use a video card output plugged into some sort of external recorder, then just record in realtime. i'm considering using this random VCR my roommate left here to do this, but some realtime dvd recorder would be ideal. unless you have a serious powerhouse it's kinda ridiculous to put your system through all the realtime rendering as well as recording to HD. although nowadays machines are way more powerful. a few years ago i had a 1.5 ghz athlon with a geforce 3 and the method i ultimately settled on was recording the audio separately to .wav, dumping each frame of the gemwin to a jpg (which on this machine had to be a smaller resolution and TERRIBLE terrible quality), then i had a complex script system to use mencoder and ffmpeg to put the stills together to a video then add the audio. eventually it somewhat worked, took LOTS of trial and error, but ultimately it never captured the true potential of what i was trying to record. recording externally will let you save ALL your overhead for realtime audio/visuals, at as high a resolution and complexity as you machine will allow (and ultimately the recording resolution of the device).
just my 2 cents, i really know nothing about external dvd recorders and have a crappy machine that can't handle the 3d i need it to so i haven't recorded in a while. but here's an example of my old method recording (and if you notice, the sync is off almost a whole beat, it's supposed to trigger changes only when notes are triggered, i got it sync'd but realized after the fact it was off a beat)
another similar video, sync is way better on this one
but ultimately these had to be dumbed down to be able to record via this backwards ass method.
record externally, then upload some HD for us!