Constrains for high level syntax elements

1. A method of processing video data, comprising:

performing a conversion between a video and a bitstream of the video according to a format rule,

wherein the format rule specifies that a bitstream general constraint is present to constraint a range of syntax elements;

wherein the format rule specifies that a first syntax element in a picture header (PH) or a second syntax element in a slice header (SH) in the bitstream is conditionally set equal to a predetermined value based on a value of a first general constraint flag which indicates whether a constraint is imposed on presence of only intra slices, and

wherein the second syntax element which is a reference picture list (RPL)-related SH syntax element is excluded from the SH and inferred to be 1 when the first general constraint flag is equal to 1 which indicates that the constraint is imposed on presence of only intra slices, and wherein the second syntax element is indicative of a presence of a third syntax element identifying a maximum index for a reference picture used for coding a slice referring to the second syntax element.

2. The method of claim 1 , wherein the second syntax element is num_ref_idx_active_override flag.

3. The method of claim 1 , wherein the first syntax element which is an inter-related PH syntax element is equal to 0 when the first general constraint flag is equal to 1 which indicates that the constraint is imposed on presence of only intra slices.

4. The method of claim 3 , wherein the first syntax element is ph_inter_slice_allowed_flag, and the value of the first syntax element being equal to 0 indicates that all slices of a picture referring to the ph_inter_slice_allowed_flag are I slices.

5. The method of claim 1 , wherein the format rule specifies that a value of a fourth syntax element in a sequence parameter set (SPS) is inferred to be 0 when a value of a second general constraint flag is equal to 1.

6. The method of claim 5 , wherein the value of the fourth syntax element being 0 indicates that a GDR (gradual decoding refresh) picture is disabled and not present in a coded layer video sequence (CLVS) referring to the SPS, and the value of the second general constraint flag being equal to 1 indicates that a constraint of not using GDR is imposed on a network abstraction layer (NAL) unit.

7. The method of claim 6 , wherein the fourth syntax element is gdr_enabled_flag, and the second general constraint flag is no_gdr_constraint_flag.

8. The method of claim 1 , wherein the format rule specifies that a value range of a fifth syntax element included in a sequence parameter set (SPS) which indicates a bit depth of samples of luma and chroma arrays is constrained by a third general constraint flag, and a value of the third general constraint flag is in a range of 0 to 8.

9. The method of claim 1 , wherein the conversion includes encoding the video into the bitstream.

10. The method of claim 1 , wherein the conversion includes decoding the video from the bitstream.

11. 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:

perform a conversion between a video and a bitstream of the video according to a format rule,

wherein the format rule specifies that a bitstream general constraint is present to constraint a range of syntax elements;

wherein the format rule specifies that a first syntax element in a picture header (PH) or a second syntax element in a slice header (SH) in the bitstream is conditionally set equal to a predetermined value based on a value of a first general constraint flag which indicates whether a constraint is imposed on presence of only intra slices, and

wherein the second syntax element which is a reference picture list (RPL)-related SH syntax element is excluded from the SH and inferred to be 1 when the first general constraint flag is equal to 1 which indicates that the constraint is imposed on presence of only intra slices, and wherein the second syntax element is indicative of a presence of a third syntax element identifying a maximum index for a reference picture used for coding a slice referring to the second syntax element.

12. The apparatus of claim 11 ,

wherein the second syntax element is num_ref_idx_active_override_flag;

wherein the first syntax element which is an inter-related PH syntax element is equal to 0 when the first general constraint flag is equal to 1 which indicates that the constraint is imposed on presence of only intra slices; and

wherein the first syntax element is ph_inter_slice_allowed_flag, and the value of the first syntax element being equal to 0 indicates that all slices of a picture referring to the ph_inter_slice_allowed_flag are I slices.

13. The apparatus of claim 11 , wherein the format rule specifies that a value of a fourth syntax element in a sequence parameter set (SPS) is inferred to be 0 when a value of a second general constraint flag is equal to 1;

wherein the value of the fourth syntax element being 0 indicates that a GDR (gradual decoding refresh) picture is disabled and not present in a coded layer video sequence (CLVS) referring to the SPS, and the value of the second general constraint flag being equal to 1 indicates that a constraint of not using GDR is imposed on a network abstraction layer (NAL) unit;

wherein the fourth syntax element is gdr_enabled_flag, and the second general constraint flag is no_gdr_constraint_flag; and

wherein the format rule specifies that a value range of a fifth syntax element included in a sequence parameter set (SPS) which indicates a bit depth of samples of luma and chroma arrays is constrained by a third general constraint flag, and a value of the third general constraint flag is in a range of 0 to 8.

