1. A method of processing video data, the method comprising:', 'determining, based at least in part on a syntax element in a scalable nesting supplemental enhancement information (SEI) message encapsulated by an SEI Network Abstraction Layer (NAL) unit, whether a nested SEI message encapsulated by the scalable nesting SEI message is applicable to a default sub-bitstream of an encoded video bitsirearn, wherein the default sub-bitstream is an operation point representation of an operation point defined by a layer identifier specified in a NA L unit header of the SEI NAL unit and a temporal identifier specified in the NAL unit header; and', 'when the nested SEI message is applicable to the default sub-bitstream, using the nested SEI message in an operation on the default sub-bitstream.

2. The method of claim L wherein a first syntax element in the NAL unit header indicates the layer identifier and a second syntax element in the NAL unit header indicates the temporal identifier.

3. The method of claim 2, wherein the default sub-bitstream is a subset of an encoded video bitsirearn and the default sub-bitstream does not include video coding layer (VCL) N AL units of the encoded video bitstream that have layer identifiers greater than the layer identifier indicated by the first syntax element of the N AL unit header or have temporal identifiers greater than the temporal identifier indicated by the second syntax element of the N AL unit header.

4. The method of claim 1, wherein the nested SEI message includes a set of hypothetical reference decoder (HRD) parameters.

5. The method of claim 4, wherein using the nested SEI message comprises using the HRD parameters in the nested SEI message in an operation that tests whether the default sub-bitstream conforms to a video coding standard.

6. The method of claim 1, wherein using the nested SEI message comprises using the nested SEI message in a decoding operation on the default sub-bitstream.

7. The method of claim 1, wherein:', 'the scalable nesting SEI message encapsulates a plurality of nested SEI messages, and', 'determining whether the nested SEI message is applicable to the default sub- bitstream comprises determining, based at feast in part on the syntax element, whether each of the nested SEI messages is applicable to the default sub-bitstream.

8. The method of claim 1, wherein:', 'the syntax element in the scalable nesting SEI message is a first syntax element, and', 'the method further comprises determining, based at least in part on a second syntax element in the scalable nesting SEI message indicating that nested SEI messages encapsulated by the scalable nesting SEI message apply to a sub-bitstream extracted from the encoded video bitstream, that the scalable nesting SEI message includes the first syntax element.

9. The method of claim 1 , wherein the method further comprises:', 'determining, based on one or more additional syntax elements in the scalable nesting SEI message, a temporal identifier of a second operation point and a maximum layer identifier of the second operation point; and', 'using the nested SEI message in an operation on an additional sub-bitstream, the additional sub-bitstream being an operation point representation of the second operation point

10. A device comprising one or more processors configured to:', 'determine, based at least in part on a syntax element in a scalable nesting supplemental enhancement information (SEI) message encapsulated by an SEI Network Abstraction Layer (NAL) unit, whether a nested SEI message encapsulated by the scalable nesting SEI message is applicable to a default sub-bitstream of an encoded video bitstream, wherein the default sub-bitstream is an operation point representation of an operation point defined by a layer identifier specified in a NAL unit header of the SEI NAL unit and a temporal identifier specified in the NAL unit header; and', 'when the nested SEI message is applicable to the default sub-bitstream, use the nested SEI message in an operation on the default sub-bitstream,11. The device of claim 10, wherein a first syntax element in the NAL unit header indicates the layer identifier and a second syntax element in the NAL unit header indicates the temporal identifier

12. The device of claim 1 1 , wherein the default sub-bitstream is a subset of the encoded video bitstream and the default sub-bitstream does not include video coding layer (VCL) NAL units of the encoded video bitstream that have layer identifiers greater than the layer identifier indicated by the first syntax element of the NAL unit header or have temporal identifiers greater than the temporal identifier indicated by the second syntax element of the NAL unit header

13. The device of claim 10, wherein the nested SEI message includes a set of hypothetical reference decoder (HRD) parameters

