JVET-W0055 AHG8: Signalling TSRC Rice parameter in slice header extension [T. Tsukuba, M. Ikeda, T. Suzuki (Sony)]
The slice header of VVC version 1 contains an extension field, called slice header extension, as a hook for the future extension; It makes it possible to signal new syntax elements to the slice header that are ignored by a version 1 decoder, but can be used by a decoder conforming to a future version. In the latest WD for VVC operation range extension, a Rice parameter index for transform-skip residual coding can be signalled in the slice header but not in the slice header extension. This contribution proposes to relocate it to the slice header extension. A patch for the proposed changes relative to VTM-13.0 is attached.
It is mentioned that this aspect had been discussed between editors earlier. It had been concluded that in the case of the flags added in operation range extensions it is not necessary to use the extension mechanism, as a v1 decoder should not be capable to decode bitstreams of a v2 profile. This depends on of whether the slice header extension is intended for non-backward-compatible extensions or only for backward compatibility.
Some participants thought that decoders should check the profile indicator and not attempt to decode the headers of bitstreams of profiles that it does not recognize. If that is the case, it does not necessarily matter whether a new syntax element is placed in the SH extension or directly into a profile-dependent part of the SH syntax structure. It was commented that both ways of extending the syntax would have about the same number of condition checks.
Further, the number of condition checks is exactly the same in the proposal as in the current syntax.
It could be done as proposed, but not necessary to take action.