What is the ‘Channel’ option under ‘Camera Settings’ on the NVR configuration menu for?

This option is for displaying and recording video from another NVR/DVR, CMX or decoder directly to the NVR.

In the corresponding IP address box, enter the IP address of the NVR/DVR, CMX or decoder you wish to record and view the channel from, then select which channel you would like from the dropdown selector. This will then show and record the channel as if it were an IP camera.