[FFmpeg-devel] MP4A-LATM support?

[Paul Kendall]

> On Wed, Nov 11, 2009 at 8:54 AM, Luca Abeni <lucabe72 at email.it> wrote:
> > Hi all,
> >
> > a patch was recently posted to implement support for MP4A-LATM in RTP.
> > I am currently working on that patch, and I am trying to understand
> > what's the better way to implement such functionality...
> >
> > In order to avoid duplicate work and to prepare a patch that is not
> > consistent with the rest of ffmpeg, I have some questions about
> > MP4A-LATM:
> > 1) It seems to me that libavformat and libavcodec do not currently
> >   support it... Is anyone working on LATM support?
>
> Some guy was working on LATM demux in the past but we haven't heard
> from him in a while. Still, he sent some code to ffmpeg-devel that you
> might be able to salvage.
That was me.

>
> > 2) Does anyone know where can I find some freely available information
> >   about LATM?
>
> No way, by making the standards cost money, they can justify delaying
> publication to give MPEG members a huge leg up implementing these
> standards.
>
> > 3) The submitted patch rework the RTP muxer to accept "regular" AAC, and
> >   to add some LATM header to it before RTP packetisation. But I got the
> >   impression that maybe a bitstream filter can be a better idea...
> >   Can anyone with some experience with LATM comment on this? If LATM
> >   support for other formats will be implemented, how will it work?
> >   Through a bitstream filter, or directly in the muxer?
>
> In the past, the consensus has been bitstream filter.
I have implemented it as a bitstream filter already, but need the patch for
the auto filtering to be in before it will work. See link below.

http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/2009-March/065739.html

With the bitstream version you can only unwrap a single stream from the
LATM multiplex, but thats OK for most things such as DVB-T broadcasts.

There we then discussions about recursive formats so you could have all
the streams from LATM pulled out.

Cheers,
Paul