JVET-AM0206 AHG9: On signalling of sei payload type in SEI processing order SEI message [H. Tan, C. Kim, J. Nam, J. Lee, J. Lim, S. Kim (LGE)]

In the current design of SEI processing order (SPO) SEI message, payload type of SEI messages included in the processing chain is signalled using fixed length coding, that is, u(12). It is asserted that while it is currently enough to cover existing SEI messages included in VSEI and SEI messages that are included in the codecs that may use VSEI (e.g., AVC, HEVC, and VVC), it is asserted that the signalling design may not be future proof considering the number of bits for signalling payload type is not fixed in the codecs that currently may use VSEI and in the future codecs that may use the VSEI.

This contribution proposes to modify the signalling of payload type in SPO as follows:

Option 1: Modify the signalling of payload type of SEI included in SPO SEI message by using ue(v) and move it to the last syntax element in the for loop.

Option 2: Do the following modifications:

• Modify the signalling of payload type of SEI included in SPO SEI message from u(12) to u(11) and use the extra bit as a new flag to specify whether or not additional value to supplement the value of payload type.
• The flag is constrained to be equal to 0 for VSEI version 4.

It was noted that the number of SEI payload types allocated so far is less than 256, but more than 200.

It was suggested that 12 bits is sufficient for future generation codecs.

No action.