FFMGPEG is available for Windows, is able to support variable bit rate and works really well for audio as well as video.
On a single file:
ffmpeg -i yourfilename.m4a -codec:v copy -codec:a libmp3lame -q:a 2 yourfilename.mp3
For batch conversion, with windows command line extensions:
SETLOCAL ENABLEEXTENSIONS
FOR I IN (*.m4a) DO ffmpeg -i %I -codec:v copy -codec:a libmp3lame -q:a 2 %~dpnI.mp3
If you wish to specify an output directory rather than putting files where the originals were you can replace %~dpn.mp3
with \path\to\ouput\dir\%~n.mp3
where \path\to\ouput\dir\
must be an existing directory.
Of course you can do a lot more with FFMPEG such as converting video formats, cutting and splicing video, extracting or adding soundtracks.
- Price: Gratis
- Open Source
- Cross Platform available for Windows, OS-X & Linux