14. The device of claim 13, wherein the one or more processors are configured to use the HRD parameters in the nested SEI message in an operation that tests whether the default sub-bitstream conforms to a video coding standard,15. The device of claim 10, wherein the one or more processors are configured to use the nested SEI message in a decoding operation on the default sub-bitstream

16. The device of claim 10, wherein:', 'the scalable nesting SEI message encapsulates a plurality of nested SEI messages, and', 'the one or more processors are configured to determine, based at least in pari on the syntax element, whether each of the nested SEI messages is applicable to the default sub-bitstream,17. The device of claim 10, wherein:', 'the syntax element in the scalable nesting SEI message is a first syntax element, and', 'the one or more processors are further configured to determine, based at least in part on a second syntax element in the scalable nesting SET message indicating that nested SEI messages encapsulated by the scalable nesting SEI message apply to a sub- bitstream extracted from the encoded video bitstream, that the scalable nesting SEI message includes the first syntax element18. The device of claim 10, wherein the one or more processors are further configured to:', 'determine, based on one or more additional syntax elements in the scalable nesting SEI message, a temporal identifier of a second operation point and a maximum layer identifier of the second operation point; and', 'use the nested SEI message in an operation on an additional sub-bitstream, the additional sub-bitstream being an operation point representation of the second operation point

19. A device comprising:', 'means for determining, based at least in part on a syntax element in a scalable nesting supplemental enhancement information (SEI) message encapsulated by an SEI Network Abstraction Layer (NAL) unit, whether a nested SEI message encapsulated by the scalable nesting SEI message is applicable to a default sub-bits tream of an encoded video bitstream, wherein the default sub-bitstream is an operation point representation of an operation point defined by a layer identifier specified in a NAL unit header of the SEI NAL unit and a temporal identifier specified in the NAL unit header; and', 'means for using, when the nested SEI message is applicable to the default sub- bitstream, the nested SEI message in an operation on the default sub-bitstream.

20. The device of claim 19, wherein:', 'a first syntax element in the N AL unit header indicates the layer identifier and a second syntax element in the NAL unit header indicates the temporal identifier, and the default sub-bitstream is a subset of an encoded video bitstream and the default sub-bitstream does not include video coding layer (VCL) N AL units of the encoded video bitstream that have layer identifiers greater than the layer identifier indicated by the first syntax element of the N AL unit header or have temporal identifiers greater than the temporal identi fier indicated by the second syntax element of the NAL unit header.

21. The device of claim 19, wherein:', 'the nested SEI message includes a set of hypothetical reference decoder (HRD) parameters, and', 'the device comprises means for using the HRD parameters in the nested SEI message in an operation that tests whether the default sub-bitstream conforms to a video coding standard.

22. A computer-readable storage medium that stores instructions that, when executed by one or more processors of a device, configure the device to:', 'determine, based at least in part on a. syntax element in a scalable nesting supplemental enhancement information (SEI) message encapsulated by an SEI Network Abstraction Layer (NAL) unit, whether a nested SEI message encapsulated by the scalable nesting SEI message is applicable to a default sub-bitstream of an encoded video bitstream, wherein the default sub-bitstream is an operation point representation of an operation point defined by a layer identifier specified in a NAL unit header of the SEI NAL unit and a temporal identifier specified in the NAL unit header; and', 'when the nested SEI message is applicable to the default sub-bitstream, use the nested SEI message in an operation on the default sub-bitstream.

23. The computer-readable storage medium of claim 22, wherein:', 'a first syntax element in the NAL unit header indicates the layer identifier and a second syntax element in the NAL unit header indicates the temporal identifier, and the default sub-bitstream is a subset of an encoded video bitstream and the default sub-bitstream does not include video coding layer (VCL) NAL units of the encoded video bitstream that have layer identifiers greater than the layer identifier indicated by the first syntax element of the NAL unit header or have temporal identifiers greater than t e temporal identifier indicated by the second syntax element of the NAL unit header.

24. The computer-readable storage medium of claim 22, wherein:', 'the nested SEI message includes a set of hypothetical reference decoder (HRD) parameters, and', 'the instructions further configure the device to use the HRD parameters in the nested SEI message in an operation that tests whether the default sub-bitstream conforms to a video coding standard.

