Abstract: Examples of video encoding methods and apparatus and video decoding methods and apparatus are described. An example method of video processing includes performing a conversion between a video and a bitstream of the video according to a rule, wherein the bitstream includes network abstraction layer (NAL) units for multiple video layers according to a rule; wherein the rule defines that a sub-bitstream extraction process to generate an output bitstream comprising an output layer set (OLS) includes one or more operations that are selectively performed responsive to the following conditions: (1) a list of NAL unit header layer identifier values in the OLS does not includes all values of NAL unit header layer identifiers in all video coding layer (VCL) NAL units in the bitstream, and (2) the output bitstream containing a supplemental enhancement information (SEI) NAL unit that contains a scalable-nesting SEI message.

Abstract: Examples of video encoding methods and apparatus and video decoding methods and apparatus are described. An example method of video processing includes performing a conversion between a video and a bitstream of the video comprising one or more output layer sets according to a rule, wherein the rule specifies that a supplemental enhancement information (SEI) network abstraction layer (NAL) unit that includes a scalable-nested SEI message carrying picture timing information is not included due to use of a same picture timing in all output layer sets in the bitstream.

Abstract: Methods, systems and devices for implementing constraints used in video encoding and video decoding are described. An example method of video processing includes performing a conversion between a video comprising one or more pictures comprising one or more slices and a bitstream of the video. The conversion conforms to a rule, and the bitstream is organized into one or more access units. The rule specifies a constraint on a number of decoded pictures stored in a decoded picture buffer (DPB). Each decoded picture of the decoded pictures is (i) marked as used for reference, (ii) has a flag indicative of the decoded picture being output, and (iii) has an output time later than a decoding time of a current picture.

Abstract: Examples of video encoding methods and apparatus and video decoding methods and apparatus are described. An example method of video processing includes performing a conversion between a video and a bitstream of the video, wherein the bitstream includes network abstraction layer (NAL) units for multiple video layers according to a rule; wherein the rule defines a sub-bitstream extraction process by which NAL units are removed from the bitstream to generate an output bitstream, and wherein the rule specifies to remove all supplemental enhancement information (SEI) NAL units that contain a non-scalable-nested SEI message with a particular payload type, responsive to a list of NAL unit header layer identifier values in an output layer set (OLS) with a target OLS index not including all values of NAL unit header layer identifiers in all video coding layer (VCL) NAL units in the bitstream that is input to the sub-bitstream extraction process.

Abstract: A video coding mechanism is disclosed. The mechanism includes receiving a bitstream including a first slice of a coded image. The coded image is associated with a picture parameter set (PPS) in the bitstream. The first slice is associated with a slice header in the bitstream. A list of identifiers (IDs) is parsed from the PPS. A first ID is parsed from the slice header of the first slice. The first ID matches one of the IDs in the list of IDs in the PPS. A list of tiles coded in the first slice is determined based on the first ID. The first slice is determined to generate a reconstructed sub-image of the coded image.

Abstract: Methods, systems and devices for implementing constraints used in video encoding and video decoding are described. An example method of video processing includes performing a conversion between a video including one or more pictures including one or more slices and a bitstream of the video, wherein the bitstream is organized into a plurality of access units (AUs), AU 0 to AU n, based on a format rule, where n is a positive integer, wherein the format rule specifies a relationship between removal times of each of the plurality of AUs from a coded picture buffer (CPB) during decoding and a number of slices in the each of the plurality of AUs.

Abstract: Techniques for video processing, including video coding, video decoding and video transcoding are described. One example method includes performing a conversion between a video picture that includes one or more tiles and one or more rectangular slices and a bitstream of the video according to a rule. The rule specifies that, for iteratively determining information about the one or more rectangular slices, a variable indicating a tile index is updated only for slices having indices that are smaller than a value equal to a number of slices in the video picture minus 1.

Abstract: Examples of video encoding methods and apparatus and video decoding methods and apparatus are descrined. An example method of video processing includes performing a conversion between a current picture of a video and a bitstream of the video according to a rule. The rule specifies that a number of entries in a reference picture list of the current picture is greater than 0 in response to (1) one or more slices in the current picture being allowed to have a slice type other than an Intra (I) slice type, and (2) reference picture list (RPL) information being present in a picture header.

Abstract: Examples of video encoding methods and apparatus and video decoding methods and apparatus are described. An example method of video processing includes performing a conversion between a video and a bitstream of the video, wherein the bitstream includes one or more output layer sets comprising one or more video layers according to a format rule, wherein the format rule specifies that a non-scalable-nested supplemental enhancement information, SEI, message that includes information regarding hypothetical reference decoder, HRD, is applicable to all output layer sets that include same video layers as the bitstream.

Abstract: Examples of video encoding methods and apparatus and video decoding methods and apparatus are described. An example method of video processing includes performing a conversion between a video and a bitstream of the video, wherein the bitstream comprises one or more supplemental enhancement information, SEI, network abstraction layer (NAL) units according to a rule, wherein the rule specifies that, responsive to an SEI NAL unit including a non-scalable-nested SEI message of a first payload type, the SEI NAL unit is disallowed to include another SEI message of a second payload type.

