JVET-Q0246 [AHG9]: On virtual boundary signalling [S. Paluri, Hendry (LGE)]
This contribution was discussed Sunday 12 January at 1445 in Track A (chaired by GJS).
In the current design, if the virtual boundary information is not needed, there are two flags (i.e., sps_virtual_boundaries_present_flag and ph_virtual_boundaries_present_flag) still need to be signalled. Particularly, the signalling of ph_virtual_boundaries_present_flag still need to be present in every picture header even when no virtual boundary is needed. It is asserted that this redundant and unnecessary signalling should be fixed.
This contribution proposes a flag (i.e., sps_virtual_boundaries_disabled_flag) in the SPS to specify whether loop filters may be disabled along virtual boundaries in the coded pictures within the CLVS. When this flag is equal to 1, virtual boundary signalling may be present in either SPS or PH, but not in both.
This is the same as what is proposed in JVET-Q0258 (except there it uses an enable flag rather than a disable flag).
It was commented that, aside from more efficient signalling, this would provide a high-level indication when virtual boundaries will not be used anywhere in the CLVS.
Decision (cleanup): Adopt as an enable flag. Text to be provided in JVET-Q0246-v3.