| JCTVC-O0095 AHG9: Skipped slice signaling [Y. He, Y. Ye, X. Xiu, Y. He (InterDigital)]
This contribution proposes syntax elements and decoding process to define enhancement layer skipped picture or skipped slice. This contribution is a follow-up of JCTVC-N0209.
Also discusses skipped pictures as well as skipped slices. The discussion focused on whole-picture operation due to the general concern expressed above (about contributions in the category of partial-picture operations currently expressed only in low-level syntax for version 1).
Proposes to enable a "skipped picture" in an enhancement layer when a direct reference layer is available.
A skipped picture is proposed to be generated by copying the (possibly upsampled) default inter-layer reference picture. It was suggested to use picture-level signalling of the dependent layer (proposed in O0265) rather than depending on default operation. Another suggestion was to use the first picture in the default reference picture list.
The contribution indicates the use case to be for encoder complexity mitigation for a "cpu-starved" condition, or for a "middle box" operation. A participant remarked that generating equivalent low-level syntax should not be difficult for the cpu-starved case. Such a case is further discussed in O0199.
It was remarked that in the middle box case, unless this is accomplishing something important that would not be accomplished by simply removing an EL picture from the bitstream, it may not be needed. The flag for indicating output of a lower layer when a target EL is not available may provide equivalent capability. Further study should be conducted to determine whether the proposed feature is needed.
It was also remarked that if the picture that is dropped is a reference picture, this envisioned dropping in a middle box could cause problems, in terms of that picture being later used as a collocated reference picture or as a reference for texture prediction.
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