The flow is bascially the other way around. One server IP address (source might be e.g. any 10.0.0.0/16 from within your ISPs network) broadcasts: "hey, I'm gonna send data to 232.0.20.234, whoever whants that data, just pick it up". Then it's your routers responsiblity to transport that broadcast into your local network, where your client can respond with "yes pease". Then your router forwards that "yes please" to that initial sender. From that moment on, the initial sender will send that video traffic to 232.0.20.234 but targeting your routers MAC address, so traffic directed not from but at this IP address will hit your router and its your routers job to now forward that traffic to your client.