Quoting Andreas Rheinhardt (2020-03-23 23:08:14) > Anton Khirnov: > > Quoting James Almer (2020-03-18 17:05:38) > >> On 3/13/2020 7:28 AM, Anton Khirnov wrote: > >>> It represents the relationship between them more naturally and will be > >>> useful in the following commits. > >>> > >>> Allows significantly more frames in fate-h264-attachment-631 to be > >>> decoded. > >> > >> That sample is odd. It has an SPS/PPS pair in extradata that's wrong for > >> the Buffering Period and Picture Timing SEI messages in-band, but > >> seemingly correct to actually decode all these frames revealed by this > >> patch. > >> The SPS that makes the aforementioned SEI messages parseable, but the > >> frames seemingly undecodeable, is in-band in the second RAP (Which fwiw > >> reports a different bitstream level). So this patch prevents the > >> extradata PPS from using the in-band SPS after it replaced the extradata > >> one in sps_list. There's no PPS in-band. > >> > >> Is this really intended? Is the active PPS' sps_id meant to reference > >> the SPS with that id that's currently "valid" and in sps_list, or the > >> whichever one was valid at the time the PPS was first parsed?. If the > >> latter, then why replace the SPS in-band but never the PPS? > >> The in-band SPS is virtually unused after this change. > > > > My guess would be that someone (or some/thing/, dun dun dun) did some > > botched/misunderstood processing on that sample, so trying to figure out > > what was intended is futile. > > > > According to the spec, SPS contents must not change within a sequence > > (they can change on sequence boundaries), so this sample is invalid. > > While this sample is invalid, isn't it possible to have a sample as > follows: First a SPS and a PPS referencing the SPS, then a coded video > sequence for which these SPS and PPS are active, then another IDR access > unit with a new SPS that overwrites the old one, but with no new PPS. > This is valid if I am not mistaken. With your patch, the second SPS > would never be used.
Hmm, this sounds pretty crazy, but I don't see anything in the spec forbidding this. But then again, we currently parse the PPS using values from the SPS. If the SPS changed, we'd have to re-parse the PPS again using new values. Since we are not doing that, we do not support this use case anyway. -- Anton Khirnov _______________________________________________ ffmpeg-devel mailing list ffmpeg-devel@ffmpeg.org https://ffmpeg.org/mailman/listinfo/ffmpeg-devel To unsubscribe, visit link above, or email ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
