Hi, I have this problem with version 2.0.6 in win7, when I make export in AAC with standard M4A(AAC) Files (FFmpeg) of Audacity with the installer or the portable version: any bitrates I force, the audio of output is always 192 Kbps, analyzed with software as MediaInfo and others. I have download audacity and ffmpeg-win-2.2.2 from your site. I have tried in another pc with the same result. The only way to vary the bitrate of output with AAC is the Custom FFmpeg Export.
This is a known problem and is noted in the Audacity 2.0.6 release notes:
M4A (AAC) exports: The Quality Slider in “Specify AAC Options” has no effect if the FFmpeg library is built with the libvo-aac encoder, as are recommended builds of FFmpeg for Windows and Mac OS X. Workaround: …[snip]… export as WAV and convert to AAC in iTunes on Windows and Mac.
Ok thanks, I didn’t read that, then I will use Custom FFmpeg Export.