JCTVC-J0456 AHG9: Mental cross-check of JCTVC-J0038 [Y.-K. Wang (Qualcomm)] [late]
JCTVC-J0064 SEI messages for gradual decoding refresh [H. Aoki, K. Chono (NEC)]
(Reviewed in Track A.)
This contribution relates to very-low-delay operation, and presents a scheme for reducing initial delay for picture output in gradual decoding refresh. In the proposal, information on displayable areas for each picture during gradual decoding refresh is embedded into the associated access unit in the form of SEI messages. Three possible sets of SEI messages to realize the scheme are also presented in this contribution. The proposed scheme enhances usability of low-delay video transmission supported by the sub-picture-based CPB operation, without any normative changes to decoders.
This was basically proposing a rectangular-sub-region recovery point SEI message capability, with the ability to send multiple recovery delays and rectangular region indicators within the same SEI message.
The proposal was to send the region-specific message after send an ordinary recovery point SEI message to indicate when a region has (already) been recovered. This aspect was questioned – it was suggested to define a message to be sent at the location of the start of the recovery process rather than upon its completion.
It was remarked that the POC difference should be signed rather than unsigned (as with the ordinary recovery point SEI message).
It was also suggested to send an SEI message at the start of the recovery process rather than at the end of it, and to move the POC difference inside the loop so that different regions would be indicated as being recovered with different POC values.
The possibility of signalling a region growth process was also discussed.
It was noted that something somewhat similar was done in AVC with slice group-based signalling.
It was suggested that this did not necessarily need to be defined in the first version of the standard.
Further study was encouraged.
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