[Ffmpeg-devel] AAC bitrate

Luca Abeni lucabe72
Tue Feb 7 10:02:33 CET 2006


On Mon, 2006-02-06 at 13:04 -0500, Media Streaming Services wrote:
> Hi All,
> got a small problem here, I've compiled
> ffmpeg version CVS, build 3276800, Copyright (c) 2000-2004 Fabrice Bellard
>  configuration:  --enable-amr_nb --enable-amr_wb --enable-faac
> --enable-faad --enable-xvid --enable-mp3lame --enable-gpl
> --enable-pthreads --disable-ffserver --disable-ffplay --enable-libogg
> --enable-vorbis --enable-pp --enable-shared
It looks like it is not the most recent CVS... Is it?

> used faac and faad as you can see, unfortunately, I can't produce AAC
> audio files (mp4 and 3gp) at ***8 kbit bitrate*** (which supposed to be the
> lowest setting for AAC- 1 channel/8000 Hz).
> The lowest ffmpeg was able to produce is 12.6 kbps AAC encoded file.
> ./ffmpeg -i 1.wav -acodec aac -ac 1 -ar 8000 -ab 8 -vol 150 test1.3gp
I just tried, and it seems to be producing audio at the correct bitrate.
Some time ago, I submitted a patch to set the cutoff frequency in faac.
The patch was committed in ffmpeg CVS on Tue Jan 10... Check if your
version of ffmpeg contains that change.

If it does and you are still not able to get the proper audio bitrate,
try to play with the cutoff frequency (-cutoff option of ffmpeg).

Anyway, are you sure that the bitrate of the audio produced by ffmpeg is
really 12.6kbps? (just checking... Be sure that you do not see a 4.6kbps
contained overhead ;-)

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