This is just a long shot, but check out gstreamer It will probably be a PITA to get going on windows, but there is a Perl module for it, and the maillist there may be quite helpful.
I had a bit of a look, before I investigate gstreamer any further, I think I may be able get the audio via MCI, just been looking at win32-api-prototype, Then I guess it's a matter of encoding and dynamically inserting the meta-data ID tag on the fly, one way or another.
Heads back to msdn ... :P
Update: MCI doesn't seem to provide an accessible output buffer of the audio...I think (gah). Lower lower lower ...