To convert all mp3 files in directory to a different bitrate, do the following. First, install "lame" if it is not already there.
sudo apt-get install lame
Then, give the following command:
for f in *.mp3 ; do lame --mp3input -b 32 "$f" "./outputdir/$f" ; done
Replace 32 with desired bitrate if you want something else. Note that this will result in some loss of sound quality but you might still have a good reason to do this, especially if you want to squeeze a little more audio on your mp3 player's memory card, which is the reason I looked into how to do this.
