This is the first time I've done this so, let me go through the suggested procedure.
1. change the CCTV dvr to DHCP.
2. on the BT homehub, in the port forward section set two separate rules/applications for port 80 and 7050, both as TCP.
3. Assign both rules/applications to the CCTV dvr device
4. Click the box on the hub so dvr always used the same Ip address
4. Check the external IP address of my hub at Whatmyip.
5 On the app, set the address to the external address and the mobile port to 7050.
Do a need to restart my hub, after all the changes to it ?