Constraints on reference picture information

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 comprising a video picture comprising a slice and a bitstream of the video according to a first rule,
• wherein the first rule specifies that a default value of a syntax element specifying a number of entries in a reference picture list syntax structure associated with a reference picture list (RPL) index is equal to 0 due to a condition being satisfied, and
• wherein the condition is satisfied in case (1) the video picture is an instantaneous decoding refresh picture, (2) a first syntax flag specifies that RPL syntax elements are not present in a slice header of the slice, and (3) a second syntax flag specifies that RPL information is not present in a picture header of the video picture.

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

• perform a conversion between a video comprising a video picture comprising a slice and a bitstream of the video according to a first rule,
• wherein the first rule specifies that a default value of a syntax element specifying a number of entries in a reference picture list syntax structure associated with a reference picture list (RPL) index is equal to 0 due to a condition being satisfied, and
• wherein the condition is satisfied in case (1) the video picture is an instantaneous decoding refresh picture, (2) a first syntax flag specifies that RPL syntax elements are not present in a slice header of the slice, and (3) a second syntax flag specifies that RPL information is not present in a picture header of the video picture.

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 a bitstream of a video according to a first rule, wherein the video comprising a video picture comprising a slice,
• wherein the first rule specifies that a default value of a syntax element specifying a number of entries in a reference picture list syntax structure associated with a reference picture list (RPL) index is equal to 0 due to a condition being satisfied, and
• wherein the condition is satisfied in case (1) the video picture is an instantaneous decoding refresh picture, (2) a first syntax flag specifies that RPL syntax elements are not present in a slice header of the slice, and (3) a second syntax flag specifies that RPL information is not present in a picture header of the video picture.