Techniques for generation of a conformant output sub-bitstream

An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

• perform a conversion between a video including one or more layers and a bitstream of the video according to a rule,
• wherein the rule specifies that, in a first process of sub-bitstream extraction to output a first output sub-bitstream, the first output sub-bitstream is extracted without removing network abstraction layer (NAL) units of a particular type and having a particular NAL unit header identifier value,
• wherein the particular type includes an access unit delimiter (AUD) NAL unit,
• wherein the rule further specifies, in a second process of sub-bitstream extraction to output a second output sub-bitstream, whether to generate non-scalable-nested supplementary enhancement information (SEI) messages by extracting scalable-nested SEI messages from a scalable nesting SEI message is based on a first flag indicating whether the scalable nesting SEI message applies to specific output layer sets (OLSs) and a second flag indicating whether the scalable nesting SEI message applies to all subpictures or only to specific subpictures, and wherein the rule further specifies to generate the non-scalable-nested SEI message when a set of conditions are satisfied, wherein the set of conditions comprises that the second flag has a second value that specifies that the SEI message that applies to the specific OLSs applies to all subpictures of the specified OLSs.

A non-transitory computer-readable storage medium storing instructions that cause a processor to:

• perform a conversion between a video including one or more layers and a bitstream of the video according to a rule,
• wherein the rule specifies that, in a first process of sub-bitstream extraction to output a first output sub-bitstream, the first output sub-bitstream is extracted without removing network abstraction layer (NAL) units of a particular type and having a particular NAL unit header identifier value,
• wherein the particular type includes an access unit delimiter (AUD) NAL unit,
• wherein the rule further specifies, in a second process of sub-bitstream extraction to output a second output sub-bitstream, whether to generate non-scalable-nested supplementary enhancement information (SEI) messages by extracting scalable-nested SEI messages from a scalable nesting SEI message is based on a first flag indicating whether the scalable nesting SEI message applies to specific output layer sets (OLSs) and a second flag indicating whether the scalable nesting SEI message applies to all subpictures or only to specific subpictures, and wherein the rule further specifies to generate the non-scalable-nested SEI message when a set of conditions are satisfied, wherein the set of conditions comprises that the second flag has a second value that specifies that the SEI message that applies to the specific OLSs applies to all subpictures of the specified OLSs.

A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

• generating the bitstream of the video including one or more layers according to a rule,
• wherein the rule specifies that, in a first process of sub-bitstream extraction to output a first output sub-bitstream, the first output sub-bitstream is extracted without removing network abstraction layer (NAL) units of a particular type and having a particular NAL unit header identifier value,
• wherein the particular type includes an access unit delimiter (AUD) NAL unit, and
• wherein the rule further specifies, in a second process of sub-bitstream extraction to output a second output sub-bitstream, whether to generate non-scalable-nested supplementary enhancement information (SEI) messages by extracting scalable-nested SEI messages from a scalable nesting SEI message is based on a first flag indicating whether the scalable nesting SEI message applies to specific output layer sets (OLSs) and a second flag indicating whether the scalable nesting SEI message applies to all subpictures or only to specific subpictures, and wherein the rule further specifies to generate the non-scalable-nested SEI message when a set of conditions are satisfied, wherein the set of conditions comprises that the second flag has a second value that specifies that the SEI message that applies to the specific OLSs applies to all subpictures of the specified OLSs.