[FFmpeg-devel] [RFC] General design for subtitles demuxers
nicolas.george at normalesup.org
Wed Jun 13 08:53:27 CEST 2012
Le sextidi 26 prairial, an CCXX, Clément Bœsch a écrit :
> Yet another subtitles thread, addressing this time several issues in a row.
> All the text subtitles formats are small files where it is interesting to
> consider them as such, and not as a stream. In practice I propose the
> 1) Parse the whole file
> Just like lavf/assdec or lavf/jacosubdec, the whole file should be parsed on
> the read_header() callback.
> Why is it done like this? Because in "format" oriented ("ASS"), the events
> can be in any order, require looking ahead, or preprocessing the file; when
> they are muxed ("SSA") the timeline must makes sense, and it doesn't matter
> since this demuxing belongs to the video demuxer.
> JACOsub also has that issue, but SubRip as well (remember the event
> numbers?), and actually all the others (see below).
> 2) Set missing durations
> Since we now have the complete list of events in a list, it's easy to work
> on them, and we can just set the packets duration when missing that
> information: this actually solves in a very simple way the
> last-to-next-subtitle feature I mentioned several times.
> 3) Sort the events
> We should then export the sorting of all these subtitles (PTS based) raw
Until now, I agree at 100%.
> events from lavf/assdec.c.
This part I am not sure I understand. Do you mean that the demuxer is
supposed to translate into ASS?
> We should take out read_seek2() from lavf/assdec.
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