Convert all mp3’s in a directory to lower bitrate with LAME:
for f in *.mp3; do lame --mp3input -b 128 "$f" "$f".n ; rm "$f" ; mv "$f".n "$f" ; done
Edit the 128 to your prefered bitrate. I use this to get more music onto a portable media. Don’t use it to store your mp3’s, it will lower the audio quality.