Value ranges for syntax elements in video coding

1. A method of encoding video data, comprising:

receiving a plurality of pictures in a bitstream, the plurality of pictures including a current picture and one or more reference pictures;

determining a reference picture set (RPS) for the current picture based at least in part on the one or more reference pictures;

determining a picture order count (POC) value of each reference picture of the one or more reference pictures in the RPS;

identifying at least one of a number of long-term reference pictures and a number of short-term reference pictures within the RPS;

constraining a number of long-term pictures and the number of short-term pictures in the RPS, the constraints being based on the POC value and a maximum decoded picture buffer size minus one, if a video parameter set (VPS) extension is in use;

if the plurality of pictures comprises a base layer of video data, constraining a sum of a number of negative pictures, a number of positive pictures, a number of longterm pictures derived based on candidate long term reference pictures specified in an active sequence parameter set (SPS), and a number of long-term pictures directly signaled in a slice header of the current picture to a value that is less than or equal to a maximum decoded picture buffer size identified in the active SPS minus one;

generating at least one syntax element identifying the RPS based on the constraints;

encoding the current picture based on the RPS and the at least one syntax element.

2. The method of claim 1 further comprising:

if the VPS extension is in use, constraining a sum of a number of negative pictures, a number of positive pictures, a number of long-term pictures derived based on candidate long term reference pictures specified in an active sequence parameter set (SPS), and a number of long-term reference pictures directly signaled in a slice header of the current picture to a value that is less than or equal to maximum decoded picture buffer size minus one.

3. The method of claim 2 wherein the VPS extension is in use if there is at least one non-base layer in the bitstream.

4. The method of claim 1 further comprising:

if the VPS extension is in use, constraining a number of negative pictures to a value between zero and the maximum decoded picture buffer size minus one, inclusive, each negative picture of the number of negative pictures having a POC value that is less than a POC value of the current picture.

5. The method of claim 1 further comprising:

if the VPS extension is in use, constraining a number of positive pictures to a value between zero and the maximum decoded picture buffer size minus one, minus a number of negative pictures, inclusive, the number of positive pictures having a POC value greater than the POC value of the current picture and the number of negative pictures having a POC value that is less than a POC value of the current picture.

6. A device for encoding video data, comprising:

a memory configured to store a plurality of pictures obtained from a bitstream, the plurality of pictures including a current picture and one or more reference pictures; and

at least one processor operably coupled to the memory and configured to determine a reference picture set (RPS) for the current picture based at least in part on the one or more reference pictures;

determine a picture order count (POC) value of each reference picture of the one or more reference pictures in the RPS;

identify at least one of a number of long-term reference pictures and a number of short-term reference pictures within the RPS;

apply constraints to the number of long-term pictures and the number of short-term pictures in the RPS, the constraints being based on the POC value and a maximum decoded picture buffer size minus one, if a video sequence parameter (VPS) extension is in use;

if the plurality of pictures comprises a base layer of video data, constrain a sum of a number of negative pictures, a number of positive pictures, number of long-term pictures derived based on candidate long term reference pictures specified in an active sequence parameter set (SPS), and a number of long-term pictures directly signaled in a slice header of the current picture to a value that is less than or equal to a maximum decoded picture buffer size identified in the active SPS minus one;

generate at least one syntax element identifying the RPS based on the constraints;

encode the current picture based on the RPS and the at least one syntax element.

7. The device of claim 6 wherein the processor is further configured to:

if the VPS extension is in use, constrain a sum of a number of negative pictures, a number of positive pictures, a number of long-term pictures derived based on candidate long term reference pictures specified in an active sequence parameter set (SPS), and a number of long-term reference pictures directly signaled in a slice header of the current picture to a value that is less than or equal to the maximum decoded picture buffer size minus one.

8. The device of claim 7 wherein the VPS extension is in use if there is at least one non-base layer in the bitstream.

9. The device of claim 6 further comprising:

if the VPS extension is in use, constrain a number of negative pictures to a value between zero and the maximum decoded picture buffer size minus one, inclusive, each negative picture of the number of negative pictures having a POC value that is less than a POC value of the current picture.

10. The device of claim 6 further comprising:

if the VPS extension is in use, constrain a number of positive pictures to a value between zero and the maximum decoded picture buffer size minus one, minus a number of negative pictures, inclusive, the number of positive pictures having a POC value greater than the POC value of the current picture and the number of negative pictures having a POC value that is less than a POC value of the current picture.

