mp3fs is a read-only FUSE filesystem which transcodes between
audio formats (currently FLAC to MP3) on the fly when files
are opened and read.

It can let you use a FLAC collection with software and/or
hardware which only understands the MP3 format, or transcode
files through simple drag-and-drop in a file browser.

Usage:

Mount your music like so (for example)
mp3fs -b 192 /mnt/music /mnt/mp3 -o allow_other,ro

or use the following entry in /etc/fstab:
/mnt/music /mnt/mp3 fuse allow_other,ro,bitrate=192 0 0