Abstract: Embodiments for video processing, including video coding, video decoding and video transcoding are described. One example method includes performing a conversion between a video having one or more video pictures in a video layer and a bitstream of the video according to a rule, wherein the rule specifies that, in a process of sub-bitstream extraction, removal of (i) a video coding layer (VCL) network abstraction layer (NAL) unit, (ii) filler data NAL units associated with the VCL NAL unit, and (iii) filler payload supplemental enhancement information (SEI) messages associated with the VCL NAL unit is performed regardless of an availability of an external means used to replace a parameter set that is removed during the sub-bitstream extraction.

Abstract: A method of processing video data includes performing a conversion between a video and a bitstream of the video. The bitstream includes one or more layers including one or more sublayers including one or more pictures including one or more subpictures according to a rule that specifies a rewriting operation selectively performed on one or more syntax structures during a subpicture sub-bitstream extraction process by which an output target sub-bitstream is extracted from the bitstream. The one or more syntax elements include information of the output target sub-bitstream.

Abstract: Several techniques for video encoding and video decoding are described. One example method includes performing a conversion between a video and a bitstream of the video according to a rule. The rule specifies that a subpicture sequence includes (1) all subpictures within the target CVSs that have a same subpicture index and belong to layers in the multi-subpicture layers, and (2) all subpictures in the target CVSs that have a subpicture index of 0 and belong to layers of the OLSs but not in the multi-subpicture layers.

Abstract: Several techniques for video encoding and video decoding are described. An example method of processing video data includes performing a conversion between a video including one or more subpictures and a bitstream of the video according to a format rule, wherein the format rule specifies that a first syntax element in a scalable nesting supplemental enhancement information message in the bitstream is set to a particular value in response to the scalable nesting supplemental enhancement information message including one or more subpicture level information supplemental enhancement information messages, and wherein the particular value of the first syntax element indicates that the scalable nesting supplemental enhancement information message includes one or more scalable-nested supplemental enhancement information messages that apply to a specific output video layer set.

Abstract: Several techniques for video encoding and video decoding are described. One example method includes performing a conversion between a video and a bitstream of the video including one or more output layer sets (OLSs) according to a rule. The rule specifies that a subpicture level information (SLI) supplemental enhancement information (SEI) message includes information about a level of subpicture sequences in a set of coded video sequences of the one or more OLSs to which the SLI SEI message applies. A syntax structure of the SLI SEI message includes at least (1) a first syntax element specifying a maximum number of sublayers for the subpicture sequences and (2) a second syntax element specifying whether level information for the subpicture sequences is present for one or more sublayer representations.

Abstract: A video coding mechanism is disclosed. The mechanism includes partitioning a picture into a plurality of first level tiles. A subset of the first level tiles is partitioned into a plurality of second level tiles. The first level tiles and the second level tiles are encoded into a bitstream. A split indication is encoded into the bitstream. The split indication indicates that at least one of the first level tiles is split into the second level tiles. The bitstream is stored for communication toward a decoder.

Abstract: Methods and apparatus for video processing are described. The video processing may include video encoding, video decoding, or video transcoding. One example video processing method includes performing a conversion between a video picture of a video and a bitstream of the video. A first syntax element in a first video unit level specifying a deblocking parameter offset for ? divided by 2 applied to a chroma component for one or more slices in a first video unit and a second syntax element in the first video unit level specifying a deblocking parameter offset for tC divided by 2 applied to the chroma component for the one or more slices in the first video unit are determined according to a rule in response to the first syntax element and the second syntax element not included in the bitstream.

Abstract: Methods, systems and devices for signaling picture information in access units in video bitstream processing are disclosed. An example method of video processing includes performing a conversion between a video comprising one or more pictures and a bitstream of the video, wherein the bitstream conforms to a format rule, wherein the format rule specifies that a flag and a syntax element, when included in the bitstream, are access unit (AU) specific, and wherein the flag indicates, in response to a current AU not being a first AU in the bitstream in a decoding order, whether a nominal coded picture buffer (CPB) removal time of the current AU is determined relative to (a) a nominal CPB removal time of a previous AU associated with a buffering period supplemental enhancement information (SEI) message, or (b) a nominal CPB removal time of the current AU.

Abstract: Methods, systems and devices for defining and using constraints on picture types in video bitstream processing are disclosed. An example method of video processing includes performing a conversion between a video including one or more pictures and a bitstream of the video, wherein the bitstream conforms to a format rule. The format rule specifies that a picture timing (PT) supplemental enhancement information (SEI) message, when included in the bitstream, is access unit (AU) specific, and wherein each picture of the one or more pictures that is a random access skipped leading (RASL) picture includes only a RASL network abstraction layer unit type (NUT).

Abstract: Methods, systems and devices for signaling of coded buffer picture information in video bitstream processing are disclosed. An example method of video processing includes performing a conversion between a video comprising one or more pictures and a bitstream of the video, wherein the bitstream conforms to a format rule, wherein the format rule specifies that a first syntax element, when included in the bitstream, is access unit (AU) specific, wherein the value of the first syntax element is based on whether an associated AU is an intra random access points (IRAP) AU or a gradual decoding refresh (GDR) AU, and wherein the value of the first syntax element specifies (i) whether a second syntax element is present in a buffering period supplemental enhancement information (SEI) message, and (ii) whether alternative timing information is present in a picture timing SEI message in a current buffering period.