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

1. A method performed by at least one processor, the method comprising:

receiving video data;

encoding the video data into a coded video stream that includes an access unit and a picture;

signaling a first flag, in an access unit delimiter of the coded video stream, that indicates whether the access unit includes either or neither one from among an intra random access point (IRAP) picture and a gradual decoding refresh (GDR) picture; and

signaling a second flag, in a picture header of the coded video stream, that indicates whether the picture is the IRAP picture,

wherein a value of the first flag and a value of the second flag are aligned, and

wherein encoding the video data is based on:

a reference picture list,

an unavailable reference picture in the reference picture list, and

bitstream conformance, for references pictures in the reference picture list, based on whether 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.

2. The method of claim 1 , further comprising:

signaling a third flag, in the picture header of the coded video stream, that indicates whether the picture is the GDR picture,

wherein the value of the first flag and a value of the third flag are aligned.

3. The method of claim 2 , wherein the third flag is signaled based on the second flag indicating that the picture is not the IRAP picture.

4. The method of claim 1 , wherein

the first flag has a value that indicates that the picture is either one from among the IRAP picture and the GDR picture,

the second flag has a value that indicates that the picture is the IRAP picture, and

the method further comprises signaling a third flag, in a slice header of a slice of the picture of the coded video stream, that indicates whether any pictures prior to the IRAP picture are outputted.

5. The method of claim 4 , further comprising:

determining a network abstraction layer (NAL) unit type of the slice,

wherein the third flag is signalled based on the NAL unit type that is determined.

6. The method of claim 5 , wherein the third flag is signalled based on the NAL unit type being determined to be equal to IDR_W_RADL, IDR_N_LP, or CRA_NUT.

7. The method of claim 5 , further comprising:

signaling a fourth flag, in the picture header of the coded video stream, that indicates whether the picture is the GDR picture.

8. The method of claim 7 , wherein the fourth flag is signaled based on the second flag indicating that the picture is not the IRAP picture.

9. The method of claim 7 , wherein a value of the first flag and a value of the fourth flag are aligned.

10. The method of claim 1 , wherein the checking bistream conformance is performed based on determining the current picture is an independent decoder refresh (IDR) picture, a clean random access (CRA) picture, or a gradual decoding refresh (GDR) picture.

11. 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:

receiving code configured to cause the at least one processor to receive video data;

encoding code configured to cause the at least one processor to encode the video data into a coded video stream that includes an access unit and a picture;

first signaling code configured to cause the at least one processor to signal a first flag, in an access unit delimiter of the coded video stream, that indicates whether the access unit includes either or neither one from among an intra random access point (IRAP) picture and a gradual decoding refresh (GDR) picture; and

second signaling code configured to cause the at least one processor to signal a second flag, in a picture header of the coded video stream, that indicates whether the picture is the IRAP picture, wherein a value of the first flag and a value of the second flag are aligned, and

wherein encoding the video data is based on:

a reference picture list,

an unavailable reference picture in the reference picture list, and

bitstream conformance, for references pictures in the reference picture list, based on whether 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.

12. The system of claim 11 , the computer code further comprises:

third signaling code configured to cause the at least one processor to signal a third flag, in the picture header of the coded video stream, that indicates whether the picture is the GDR picture,

wherein the value of the first flag and a value of the third flag are aligned.

13. The system of claim 12 , wherein the third flag is signaled based on the second flag indicating that the picture is not the IRAP picture.

14. The system of claim 11 , wherein

the first flag has a value that indicates that the picture is either one from among the IRAP picture and the GDR picture,

the second flag has a value that indicates that the picture is the IRAP picture, and

the computer code further comprises third signaling code configured to cause the at least one processor to signal a third flag, in a slice header of a slice of the picture of the coded video stream, that indicates whether any pictures prior to the IRAP picture are outputted.

15. The system of claim 14 , the computer code further comprises:

determining code configured to cause the at least one processor to determine a network abstraction layer (NAL) unit type of the slice,

wherein the third flag is signalled based on the NAL unit type that is determined.

16. The system of claim 15 , wherein the third flag is signalled based on the NAL unit type being determined to be equal to IDR_W_RADL, IDR_N_LP, or CRA_NUT.

17. The system of claim 15 , the computer code further comprises:

fourth signaling code configured to cause the at least one processor to signal a fourth flag, in the picture header of the coded video stream, that indicates whether the picture is the GDR picture.

18. The system of claim 17 , wherein the fourth flag is signaled based on the second flag indicating that the picture is not the IRAP picture.

19. The system of claim 17 , wherein the value of the first flag and a value of the fourth flag are aligned.

20. A method for determining bitstream conformance:

receiving an encoded bitstream, wherein the bitstream includes:

a first flag, in an access unit delimiter of the encoded bitstream, that indicates whether an access unit of video data of the encoded bitstream includes either or neither one from among an intra random access point (IRAP) picture and a gradual decoding refresh (GDR) picture,

a second flag, in a picture header of video data of the encoded bitstream, that indicates whether the picture is the IRAP picture, and

a value of the first flag and a value of the second flag are aligned; and

checking bitstream conformance, for references pictures in a reference picture list having an unavailable reference picture, that 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.