JVET-AG0334 AHG12: Fix for coding at high QPs [K. Andersson, C. Hollmann (Ericsson)] [late]

It was discovered that ECM-11.0 cannot encode in low-delay configuration for QP equal to 55 or higher. The reason is that for high QP the lambda as part of ARMC can exceed 10 bits but the lambda is encoded with at most 10 bits.

One solution is to set the lambda for the highest QP to 1023 instead of 1125.369910 which then would fit the current encoding of the lambda with at most 10 bits.

One alternative solution is to increase the number of bits for encoding lambda to 11 bits.

It is proposed to include one of the proposed fixes to enable encoding at high QP with ECM.

It was confirmed by the original proponents of the lambda syntax element that there is a problem. They suggest that the second solution (increasing from 10 to 11 bits) would be preferable.

In CTC, this does not have any impact, and only low delay B at high QP would be affected.

The problem was detected when investigations were made in the context of AHG8 with high QP encoding.

It was commented that the second solution might increase the bit rate, whereas the first solution might just be an encoder bug fix, clipping the value to the highest allowed.

Decision (SW/BF): Adopt JVET-AG0334 first solution.

High-level syntax (HLS) and related proposals (46)

AHG9: SEI messages on NNPF aspects other than grouping (2)

Contributions in this area were discussed at 0730–0920 on Thursday 18 Jan. 2024 (chaired by JRO).