JVET-P1018 Non-CE8: An alternative IBC virtual buffer setting to avoid reference sample wrapping around [J. Xu, L. Zhang, W. Zhu, K. Zhang, H. Liu (Bytedance Inc), X. Xu, X. Li, S. Liu (Tencent)] [late]
This proposal presents an IBC virtual buffer setting to avoid sample-wise IBC reference wrapping around. It is asserted that there is no performance change compared to VTM-6.0 encoder.
Unlike the original proposal JVET-P0454, this solution does not have an impact on performance. By re-defining the virtual buffer as 2 CTU (but requiring only 1 CTU physical memory) and just disabling the case of “physical wraparound” (whereas wraparound within the virtual buffer is still possible), the problem is solved.
It is also pointed out that this matches with the BV restrictions of the VTM5 encoder (which explains that there is no performance change).
Decision: Adopt JVET-P1018. Requires also software change of decoder, whereas encoder does not need a change.
It is also noted that in terms of conformance testing, a different encoder would be needed that all possible BV range of the virtual buffer restriction.