Hi squin,
not sure if I get you right here, but I had a similar issue

The way I solved it is as follows:
1) Recorded the sound seperately (easy one)
2) Recorded the animation, not directly the video but the data used to render one frame
3a) Ran the animation again, not realtime but reading the data-structure with reduced framerate
3b) Paralell writing the movie, using MovieMaker (framerate-parameter set here to the actual framerate of the original Sketch  - Using MJPEG-codec with high quality)
4) Rendered Movie from MJPEG QT with sound to another H.264 quicktime. (You can use any Video-Editing program, I actually used ableton life here where I generate the music, too.)

I your machine is fast, you may skip 2) and 3a)!
Sounds a bit complicated but this works perfect and easy for me.
There may be other solutions, but that's the one I came up with to avoid frame-drops and keep the music synced, even at high resolutions.
One (yet unfinished) result can be seen, in case you are interested, on vimeo.com if you search for "f'alasifa" there. (As a "newbie" on this board I am not allowed to post links yet

BTW: I am not using Processing directly, but ruby-processing
- this should not matter here.

Regards, Mathias