[FFmpeg-devel] yadif frame doubling - incorrect closed captioning
michael at niedermayer.cc
Mon Jan 14 19:45:12 EET 2019
On Mon, Jan 14, 2019 at 11:11:59AM -0500, Devin Heitmueller wrote:
> > > In short, a centralized function would be good, but we probably need
> > > to think through what the API looks like so we don't have to introduce
> > > a new API in libavutil and then deprecate it once we want to make the
> > > splitting/combining logic work according to the spec.
> > I fear that no matter how hard we try we will likely eventually run
> > into cases that it cannot handle
> Oh, I completely agree. Some captions are just going to be too
> screwed up to render. However I think there are cases we can recover
> from, and in particular I would like to make sure that streams created
> with versions of ffmpeg before this patch continue to play properly
> (i.e. where the stream only has caption data on every other frame and
> the cc_count is 2x what it is supposed to be).
> > also maybe 2 functions would keep this simpler
> > one to deal with temporal transformations (frame drop, duplicate, interpolate,
> > combine)
> > one to deal with spatial transformations, crop, pad, scale, rotate
> There shouldn't be any need for a function for spatial
> transformations. The expected cc_count is unrelated to the resolution
> of the video. It's tied exclusively to the framerate and whether you
> are doing frame or field-level encoding when the video is interlaced.
> The underlying goal was to ensure that the bitrate of the caption data
> is a constant 9600bps and thus they wanted it to be spread evenly
> across the frames/fields. When people encounter problems going from
> 1080i to 720p for example, it's because that also involves framerate
> conversion, not because the resolution of the individual video frames
> is being changed.
well, there are other types of side data too. for example motion
vectors would need to be updated on crop depending on which rectangle
is croped out
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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