Live Green Screen Preview with 5D/7D?

[digitalskylight]

Just wondering if anyone has solutions for live green screen preview with the 5D and 7D? I want to ensure that I'm lining things up correctly, and I think the problem with using something like "Veescope" is that the HDSLRs don't output firewire.

Any help would be great!

 

[kevinottawa]

Get a firewire video capture box, just like the usb video in sticks, but its firewire.
Unfortunately, it would be SD, unless you can find a HDMI input capture box.