If I am streaming on a host using the internet outside my nat, how is multcast addressing work with respect to streaming for example, if the application outside sends to 188.8.131.52 how is the packet finding its way to my machine?
First off, 184.108.40.206 is a very bad choice of example multicast address. (Why is left up to the reader to learn.)
If you want multicast traffic to span your firewall -- or a NAT router pretending to be one -- explicit rules will be required. And some level of multicast routing, or IGMP proxy will be needed. In some simple cases, it may suffice to simply bridge multicast, but that can be problematic. (multicast is uni-directional; if the thing(s) listening to a stream ever want to communicate with the sender, it will have to be done via unicast.)