[FFmpeg-devel] [RFC] Format of packets for text subtitles

Michael Niedermayer michaelni at gmx.at
Fri Jun 8 00:00:10 CEST 2012

On Thu, Jun 07, 2012 at 10:48:14PM +0200, Nicolas George wrote:
> Le decadi 20 prairial, an CCXX, Clément Bœsch a écrit :
> > You might want to look at
> > http://gpac.wp.mines-telecom.fr/mp4box/ttxt-format-documentation/ though
> > (MP4 related).
> Unless I am mistaken, it does not explain the format of the packets inside
> the ISOM structure. That would be the interesting point.
> > About timing, the DTS is also generally set; maybe it can be useful for
> > reordering subtitles?
> Actually, I do not understand the point of DTS at all, but I would be
> interested by explanations.
> > Note: what to do about unrelated information such as comments? JACOSub for
> > instance can be filled with random comments all over the file. ATM I'm
> > dropping them (because it's a pain to handle). Should we "standardize"
> > the way of handling this?
> That could go in side_data, maybe?
> > > All subtitle packets are flagged as keyframes.
> > Demuxers must do it? In what case wouldn't you put them?
> I guess: a demuxer for a generic format takes the flag from the container,
> and we hope the file has the flag set; a demuxer for a specialized format
> sets it.
> > Should we make an "input subtitle encoding" option available for all
> > subtitles format at a lavf top level? (available in with CONFIG_ICONV)
> I am not sure whether that belongs at the top level or on a per-demuxer
> basis. What format do you know, apart from MKV, MP4 and OGM, that can hold
> text subtitles?

it should be possible to store anything in NUT, so also text subtitles
though iam not sure if such files exist, if not this would also give
us some freedom on how to exactly implement it for NUT


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

If a bugfix only changes things apparently unrelated to the bug with no
further explanation, that is a good sign that the bugfix is wrong.
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