[FFmpeg-devel] [RFC/PATCHES] AAC LATM decoder

Alex Converse alex.converse
Mon Oct 18 00:39:48 CEST 2010

On Sun, Oct 17, 2010 at 3:39 AM, Janne Grunau <janne-ffmpeg at jannau.net> wrote:
> Hi,
> I'm too annoyed by LATM in MPEG-TS to get the chained demuxers working.
> The last annoyance which triggered my capitulation was that multiple LATM
> frames are packed into a single PES packet.
> Based on one of Paul Kendall's libfaad LATM decoder patches I wrote a
> decoder using FFmpeg's AAC decoder.
> I know that it's technically unclean but it's vastly simpler and less
> annoying for the AAC LATM usage we see. All current digital TV
> transmission use only a single stream in LATM. I have even samples with
> multiple LATM elementary stream in MPEG-TS for a single program.

IIRC someone on IRC said that multiple stream LATM is becoming more
popular. Where is fftrollbot when we need him?

What do we want to do about LATM? Multiple people have made attempts
on it and we never seem to get anywhere. The realities of LATM don't
seem to align nicely with the assumption FFmpeg is currently designed

> One (currently theoretical) advantage of the decoder approach over the
> demuxer approach is that it could avoid the copying of the unaligned
> aac data by passing the GetBitContext to the AAC decoder.

What are the byte alignments inside the AAC bitstream in relation to
IIRC there was a COR about this.

> I've committed a version of this patch to MythTV's libavcodec copy. So
> we will see in the next days if it causes trouble or doesn't work with
> certain real life streams.

Thanks for the improvements that you have made to this patch.


Alex Converse

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