Automatically convert audio files in a certain folder
MP3FS is a FUSE filesystem for converting FLAC into MP3.
mkdir /path/to/mp3s
mp3fs /path/to/flacs,128 /path/to/mp3s
After running that command, for every .flac file under /path/to/flacs, there will be a corresponding .mp3 under /path/to/mp3s.
Performance note: the conversion is performed when you read the file, not when you drop the .flac file into place.
This requires an operating system that supports FUSE. That includes most unix variants, including Linux and Mac OS X, but not Windows.