1. A method for decoding video data, the method comprising:', 'decoding a sub-picture timing supplemental enhancement information (SEI) message associated with a first decoding unit (DU) of an access unit (AU);', 'determining, from the sub-picture timing SEI message, a duration between coded picture buffer (CPB) removal time of a second DU of the AU in decoding order and CPB removal time of the first DU in the sub-picture SEI message; and', 'deriving a CPB removal time of the first DU based at least in part on the sub- picture timing SEI message.

2. The method of claim 1, further comprising:', 'decoding a sequence level flag to determine the presence of one or more sub- picture level CPB parameters either in the sub-picture timing SEI message or a picture timing SEI message associated with the first DU.

3. The method of claim 1, further comprising:', 'decoding the sub-picture level CPB parameters, wherein determining the CPB removal time of the first DU is further based at least in part on the sub-picture level CPB parameters.

4. The method of claim 3, wherein the sequence level flag indicates the sub-picture level CPB parameters are to be present in the sub-picture timing SEI message, and wherein decoding the sub-picture level CPB parameters comprises:', 'decoding the sub-picture timing SEI message associated with the first DU.

5. The method of claim 4, wherein the second DU is a last DU in the AU in decoding order, and wherein decoding the sub-picture SEI message comprises:', 'decoding the duration between a removal time of the last DU and the removal time of the first DU in the sub-picture timing SEI message.

6. The method of claim 1 , wherein the second DU is a last DU in the AU in decoding order.

7. The method of claim 1, wherein the second DU is immediately subsequent to the first DU in the AU in decoding order.

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, EOB NUT, in the range of RSV NVCL44 to RSV_NVCL47 or in the range of UNSPEC48 to UNSPEC12.

9. The method of claim 1, wherein determining the removal time of the first DU comprises determining the removal time of the first DU without decoding an initial CPB removal delay and offset

10. A video decoding device comprising a video decoder configured to:', 'decode a sub-picture timing supplemental enhancement information (SEI) message associated with a first decoding unit (DU) of an access unit (AU);', 'determine, from the sub-picture timing SEI message, a duration between coded picture buffer (CPB) removal time of a second DU of the AU in decoding order and CPB removal time of the first DU in the sub-picture SEI message; and', 'derive a CPB removal time of the first DU based at least in part on the sub- picture timing SEI message

11. The video decoding device of claim 10, the video decoder further configured to decode a sequence level flag to determine the presence of one or more sub-picture level CPB parameters either in the sub-picture timing SEI message or a picture timing SEI message associated with the first DU

12. The video decoding device of claim 10, the video decoder further configured to decode the sub-picture level CPB parameters, wherein determine the CPB removal time of the first DU is further based at least in part on the sub-picture level CPB parameters

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

14. The video decoding device of claim 13, wherein the second DU is a last DU in the AU in decoding order, and wherein the video decoder is configured to decode the sub-picture SEI message comprises the video decoder is configured to decode the duration between a removal time of the last DU and the removal time of the first DU in the sub-picture timing SEI message

15. The video decoding device of claim 10, wherein the second DU is a last DU in the AU in decoding order

16. The video decoding device of claim 10, wherein the second DU is immediately subsequent to the first DU in the AU in decoding order

17. The video decoding device of claim 10, wherein the first DU comprises a non- video coding layer (VCL) network abstraction layer (NAL) unit with nal unit type equal to UNSPEC0, EOS_NUT, EOB NUT, in the range of RSV NVCL44 to', 'RSV_NVCL47 or in the range of UNSPEC48 to UNSPEC12

18. The video decoding device of claim 10, wherein the video decoder is configured to determine the removal time of the first DU further comprises the video decoder is configured to determine the removal time of the first DU without decoding an initial CPB removal delay and offset

19. 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 sub-picture timing supplemental enhancement information (SEI) message associated with a first decoding unit (DU) of an access unit (AU);', 'determine, from the sub-picture timing SEI message, a duration between coded picture buffer (CPB) removal time of a second DU of the AU in decoding order and CPB removal time of the first DU in the sub-picture SEI message; and', 'derive a CPB removal time of the first DU based at least in part on the sub- picture timing SEI message.

20. The computer-readable storage medium of claim 19, the instructions, when executed, further causing 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 CPB parameters either in the sub-picture timing SEI message or a picture timing SEI message associated with the first DU.

21. The computer-readable storage medium of claim 19, the instructions, when executed, further causing a processor of a device for coding video data to:', 'decode the sub-picture level CPB parameters, wherein determine the CPB removal time of the first DU is further based at least in part on the sub-picture level CPB parameters.

22. The computer-readable storage medium of claim 19, wherein the sequence level flag indicates the sub-picture level CPB parameters are to be present in the sub-picture timing SEI message, and wherein decode the sub-picture level CPB parameters comprises decode the sub-picture timing SEI message associated with the first DU.

