Techniques for random access point indication and picture output in coded video stream

A system comprising:

• at least one processor that is configured to receive a coded video stream that includes an access unit, including a picture
• memory storing computer code, the computer code comprising:
• first determining code configured to cause the at least one processor to determine whether a first flag, in an access unit delimiter of the coded video stream, indicates that the access unit includes one from among an intra random access point (IRAP) picture and a gradual decoding refresh (GDR) picture;
• second determining code configured to cause the at least one processor to determine whether a second flag, in a picture header of the coded video stream, indicates that the picture is the IRAP picture;
• and
• decoding code configured to cause the at least one processor to decode the picture, as a current picture, based on the first flag and the second flag,
• wherein a value of the first flag and a value of the second flag are aligned, and
• wherein the decoding code comprises:
• constructing code configured to cause the at least one processor to construct a reference picture list;
• generating code configured to cause the at least one processor to generate an unavailable reference picture in the reference picture list;
• and
• checking code configured to cause the at least one processor to check bitstream conformance, for references pictures in the reference picture list, that any of the following constraints apply:
• a number of entries that are indicated to be in the reference picture list is not less than a number of active entries that are indicated to be in the reference picture list,
• each picture referred to by an active entry in the reference picture list is present in a decoded picture buffer (DPB) and has a temporal identifier value less than or equal to a temporal identifier value of the current picture, and
• each picture referred to by an entry in the reference picture list is not the current picture and is indicated by a picture header flag to potentially be a reference picture.

A non-transitory computer-readable medium storing computer instructions that, when executed by at least one processor that receives a coded video stream that includes an access unit, including a picture, cause the at least one processor to:

• determining whether a first flag, in an access unit delimiter of the coded video stream, indicates that the access unit includes one from among an intra random access point (IRAP) picture and a gradual decoding refresh (GDR) picture;
• determining whether a second flag, in a picture header of the coded video stream, indicates that the picture is the IRAP picture;
• and
• decode the picture, as a current picture, based on the first flag and the second flag,
• wherein a value of the first flag and a value of the second flag are aligned, and
• wherein the decoding comprises:
• constructing a reference picture list;
• generating an unavailable reference picture in the reference picture list;
• and
• checking bitstream conformance, for references pictures in the reference picture list, that any of the following constraints apply:
• a number of entries that are indicated to be in the reference picture list is not less than a number of active entries that are indicated to be in the reference picture list,
• each picture referred to by an active entry in the reference picture list is present in a decoded picture buffer (DPB) and has a temporal identifier value less than or equal to a temporal identifier value of the current picture, and
• each picture referred to by an entry in the reference picture list is not the current picture and is indicated by a picture header flag to potentially be a reference picture.