[FFmpeg-user] Video Capture: how to get started?

[James Board]

I have a BlackMagic Intensity Pro Video Capture Card.  It
has it's own video capture software, but I'd like to use ffmpeg,
instead.

How would I get started?  I'm on a Linux machine.  What
would an example capture command look like (assuming 1920x1080
video, and 29.97 fps, etc)?  Also, assuming that works, how do I tell
ffmpeg to stop capturing?  

Thanks