23. A video decoding device, comprising:', 'means for decoding a sub-picture timing supplemental enhancement information (SEI) message associated with a first decoding unit (DU) of an access unit (AU);', 'means for determining, from the sub-picture timing SEI message, a duration between coded picture buffer (CPB) removal time of a second DU of the AU in decoding order and CPB removal time of the first DU in the sub-picture SEI message; and', 'means for deriving a CPB removal time of the first DU based at least in part on the sub-picture timing SEI message.

24. The video decoding device of claim 23, further comprising:', 'means for decoding a sequence level flag to determine the presence of one or more sub-picture level CPB parameters either in the sub-picture timing SEI message or a picture timing SEI message associated with the first DU.

25. The video decoding device of claim 23, further comprising:', 'means for decoding the sub-picture level CPB parameters, wherein determining the CPB removal time of the first DU is further based at least in part on the sub-picture level CPB parameters.

26. The video decoding device of claim 25, wherein the sequence level flag indicates the sub-picture level CPB parameters are to be present in the sub-picture timing SEI message, and wherein means for decoding the sub-picture level CPB parameters comprises means for decoding the sub-picture timing SEI message associated with the first DU.

27. A method for encoding video data, the method comprising:', 'determining a duration between coded picture buffer (CPB) removal time of a first decoding unit (DU) in an access unit (AU) and CPB removal time of a second DU in the AU; and', 'encoding the duration in a sub-picture timing supplemental enhancement information (SEI) message associated with the AU.

28. The method of claim 27, further comprising encoding one or more sub-picture level CPB parameters.

29. The method of claim 28, further comprising:', 'encoding a sequence level flag to indicate the presence of the one or more sub- picture level CPB parameters in either the sub-picture timing SEI message or a picture timing SEI message associated with the first DU.

30. The method of claim 29, wherein the sequence level flag indicates the sub- picture level CPB parameters are present in the sub-picture timing SEI message, and wherein encoding the one or more sub-picture level CPB parameters comprises encoding the sub-picture timing SEI message associated with the AU.

31. The method of claim 27, wherein the second DU is a last DU in the AU in decoding order.

32. The method of claim 27, wherein the second DU is immediately subsequent to the first DU in the AU in decoding order.

33. The method of claim 27, 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, EOB NUT, in the range of RSV NVCL44 to RSV NVCL47 or in the range of UNSPEC48 to UNSPEC12.

34. The method of claim 27, wherein determining the duration comprises determining a removal time of the first DU without encoding an initial CPB removal delay and offset.

35. A video encoding device comprising a video encoder configured to:', 'determine a duration between coded picture buffer (CPB) removal time of a first decoding unit (DU) in an access unit (AU) and CPB removal time of a second DU in the AU; and', 'encode the duration in a sub-picture timing supplemental enhancement information (SEI) message associated with the AU.

36. The video encoding device of claim 35, further comprising encode one or more sub-picture level CPB parameters.

37. The video encoding device of claim 36, the video encoder further configured to encode a sequence level flag to indicate the presence of the one or more sub-picture level CPB parameters in either the sub-picture timing SEI message or a picture timing SEI message associated with the first DU.

38. The video encoding device of claim 37, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEI message, and wherein encode the one or more sub-picture level CPB parameters comprises encode the sub-picture timing SEI message associated with the AU.

39. The video encoding device of claim 35, wherein the second DU is a last DU in the AU in decoding order.

40. The video encoding device of claim 35, wherein the second DU is a last DU in the AU in decoding order.

41. The video encoding device of claim 35, wherein the second DU is immediately subsequent to the first DU in the AU in decoding order.

42. The video encoding device of claim 35, 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, EOB NUT, in the range of RSV NVCL44 to', 'PvSV_NVCL47 or in the range of UNSPEC48 to UNSPEC12.

43. The video encoding device of claim 35, wherein the video encoder is configured to determine the duration further comprises the video encoder is configured to determine a removal time of the first DU without encoding an initial CPB removal delay and offset.

44. A computer-readable storage medium having stored thereon instructions that, when executed, cause a processor of a device for coding video data to:', 'determine a duration between coded picture buffer (CPB) removal time of a first decoding unit (DU) in an access unit (AU) and CPB removal time of a second DU in the AU; and', 'encode the duration in a sub-picture timing supplemental enhancement information (SEI) message associated with the AU.

45. The computer-readable storage medium of claim 44, the instructions, when executed, further causing a processor of a device for coding video data to:', 'encode one or more sub-picture level CPB parameters.

46. The computer-readable storage medium of claim 44, the instructions, when executed, further causing a processor of a device for coding video data to:', 'encode a sequence level flag to indicate the presence of the one or more sub- picture level CPB parameters in either the sub-picture timing SEI message or a picture timing SEI message associated with the first DU.

47. The computer-readable storage medium of claim 46, wherein the sequence level flag indicates the sub-picture level CPB parameters are present in the sub-picture timing SEI message, and wherein encode the one or more sub-picture level CPB parameters comprises encode the sub-picture timing SEI message associated with the AU.']