Open a terminal and type:

ffmpeg -i [file.wma] -acodec libmp3lame -ab 128k [file.mp3]

file.wma: it is the file you want to convert.
-ab: audio bitrate in kbit/s. The default value is 64k.
-acodec: it sets the codec to be used. In this case mp3.
file.mp3: File name will be created.

For example:

ffmpeg -i music.wma -acodec libmp3lame -ab 128k music.mp3


sounds a little „damp“ (little treble) but ok 🙂 at least a fast and easy way 🙂

source / creditz: