[FFmpeg-devel] [PATCH] libavcodec/videotoolbox: fix decoding of h264 streams with minor SPS changes

[Aman Gupta]

On Wed, Nov 15, 2017 at 1:57 PM, Hendrik Leppkes <h.leppkes at gmail.com>
wrote:

> On Wed, Nov 15, 2017 at 10:15 PM, Aman Gupta <ffmpeg at tmm1.net> wrote:
> > From: Aman Gupta <aman at tmm1.net>
> >
> > Previously the codec kept an entire copy of the SPS, and restarted the
> VT decoder
> > session whenever it changed. This fixed decoding errors in [1], as
> > described in 9519983c. On further inspection, that sample features an
> SPS change
> > from High/4.0 to High/3.2 while moving from one scene to another.
> >
> > Yesterday I received [2], which contains minor SPS changes where the
> > profile and level do not change. These occur frequently and are not
> associated with
> > scene changes. After 9519983c, the VT decoder session is recreated
> unnecessarily when
> > these are encountered causing visual glitches.
> >
> > This commit simplifies the state kept in the VTContext to include just
> the first three
> > bytes of the SPS, containing the profile and level details. This is
> populated initially
> > when the VT decoder session is created, and used to detect changes and
> force a restart.
> >
> > This means minor SPS changes are fed directly into the existing decoder,
> whereas
> > profile/level changes force the decoder session to be recreated with the
> new parameters.
> >
>
> The profile and level are not exactly the only things that can change
> to force a decoder to be re-created.
> How about the frame dimensions, within the same level?
>

If you know somewhere I can find such a sample, I can try it with
VideoToolbox to see if it requires the session to be recreated or not.

Aman


>
> - Hendrik
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