25. A method of encoding video data, the method comprising:', 'including, in a scalable nesting supplemental enhancement information (SEI) message encapsulated by an SEI Network Abstraction Layer (NAL) unit, a syntax element that indicates whether a nested SEI message encapsulated by the scalable nesting SEI message is applicable to a default sub-bitstream of an encoded video bitstream, wherein the default sub~bitstream is an operation point representation of an operation point defined by a layer identifier specified in a NAL unit header of the SEI NAL unit and a temporal identifier specified in the NAL unit header; and', 'signaling the scalable nesting SEI message in the encoded video bitstream.

26. The method of claim 25, wherein a first syntax element in the NAL unit header indicates the layer identifier and a second syntax element in the NAL unit header indicates the temporal identifier.

27. The method of claim 26, wherein the default sub-bitstream is a subset of the encoded video bitstream and the default sub-bitstream does not include video coding layer (VCL) NAL units of the encoded video bitstream that have layer identifiers greater than the layer identifier indicated by the first syntax element of the NAL unit header or have temporal identifiers greater than the temporal identifier indicated by the second syntax element of the NAL unit header.

28. The method of claim 25, wherein the nested SEI message includes a set of hypothetical reference decoder (HRD) parameters.

29. The method of claim 28, further comprising using the HRD parameters in the nested SEI message in an operation that tests whether the default sub-bitstream conforms to a video coding standard.

30. The method of claim 25, wherein:', 'the scalable nesting SEI message encapsulates a plurality of nested SEI messages, and', 'the syntax element indicates whether each of the nested SEI messages is applicable to the default sub-bitstream.

31. The method of claim 25, wherein:', 'the syntax element in the scalable nesting SEI message is a first syntax element in the scalable nesting SEI message,', 'the method further comprises including a second syntax element in the scalable nesting SEI message, the second syntax element indicating whether nested SEI messages encapsulated by the scalable nesting SEI message apply to a sub-bitstream extracted from the encoded video bitstream or whether the nested SEI messages apply to specific layers and sub-layers of the encoded video bitstream, and', 'the scalable nesting SEI message includes the first syntax element only when the second syntax element indicates that the nested SEI messages apply to the sub-bitstream extracted from the encoded video bi ts tream,

32. The method of claim 25, wherein:', 'the operation point identified by one or more syntax elements of a NAL unit header of the SEI NAL unit is a first operation point, and', 'the method further comprises including, in the scalable nesting SEI message, one or more additional syntax elements that identify a temporal identifier of a second operation point and a maximum layer Identifier of the second operation point.

33. A video encoding device comprising one or more processors configured to: include, in a scalable nesting supplemental enhancement information (SEI) message encapsulated by an SEI Network Abstraction Layer (NAL) unit, a syntax element that indicates whether a nested SEI message encapsulated by the scalable nesting SEI message is applicable to a default sub-bitstream of an encoded video bitstream, wherein the default sub-bitstream is an operation point representation of an operation point defined by a layer identifier specified in a NAL unit header of the SEI NAL unit and a temporal identifier specified in the NAL unit header; and', 'signal the scalable nesting SEI message in the encoded video bitstream.

34. The video encoding device of claim 33, wherein a first syntax element in the NAL unit header indicates the layer identifier and a second syntax element in the NAL unit header indicates the temporal identifier.

35. The video encoding device of claim 34, wherein the default sub-bitstreani is a subset of the encoded video bitstream and the default sub - bitstream does not include video coding layer (VCL) NAL units of the encoded video bitstream that have layer identifiers greater than the layer identifier indicated by the first syntax element of the NAL unit header or have temporal identifiers greater than the temporal identifier indicated by the second syntax element of the NAL unit header.

36. The video encoding device of claim 33, wherein the nested SEI message includes a set of hypothetical reference decoder (HRD) parameters.

37. The video encoding device of claim 36, wherein the one or more processors are further configured to use the HRD parameters in the nested SEI message in an operation that tests whether the default sub-bitstream conforms to a video coding standard.

