling information indicative of a picture order count (POC) value in a picture header. 
     Clause 2 A method of processing video data, the method comprising parsing information indicative of a picture order count (POC) value in a picture header. 
     Clause 3. The method of any of clauses 1 or 2, wherein information indicative of the POC value comprises information indicative of one or more least significant bits (LSBs) of the POC value. 
     Clause 4. The method of any of clauses 1-3, wherein the picture header comprises a syntax structure that includes syntax elements that apply to all slices of a coded picture. 
     Clause 5. A method of processing video data, the method comprising signaling one or more syntax elements, in a picture header, indicative of at least one of intra slice syntax elements or inter slice syntax elements and selectively signaling one or more syntax elements for intra slices or inter slices based on the one or more syntax elements indicative of at least one of intra slice syntax elements or inter slice syntax elements. 
     Clause 6. A method of processing video data, the method comprising parsing one or more syntax elements, in a picture header, indicative of at least one of intra slice syntax elements or inter slice syntax elements and selectively parsing one or more syntax elements for intra slices or inter slices based on the one or more syntax elements indicative of at least one of intra slice syntax elements or inter slice syntax elements. 
     Clause 7. The method of any of clauses 5 or 6, wherein the intra slice syntax elements comprises a pic_intra_present_flag indicative of whether intra slice syntax elements are present in the picture header, and the inter slice syntax elements comprises a pic_inter_present_flag indicative of whether inter slice syntax elements are present in the picture header. 
     Clause 8. The method of any of clauses 5-7, wherein the picture header comprises a syntax structure that includes syntax elements that apply to all slices of a coded picture. 
     Clause 9. A method of processing video data, the method comprising signaling constant picture header parameters in a picture header, wherein the constant picture header parameters exclude values indicative of whether a flag is present that specifies that a collocated picture used for temporal motion vector prediction is derived from reference picture list  0  or reference picture list  1 . 
     Clause 10. A method of processing video data, the method comprising parsing constant picture header parameters in a picture header, wherein the constant picture header parameters exclude values indicative of whether a flag is present that specifies that a collocated picture used for temporal motion vector prediction is derived from reference picture list  0  or reference picture list  1 . 
     Clause 11. The method of any of clauses 9 or 10, wherein the values excluded from the picture header parameters include a value of pps_collocated_from_l0_idc equal to 0 that specifies that the syntax element collocated_from_l0_flag is present in slice header of slices referring to a picture parameter set (PPS), and a value of pps_collocated_from_l0_idc equal to 1 or 2 that specifies that the syntax element collocated_from_l0_flag is not present in slice header of slices referring to the PPS, and wherein a value of collocated_from_l0_flag equal to 1 specifies that the collocated picture used for temporal motion vector prediction is derived from reference picture list  0 , and a value of collocated_from_l0_flag equal to 0 specifies that the collocated picture used for temporal motion vector prediction is derived from reference picture list  1 . 
     Clause 12. The method of any of clauses 9-11, wherein the parameters in the constant picture header parameters include one or more of pps_dep_quant_enabled_idc, wherein pps_dep_quant_enabled_idc equal to 0 specifies that the syntax element pic_dep_quant_enabled_flag is present in picture headers referring to the picture parameter set (PPS), and pps_dep_quant_enabled_idc equal to 1 or 2 specifies that the syntax element pic_dep_quant_enabled_flag is not present in picture headers referring to the PPS, pps_ref_pic_list_sps_idc, wherein pps_ref_pic_list_sps_idc[ i ] equal to 0 specifies that the syntax element pic_rpl_sps_flag[ i ] is present in picture headers referring to the PPS or slice_rpl_sps_flag[ i ] is present in slice header referring to the PPS, and pps_ref_pic_list_sps_idc[ i ] equal to 1 or 2 specifies that the syntax element pic_rpl_sps_flag[ i ] is not present in picture headers referring to the PPS and slice_rpl_sps_flag[ i ] is not present in slice header referring to the PPS; 
     pps_mvd_l1_zero_idc, wherein pps_mvd_l1_zero_idc equal to 0 specifies that the syntax element mvd_l1_zero_flag is present in picture headers referring to the PPS, and pps_mvd_l1_zero_idc equal to 1 or 2 specifies that mvd_l1_zero_flag is not present in picture headers referring to the PPS, pps_six_minus_max_num_merge_cand_plus1, wherein pps_six_minus_max_num_merge_cand_plus1 equal to 0 specifies that pic_six_minus_max_num_merge_cand is present in picture headers referring to the PPS, and pps_six_minus_max_num_merge_cand_plus1 greater than 0 specifies that pic_six_minus_max_num_merge_cand is not present in picture headers referring to the PPS, and pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1, wherien pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1 equal to 0 specifies that pic_max_num_merge_cand_minus_max_num_triangle_cand is present in picture headers of slices referring to the PPS, and pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1, wherein pps_max_num_merge_cand_minus_max_num_triangle_cand_plus1 greater than 0 specifies that pic_max_num_merge_cand_minus_max_num_triangle_cand is not present in picture headers referring to the PPS. 
     Clause 13. The method of any of clauses 9-12, wherein the picture header comprises a syntax structure that includes syntax elements that apply to all slices of a coded picture. 
     Clause 14. A method of processing video data, the method comprising signaling information indicative of an identifier for a sequence parameter set (SPS) for reference by other syntax elements as first element in the SPS before other elements in the SPS. 
     Clause 15. A method of processing video data, the method comprising parsing information indicative of an identifier for a sequence parameter set (SPS) for reference by other syntax elements as a first element in the SPS before other elements in the SPS. 
     Clause 16. The method of any of clauses 14 or 15, wherein the identifier for the SPS is a sps_seq_parameter_set_id. 
     Clause 17. The method of any one or combination of clauses 1-16. 
     Clause 18. A device for processing video data, the device comprising memory for storing syntax elements of syntax structures and processing circuitry coupled to the memory and configured to perform the method of any one or combination of clauses 1-17. 
     Clause 19. The device of clause 18, further comprising a display configured to display decoded video data. 
     Clause 20. The device of any of clauses 18 and 19, wherein the device comprises one or more of a camera, a computer, a mobile device, a broadcast receiver device, or a set-top box. 
     Clause 21. The device of any of clauses 18-20, wherein the device comprises a video decoder. 
     Clause 22. The device of any of clauses 18-20, wherein the device comprises a video encoder. 
     Clause 23. A computer-readable storage medium having stored thereon instructions that, when executed, cause one or more processors to perform the method of any one or combination of clauses 1-17. 
     Clause 24. A device for processing video data, the device comprising means for performing the method of any one or combination of clauses 1-17. 
     It is to be recognized that depending on the example, certain acts or events of any of the techniques described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the techniques). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially. 
     In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium. 
     By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. 
     Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the terms “processor” and “processing circuitry,” as used herein may refer to any of the foregoing structures or any other structure suitable for implementation of the techniques described herein. In addition, in some aspects, the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements. 
     The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set). Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware. 
     Various examples have been described. These and other examples are within the scope of the following claims.