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

[Aurelien Jacobs]

On Thu, 17 Jan 2008 01:00:26 +0100
Aurelien Jacobs <aurel at gnuage.org> wrote:

> 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 ?

If there is no comment about this, I will apply this patch soon
(including the new CODEC_ID_TTF).

Aurel