Batch script for audio encoding. Supports MP3, AAC, Vorbis, Opus,
FLAC, AC3 and WAV output and is intended to be used on directories
with audio files. Filtering through MPlayer and automatic tagging with
MediaInfo is also supported.

Optional requirements:
faac, or fdkaac and libfdk-aac (for AAC)
lame, or twolame (for MP3)
opencore-amr (for AMR)
aften (for AC3)
opus
dcaenc (for dts, note: this is a legal quagmire)

All of these are available from SlackBuilds.org.  This script still functions
without them, but you will be limited to Vorbis, FLAC, and WAV.

http://audenc.sourceforge.net/