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

perform a conversion between a video and a bitstream of the video according to a format rule,

wherein the format rule specifies that a bitstream general constraint is present to constraint a range of syntax elements;

wherein the format rule specifies that a first syntax element in a picture header (PH) or a second syntax element in a slice header (SH) in the bitstream is conditionally set equal to a predetermined value based on a value of a first general constraint flag which indicates whether a constraint is imposed on presence of only intra slices, and

wherein the second syntax element which is a reference picture list (RPL)-related SH syntax element is excluded from the SH and inferred to be 1 when the first general constraint flag is equal to 1 which indicates that the constraint is imposed on presence of only intra slices, and wherein the second syntax element is indicative of a presence of a third syntax element identifying a maximum index for a reference picture used for coding a slice referring to the second syntax element.

15. The non-transitory computer-readable storage medium of claim 14 ,

wherein the first syntax element which is an inter-related PH syntax element is equal to 0 when the first general constraint flag is equal to 1 which indicates that the constraint is imposed on presence of only intra slices; and

wherein the first syntax element is ph_inter_slice_allowed_flag, and the value of the first syntax element being equal to 0 indicates that all slices of a picture referring to the ph_inter_slice_allowed_flag are I slices.

16. The non-transitory computer-readable storage medium of claim 14 , wherein the format rule specifies that a value of a fourth syntax element in a sequence parameter set (SPS) is inferred to be 0 when a value of a second general constraint flag is equal to 1;

wherein the value of the fourth syntax element being 0 indicates that a GDR (gradual decoding refresh) picture is disabled and not present in a coded layer video sequence (CLVS) referring to the SPS, and the value of the second general constraint flag being equal to 1 indicates that a constraint of not using GDR is imposed on a network abstraction layer (NAL) unit;

wherein the fourth syntax element is gdr_enabled_flag, and the second general constraint flag is no_gdr_constraint_flag; and

wherein the format rule specifies that a value range of a fifth syntax element included in a sequence parameter set (SPS) which indicates a bit depth of samples of luma and chroma arrays is constrained by a third general constraint flag, and a value of the third general constraint flag which is in a range of 0 to 8.

17. 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:

generating the bitstream of the video according to a format rule,

wherein the format rule specifies that a bitstream general constraint is present to constraint a range of syntax elements;

wherein the format rule specifies that a first syntax element in a picture header (PH) or a second syntax element in a slice header (SH) in the bitstream is conditionally set equal to a predetermined value based on a value of a first general constraint flag which indicates whether a constraint is imposed on presence of only intra slices, and

wherein the second syntax element which is a reference picture list (RPL)-related SH syntax element is excluded from the SH and inferred to be 1 when the first general constraint flag is equal to 1 which indicates that the constraint is imposed on presence of only intra slices, and wherein the second syntax element is indicative of a presence of a third syntax element identifying a maximum index for a reference picture used for coding a slice referring to the second syntax element.

18. The non-transitory computer-readable recording medium of claim 17 ,

wherein the second syntax element is num_ref_idx_active_override_flag;

wherein the first syntax element which is an inter-related PH syntax element is equal to 0 when the first general constraint flag is equal to 1 which indicates that the constraint is imposed on presence of only intra slices; and

wherein the first syntax element is ph_inter_slice_allowed_flag, and the value of the first syntax element being equal to 0 indicates that all slices of a picture referring to the ph_inter_slice_allowed_flag are I slices.

19. The non-transitory computer-readable recording medium of claim 17 , wherein the format rule specifies that a value of a fourth syntax element in a sequence parameter set (SPS) is inferred to be 0 when a value of a second general constraint flag is equal to 1;

wherein the value of the fourth syntax element being 0 indicates that a GDR (gradual decoding refresh) picture is disabled and not present in a coded layer video sequence (CLVS) referring to the SPS, and the value of the second general constraint flag being equal to 1 indicates that a constraint of not using GDR is imposed on a network abstraction layer (NAL) unit;

wherein the fourth syntax element is gdr_enabled_flag, and the second general constraint flag is no_gdr_constraint_flag; and

wherein the format rule specifies that a value range of a fifth syntax element included in a sequence parameter set (SPS) which indicates a bit depth of samples of luma and chroma arrays is constrained by a third general constraint flag, and a value of the third general constraint flag which is in a range of 0 to 8.