1. A method for decoding video data, the method comprising:', 'decoding a sequence level flag to determine the presence of one or more sub- picture level coded picture buffer (CPB) parameters for a decoding unit (DU) of an access unit (AU) in either in a picture timing supplemental enhancement information (SEl) message or a sub-picture timing SEl message associated with the DU; and', 'decoding the one or more sub-picture level CPB parameters from the picture timing SEl message or the sub-picture timing SEl message based on the sequence level flag.

2. The method of claim 1, wherein the one or more sub-picture level CPB parameters are present in only one of the picture timing SEl message or the sub-picture timing SEl message.

3. The method of claim 1, further comprising:', 'determining a CPB removal time of the DU based at least in part on the one or more sub-picture level CPB parameters.

4. The method of claim 3, wherein determining the CPB removal time of the DU comprises determining the CPB removal time of the DU without decoding an initial CPB removal delay and offset.

5. The method of claim 1, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEl message, and wherein decoding the sub-picture level CPB parameters comprises decoding the sub-picture timing SEl message associated with the DU.

6. The method of claim 1, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the picture timing SEl message, and wherein decoding the sub-picture level CPB parameters comprises decoding the picture timing SEl message associated with the DU.

7. The method of claim 1 , wherein the DU is a first DU, the method further comprising:', 'deriving a CPB removal time of the first DU based at least in part on the sub- picture level CPB parameters;', 'decoding a duration between CPB removal time of a second DU of the AU in decoding order and the CPB removal time of the first DU; and', 'decoding video data of the first DU based at least in part on the CPB removal times.

8. The method of claim 7, wherein the second DU is either a last DU in the AU in decoding order or immediately subsequent to the first DU in the AU in decoding order.

9. The method of claim 1, wherein the DU comprises a non- video 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 UNSPEC12

10. 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 SEI message or a recovery point SEI message associated with the AU

11. The method of claim 1 , further comprising:', 'deriving at least one of a CPB arrival time and a CPB nominal removal time for the AU at both an access unit level and a sub-picture level regardless of a value of a syntax element that defines whether the first DU is the AU

12. A video decoding device comprising a video decoder configured to:', 'decode a sequence level flag to determine the presence of one or more sub- picture level coded picture buffer (CPB) parameters for a decoding unit (DU) of an access unit (AU) in either in a picture timing supplemental enhancement information (SEI) message or a sub-picture timing SEI message associated with the DU; and', 'decode the one or more sub-picture level CPB parameters from the picture timing SEI message or the sub-picture timing SEI message based on the sequence level flag

13. The video decoding device of claim 12, wherein the one or more sub-picture level CPB parameters are present in only one of the picture timing SEI message or the sub-picture timing SEI message

14. The video decoding device of claim 12, the video decoder further configured to determine a CPB removal time of the DU based at least in part on the one or more sub- picture level CPB parameters

15. The video decoding device of claim 14, wherein the video decoder configured to determine the CPB removal time of the DU comprises the video decoder configured to determine the CPB removal time of the DU without decoding an initial CPB removal delay and offset

16. The video decoding device of claim 12, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEI message, the video decoder configured to decode the sub-picture level CPB parameters further comprises the video decoder configured to decode the sub-picture timing SEI message associated with the DU

17. The video decoding device of claim 12, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the picture timing SEI message, and wherein the video decoder configured to decode the sub-picture level CPB parameters further comprises the video decoder configured to decode the picture timing SEI message associated with the DU

18. The video decoding device of claim 12, wherein the DU is a first DU, the video decoder further configured to:', 'derive a CPB removal time of the first DU based at least in part on the sub- picture level CPB parameters;', 'decode a duration between CPB removal time of a second DU of the AU in decoding order and the CPB removal time of the first DU; and', 'decode video data of the first DU based at least in part on the CPB removal times

19. The video decoding device of claim 18, wherein the second DU is either a last DU in the AU in decoding order or immediately subsequent to the first DU in the AU in decoding order.

20. The video decoding device of claim 12, wherein the DU comprises a non-video 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 UNSPEC12.

21. The video decoding device of claim 12, wherein the AU has a Temporalld equal to 0, the video decoder further configured to decode at least one of a buffering period SEI message or a recovery point SEI message associated with the AU.

22. The video decoding device of claim 12, the video decoder further configured to derive at least one of a CPB arrival time and a CPB nominal removal time for the AU at both an access unit level and a sub-picture level regardless of a value of a syntax element that defines whether the first DU is the AU.

