Techniques for signaling combination of reference picture resampling and spatial scalability

1. A method of decoding a video bitstream using at least one processor, the method comprising:

obtaining from the video bitstream a first flag indicating that reference picture resampling is enabled fora coded video sequence (CVS);

in response to the first flag indicating that the reference picture resampling is enabled for the CVS, determining whether a picture resolution change is allowed in the CVS based on a second flag;

based on the second flag indicating that the picture resolution change is allowed in the CVS, decoding the CVS using the reference picture resampling for spatial scalability and adaptive resolution change (ARC); and

based on the second flag indicating that the picture resolution is not changed in the CVS, decoding the CVS using the reference picture resampling for the spatial scalability without using the reference picture resampling for the ARC, and obtaining a third flag indicating whether subpicture information is present for the CVS.

2. The method of claim 1 , wherein the CVS is a coded layer-wise video sequence (CLVS).

3. The method of claim 1 , wherein the second flag is not signaled in the video bitstream, and

wherein the value of the second flag is inferred to indicate that the picture resolution is not changed in the CVS.

4. The method of claim 1 , further comprising:

based on the value of the second flag indicating that the picture resolution is not changed in the CVS, obtaining a fourth flag indicating whether virtual boundary information is signaled.

5. The method of claim 1 , wherein based on the value of the second flag indicating that the picture resolution is not changed in the CVS, scaling window parameters are not signaled.

6. The method of claim 1 , wherein the first flag and the second flag are signaled in a sequence parameter set (SPS).

7. The method of claim 6 , wherein based on the value of the second flag indicating that the picture resolution is changed in the CVS, a fifth flag included in a picture parameter set (PPS) referring to the SPS indicates that the picture resolution is changed in the CVS, and

wherein based on the fifth flag indicating that the picture resolution is changed in the CVS, at least one of a width and a height of a picture corresponding to the PPS is explicitly signaled.

8. The method of claim 6 , wherein based on the value of the second flag indicating that the picture resolution is not changed in the CVS, a fifth flag included in a picture parameter set (PPS) referring to the SPS indicates that the picture resolution is not changed in the CVS,

wherein based on the fifth flag indicating that the picture resolution is not changed in the CVS, at least one of a width and a height of a picture corresponding to the PPS is not explicitly signaled, and

wherein the at least one of the width and the height is inferred to be equal to at least one of a maximum width and a maximum height signaled in the SPS.

9. A device for decoding a video bitstream, the device comprising:

at least one memory configured to store program code; and

at least one processor configured to read the program code and operate as instructed by the program code, the program code including:

first obtaining code configured to cause the at least one processor to obtain from the video bitstream a first flag indicating that reference picture resampling is enabled for a coded video sequence (CVS);

determining code configured to cause the at least one processor to, in response to the first flag indicating that the reference picture resampling is enabled for the CVS, whether a picture resolution change is allowed in the CVS based on a second flag;

first decoding code configured to cause the at least one processor to, based on the value of the second flag indicating that the picture resolution change is allowed in the CVS, decode the CVS using the reference picture resampling for spatial scalability and adaptive resolution change (ARC); and

second decoding code configured to cause the at least one processor to, based on the second flag indicating that the picture resolution is not changed in the CVS, decode the CVS using the reference picture resampling for the spatial scalability without using the reference picture resampling for the ARC, and obtaining a third flag indicating whether subpicture information is present for the CVS.

10. The device of claim 9 , wherein the CVS is a coded layer-wise video sequence (CLVS).

11. The device of claim 9 , wherein the second flag is not signaled in the video bitstream, and

wherein the value of the second flag is inferred to indicate that the picture resolution is not changed in the CVS.

12. The device of claim 9 , wherein the program code further includes:

second obtaining code configured to cause the at least one processor to, based on the value of the second flag indicating that the picture resolution is not changed in the CVS, obtain a fourth flag indicating whether virtual boundary information is signaled.

13. The device of claim 9 , wherein based on the value of the second flag indicating that the picture resolution is not changed in the CVS, scaling window parameters are not signaled.

14. The device of claim 9 , wherein the first flag and the second flag are signaled in a sequence parameter set (SPS).

15. The device of claim 14 , wherein based on the value of the second flag indicating that the picture resolution is changed in the CVS, a fifth flag included in a picture parameter set (PPS) referring to the SPS indicates that the picture resolution is changed in the CVS, and

wherein based on the fifth flag indicating that the picture resolution is changed in the CVS, at least one of a width and a height of a picture corresponding to the PPS is explicitly signaled.

16. The device of claim 14 , wherein based on the value of the second flag indicating that the picture resolution is not changed in the CVS, a fifth flag included in a picture parameter set (PPS) referring to the SPS indicates that the picture resolution is not changed in the CVS,

wherein based on the fifth flag indicating that the picture resolution is not changed in the CVS, at least one of a width and a height of a picture corresponding to the PPS is not explicitly signaled, and

wherein the at least one of the width and the height is inferred to be equal to at least one of a maximum width and a maximum height signaled in the SPS.

17. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by one or more processors of a device for decoding a video bitstream, cause the one or more processors to:

obtain from the video bitstream a first flag indicating that reference picture resampling is enabled fora coded video sequence (CVS);

in response to the first flag indicating that the reference picture resampling is enabled for the CVS, determine whether a picture resolution change is allowed in the CVS based on a second flag;

based on the second flag indicating that the picture resolution change is allowed in the CVS, decode the CVS using the reference picture resampling for spatial scalability and adaptive resolution change (ARC); and

based on the second flag indicating that the picture resolution is not changed in the CVS, decode the CVS using the reference picture resampling for the spatial scalability without using the reference picture resampling for the ARC, and obtaining a third flag indicating whether subpicture information is present for the CVS.

18. The non-transitory computer-readable medium of claim 17 , wherein the first flag and the second flag are signaled in a sequence parameter set (SPS).