TECHNIQUES FOR RANDOM ACCESS POINT INDICATION AND PICTURE OUTPUT IN CODED VIDEO STREAM

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

receiving a coded video stream that includes an access unit, including a picture;

determining whether a first flag, in an access unit delimiter of the coded video stream, indicates that the access unit includes either or neither 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

decoding 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 reference pictures in the reference picture list, that at least a plurality 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.

2 . The method of claim 1 , further comprising:

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

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

wherein the third flag is based on the second flag indicating that the picture is not the IRAP picture.

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

4 . The method of claim 3 , further comprising:

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

wherein the third flag is based on the NAL unit type that is determined, and

wherein the third flag is based on the NAL unit type being determined to be equal to IDR_W_RADL, IDR_N_LP, or CRA_NUT.

5 . The method of claim 4 , further comprising:

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

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

wherein the fourth flag is based on the second flag indicating that the picture is not the IRAP picture.

6 . The method of claim 1 , wherein checking bitstream conformance, for reference pictures in the reference picture list, comprises checking, in order, that each of the following constraints apply:

the number of entries that are indicated to be in the reference picture list is not less than the number of active entries that are indicated to be in the reference picture list,

each picture referred to by the active entry in the reference picture list is present in the decoded picture buffer (DPB) and has the temporal identifier value less than or equal to the temporal identifier value of the current picture, and

each picture referred to by the entry in the reference picture list is not the current picture and is indicated by the picture header flag to potentially be the reference picture.

7 . The method of claim 1 , wherein the checking bitstream 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.

8 . A method of video encoding performed by at least one processor, the method comprising:

receiving a video data including a picture;

encoding the video data such that a coded video stream comprises a first flag, in an access unit delimiter of the coded video stream indicating that 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 a second flag, in a picture header of the coded video stream, indicating that the picture is the IRAP picture; and

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

wherein the coded video stream signals to:

construct a reference picture list;

generate an unavailable reference picture in the reference picture list; and

check bitstream conformance, for reference pictures in the reference picture list, that at least a plurality 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.

9 . The method of claim 8 , wherein the coded video stream further signals to:

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

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

wherein the third flag is based on the second flag indicating that the picture is not the IRAP picture.

10 . The method of claim 8 , 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 coded video stream further signals to determine whether a third flag, in a slice header of a slice of the picture of the coded video stream, indicates that any pictures prior to the IRAP picture are outputted.

11 . The method of claim 10 , the coded video stream further signals to determine a network abstraction layer (NAL) unit type of the slice,

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

wherein the third flag is based on the NAL unit type being determined to be equal to IDR_W_RADL, IDR_N_LP, or CRA_NUT.

12 . The method of claim 11 , the coded video stream further signals to determine whether a fourth flag, in the picture header of the coded video stream, indicates that the picture is the GDR picture,

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

wherein the fourth flag is based on the second flag indicating that the picture is not the IRAP picture.

13 . The method of claim 8 , wherein checking bitstream conformance, for reference pictures in the reference picture list, comprises checking, in order, that each of the following constraints apply:

the number of entries that are indicated to be in the reference picture list is not less than the number of active entries that are indicated to be in the reference picture list,

each picture referred to by the active entry in the reference picture list is present in the decoded picture buffer (DPB) and has the temporal identifier value less than or equal to the temporal identifier value of the current picture, and

each picture referred to by the entry in the reference picture list is not the current picture and is indicated by the picture header flag to potentially be the reference picture.

14 . The method of claim 8 , wherein the checking bitstream conformance is 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.

15 . A non-transitory computer-readable storage medium storing a video bitstream that is generated by a video encoding method, the video encoding method comprising:

signaling, in the video bitstream, a first flag, in an access unit delimiter of the bitstream and indicating that 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 a second flag, in a picture header of the bitstream, indicating that the picture is the IRAP picture. a value of the first flag and a value of the second flag are aligned; and

signaling, in the video bitstream, to:

construct a reference picture list;

generate an unavailable reference picture in the reference picture list; and

check bitstream conformance, for reference pictures in the reference picture list, that at least a plurality 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.

16 . The method of claim 15 , wherein the bitstream further signals to determine whether a third flag, in the picture header of the coded video stream, indicates that the picture is the GDR picture,

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

wherein the third flag is based on the second flag indicating that the picture is not the IRAP picture.

17 . The method of claim 15 , 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

wherein the bitstream further signals to determine whether a third flag, in a slice header of a slice of the picture of the coded video stream, indicates that any pictures prior to the IRAP picture are outputted.

18 . The method of claim 17 , wherein the bitstream further signals to determine a network abstraction layer (NAL) unit type of the slice,

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

wherein the third flag is based on the NAL unit type being determined to be equal to IDR_W_RADL, IDR_N_LP, or CRA_NUT.

19 . The method of claim 15 , wherein the bitstream further signals to determine whether a fourth flag, in the picture header of the coded video stream, indicates that the picture is the GDR picture,

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

wherein the fourth flag is based on the second flag indicating that the picture is not the IRAP picture.

20 . The method of claim 15 , wherein checking bitstream conformance, for reference pictures in the reference picture list, comprises checking that each of the following constraints apply:

the number of entries that are indicated to be in the reference picture list is not less than the number of active entries that are indicated to be in the reference picture list,

each picture referred to by the active entry in the reference picture list is present in the decoded picture buffer (DPB) and has the temporal identifier value less than or equal to the temporal identifier value of the current picture, and

each picture referred to by the entry in the reference picture list is not the current picture and is indicated by the picture header flag to potentially be the reference picture.