1. A method for coding video data, the method comprising:', 'coding a supplemental enhancement information (SEI) message in an access unit, wherein the access unit includes the video data for reconstructing at least one picture, and the SEI message defines a characteristic of the video data; and', 'coding a copy of the SEI message in the access unit.

2. The method of claim 1, further comprising:', 'including the SEI message before a first video coding layer (VCL) network abstraction layer (NAL) unit in decoding order in the access unit; and', 'including the copy of the SEI message after the first VCL NAL unit in decoding order and before a last VCL NAL unit in decoding order in the access unit,', 'wherein coding the SEI message comprises encoding the SEI message that is included before the first VCL NAL unit, and', 'wherein coding the copy of the SEI message comprises encoding the copy of the SEI message that included after the first VCL NAL unit and before the last VCL NAL unit.

3. The method of claim 1, further comprising:', 'decoding a first video coding layer (VCL) network abstraction layer (NAL) unit in decoding order in the access unit; and', 'decoding a last VCL NAL unit in decoding order in the access unit,', 'wherein coding the SEI message comprises decoding the SEI message prior to decoding the first VCL NAL unit, and', 'wherein coding the copy of the SEI message comprises decoding the copy of the SEI message after decoding the first VCL NAL unit and prior to decoding the last VCL NAL unit.

4. The method of claim 1, further comprising:', 'determining a type of the SEl message;', 'determining a temporal identification value of the access unit; and determining whether a presence of the SEl message is allowed based on the temporal identification value of the access unit and the type of SEl message,', 'wherein coding the SEl message comprises coding the SEl message based on determination of whether the presence of the SEl message is allowed.

5. The method of claim 1, wherein the SEl message comprises one of:', 'a buffering period SEl message;', 'a picture timing SEl message;', 'a pan-scan rectangle SEl message;', 'a filler payload SEl message;', 'a user data registered SEl message;', 'a user data unregistered SEl message;', 'a recovery point SEl message;', 'a scene information SEl message;', 'a full-frame snapshot SEl message;', 'a progressive refinement segment start SEl message;', 'a progressive refinement segment end SEl message;', 'a film grain characteristics SEl message;', 'a deblocking filter display preference SEl message;', 'a post-filter hint SEl message;', 'a tone mapping information SEl message;', 'a frame packing arrangement SEl message;', 'a display orientation SEl message;', 'a structure of pictures description SEl message;', 'a field indication SEl message;', 'a decoded picture hash SEl message;', 'an active parameter sets SEl message; and', 'a sub-picture timing SEl message.

6. The method of claim 1, wherein coding the SEI message comprises coding the SEI message in the access unit for a multi-session transmission, and wherein coding the copy of the SEI message comprises coding the copy of the SEI message in the access unit for the multi-session transmission.

7. A device for coding video data, the device comprising a video coder configured to:', 'code a supplemental enhancement information (SEI) message in an access unit, wherein the access unit includes the video data for reconstructing at least one picture, and the SEI message defines a characteristic of the video data; and', 'code a copy of the SEI message in the access unit.

8. The device of claim 7, wherein the video coder comprises a video encoder, and wherein the video encoder is configured to:', 'include the SEI message before a first video coding layer (VCL) network abstraction layer (NAL) unit in decoding order in the access unit;', 'include the copy of the SEI message after the first VCL NAL unit in decoding order and before a last VCL NAL unit in decoding order in the access unit;', 'encode the SEI message that is included before the first VCL NAL unit; and encode the copy of the SEI message that included after the first VCL NAL unit and before the last VCL NAL unit.

9. The device of claim 7, wherein the video coder comprises a video decoder, and wherein the video decoder is configured to:', 'decode a first video coding layer (VCL) network abstraction layer (NAL) unit in decoding order in the access unit;', 'decode a last VCL NAL unit in decoding order in the access unit;', 'decode the SEI message prior to decoding the first VCL NAL unit; and decode the copy of the SEI message after decoding the first VCL NAL unit and prior to decoding the last VCL NAL unit

10. The device of claim 7, wherein the video coder is configured to:', 'determine a type of the SEI message;', 'determine a temporal identification value of the access unit; and', 'determine whether a presence of the SEI message is allowed based on the temporal identification value of the access unit and the type of SEI message, and wherein the video coder is configured to code the SEI message based on the determination of whether the presence of the SEI message is allowed

