[FFmpeg-devel] MP4A-LATM support?

[Luca Abeni]

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
> MP4A-LATM:
[...]

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
    ID CODEC_ID_AAC)
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 :).


			Thanks,
				Luca