1. A method for decoding video data, the method comprising: deriving at least one of a coded picture buffer (CPB) arrival time or a CPB nominal removal time for an access unit (AU) at both an access unit level and a subpicture level regardless of a value of a syntax element that defines whether a decoding unit (DU) is the entire AU; determining a removal time of the AU based at least in part on one of the CPB arrival time or the CPB nominal removal time; and decoding video data of the AU based at least in part on the removal time.

2. The method of claim 1, further comprising: responsive to the syntax element having a true value, deriving a CPB removal time only for the AU level; and responsive to the syntax element having a false value, deriving a CPB removal time only for the sub-picture level.

3. The method of claim 1, wherein the at least one of the CPB arrival time or the CPB nominal removal time are derived only when a syntax flag that indicates CPB parameters are present has a true value.

4. The method of claim 1, further comprising: decoding a duration between CPB removal of a first DU in the AU and CPB removal of a second DU; determining a removal time of the first DU based at least in part on the decoded duration; and decoding video data of the first DU based at least in part on at least one of the removal time, the CPB arrival time, or the CPB nominal removal time.

5. The method of claim 4, wherein the second DU is subsequent to the first DU in decoding order and in the same AU as the first DU.

6. The method of claim 4, further comprising: decoding one or more sub-picture level CPB parameters, wherein determining the removal time of the first DU comprises determining the removal time of the first DU based at least in part on the decoded duration and the sub-picture level CPB parameters.

7. The method of claim 1, further comprising: decoding a sequence level flag to determine the presence of sub-picture level CPB parameters either in picture timing SEI messages or in sub-picture timing SEI messages.

8. The method of claim 1, wherein the first DU comprises a non-video coding layer (VCL) network abstraction layer (NAL) unit with nal_unit_type equal to UNSPECO, EOS_NUT, EOBJNUT, in the range of RSV_NVCL44 to RSV_NVCL47 or in the range of UNSPEC48 to UNSPEC63.

9. The method of claim 1, wherein the AU has a Temporalld equal to 0, the method further comprising: decoding at least one of a buffering period supplemental enhancement information (SEI) message or a recovery point SEI message associated with the AU

10. A video decoding device comprising a video decoder configured to: derive at least one of a coded picture buffer (CPB) arrival time or a CPB nominal removal time for an access unit (AU) at both an access unit level and a subpicture level regardless of a value of a syntax element that defines whether a decoding unit (DU) is the entire AU; determine a removal time of the AU based at least in part on one of the CPB arrival time or the CPB nominal removal time; and decode video data of the AU based at least in part on the removal time

11. The video decoding device of claim 10, the video decoder further configured to: responsive to the syntax element having a true value, derive a CPB removal time only for the AU level; and responsive to the syntax element having a false value, derive a CPB removal time only for the sub-picture level

12. The video decoding device of claim 10, wherein the at least one of the CPB arrival time or the CPB nominal removal time are derived only when a syntax flag that indicates CPB parameters are present has a true value

13. The video decoding device of claim 10, the video decoder further configured to: decode a duration between CPB removal of a first DU in the AU and CPB removal of a second DU; determine a removal time of the first DU based at least in part on the decoded duration; and decode video data of the first DU based at least in part on at least one of the removal time, the CPB arrival time, or the CPB nominal removal time

14. The video decoding device of claim 13, wherein the second DU is subsequent to the first DU in decoding order and in the same AU as the first DU

15. The video decoding device of claim 13, the video decoder further configured to decode one or more sub-picture level CPB parameters, wherein determine the removal time of the first DU comprises determine the removal time of the first DU based at least in part on the decoded duration and the sub-picture level CPB parameters

16. The video decoding device of claim 10, the video decoder further configured to decode a sequence level flag to determine the presence of sub-picture level CPB parameters either in picture timing SEI messages or in sub-picture timing SEI messages

17. The video decoding device of claim 10, wherein the first DU comprises a nonvideo coding layer (VCL) network abstraction layer (NAL) unit with nal_unit_type equal to UNSPECO, EOS_NUT, EOB NUT, in the range of RSV_NVCL44 to RSV_NVCL47 or in the range of UNSPEC48 to UNSPEC63

18. The video decoding device of claim 10, wherein the AU has a Temporalld equal to 0, the video decoder further configured to decode at least one of a buffering period supplemental enhancement information (SEI) message or a recovery point SEI message associated with the AU

19. A computer-readable storage mediu having stored thereon instructions that, when executed, cause a processor of a device for decoding video data to: derive at least one of a coded picture buffer (CPB) arrival time or a CPB no inal removal time for an access unit (AU) at both an access unit level and a sub-picture level regardless of a value of a syntax element that defines whether a decoding unit (DU) is the entire AU; determine a removal time of the AU based at least in part on one of the CPB arrival time or the CPB nominal removal time; and decode video data of the AU based at least in part on the removal time.

20. The computer-readable storage medium of claim 19, the instructions further cause the processor to: responsive to the syntax element having a true value, derive a CPB removal time only for the AU level; and responsive to the syntax element having a false value, derive a CPB removal time only for the sub-picture level.

21. The computer-readable storage medium of claim 19, wherein the at least one of the CPB arrival time or the CPB nominal removal time are derived only when a syntax flag that indicates CPB parameters are present has a true value.

