I have uploaded a compiled version of Red5 r4380 here:
We found both audio recording and audio playback of audio files works correctly with this version.
More details here:
But the issue is also solved in the recently released (8th of June 2012) Flash Player 11.3
No need for special versions of Red5 anymore.
Recording audio from Flash trough a media server is now obsolete because it is now possible (with some Flash magic of course) to record MP3 files directly from the browser without the need for a media server.
Proof of concept from 2010:
Commercial, supported flash script:
I have been on the phone and email with the guys at adobe and they refuse to admit that they are at fault. I have been told that it is my xml doctype. Tried every doctype out there and still no sound from audio .flv files. I am at a total loss now.