The second bigest ISP in France as launched an UPNP AV solution between an IPTV box (directly connected to the ADSL Modem and computers inside the LAN.
In the case your computer is behind a personnal router, you need to use an igmp proxy to route multicast traffic (SSDP). The case is that there is an IGMP handshake between the computer and the IPTV (located on the wan side).
Igmpproxy seems only to be able to route igmp traffic in one direction.
It would be great if it was possible to do it in 2 direction