Sounds like a cool project, I had similar ideas but never committed time to it. Take a look at this, might be useful.
https://pimylifeup.com/raspberrypi-hdmi-cec/
I've started playing with node red, with the above info might be achievable.
What NVR do you have and where do the cameras connect to ?. Do the cameras go to the POE switch or directly to the NVR?,
Either way you need to verify internet connectivity. Place a PC on that connection and try browsing the web. Ensure your NVR has DNS configured.
I'm pretty sure cameras made specifically for mobile purposes do not have a mechanical IR cut filter. Using standard type cameras may result in early failure of that part due to vibration.
Thanks for your reply, l re-checked my email and the Netgate web site (with optimism) but it's EOL. My plan however is to continue using it.
From the email "This is due to FreeBSD, the underlying operating system for pfSense Plus software, no longer supporting 32-bit platforms like the Netgate...
My NetGate pfsense SG-3100 has been rock solid for last 5 years but NetGate advised this week that it's end of life.
Their recommended replacement (2100) is a step down in performance and current exchange rate make me question where to go !!! :confused: