Can I extract 1 channel from a stereo mp3?

Archived from groups: rec.audio.pro (More info?)

I have a lot of mp3's that were recorded as stereo files even though
the audio content is really the same in both channels. The encoding is
very inefficient because each file is twice as large as it would be if
it had originally been recorded as a mono file.

I have been looking all over the net for an audio converter than can
extract one channel from a stereo mp3 file. I want to preserve the
sound quality but convert to new mp3 files that are half the size. I
don't want to re-sample or re-encode anything! Does such a product
exist? Thanks! R2