Well... it's a long way around, but I've got a box (I'm at work, I forget it's name... I'll repost when I get home) that captures the output to my television and makes it into a digital movie file (I also forget the type of file it makes).
I bought it to convert analogue video camera output into digital, and discovered it records anything as seen on my tv screen.
That would do it for you.
It's not what you were asking... I know you want to use the actual feed and capture it, but it would work.