I used to have code that did that. I don't know whether I can dig it out
(definitely can't this week, I'm off to Toronto for the Smalltalk
Solutions conference in an hour) but it's not hard to do -- use FFI to
make calls to Quicktime routines.
I never tried it with Apple video hardware (my beige G3 doesn't have
that option) but the same code worked through a higher-end video input
PCI card system and a FireWire webcam. They used a uniform Quicktime
interface to software, so I imagine the Apple hardware probably did as well.