22. A video decoding device comprising: means for deriving at least one of a coded picture buffer (CPB) arrival time or a CPB nominal removal time for an access unit (AU) at both an access unit level and a sub-picture level regardless of a value of a syntax element that defines whether a decoding unit (DU) is the entire AU; means for determining a removal time of the AU based at least in part on one of the CPB arrival time or the CPB nominal removal time; and means for decoding video data of the AU based at least in part on the removal time.

23. The video decoding device of claim 22, further comprising: responsive to the syntax element having a true value, means for deriving a CPB removal time only for the AU level; and responsive to the syntax element having a false value, means for deriving a CPB removal time only for the sub-picture level.

24. The video decoding device of claim 22, wherein the at least one of the CPB arrival time or the CPB nominal removal time are derived only when a syntax flag that indicates CPB parameters are present has a true value.

25. A method for encoding video data, the method comprising: deriving at least one of a coded picture buffer (CPB) arrival time or a CPB nominal removal time for an access unit (AU) at both an access unit level and a subpicture level regardless of a value of a syntax element that defines whether a decoding unit (DU) is the entire AU; determining a removal time of the AU based at least in part on one of the CPB arrival time or the CPB nominal removal time; and encoding the removal time,

26. The method of claim 25, further comprising: responsive to the syntax element having a true value, encoding a CPB removal time only for the AU level; and responsive to the syntax element having a false value, encoding a CPB removal time only for the sub-picture level.

27. The method of claim 25, wherein the at least one of the CPB arrival time or the CPB nominal removal time are encoded only when a syntax flag that indicates CPB parameters are present has a true value.

28. The method of claim 25, further comprising: encoding a duration between CPB removal of a first DU in the AU and CPB removal of a second DU, wherein encoding the removal time further comprises encoding the duration.

29. The method of claim 28, wherein the second DU is subsequent to the first DU in decoding order and in the same AU as the first DU.

30. The method of claim 28, further comprising: encoding one or more sub-picture level CPB parameters, wherein determining the removal time of the first DU comprises determining the removal time of the first DU based at least in part on the duration and the sub-picture level CPB parameters.

31. The method of claim 25, further comprising: encoding a sequence level flag to indicate the presence of sub-picture level CPB parameters either in picture timing SEI messages or in sub-picture timing SEl messages.

32. The method of claim 25, wherein the first DU comprises a non-video coding layer (VCL) network abstraction layer (NAL) unit with nal_unit_type equal to UNSPECO, EOSJMUT, EOB_NUT, in the range of RSVJMVCL44 to RSV_NVCL47 or in the range of UNSPEC48 to UNSPEC63.

33. The method of claim 25, wherein the AU has a Tempo ralld equal to 0, the method further comprising: encoding at least one of a buffering period supplemental enhancement information (SEI) message or a recovery point SEI message associated with the AU.

34. A video encoding device comprising a video encoder configured to: derive at least one of a coded picture buffer (CPB) arrival time or a CPB nominal removal time for an access unit (AU) at both an access unit level and a sub picture level regardless of a value of a syntax element that defines whether a decoding unit (DU) is the entire AU; determine a removal time of the AU based at least in part on one of the CPB arrival time or the CPB nominal removal time; and encode the removal time.

35. The video encoding device of claim 34, the video encoder further configured to: responsive to the syntax element having a true value, encode a CPB removal time only for the AU level; and responsive to the syntax element having a false value, encode a CPB removal time only for the sub-picture level.

36. The video encoding device of claim 34, wherein the at least one of the CPB arrival time or the CPB nominal removal time are encoded only when a syntax flag that indicates CPB parameters are present has a true value.

37. The video encoding device of claim 34, the video encoder is further configured to encode a duration between CPB removal of a first DU in the AU and CPB removal of a second DU, wherein encode the removal time further comprises encode the duration.

38. The video encoding device of claim 37, wherein the second DU is subsequent to the first DU in decoding order and in the same AU as the first DU.

39. The video encoding device of claim 37, the video encoder further configured to encode one or more sub-picture level CPB parameters, wherein determining the removal time of the first DU comprises determining the removal time of the first DU based at least in part on the duration and the sub-picture level CPB parameters.

40. The video encoding device of claim 34, the video encoder further configured to encode a sequence level flag to indicate the presence of sub-picture level CPB parameters either in picture timing SEI messages or in sub-picture timing SEI messages.

41. The video encoding device of claim 34, wherein the first DU comprises a non video coding layer (VCL) network abstraction layer (NAL) unit with na!_unit_type equal to UNSPECO, EOS_NUT, EOB^NUT, in the range of RSV_NVCL44 to RSV_NVCL47 or in the range of UNSPEC48 to UNSPEC63.

42. The video encoding device of claim 34, wherein the AU has a Temporalld equal to 0, the video encoder further configured to encode at least one of a buffering period supplemental enhancement information (SEI) message or a recovery point SEI message associated with the AU.

43. A computer-readable storage medium having stored thereon instructions that, when executed, cause a processor of a device for encoding video data to: derive at least one of a coded picture buffer (CPB) arrival time or a CPB nominal removal time for an access unit (AU) at both an access unit level and a sub picture level regardless of a value of a syntax element that defines whether a decoding']