Sometimes we call this crash record.
Hook up your camera or deck (with a tape in it) via fw to the mac. Set the camera to VTR mode. Open up FCP and it should recognize the deck/camera. Make sure to go VIEW – VIEW EXTERNAL — ALL FRAMES. Then, also check that AUDIO FOLLOWS VIDEO.
Then hit RECORD on the camera… NOT the button for recording camera imput… there should be anoter button.
Then start the timeline. The camera will record what’s on the timeline. Make sure you render EVERYTHING Option-R and Option-Apple-R before you try this. Also even before you do that, change your RT settings to PLAYBACK HIGH… not sure that actually effects the FW playback, but it won’t hurt.
Good luck,
CaptM