Looking for a way to use Ultra as CCTV storage

I have had a Ultra now for a while, mainly running plex and storage for photos etc. I have recently purchased a IP CCTV camera, which works really well for “live” viewing. Is there a tutorial anywhere which can help me work out how to use some of the storage i have available on the Ultra to save recorded 24/7/365 video ? I do have a separate 4 channel NVR which works brilliantly, but no way to add a additional channel for recording. Any suggestions would be really appreciated…thanks