MP3FS is a read-only FUSE filesystem which transcodes audio formats (currently FLAC) to MP3 on the fly when opened and read.
Now, why would you want to do that?
Well, for one there are not a lot of FLAC capable media players out there. You therefore have to transcode these into mp3 – a rather laborious process, which makes you end up with two (almost) identical sounding files. This messes up my media library as well.
The way you use this program is by mounting a directory containing your flac files (and other files) ontop of another directory. Say I have a directory called «Music». I then create a directory called flac2mp3, which is where I will access my pseudo-mp3s, and mount the first on top of the last using mp3fs. To wrap this into a script, use this code:
mp3fs $FLACDIR,192 $MP3FSDIR -o allow_other,ro
In case you use the newest Ubuntu 8.04, called Hardy Heron, you can use this package I build myself. You will additionally use some other libraries, such as libid3. Test out and report me any errors.
edit: I have compiled three versions. Give feedback if they work or not!