[FFmpeg-devel] [RFC] handling of subtitles

Michael Niedermayer michaelni
Sun Apr 6 20:14:58 CEST 2008

On Sun, Apr 06, 2008 at 12:02:15AM +0200, Benjamin Larsson wrote:
> Hi, the XBMC project is thinking of running a GSoC task of creating a
> unified subtitle handling lib:
> http://xbmc.org/wiki/?title=GSoC_-_Unified_Subtitle_Parser
> While the wiki page might not make sense, what support has FFmpeg for
> text subtitles and if there is none how should it be implemented ?

Well the first part is demuxing, dvb/dvd/text/ass/ssa/xsub and possibly others
are supported already. Adding more should be trivial matter of adding the
entries in the codec_tag/codec_id tables ...

Second is decoding, here the subtitle packets are converted into a common
and easy to digest format (AVSubtitle) we currently only have dvb
dvd ad xsub decoders. Adding text/ass/ssa/... will require AVSubtitle to
be extended to support text (with all the bells and whistles these formats
allow) in addition to bitmaps.

Third is rendering, the code in ffplay (which should be moved to avfilter)
supports what AVSubtitle supports currently.

Encoders which turn bitmap based AVSubtitles into their native format exist
for dvb and dvd subs.

No new library or other large scale redesign seem to be needed.

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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