JVET-AP0137 AHG9: On payload sizes for versatile SEI messages [M. Pettersson, M. Damghanian, S. Harribey, R. Sjöberg (Ericsson)]
This contribution proposes updates to the signalling and inference of the payload size of the versatile SEI message in the TuC for future extension of VSEI. Two independent proposals are suggested where the first proposal is an asserted bug fix for inferring the payload size when it is not present and the second proposal proposes an updated extendable signalling of the payload size. The following is proposed:
- When the payload size for an SEI message is not present, infer the payload size to be equal to NumBytesInNalUnit − 3 − vseiPayloadType/256, instead of inferring it to be equal to NumBytesInNalUnit − 4 as in the TuC.
Chaired by S. Deshpande on 25 April 2026 from 9:15-9:95 CEST
This was discussed together with item 1 of JVET-AP0069. It was asked if the division should be by 255 instead of 256.
It was also commented that we should not assume 2 byte NAL unit header which this contribution does. JVET-AP0069 is more general about the NAL unit header size.
- Signal the payload size with an extendable number of bytes for each SEI message. Two alternatives are proposed:
- Replace vsei_payload_size with two new syntax elements vsei_payload_7bits and vsei_payload_extension_flag and derive vseiPayloadSize according to:
vseiPayloadSize = 0 | |
do { | |
vsei_payload_7bits | u(7) |
vseiPayloadSize = (vseiPayloadSize << 7) + vsei_payload_7bits | |
vsei_payload_extension_flag | u(1) |
} while (vsei_payload_extension_flag) |
- Signal the vsei_payload_size using a new eu(n) descriptor exercising the method of alternative A. The solutions in alternatives A and B are asserted to produce bit exact output. The proponents claim that the eu(n) descriptor may be beneficial for other syntax elements of the codec with large values.
Both alternatives also propose to replace the vsei_payload_size_byte syntax element with a vsei_payload_size_flag syntax element, that specifies whether syntax elements for the payload size are present or not.
It is asserted by the proponents that the extendable signalling provides a more flexible and future proof solution for signalling the payload size for individual SEI messages.
It is proposed to update the solution in the TuC for future extension of VSEI with the two proposals.
Proposal 2 chaired by J. Boyce.
Proposes extendable syntax for payload size.
The proposed syntax saves 3 bytes for large SEI message. It was suggested that it adds a byte for some other SEI message lengths. No action was taken on proposal 2.