Subpicture dependent signaling in video bitstreams

1. A method of processing video data, comprising:

determining, for a conversion between a video unit of a video and a bitstream of the video, whether a resolution-changing mode is enabled for the video unit, wherein the video unit comprises one or more video pictures, and

disabling a sub-picture coding mode for the video unit due to the determining that the resolution-changing mode is enabled for the video unit,

wherein the sub-picture coding mode is a mode in which a video picture is divided into multiple sub-pictures, and the resolution-changing coding mode is a mode in which a spatial resolution is allowed to change between the video pictures of the video unit.

2. The method of claim 1 , wherein the video unit comprises a video sequence.

3. The method of claim 1 , wherein a first syntax element is included in the bitstream to indicate whether the sub-picture coding mode is enabled for the coding unit.

4. The method of claim 3 , wherein in case that the resolution-changing coding mode is disabled, a width of the video picture in the video unit is set to be equal to a maximum width allowed for the video pictures in the video unit.

5. The method of claim 4 , wherein a second syntax element is included in the bitstream to indicate the maximum width allowed for the video pictures in the video unit.

6. The method of claim 5 , wherein a value of the second syntax element is restricted to be no smaller than 8.

7. The method of claim 5 , wherein a third syntax element is included in the bitstream to indicate a maximum height allowed for the video pictures in the video unit, and a value of the third syntax element is restricted to be no smaller than 8.

8. The method of claim 1 , wherein a fourth syntax element is included in the bitstream to indicate a width of a sub-picture, and a fifth syntax element is included in the bitstream to indicate a height of a sub-picture.

9. The method of claim 1 , wherein a sixth syntax element is included in the bitstream to indicate a top-left position of a sub-picture.

10. The method of claim 1 , wherein a position and a dimension of a sub-picture are determined excluding referring to a sub-picture identification.

11. The method of claim 1 , wherein a reference picture resampling and the sub-picture coding mode are allowed to be both enabled for the video unit.

12. The method of claim 1 , wherein a resolution-changing coding mode is enabled when a reference picture resampling is enabled.

13. The method of claim 1 , wherein the conversion comprises encoding the video into the bitstream.

14. The method of claim 1 , wherein the conversion comprises decoding the video from the bitstream.

15. An apparatus for processing video data comprising a processor and a non-transitory memory with instructions thereon, wherein the instructions upon execution by the processor, cause the processor to:

determine, for a conversion between a video unit of a video and a bitstream of the video, whether a resolution-changing mode is enabled for the video unit, wherein the video unit comprises one or more video pictures, and

disable a sub-picture coding mode for the video unit due to the determining that the resolution-changing mode is enabled for the video unit,

wherein the sub-picture coding mode is a mode in which a video picture is divided into multiple sub-pictures, and the resolution-changing coding mode is a mode in which a spatial resolution is allowed to change between the video pictures of the video unit.

16. The apparatus of claim 15 , wherein the video unit comprises a video sequence;

a first syntax element is included in the bitstream to indicate whether the sub-picture coding mode is enabled for the coding unit;

in case that the resolution-changing coding mode is disabled, a width of the video picture in the video unit is set to be equal to a maximum width allowed for the video pictures in the video unit;

a second syntax element is included in the bitstream to indicate the maximum width allowed for the video pictures in the video unit;

a value of the second syntax element is restricted to be no smaller than 8;

a third syntax element is included in the bitstream to indicate a maximum height allowed for the video pictures in the video unit, and a value of the third syntax element is restricted to be no smaller than 8;

a fourth syntax element is included in the bitstream to indicate a width of a sub-picture, and a fifth syntax element is included in the bitstream to indicate a height of a sub-picture; and

a sixth syntax element is included in the bitstream to indicate a top-left position of a sub-picture.

17. A non-transitory computer-readable storage medium storing instructions that cause a processor to:

determine, for a conversion between a video unit of a video and a bitstream of the video, whether a resolution-changing mode is enabled for the video unit, wherein the video unit comprises one or more video pictures, and

disable a sub-picture coding mode for the video unit due to the determining that the resolution-changing mode is enabled for the video unit,

wherein the sub-picture coding mode is a mode in which a video picture is divided into multiple sub-pictures, and the resolution-changing coding mode is a mode in which a spatial resolution is allowed to change between the video pictures of the video unit.

18. The non-transitory computer-readable storage medium of claim 17 , wherein the video unit comprises a video sequence;

a first syntax element is included in the bitstream to indicate whether the sub-picture coding mode is enabled for the coding unit;

in case that the resolution-changing coding mode is disabled, a width of the video picture in the video unit is set to be equal to a maximum width allowed for the video pictures in the video unit;

a second syntax element is included in the bitstream to indicate the maximum width allowed for the video pictures in the video unit;

a value of the second syntax element is restricted to be no smaller than 8;

a third syntax element is included in the bitstream to indicate a maximum height allowed for the video pictures in the video unit, and a value of the third syntax element is restricted to be no smaller than 8;

a fourth syntax element is included in the bitstream to indicate a width of a sub-picture, and a fifth syntax element is included in the bitstream to indicate a height of a sub-picture; and

a sixth syntax element is included in the bitstream to indicate a top-left position of a sub-picture.

19. A non-transitory computer-readable recording medium storing a bitstream of a video which is generated by a method performed by a video processing apparatus, wherein the method comprises:

determining, for a video unit of the video, whether a resolution-changing mode is enabled for the video unit, wherein the video unit comprises one or more video pictures,

disabling a sub-picture coding mode for the video unit due to the determining that the resolution-changing mode is enabled for the video unit, and

generating the bitstream based on the determining,

wherein the sub-picture coding mode is a mode in which a video picture is divided into multiple sub-pictures, and the resolution-changing coding mode is a mode in which a spatial resolution is allowed to change between the video pictures of the video unit.

20. The non-transitory computer-readable recording medium of claim 19 , wherein the video unit comprises a video sequence;

a first syntax element is included in the bitstream to indicate whether the sub-picture coding mode is enabled for the coding unit;

in case that the resolution-changing coding mode is disabled, a width of the video picture in the video unit is set to be equal to a maximum width allowed for the video pictures in the video unit;

a second syntax element is included in the bitstream to indicate the maximum width allowed for the video pictures in the video unit;

a value of the second syntax element is restricted to be no smaller than 8;

a third syntax element is included in the bitstream to indicate a maximum height allowed for the video pictures in the video unit, and a value of the third syntax element is restricted to be no smaller than 8;

a fourth syntax element is included in the bitstream to indicate a width of a sub-picture, and a fifth syntax element is included in the bitstream to indicate a height of a sub-picture; and

a sixth syntax element is included in the bitstream to indicate a top-left position of a sub-picture.