I'm not sure if UPnP is a new solution to the problem, but if it isn't, you have to use DMZ. Video apps don't use one single port chosen at random, they use a wide range of ports simultaneously. Many are for the video, some for audio, one for chat, one for incoming calls, some for indexes etc. That is the problem. You either have to open a wide string of ports to your firewall and forward all of those ports to the video app machine, or work on DMZ. Problem is if you forward a wide string of ports to one computer on a lan, no other computer can ever use those ports and you will likely find things not working properly on other machines. Besides if you are going to open all those ports in your firewall you may as well be on DMZ anyway.
The only solution is to put that machine on DMZ and then run a software firewall configured for the app you are running. A software firewall like ZoneAlarm will check to see if the program using those ports is a program approved by you. If it is great. If something else tries to access those ports it will be blocked. Most software firewalls must be run on the medium setting to work. This keeps your ports blocked and protected but not stealth.