23. A computer-readable storage medium having stored thereon instructions that, when executed, cause a processor of a device for coding video data to:', 'decode a sequence level flag to determine the presence of one or more sub- picture level coded picture buffer (CPB) parameters for a decoding unit (DU) of an access unit (AU) in either in a picture timing supplemental enhancement information (SEl) message or a sub-picture timing SEl message associated with the DU; and', 'decode the one or more sub-picture level CPB parameters from the picture timing SEl message or the sub-picture timing SEl message based on the sequence level flag.

24. The computer-readable storage medium of claim 23, wherein the one or more sub-picture level CPB parameters are present in only one of the picture timing SEl message or the sub-picture timing SEl message.

25. The computer-readable storage medium of claim 23, the instructions, when executed, further causing the processor of the device for coding video data to determine a CPB removal time of the DU based at least in part on the one or more sub-picture level CPB parameters.

26. The computer-readable storage medium of claim 25, wherein determine the CPB removal time of the DU comprises determine the CPB removal time of the DU without decoding an initial CPB removal delay and offset.

27. The computer-readable storage medium of claim 23, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEl message, and wherein decode the sub-picture level CPB parameters further comprises decode the sub-picture timing SEl message associated with the DU.

28. The computer-readable storage medium of claim 23, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the picture timing SEl message, and wherein decode the sub-picture level CPB parameters comprises decode the picture timing SEl message associated with the DU.

29. A video decoding device, comprising:', 'means for decoding a sequence level flag to determine the presence of one or more sub-picture level coded picture buffer (CPB) parameters for a decoding unit (DU) of an access unit (AU) in either in a picture timing supplemental enhancement information (SEl) message or a sub-picture timing SEl message associated with the DU; and', 'means for decoding the one or more sub-picture level CPB parameters from the picture timing SEl message or the sub-picture timing SEl message based on the sequence level flag.

30. The video decoding device of claim 29, wherein the one or more sub-picture level CPB parameters are present in only one of the picture timing SEl message or the sub-picture timing SEl message.

31. The video decoding device of claim 29, further comprising means for determining a CPB removal time of the DU based at least in part on the one or more sub-picture level CPB parameters.

32. The video decoding device of claim 31 , wherein means for determining the CPB removal time of the DU comprises means for determining the CPB removal time of the DU without decoding an initial CPB removal delay and offset.

33. The video decoding device of claim 29, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEl message, and wherein means for decoding the sub-picture level CPB parameters comprises means for decoding the sub-picture timing SEl message associated with the DU.

34. The video decoding device of claim 29, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the picture timing SEl message, and wherein means for decoding the sub-picture level CPB parameters comprises means for decoding the picture timing SEl message associated with the DU.

35. A method for encoding video data, the method comprising:', 'encoding one or more sub-picture level coded picture buffer (CPB) parameters for a decoding unit (DU) of an access unit (AU) in either a picture timing SEI message or a sub-picture timing SEI message; and', 'encoding a sequence level flag to indicate the presence of one or more sub- picture level CPB parameters for a DU of an AU in either in the picture timing SEI message or the sub-picture timing SEI message associated with the DU.

36. The method of claim 35, wherein encoding the one or more sub-picture level CPB parameters further comprises encoding the one or more sub-picture level CPB parameters in only one of the picture timing SEI message or the sub-picture timing SEI message.

37. The method of claim 35, further comprising:', 'determining a CPB removal time of the DU based at least in part on the one or more sub-picture level CPB parameters.

38. The method of claim 37, wherein determining the CPB removal time of the DU comprises determining the CPB removal time of the DU without encoding an initial CPB removal delay and offset.

39. The method of claim 35, wherein encoding the one or more sub-picture level CPB parameters further comprises encoding the one or more sub-picture level CPB parameters in the sub-picture timing SEI message associated with the DU, and wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEI message.

40. The method of claim 35, wherein encoding the one or more sub-picture level CPB parameters further comprises encoding the one or more sub-picture level CPB parameters in the picture timing SEI message associated with the DU, and wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the picture timing SEI message.

41. The method of claim 35, wherein the DU is a first DU, the method further comprising:', 'deriving a CPB removal time of the first DU based at least in part on the sub- picture level CPB parameters; and', 'encoding a duration between CPB removal time of a second DU of the AU in decoding order and the CPB removal time of the first DU.

42. The method of claim 41 , wherein the second DU is either a last DU in the AU in decoding order or immediately subsequent to the first DU in the AU in decoding order.

43. The method of claim 35, wherein the DU comprises a non- video 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 UNSPEC12.

