motion-activated video recording

I'm looking for a way to record video to disk when there's a certain level of activity in an installation I'm designing. So far I've gotten it to trigger a jit.dx.grab object after it senses a sustained amount of motion, but whenever that happens I receive a "save as" prompt for the movie file (which I won't be around to click). When I specify a filename in the "write" argument, it just continues to write over the same file (or deletes it when I send a "stop" message).

What's the best way to go about doing this? How can I build a library of individually named clips without being there to name them (i.e. implementing a $1 argument in the filename)? Is there a way to record incrementally to a single movie file? Ideally I'd just send stop/record messages to a DV cam and record straight to tape, but I don't have enough firewire cable to do that for this kind of distance.

Anyway, thanks in advance for your help - any ideas would be much appreciated.