You might have an older CCTV system but hopefully it has a built-in DDNS client. If so set up an account with a DDNS provider (some are free like Duck DNS and Dynu) and enter your DDNS client credentials, this way WAN IP addresses get resolved automatically.
Now in your hub identify the CCTV's LAN IP address (meaning the DVR's IP address), reserve it (best practice) by adding a reserved rule using DVR's MAC address and the IP address) and create a port forward rule (you can usually use the same port number of, say, 8000 for all four ports) to send requests to the IP address of your CCTV system.
If all of this sounds too hard I recommend upgrading to a cloud-based system.