38. The video encoding device of claim 33, wherein:', 'the scalable nesting SEI message encapsulates a plurality of nested SEI messages, and', 'the syntax element indicates whether each of the nested SEI messages is applicable to the default sub-bitstream .

39. The video encoding device of claim 33, wherein:', 'the syntax element in the scalable nesting SEI message is a first syntax element in the scalable nesting SEI message,', 'the one or more processors are further configured to include a second syntax element in the scalable nesting SEI message, the second syntax element indicating whether nested SEI messages encapsulated by the scalable nesting SEI message apply to a sub-bitstream extracted from the encoded video bitstream or whether the nested SEI messages apply to specific layers and sub-layers of the encoded video bitstream, and the scalable nesting SEI message includes the first syntax element only when the second syntax element indicates that the nested SEI messages apply to the sub-bitstream extracted from the encoded video bitstream.

40. The video encoding device of claim 33 , wherein:', 'the operation point identified by one or more syntax elements of a NAL unit header of the SEI NAL unit is a first operation point, and', 'the one or more processors are further configured to include, in the scalable nesting SEI message, one or more additional syntax elements that identify a temporal identifier of a second operation point and a maximum layer identifier of the second operation point.

41. A video encoding device comprising:', 'means for including, in a scalable nesting supplemental enhancement information (SEI) message encapsulated by an SEI Network Abstraction Layer (NAL) unit, a syntax element that indicates whether a nested SEI message encapsulated by the scalable nesting SEI message is applicable to a default sub-bitstream of an encoded video bitstream, wherein the default sub-bitstream is an operation point representation of an operation point defined by a layer identifier specified in a NAL unit header of the SEI NAL unit and a temporal identifier specified in the NAL unit header; and', 'means for signaling the scalable nesting SEI message in the encoded video bitstream.

42. The video encoding device of claim 41 , wherein:', 'a first syntax element in the NAL unit header indicates the layer identifier and a second syntax element in the NAL unit header indicates the temporal identifier, and the default sub-bitstream is a subset of an encoded video bitstream and the default sub-bitstream does not include video coding layer (VCL) NAL units of the encoded video bitstream that have layer identifiers greater than the layer identifier indicated by the first syntax element of the NAL unit header or have temporal identifiers greater than the temporal identifier indicated by the second syntax element of the NAL unit header.

43. The video encoding device of claim 41 , wherein:', 'the nested SEI message includes a set of hypothetical reference decoder (HRD) parameters, and', 'the video encoding device comprises means for using the HRD parameters in the nested SEI message in an operation that tests whether the default sub-bitstream conforms to a video coding standard.

44. A computer-readable storage medium that stores instructions that, when executed by a video encoding device, configure the video encoding device to:', 'include, in a scalable nesting supplemental enhancement information (SEI) message encapsulated by an SEI Network Abstraction Layer (NAL) unit, a syntax element that indicates whether a nested SEI message encapsulated by the scalable nesting SEI message is applicable to a default sub-bitstream of an encoded video bitstream, wherein the default sub-bitstream is an operation point representation of an operation point defined by a layer identifier specified in a NAL unit header of the SEI NAL unit and a temporal identifier specified in the NAL unit header; and', 'signal the scalable nesting SEI message in the encoded video bitstream.

45. The computer-readable storage medium of claim 44, wherein:', 'a first syntax element in the NAL unit header indicates the layer identifier and a second syntax element in the N AL unit header indicates the temporal identifier, and the default sub-bitstream is a subset of an encoded video bitstream and the default sub-bitstream does not include video coding layer (VCL) N AL units of the encoded video bitstream that have layer identifiers greater than the layer identifier indicated by the first syntax element of the N AL unit header or have temporal identifiers greater than the temporal identifier indicated by the second syntax element of the NAL unit header.

46. The compiiter-readable storage medium of claim 44, wherein:', 'the nested SEI message includes a set of hypothetical reference decoder (HRD) parameters, and', 'the instructions further configure the video encoding device to use the HRD parameters in the nested SEI message in an operation that tests whether the default sub- bitstream conforms to a video coding standard.']