[FFmpeg-devel] [PATCH] attachments support in matroska demuxer

[Aurelien Jacobs]

Evgeniy Stepanov wrote:

> On Thursday 03 January 2008 04:23:09 Michael Niedermayer wrote:
> > On Thu, Jan 03, 2008 at 01:38:39AM +0100, Aurelien Jacobs wrote:
> > > On Sat, 29 Dec 2007 22:38:24 +0300
> > > Evgeniy Stepanov <eugeni.stepanov at gmail.com> wrote:
> >
> > [...]
> >
> > > Conclusions:
> > > - Attachment really looks like a stream itself. You can select
> > >   the one you want to remux. For example the film poster would
> > >   just be a jpeg stream with a single picture. The specificity
> > >   of those streams would be:
> > >
> > >     * contain one single packet
> > >     * not pts
> >
> > Contain no packets, just one global extradata, this was proposed
> > already. If you use normal packets there will be problems with them
> > disapearing if a stream is split timewise or if you seek before
> > demuxing the first packet.
> > Iam not completely happy with this use of streams but we will need
> > some solution and maybe its the least ugly, we will see ...
> >
> > at least iam pretty sure extradata to be a better choice than 1
> > normal packet
> >
> > >     * has a filename (important so that an ASS decoder can
> > >       select the proper ttf based on it's name)
> > >
> > >     * always demuxed before other (normal) streams (IIRC)
> >
> > extradata should be available before packets ...
> >
> > >   It seems to me that attachment would fit pretty well, each one
> > >   in its own AVStream. Does this sound reasonable ?
> > > - Here is how remuxing to other formats (avi, mov...) could work:
> > >     * supported codec (jpeg poster) could be muxed as a normal
> > >       JPEG stream with only one picture
> > >     * ttf streams should be written in a separate file (that's
> > >       the way various players expect to find ttf fonts when
> > >       demuxing AVI, IIRC)
> > >
> > > - I think the only required API modifications to support this
> > >   would be:
> > >     * adding AVStream.filename and maybe
> > > AVStream.id_of_link_stream.
> > >     * adding CODEC_ID_TTF ? (ugly, but shouldn't cause much
> > > trouble)
> > >     * adding a way to mux ttf font in a separate file (maybe use
> > >       a separate muxer for this, ie. call 2 different muxers from
> > >       ffmpeg. seems ugly, but I've no better idea right now).
> >
> > Well, there are a few more things i think
> > We need name / (mime) type to remux attachments
> > (CD Cover / ? / tiff)
> > (Fan art / image/x-photoshop / psd)
> > There also could be other things like Author, ...
> >
> > Also we need a way to get the attachments to the decoders, yes we
> > dont have a ASS/SSA decoder but lets assume we had.
> >
> > And while we can just store the streams in avi/mov, where does the
> > filename/name/type go? if its dropped you could end up with a huge
> > number of images and not know what each is.
> >
> > > What do you think about this proposal ? Does it sounds like a
> > > reasonable base ?
> > >
> > > If it's not, the only viable alternative seems to be
> > > AVFormatContext.attachments just like in the original patch,
> > > but with some additionnal code to allow "remuxing", etc...
> >
> > yes, these seem to be the 2 options we have
> 
> This patch implements attachments as separate streams with extradata.

OK. Here are things issues in this patch:
 - CODEC_TYPE_NB must stay at the end of the enum.
 - Adding attachments to AVFormatContext is probably a leftover from
   your previous patch.
 - I don't like the fake MATROSKA_TRACK_TYPE_ATTACHMENT and everything
   depending on it.
 - I don't think CODEC_ID_ATTACHMENT is of any use if it's used for
   every kind of attachement. CODEC_TYPE_ATTACHMENT already gives the
   same information.

I fixed all those issues in the attached patch.

Moreover, I tried to associate a specific CODEC_ID_* to different kind
of attachements. To me, this seems like a good idea, but I would like
to know what others think about it ?

Aurel
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