[FFmpeg-devel] DVD subtitles

Aurelien Jacobs aurel
Fri Feb 29 14:27:06 CET 2008

Wolfram Gloger wrote:

> > From: Vitor Sessak <vitor1001 at gmail.com>
> >
> > Erik Slagter wrote:
> > > Ehmmm, afaik subtitles are pixel-format internally in libav*. If
> > > not, there would really be a problem using DVD subtitles.
> > 
> > Are you sure? I'd say it is more as a codec as any other, but not a 
> > pixel format... Anyway, I have never touched the subtitle code, so
> > maybe you know better...
> Yes, subtitles are definitely stored as pixels in AVSubtitle, so a
> "capitalization" filter would be really hard.  I believe AVSubtitle
> was designed closely modelling DVB subtitles.

That's true regarding AVSubtitle.
On the other hand, not all subtitle streams are using AVSubtitle.
In fact subtitle streams (the one which have CODEC_TYPE_SUBTITLE)
are stored in native format. So this means they are stored as a
kind of bitmap picture for DVD subtitles, but they can be stored
as raw utf-8 text or ASS formated text in matroska for example.

So, this is definitely possible (and easy) to create a subtitle
uppercasing filter for those kind of text subtitles.


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