Freeware Advanced Audio Coder
Freeware Advanced Audio Coder (FAAC) is a compression software that can create AAC audio files from other formats, especially WAV.
AAC is the most common file played on iPods.
FAAC was originally free and open source but now appears to contain code from in its ISO MPEG reference code, meaning it can no longer be distributed as free software.
The audio coder is for Linux/Unix users and is the main alternative to neroAACenc.
FAAC features "reasonably" fast encoding as well as support for AAC-LC and AAC-LTP.