Method for signaling mixed NAL unit type and subpicture partitioning in coded video stream

1. A method for coding video data, executable by a processor, comprising:

receiving video data comprising one or more subpictures;

identifying a network abstraction layer (NAL) unit type associated with each of the one or more subpictures based on checking a flag corresponding to mixed NAL units in the one or more subpictures; and

decoding the video data based on the identified NAL unit types, wherein a picture with two or more NAL unit types associated with the one or more subpictures is decoded as a trailing picture, and wherein boundaries associated with the one or more subpictures are treated as picture boundaries without loop filtering across the boundaries based on the picture with two or more NAL unit types being associated with the one or more subpictures.

2. The method of claim 1 , wherein a HandleCraAsCvsStartFlag flag being equal to one indicates a current picture is a start point of a current coded video sequence.

3. The method of claim 2 , wherein based on a presence of mixed NAL unit types and a video coding layer NAL unit having a clean random access type, the HandleCraAsCvsStartFlag flag and a NoOutputBeforeRecoveryFlag flag for the video data are both set equal to 0.

4. The method of claim 3 , wherein based on the HandleCraAsCvsStartFlag being set equal to 0 , a current subpicture is not be handled as a coded video sequence start picture.

5. The method of claim 2 , wherein based on a presence of mixed NAL unit types and a video coding layer NAL unit having a clean random access type, a leading picture associated with the video data is output.

6. The method of claim 5 , wherein HandleCraAsCvsStartFlag and NoOutputBeforeRecoveryFlag flags for the video data are both set equal to 0.

7. The method of claim 6 , wherein based on the presence of mixed NAL unit types, a pps_subpic_treated_as_pic_flag flag is set equal to 1.

8. A computer system for coding video data, the computer system comprising:

one or more computer-readable non-transitory storage media configured to store computer program code; and

one or more computer processors configured to access said computer program code and operate as instructed by said computer program code, said computer program code including:

receiving code configured to cause the one or more computer processors to receive video data comprising one or more subpictures;

identifying code configured to cause the one or more computer processors to identify a network abstraction layer (NAL) unit type associated with each of the one or more subpictures based on checking a flag corresponding to mixed NAL units in the one or more subpictures; and

decoding code configured to cause the one or more computer processors to decode the video data based on the identified NAL unit types, wherein a picture with two or more NAL unit types associated with the one or more subpictures is decoded as a trailing picture, and wherein boundaries associated with the one or more subpictures are treated as picture boundaries without loop filtering across the boundaries based on the picture with two or more NAL unit types being associated with the one or more subpictures.

9. The computer system of claim 8 , wherein a HandleCraAsCvsStartFlag flag being equal to one indicates a current picture is a start point of a current coded video sequence.

10. The computer system of claim 9 , wherein based on a presence of mixed NAL unit types and a video coding layer NAL unit having a clean random access type, the HandleCraAsCvsStartFlag flag and a NoOutputBeforeRecoveryFlag flag for the video data are both set equal to 0.

11. The computer system of claim 10 , wherein based on the HandleCraAsCvsStartFlag being set equal to 0 , a current subpicture is not be handled as a coded video sequence start picture.

12. The computer system of claim 9 , wherein based on a presence of mixed NAL unit types and a video coding layer NAL unit having a clean random access type, a leading picture associated with the video data is output.

13. The computer system of claim 12 , wherein HandleCraAsCvsStartFlag and NoOutputBeforeRecoveryFlag flags for the video data are both set equal to 0.

14. The computer system of claim 13 , wherein based on the presence of mixed NAL unit types, a pps_subpic_treated as_pic_flag flag is set equal to 1.

15. A non-transitory computer readable medium having stored thereon a computer program for coding video data, the computer program configured to cause one or more computer processors to:

receive video data comprising one or more subpictures;

identify a network abstraction layer (NAL) unit type associated with each of the one or more subpictures based on checking a flag corresponding to mixed NAL units in the one or more subpictures; and

decode the video data based on the identified NAL unit types, wherein a picture with two or more NAL unit types associated with the one or more subpictures is decoded as a trailing picture, and wherein boundaries associated with the one or more subpictures are treated as picture boundaries without loop filtering across the boundaries based on the picture with two or more NAL unit types being associated with the one or more subpictures.

16. The computer readable medium of claim 15 , wherein a HandleCraAsCvsStartFlag flag being equal to one indicates a current picture is a start point of a current coded video sequence.

17. The computer readable medium of claim 16 , wherein based on a presence of mixed NAL unit types and a video coding layer NAL unit having a clean random access type, the HandleCraAsCvsStartFlag flag and a NoOutputBeforeRecoveryFlag flag for the video data are both set equal to 0.

18. The computer readable medium of claim 17 , wherein based on the HandleCraAsCvsStartFlag being set equal to 0, a current subpicture is not be handled as a coded video sequence start picture.

19. The computer readable medium of claim 16 , wherein based on a presence of mixed NAL unit types and a video coding layer NAL unit having a clean random access type, a leading picture associated with the video data is output.

20. The computer readable medium of claim 19 , wherein HandleCraAsCvsStartFlag and NoOutputBeforeRecoveryFlag flags for the video data are both set equal to 0.