[Ffmpeg-devel] -ab 128 doesn't work with aac encoding?

[Justin Ruggles]

Patrice Bensoussan wrote:
> Does it mean that the -ab option is just ignored when encoding in AAC?
> or is it used to give the max value which should be used during  
> encoding?

The value is passed to libfaac to do the encoding.  One of the reasons
the bitrate isn't very accurate is that the quality setting in FAAC
defaults to 100 in ABR mode.  If you desire a bitrate too low or high
for the default quality, it just gets as close as it can.  If you really
want to make the bitrate higher, you can use the -aq option instead and
do some trial & error.  It will fluctuate much more than ABR though.

-Justin