[FFmpeg-devel] [RFC] Talk about subtitles

Michael Niedermayer michaelni at gmx.at
Sat Dec 17 23:43:03 CET 2011

On Sat, Dec 17, 2011 at 11:34:56PM +0100, Clément Bœsch wrote:
> On Tue, Nov 22, 2011 at 07:56:41PM +0100, Clément Bœsch wrote:
> > Hi everyone,
> > 
> > [TL;DR: I want to improve/rewrite a real subtitles support in FFmpeg and need
> > some hints.]
> > 
> [...]
> Here is some news about the current state. To be honest I didn't produce
> anything usable as a PoC yet, but I expected a few issues we need to
> solve.
> First, writing the smovie source filter means adding the subtitles in the
> filterchain. Since the AVFrame is not in lavfi, maybe AVSubtitle hasn't
> its place either.
> Another related issue is what needs to be part of AVFilterBuffer and what
> needs to be part of AVFilterBufferRef. I started with a AVSubtitle in
> AVFilterBuffer, but I guess it won't be enough at some point.
> Now the real blocking thing ATM seems to be the (apparent?) inability of
> the filters to deal with different types between in & out: whatever
> solution we will select with filters will lead to a filter which needs to
> make the link between the subtitles and the video output. This is exactly
> the same issue as the visualizations: audio input & video output. Maybe a
> first simple step will be to update the API so this kind of thing work.
> I tried to write some kind of video source filter, but added an audio
> input; the filtergraph seems to deal fine with it ATM (-f lavfi
> amovie=a.mp3,visualization) and just outputs video, but of course the
> filter_samples() callback of the audio input is never called; so it's
> actually pretty useless. I'm not sure the current state of the API could
> deal with such issue; I'm trying right now to manually request some audio
> directly in the video request_frame() callback...
> Anyway, this is just a feedback on the current situation; any hint, advise
> or other kind of help welcome ;)

iam not sure request_frame() is fully implemented for the audio filter
framework. (if not this has to be fixed at some point quite independant
of subtitles)


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If you think the mosad wants you dead since a long time then you are either
wrong or dead since a long time.
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