44. The method of claim 35, wherein the AU has a Temporalld equal to 0, the method further comprising:', 'encoding at least one of a buffering period SEI message or a recovery point SEI message associated with the AU.

45. The method of claim 35, further comprising:', 'deriving at least one of a CPB arrival time and a CPB nominal removal time for the AU at both an access unit level and a sub-picture level regardless of a value of a syntax element that defines whether the first DU is the AU.

46. A video encoding device comprising a video encoder configured to:', 'encode one or more sub-picture level coded picture buffer (CPB) parameters for a decoding unit (DU) of an access unit (AU) in either a picture timing SEI message or a sub-picture timing SEI message; and', 'encode a sequence level flag to indicate the presence of one or more sub-picture level CPB parameters for a DU of an AU in either in the picture timing SEI message or the sub-picture timing SEI message associated with the DU.

47. The video encoding device of claim 46, wherein the video encoder is configured to encode the one or more sub-picture level CPB parameters further comprises the video encoder is configured to encode the one or more sub-picture level CPB parameters in only one of the picture timing SEI message or the sub-picture timing SEI message.

48. The video encoding device of claim 46, the video encoder further configured to determine a CPB removal time of the DU based at least in part on the one or more sub- picture level CPB parameters.

49. The video encoding device of claim 48, wherein the video encoder configured to determine the CPB removal time of the DU comprises the video encoder configured to determine the CPB removal time of the DU without encoding an initial CPB removal delay and offset.

50. The video encoding device of claim 46, wherein the video encoder is configured to encode the one or more sub-picture level CPB parameters further comprises the video encoder is further configured to encode the one or more sub-picture level CPB parameters in the sub-picture timing SEI message associated with the DU, and wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEI message.

51. The video encoding device of claim 46, wherein the video encoder is configured to encode the one or more sub-picture level CPB parameters further comprises the video encoder is further configured to encode the one or more sub-picture level CPB parameters in the picture timing SEI message associated with the DU, and wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the picture timing SEI message.

52. The video encoding device of claim 46, wherein the DU is a first DU, the video encoder further configured to:', 'derive a CPB removal time of the first DU based at least in part on the sub- picture level CPB parameters;', 'encode a duration between CPB removal time of a second DU of the AU in decoding order and the CPB removal time of the first DU; and', 'encode video data of the first DU based at least in part on the CPB removal times.

53. The video encoding device of claim 46, wherein the second DU is either a last DU in the AU in decoding order or immediately subsequent to the first DU in the AU in decoding order.

54. The video encoding device of claim 46, wherein the DU comprises a non-video 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 UNSPEC12.

55. The video encoding device of claim 46, wherein the AU has a Temporalld equal to 0, the video encoder further configured to encode at least one of a buffering period SEI message or a recovery point SEI message associated with the AU.

56. The video encoding device of claim 46, the video encoder further configured to derive at least one of a CPB arrival time and a CPB nominal removal time for the AU at both an access unit level and a sub-picture level regardless of a value of a syntax element that defines whether the first DU is the AU.

57. A computer-readable storage medium having stored thereon instructions that, when executed, cause a processor of a device for coding video data to:', 'encode one or more sub-picture level coded picture buffer (CPB) parameters for a decoding unit (DU) of an access unit (AU) in either a picture timing SEI message or a sub-picture timing SEI message; and', 'encode a sequence level flag to indicate the presence of one or more sub-picture level CPB parameters for a DU of an AU in either in the picture timing SEI message or the sub-picture timing SEI message associated with the DU.

58. The computer-readable storage medium of claim 57, wherein encode the one or more sub-picture level CPB parameters further comprises encode the one or more sub- picture level CPB parameters in only one of the picture timing SEI message or the sub- picture timing SEI message.

59. The computer-readable storage medium of claim 57, the instructions, when executed, further causing the processor of the device for coding video data to determine a CPB removal time of the DU based at least in part on the one or more sub-picture level CPB parameters.

60. The computer-readable storage medium of claim 59, wherein determine the CPB removal time of the DU comprises determine the CPB removal time of the DU without encoding an initial CPB removal delay and offset.

61. The computer-readable storage medium of claim 57, wherein encode the one or more sub-picture level CPB parameters further comprises encode the one or more sub- picture level CPB parameters in the sub-picture timing SEI message associated with the DU, and wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEI message.

62. The computer-readable storage medium of claim 57, wherein encode the one or more sub-picture level CPB parameters further comprises encode the one or more sub- picture level CPB parameters in the picture timing SEI message associated with the DU, and wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the picture timing SEI message.']