[FFmpeg-devel] [PATCH 13/18] h264_sei: parse the picture timing SEIs correctly

[Anton Khirnov]

Quoting Kieran Kunhya (2020-03-22 05:24:35)
> On Fri, 13 Mar 2020 at 10:32, Anton Khirnov <anton at khirnov.net> wrote:
> 
> > Those SEIs refer to the currently active SPS. However, since the SEI
> > NALUs precede the coded picture data in the bitstream, the active SPS is
> > in general not known when we are decoding the SEI.
> >
> 
> The spec disagrees with this statement (7.4.1.2.1 Order of sequence and
> picture parameter set RBSPs and their activation). There are reasonably
> clear rules about SPS activation.
> (Whether real world bitstreams comply is a different issue of course).

I don't think you read that section carefully enough. What it says (in
my interpretation) is that an SPS can be activated only by:
- buffering period SEI
- a PPS (which is itself activated by picture data)
Picture timing SEI is neither of those.

Also see D.2.2 Note 1, which suggests exactly what I'm doing with this
patch.

-- 
Anton Khirnov