Audio/Video protocols and NAT are not a great combination. The problem is that the audio/video protocols often include source & destination IP addresses inside the protocol packets.
You need a NAT that does more than just re-write the IP headers: It has to dig inside the packets, understanding the higher level protocols and re-write any addresses in there too. (Sometimes called protocol inspection)
For audio/video you typically get what are called firewall traversal or border controllers which actively participate in the audio/video protocol between the endpoints. Products like CUBE & VCS do this and you should look at them instead of NAT.
GTG
Please rate all helpful posts.