11. A method for decoding video data, comprising:

obtaining a picture order count (POC) of a current picture and POC values for one or more reference pictures from a bitstream;

determining a reference picture set (RPS) having the one or more reference pictures based on the POC values of the current picture and the POC values of the one or more reference pictures;

identifying the one or more reference pictures in the RPS as at least one of a

number of long-term pictures and a number of short-term pictures, the number of long-term pictures and the number of short-term pictures being based on constraints, the constraints being based on the POC value and a maximum decoded picture buffer size minus one, if a video parameter set (VPS) extension is in use;

wherein if the current picture is in a base layer, a sum of a number of negative pictures, a number of positive pictures, a number of long-term pictures derived based on candidate long term reference pictures specified in an active sequence parameter set (SPS), and a number of long-term pictures directly signaled in a slice header of the current picture is constrained to a value that is less than or equal to a maximum decoded picture buffer size identifies in the active SPS minus one; and

decoding the current picture based on the RPS.

12. The method of claim 11 , wherein if the VPS extension is in use, a sum of a number of negative pictures, a number of positive pictures, a number of long-term pictures derived based on candidate long term reference pictures specified in an active sequence parameter set (SPS), and a number of long-term reference pictures directly signaled in a slice header of the current picture is constrained to a value that is less than or equal to maximum decoded picture

buffer size minus one.

13. The method of claim 11 , wherein the VPS extension is in use if there is at least one non-base layer in the bitstream.

14. The method of claim 11 , wherein if the VPS extension is in use, a number of negative pictures is constrained to a value between zero and the maximum decoded picture buffer size minus one, inclusive, each negative picture of the number of negative pictures having a POC value that is less than a POC value of the current picture.

15. The method of claim 11 , wherein, if the VPS extension is in use, a number of positive pictures is constrained to a value between zero and the maximum decoded picture buffer size minus one, minus a number of negative pictures, inclusive, the number of positive pictures having a POC value greater than the POC value of the current picture and the number of negative pictures having a POC value that is less than a POC value of the current picture.

16. A device for decoding video data, comprising:

a memory configured store a current picture, a picture order count (POC) of a current picture, and POC values for one or more reference pictures, the POC values and the current picture being obtained from a bitstream; and

a processor operably coupled to the memory and configured to determine a reference picture set (RPS) having the one or more reference pictures based on the POC values of the current picture and the POC values of the

one or more reference pictures, identify the one or more reference pictures in the RPS as at least one of a number of long-term pictures and a number of short-term pictures, the number of long-term pictures and the number of short-term pictures being based on constraints, the constraints being based on the POC value and a maximum decoded picture buffer size minus one, if a video parameter set (VPS) extension is in use, and

wherein if the current picture is in a base layer, a sum of a number of negative pictures, a number of positive pictures, a number of long-term pictures derived based on candidate long term reference pictures specified in an active sequence parameter set (SPS), and a number of long-term pictures directly signaled in a slice header of the current picture is constrained to a value that is less than or equal to a maximum decoded picture buffer size identified in the active SPS minus one, and

decode the current picture based on the RPS.

17. The device of claim 16 , wherein if the VPS extension is in use, a sum of a number of negative pictures, a number of positive pictures, a number of long-term pictures derived based on candidate long term reference pictures specified in an active sequence parameter set (SPS), and a number of long-term reference pictures directly signaled in a slice header of the current picture is constrained to a value that is less than or equal to maximum decoded picture buffer size minus one.

18. The method of claim 16 , wherein the VPS extension is in use if there is at least one non-base layer in the bitstream.

19. The method of claim 16 , wherein if the VPS extension is in use, a number of negative pictures is constrained to a value between zero and the maximum decoded picture buffer size minus one, inclusive, each negative picture of the number of negative pictures having a POC value that is less than a POC value of the current picture.

20. The method of claim 16 , wherein, if the VPS extension is in use, a number of positive pictures is constrained to a value between zero and the maximum decoded picture buffer size minus one, minus a number of negative pictures, inclusive, the number of positive pictures having a POC value greater than the POC value of the current picture and the number of negative pictures having a POC value that is less than a POC value of the current picture.