OT: mp3 -> ac3 -> SP/DIF output?

[Tom Horsley]

I've seen talk of an alsa ffmpeg plugin that can convert
simple stero sound to an ac3 stream for output to a
sound system via SP/DIF output of a soundcard. (But I get
the impression I'd have to rebuild alsa and alsa kernel
modules from scratch to support it).

I have successfully played DVDs with the raw digital audio stream
sent directly to the SP/DIF output, so I know if the right stuff
gets sent, I can do digital output to my receiver.

What I'm wondering is: Is there a media player that can do
something like use the ffmpeg libraries to do the ac3 encoding
on the fly and send the digital stream to my SP/DIF output?
Something stand-alone where I don't need to rebuild the whole
sound system from source (I might as well switch to gentoo if
I wanted to do that :-).