[FFmpeg-devel] [PATCH v2] lavc/vvc: Error if SPS ID is duplicated within CVS

[Anton Khirnov]

Quoting Frank Plowman (2024-04-06 15:46:09)
> Key line from the spec is:
> 
> "All SPS NAL units with a particular value of sps_seq_parameter_set_id
> in a CVS shall have the same content."
> 
> Prior to this patch, the VVC decoder's behaviour on encountering a
> duplicated SPS ID (within the entire bitstream, not restricted to
> a CVS) was simply to replace the entry in the SPS lookup table with the
> new data.  Illegal bitstreams with multiple SPSs in the same CVS sharing
> an ID but differing elsewhere could cause all manner of issues.
> 
> The patch tracks which SPS IDs have been used in the given CVS using the
> new sps_id_used field of VVCParamSets.  If it encounters an SPS with an
> ID already in use and whose content differs from the previous SPS, it
> throws an AVERROR_INVALIDDATA.

I wonder if it wouldn't be better to do what H264/HEVC do, which is
replace the SPS, invalidate the PPSes that depend on the old one, and
start a new CVS.

-- 
Anton Khirnov