Signalling of general constrains flag

1. A method of video processing, comprising:

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

wherein the rule specifies that a first syntax element is included in a profile, tier, level information syntax structure when a value of a profile tier present flag is equal to one, which indicates that profile, tier, and general constraints information is allowed to be present,

wherein a value of the first syntax element indicates whether one or more general constraint information syntax elements are included in a general constraint information syntax structure,

wherein when the value of the first syntax element is equal to zero, the one or more general constraint information syntax elements are not included in the general constraint information syntax structure, and the general constraint information syntax structure does not impose any constraint, and

wherein the first syntax element is coded with unsigned integer using N bits, wherein N is equal to 1.

2. The method of claim 1 , wherein a second syntax element specifying a level information to which one or more output layer sets conform is included in the profile, tier, level information syntax structure; and

wherein the rule specifies that a starting position of the second syntax element in the profile, tier, level information syntax structure is constrained to align to a byte boundary.

3. The method of claim 1 , wherein the rule specifies a third syntax element indicative of a number of reserved bits in the general constraint information syntax structure is included in the general constraint information syntax structure.

4. The method of claim 3 , wherein the third syntax element is coded with unsigned integer using M bits, wherein M is an integer.

5. The method of claim 3 , wherein a reserved general constraints information syntax element is included in the general constraint information syntax structure, and

wherein the reserved general constraints information syntax element is gci_reserved_zero_bit[i], wherein i ranges from 0 to a value of the third syntax element minus 1.

6. The method of claim 5 , wherein the reserved general constraints information syntax element is coded with unsigned integer using S bits, wherein S is equal to 1.

7. The method of claim 1 , wherein the rule specifies that one or more syntax elements in a sequence parameter set, a picture parameter set, a picture header, or a slice header are constrained according to a fourth syntax element included in the general constraint information syntax structure, and wherein the fourth syntax element specifies whether no network abstraction layer (NAL) unit with NAL unit type equal to PREFIX_APS_NUT or SUFFIX_APS_NUT is present, and

wherein when a value of the fourth syntax element is equal to 1 and specifies that no NAL unit with NAL unit type equal to PREFIX_APS_NUT or SUFFIX_APS_NUT is present,

a value of a fifth syntax element in the sequence parameter set is constrained to be equal to 0, which specifies that a cross-component adaptive loop filter is disabled,

a value of a sixth syntax element in the picture header is constrained to be equal to 0, which specifies that a number of adaptive loop filter (ALF) adaptive parameter sets (APSs) that a picture refers to is equal to 0,

a value of a seventh syntax element in the slice header is constrained to be equal to 0, which specifies that a number of ALF APS that a slice refers to is equal to 0,

a value of an eighth syntax element in the picture header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cb colour component of a picture,

a value of a ninth syntax element in the picture header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cr colour component of a picture,

a value of a tenth syntax element in the slice header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cb colour component of a slice,

a value of an eleventh syntax element in the slice header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cr colour component of a slice.

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

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

10. 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 rule,

wherein the rule specifies that a first syntax element is included in a profile, tier, level information syntax structure when a value of a profile tier present flag is equal to one, which indicates that profile, tier, and general constraints information is allowed to be present,

wherein a value of the first syntax element indicates whether one or more general constraint information syntax elements are included in a general constraint information syntax structure,

wherein when the value of the first syntax element is equal to zero, the one or more general constraint information syntax elements are not included in the general constraint information syntax structure, and the general constraint information syntax structure does not impose any constraint, and

wherein the first syntax element is coded with unsigned integer using N bits, wherein N is equal to 1.

11. The apparatus of claim 10 , wherein a second syntax element specifying a level information to which one or more output layer sets conform is included in the profile, tier, level information syntax structure; and

wherein the rule specifies that a starting position of the second syntax element in the profile, tier, level information syntax structure is constrained to align to a byte boundary.

12. The apparatus of claim 10 , wherein the rule specifies a third syntax element indicative of a number of reserved bits in the general constraint information syntax structure is included in the general constraint information syntax structure.

13. The apparatus of claim 12 , wherein the third syntax element is coded with unsigned integer using M bits, wherein M is an integer,

wherein a reserved general constraints information syntax element is included in the general constraint information syntax structure,

wherein the reserved general constraints information syntax element is gci_reserved_zero_bit[i], wherein i ranges from 0 to a value of the third syntax element minus 1, and

wherein the reserved general constraints information syntax element is coded with unsigned integer using S bits, wherein S is equal to 1.

14. The apparatus of claim 10 , wherein the rule specifies that one or more syntax elements in a sequence parameter set, a picture parameter set, a picture header, or a slice header are constrained according to a fourth syntax element included in the general constraint information syntax structure, and wherein the fourth syntax element specifies whether no network abstraction layer (NAL) unit with NAL unit type equal to PREFIX_APS_NUT or SUFFIX_APS_NUT is present, and

wherein when a value of the fourth syntax element is equal to 1 and specifies that no NAL unit with NAL unit type equal to PREFIX_APS_NUT or SUFFIX_APS_NUT is present,

a value of a fifth syntax element in the sequence parameter set is constrained to be equal to 0, which specifies that a cross-component adaptive loop filter is disabled,

a value of a sixth syntax element in the picture header is constrained to be equal to 0, which specifies that a number of adaptive loop filter (ALF) adaptive parameter sets (APSs) that a picture refers to is equal to 0,

a value of a seventh syntax element in the slice header is constrained to be equal to 0, which specifies that a number of ALF APS that a slice refers to is equal to 0,

a value of an eighth syntax element in the picture header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cb colour component of a picture,

a value of a ninth syntax element in the picture header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cr colour component of a picture,

a value of a tenth syntax element in the slice header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cb colour component of a slice,

a value of an eleventh syntax element in the slice header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cr colour component of a slice.

