realtime recording of manipulated flash movies

Hello, apologies if this is covered elsewhere, but couldn find it in list....

I have a couple of flash animations which i need to re-record in response to an audio input. Essentially i am driving either framenumber or rate with some audio analysis. This works fine, but i want to record them to commit to dvd rather than do this live in performance.

Using the frame-number version as an example, I can reliably record a qt movie at 25 or 15 fps by stopping movie in player, and banging through new frame number according to current audio levels every 40/66.67 ms.
This works fine @ 320*240. As i increase size to a more desirable 768*576 or 1024, recorded movie gets shorter (and faster), as if i had changed the frame rate. I would expect this if CPU was really being canned, but it remains below 65% .

I guess another option would be to send out to a dv camera to record, but this is another generation of codec-ing i'd like to avoid ...

any suggestions very very welcome.

cheers

alice
(very new to video!)