[Ffmpeg-devel] FAAC rate control broken?

Michael Niedermayer michaelni
Wed Dec 21 13:47:36 CET 2005


On Wed, Dec 21, 2005 at 12:09:20PM +0100, Luca Abeni wrote:
> On Tue, 2005-12-20 at 16:49 +0100, Luca Abeni wrote:
> [...]
> > Reducing the faac_cfg->bandWidth value a lot (something like
> > avctx->sample_rate / 8) does work...
> > Any suggestion about a proper value for "bandWidth"?
> Ok, after some investigation it looks like the safest thing to do is to
> se "bandWidth" to 0 (leaving to libfaac the responsibility to decide a
> correct value).
> With the attached patch, ffmpeg is able to encode in AAC 64kbps stereo
> audio at 44100Hz...
> It cannot go under 60kbps because libfaac thinks that it is impossible
> to encode audio at 44100Hz at less than 29500bps per channel :(
> (libfaac contains a bitrate <--> bandwidth table that needs to be fixed,
> but this is another story... A possible workaround would be to include a
> similar table in libavcodec/faac.c and to set bandWidth to a proper
> value).
> Anyway, does the simples thing by leaving the "bandWidth" decision to
> libfaac... Can it be applied?

IMHO it would be better if the user could set bandWidth and the default
where 0 so that faac would select one



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