15. 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 rule,

wherein the rule specifies that a first syntax element is included in a profile, tier, level information syntax structure when a value of a profile tier present flag is equal to one, which indicates that profile, tier, and general constraints information is allowed to be present,

wherein a value of the first syntax element indicates whether one or more general constraint information syntax elements are included in a general constraint information syntax structure,

wherein when the value of the first syntax element is equal to zero, the one or more general constraint information syntax elements are not included in the general constraint information syntax structure, and the general constraint information syntax structure does not impose any constraint, and

wherein the first syntax element is coded with unsigned integer using N bits, wherein N is equal to 1.

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

wherein a second syntax element specifying a level information to which one or more output layer sets conform is included in the profile, tier, level information syntax structure,

wherein the rule specifies that a starting position of the second syntax element in the profile, tier, level information syntax structure is constrained to align to a byte boundary,

wherein the rule specifies a third syntax element indicative of a number of reserved bits in the general constraint information syntax structure is included in the general constraint information syntax structure,

wherein the third syntax element is coded with unsigned integer using M bits, wherein M is an integer,

wherein a reserved general constraints information syntax element is included in the general constraint information syntax structure,

wherein the reserved general constraints information syntax element is gci_reserved_zero_bit[i], wherein i ranges from 0 to a value of the third syntax element minus 1,

wherein the reserved general constraints information syntax element is coded with unsigned integer using S bits, wherein S is equal to 1,

wherein the rule specifies that one or more syntax elements in a sequence parameter set, a picture parameter set, a picture header, or a slice header are constrained according to a fourth syntax element included in the general constraint information syntax structure, and wherein the fourth syntax element specifies whether no network abstraction layer (NAL) unit with NAL unit type equal to PREFIX_APS_NUT or SUFFIX_APS_NUT is present, and

wherein when a value of the fourth syntax element is equal to 1 and specifies that no NAL unit with NAL unit type equal to PREFIX_APS_NUT or SUFFIX_APS_NUT is present,

a value of a fifth syntax element in the sequence parameter set is constrained to be equal to 0, which specifies that a cross-component adaptive loop filter is disabled,

a value of a sixth syntax element in the picture header is constrained to be equal to 0, which specifies that a number of adaptive loop filter (ALF) adaptive parameter sets (APSs) that a picture refers to is equal to 0,

a value of a seventh syntax element in the slice header is constrained to be equal to 0, which specifies that a number of ALF APS that a slice refers to is equal to 0,

a value of an eighth syntax element in the picture header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cb colour component of a picture,

a value of a ninth syntax element in the picture header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cr colour component of a picture,

a value of a tenth syntax element in the slice header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cb colour component of a slice,

a value of an eleventh syntax element in the slice header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cr colour component of a slice.

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 rule,

wherein the rule specifies that a first syntax element is included in a profile, tier, level information syntax structure when a value of a profile tier present flag is equal to one, which indicates that profile, tier, and general constraints information is allowed to be present,

wherein a value of the first syntax element indicates whether one or more general constraint information syntax elements are included in a general constraint information syntax structure,

wherein when the value of the first syntax element is equal to zero, the one or more general constraint information syntax elements are not included in the general constraint information syntax structure, and the general constraint information syntax structure does not impose any constraint, and

wherein the first syntax element is coded with unsigned integer using N bits, wherein N is equal to 1.

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

wherein a second syntax element specifying a level information to which one or more output layer sets conform is included in the profile, tier, level information syntax structure,

wherein the rule specifies that a starting position of the second syntax element in the profile, tier, level information syntax structure is constrained to align to a byte boundary,

wherein the rule specifies a third syntax element indicative of a number of reserved bits in the general constraint information syntax structure is included in the general constraint information syntax structure,

wherein the third syntax element is coded with unsigned integer using M bits, wherein M is an integer,

wherein a reserved general constraints information syntax element is included in the general constraint information syntax structure,

wherein the reserved general constraints information syntax element is gci_reserved_zero_bit[i], wherein i ranges from 0 to a value of the third syntax element minus 1,

wherein the reserved general constraints information syntax element is coded with unsigned integer using S bits, wherein S is equal to 1,

wherein the rule specifies that one or more syntax elements in a sequence parameter set, a picture parameter set, a picture header, or a slice header are constrained according to a fourth syntax element included in the general constraint information syntax structure, and wherein the fourth syntax element specifies whether no network abstraction layer (NAL) unit with NAL unit type equal to PREFIX_APS_NUT or SUFFIX_APS_NUT is present, and

wherein when a value of the fourth syntax element is equal to 1 and specifies that no NAL unit with NAL unit type equal to PREFIX_APS_NUT or SUFFIX_APS_NUT is present,

a value of a fifth syntax element in the sequence parameter set is constrained to be equal to 0, which specifies that a cross-component adaptive loop filter is disabled,

a value of a sixth syntax element in the picture header is constrained to be equal to 0, which specifies that a number of adaptive loop filter (ALF) adaptive parameter sets (APSs) that a picture refers to is equal to 0,

a value of a seventh syntax element in the slice header is constrained to be equal to 0, which specifies that a number of ALF APS that a slice refers to is equal to 0,

a value of an eighth syntax element in the picture header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cb colour component of a picture,

a value of a ninth syntax element in the picture header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cr colour component of a picture,

a value of a tenth syntax element in the slice header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cb colour component of a slice,

a value of an eleventh syntax element in the slice header is constrained to be equal to 0, which specifies that the adaptive loop filter is disabled for a Cr colour component of a slice.