[FFmpeg-devel] MP4A-LATM support?

Luca Abeni lucabe72
Fri Nov 13 12:33:40 CET 2009

Luca Abeni wrote:
> 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

Ok, thanks to everyone who replied and provided links and information.
After a little bit of reading, I think I now have an idea about this
LATM stuff. Of course, it can be wrong, so please correct me if I
misunderstood something. Anyway, this is my understanding of the situation:
1) LATM can be seen as a different bitstream syntax for AAC (I hope I
    am not oversimplifying anything, here... :)
2) codecs in libavcodec will see the "regular" AAC bitstream (with codec
3) muxers and demuxers in libavformat will see the LATM bitstream
4) someone between codec and muxer is in charge of transforming the
    bitstream in LATM (this can be a bitstream filter, I suppose)
5) how can the muxer know if the bitstream is "regular AAC" or LATM?
    I think we need a "fake" codec ID (CODEC_ID_LATM, or something like
    this) for identifying LATM streams. When the AAC stream is transformed
    in LATM (or vice-versa) by the bitstream filter, the codec ID is changed
    from CODEC_ID_AAC to CODEC_ID_LATM (or vice-versa).

Is this correct/reasonable? I am starting to work on the RTP muxer assuming
that some filter provides it with the LATM stream (and a LATM codec ID),
which simplifies things a lot :).


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