Dear David,
I don’t know of anyrthing particular Rubyish,
but otherwise, there is Sox (Sound exchange), which has a
Windows binary and tar files you could compile under
Mingw or Cygwin, if you like
_SoX - Sound eXchange | HomePage (http://sox.sourceforge.net/)
You can use it as a command-line tool, there are
some descriptions for conversions between
flac and mp3 and other formats here:
O'Reilly Media - Technology and Business Training.
html
(http://www.oreillynet.com/onlamp/blog/2004/11/convert_audio_between_mp3_flac.html)
Best regards,
Axel