11. The device of claim 7, wherein the SEI message comprises one of:', 'a buffering period SEI message;', 'a picture timing SEI message;', 'a pan-scan rectangle SEI message;', 'a filler payload SEI message;', 'a user data registered SEI message;', 'a user data unregistered SEI message;', 'a recovery point SEI message;', 'a scene information SEI message;', 'a full-frame snapshot SEI message;', 'a progressive refinement segment start SEI message;', 'a progressive refinement segment end SEI message;', 'a film grain characteristics SEI message;', 'a deblocking filter display preference SEI message;', 'a post-filter hint SEI message;', 'a tone mapping information SEI message;', 'a frame packing arrangement SEI message;', 'a display orientation SEI message;', 'a structure of pictures description SEI message;', 'a field indication SEI message;', 'a decoded picture hash SEI message;', 'an active parameter sets SEI message; and', 'a sub-picture timing SEI message

12. The device of claim 7, wherein the video coder is configured to code the SEI message in the access unit for a multi-session transmission, and wherein the video coder is configured to code the copy of the SEI message in the access unit for the multi- session transmission

13. The device of claim 7, wherein the device comprises one of:', 'a microprocessor;', 'an integrated circuit; and', 'a wireless communication device that includes the video coder

14. A computer-readable storage medium having instructions stored thereon that when executed by one or more processors of a device for coding video data cause the one or more processors to:', 'code a supplemental enhancement information (SEI) message in an access unit, wherein the access unit includes the video data for reconstructing at least one picture, and the SEI message defines a characteristic of the video data; and', 'code a copy of the SEI message in the access unit

15. The computer-readable storage medium of claim 14, further comprising instructions that cause the one or more processors to:', 'determine a type of the SEI message;', 'determine a temporal identification value of the access unit; and', 'determine whether a presence of the SEI message is allowed based on the temporal identification value of the access unit and the type of SEI message, and', 'wherein the instructions that cause the one or more processors to code the SEI message comprise instructions that cause the one or more processors to code the SEI message based on the determination of whether the presence of the SEI message is allowed

16. The computer-readable storage medium of claim 14, wherein the SEI message comprises one of:', 'a buffering period SEI message;', 'a picture timing SEI message;', 'a pan-scan rectangle SEI message;

a filler payload SEl message;', 'a user data registered SEl message;', 'a user data unregistered SEl message;', 'a recovery point SEl message;', 'a scene information SEl message;', 'a full-frame snapshot SEl message;', 'a progressive refinement segment start SEl message;', 'a progressive refinement segment end SEl message;', 'a film grain characteristics SEl message;', 'a deblocking filter display preference SEl message;', 'a post-filter hint SEl message;', 'a tone mapping information SEl message;', 'a frame packing arrangement SEl message;', 'a display orientation SEl message;', 'a structure of pictures description SEl message;', 'a field indication SEl message;', 'a decoded picture hash SEl message;', 'an active parameter sets SEl message; and', 'a sub-picture timing SEl message.17. The computer-readable storage medium of claim 14, wherein the instructions that cause the one or more processors to code the SEl message comprise instructions that cause the one or more processors to code the SEl message in the access unit for a multi-session transmission, and wherein the instructions that cause the one or more processors to code the copy of the SEl message comprise instructions that cause the one or more processors to code the copy of the SEl message in the access unit for the multi- session transmission.18. A device for coding video data, the device comprising:', 'means for coding a supplemental enhancement information (SEl) message in an access unit, wherein the access unit includes the video data for reconstructing at least one picture, and the SEl message defines a characteristic of the video data; and', 'means for coding a copy of the SEl message in the access unit.19. The device of claim 18, further comprising:', 'means for including the SEl message before a first video coding layer (VCL) network abstraction layer (NAL) unit in decoding order in the access unit; and', 'means for including the copy of the SEl message after the first VCL NAL unit in decoding order and before a last VCL NAL unit in decoding order in the access unit, wherein the means for coding the SEl message comprises means for encoding the SEl message that is included before the first VCL NAL unit, and', 'wherein the means for coding the copy of the SEl message comprises means for encoding the copy of the SEl message that included after the first VCL NAL unit and before the last VCL NAL unit.

20. The device of claim 18, further comprising:', 'means for decoding a first video coding layer (VCL) network abstraction layer (NAL) unit in decoding order in the access unit; and', 'means for decoding a last VCL NAL unit in decoding order in the access unit, wherein the means for coding the SEl message comprises means for decoding the SEl message prior to decoding the first VCL NAL unit, and', 'wherein the means for coding the copy of the SEl message comprises means for decoding the copy of the SEl message after decoding the first VCL NAL unit and prior to decoding the last VCL NAL unit.']