Audio Ease - BarbaBatch - Supported Filetypes - mp3 (LAME)
MP3 files can be read by BarbaBatch without the presence of the LAME codec, however, if you want to produce MP3 files, you need to install the (FREE) third party encoder called LAME. LAME is known for high quality mp3 conversion, but mediocre quality samplerate conversion. That's why BarbaBatch handles any samplerate conversions involved prior to encoding.
Obtaining and installing the LAME mp3 Codec:
You should download and install the LAME codec from here
When you launch BarbaBatch after that, the mp3 item will no longer be greyed out in the file popup menu.