With a bit of help from a friend I got it working! First thing was to hunt down some documentation, which was actually very tricky. I've hosted it on my Google Drive:
Then I found the section about Outputs and first tested that I was interfacing with the right part of the camera connected to...
Thanks for your detailed reply. I did actually get my intended solution working. I'll post it below, but your solution is very interesting and possibly useful.
The alarm out on our NVR is wired back into the NVR where it controls a camera (down by our gate). The camera then holds the gate open when the alarm out it ON, and releases the gate when it is OFF. I want to automate the closing of the gate every night (so that if someone has held the gate...