The Nautilus-Sound-Converter extension allows you to convert audio files to different formats using the GStreamer framework.
If you don't want to use the source directory as the default output destination, run the following: gconftool-2 --set /apps/nautilus-sound-converter/source_dir --type bool false
Please report bugs to: http://code.google.com/p/nautilus-sound-converter/issues/list
n-s-c can be check out with the following command: svn checkout http://nautilus-sound-converter.googlecode.com/svn/trunk/ nautilus-sound-converter
Patches welcomed!