Methods for coding or decoding video parameter set or sequence parameter set

1. A computer-implemented method for encoding video, comprising:

determining whether a coded video sequence (CVS) contains equal number of profile, tier and level (PTL) syntax structures and output layer sets (OLSs); and

in response to the CVS containing equal number of PTL syntax structures and OLSs, coding a bitstream without signaling a first PTL syntax element specifying an index, to a list of PTL syntax structures in a video parameter set (VPS), of a PTL syntax structure that applies to a corresponding OLS in the VPS.

2. The method according to claim 1 , further comprising:

determining whether the number of PTL syntax structures being equal to one; and

in response to the number of PTL syntax structures being equal to one, coding the bitstream without signaling the first PTL syntax element in the VPS.

3. The method according to claim 1 , further comprising:

in response to the number of PTL syntax structures being greater than one and different from the number of the OLSs, signaling, in the VPS, the first PTL syntax element with a fixed length.

4. The method according to claim 1 , further comprising:

determining whether at least one of the PTL syntax structure, a decoded picture buffer (DPB) parameters syntax structure, or a hypothetical reference decoder (HRD) parameters syntax structure is present in a Sequence Parameter Set (SPS) of the bitstream;

determining whether a first value is greater than one, the first value specifying a maximum number of temporal sublayers present in a coded layer video sequence (CLVS) referring to the SPS; and

when at least one of the PTL syntax structure, the DPB parameters syntax structure, or the HRD parameters syntax structure is present in the SPS and the first value is greater than one, signaling a flag configured to control a presence of syntax elements in the DPB parameters syntax structure in the SPS.

5. The method of claim 4 , further comprising:

when the first value is equal to or smaller than one, signaling one or more syntax elements in the DPB parameters syntax structure, without signaling the flag in the SPS.

6. The method according to claim 1 , further comprising:

determining a value of a first Sequence Parameter Set (SPS) syntax element, the first SPS syntax element specifying an identifier of the VPS referred to by the SPS when the value of the first SPS syntax element is greater than zero;

in response to the value of the first SPS syntax element is greater than zero, assigning a range of a second SPS syntax element specifying a maximum number of temporal sublayers present in each coded layer video sequence (CLVS) referring to the SPS based on a corresponding VPS syntax element; and

in response to the value of the first SPS syntax element equal to zero, assigning the range of the second SPS syntax element specifying the maximum number of temporal sublayers present in each CLVS referring to the SPS to be an inclusive range of zero to a fixed value.

7. A computer-implemented method for decoding video, comprising:

receiving a bitstream comprising a coded video sequence (CVS);

determining whether the CVS has equal number of profile, tier and level (PTL) syntax structures and output layer sets (OLSs); and

in response to the number of PTL syntax structures being equal to the number of the OLSs, skipping decoding a first PTL syntax element specifying an index, to a list of PTL syntax structures in a video parameter set (VPS), of a PTL syntax structure that applies to a corresponding OLS when decoding the VPS.

8. The method according to claim 7 , further comprising:

in response to the number of PTL syntax structures being equal to the number of the OLSs, determining the first PTL syntax element to be equal to an index of the OLS to which the PTL syntax structure specified by the first PTL syntax element applies.

9. The method according to claim 7 , further comprising:

determining whether the number of PTL syntax structures being equal to one; and

in response the number of PTL syntax structures being equal to one, skipping decoding the first PTL syntax element when decoding the VPS.

10. The method according to claim 9 , further comprising:

in response to the number of PTL syntax structures being equal to one, determining the first PTL syntax element to be zero.

11. The method according to claim 7 , further comprising:

in response to the number of PTL syntax structures being greater than one and different from the number of the OLSs, decoding the first PTL syntax element with a fixed length in the VPS.

12. The method according to claim 7 , wherein the bitstream comprising the VPS and a Sequence Parameter Set (SPS), the method further comprising:

in response to at least one of the PTL syntax structure, a decoded picture buffer (DPB) parameters syntax structure, or a hypothetical reference decoder (HRD) parameters syntax structure being present in the SPS, determining whether a first value specifying a maximum number of temporal sublayers being present in each coded layer video sequence (CLVS) referring to the SPS is greater than one; and

in response to the first value being greater than one, decoding a flag configured to control a presence of syntax elements in the DPB parameters syntax structure in the SPS.

13. The method of claim 12 , further comprising:

in response to the first value being equal to or smaller than one, inferring the flag equal to zero and decoding one or more syntax elements in the DPB parameters syntax structure without decoding the flag in the SPS.

14. The method of claim 7 , further comprising: determining a value of a first Sequence Parameter Set (SPS) syntax element, the first SPS syntax element specifying an identifier of the VPS referred to by a SPS when the value of the first SPS syntax element is greater than zero; and

decoding a second SPS syntax element specifying a maximum number of temporal sublayers present in each coded layer video sequence (CLVS) referring to the SPS, a range of the second SPS syntax element being based on a corresponding VPS syntax element of the VPS referred to by the SPS when the value of the first SPS syntax element is greater than zero, or being based on a fixed value when the value of the first SPS syntax element is equal to zero.

15. An apparatus, comprising:

a memory configured to store instructions; and

a processor coupled to the memory and configured to execute the instructions to cause the apparatus to:

receive a bitstream comprising a coded video sequence (CVS);

determine whether the CVS has equal number of profile, tier and level (PTL) syntax structures and output layer sets (OLSs); and

in response to the number of PTL syntax structures being equal to the number of the OLSs, skip decoding a first PTL syntax element specifying an index, to a list of PTL syntax structures in a video parameter set (VPS), of a PTL syntax structure that applies to a corresponding OLS when decoding the VPS.

16. The apparatus of claim 15 , wherein the processor is configured to execute the instructions to:

in response to the number of PTL syntax structures being equal to the number of the OLSs, determine the first PTL syntax element to be equal to an index of the OLS to which the PTL syntax structure specified by the first PTL syntax element applies.

17. The apparatus of claim 15 , wherein the processor is configured to execute the instructions to:

determine whether the number of PTL syntax structures being equal to one; and

in response the number of PTL syntax structures being equal to one, skip decoding the first PTL syntax element when decoding the VPS.

18. The apparatus of claim 17 , wherein the processor is configured to execute the instructions to:

in response to the number of PTL syntax structures being equal to one, determining the first PTL syntax element to be zero.

19. The apparatus of claim 15 , wherein the processor is configured to execute the instructions to:

in response to the number of PTL syntax structures being greater than one and different from the number of the OLSs, decode the first PTL syntax element with a fixed length in the VPS.

20. The apparatus of claim 15 , wherein the processor is configured to execute the instructions to:

determine a value of a first Sequence Parameter Set (SPS) syntax element, the first SPS syntax element specifying an identifier of the VPS referred to by a SPS when the value of the first SPS syntax element is greater than zero; and

decode a second SPS syntax element specifying a maximum number of temporal sublayers present in each coded layer video sequence (CLVS) referring to the SPS, a range of the second SPS syntax element being based on a corresponding VPS syntax element of the VPS referred to by the SPS when the value of the first SPS syntax element is greater than zero, or being based on a fixed value when the value of the first SPS syntax element is equal to zero.