How does video streaming proxy work in routers?

Question

linux

Foreword
Not so long ago I dealt with issues of IPTV proxying for the home network (there was a house server that clung to the Internet, and home computers clung to the server). For linux I used 2 tools-UDPXY and IGMPProxy.
While working, I found the following “for myself”:
1. For UDPXY to work, you need to write the address of UDPXY itself in the playlist, and then the address of the stream. Then the broadcast goes to only one port (to the one “from which they look”).
2. IGMPProxy does not require modification of the playlist, but it scatters the stream to all allowed interfaces at once, regardless of whether they watch TV from them or not. There is also no way to watch multiple channels at the same time, although the UDPXY setting is fine.
Question
Now I bought the most common SOHO router tl mr3220. It claims to support IPTV. Indeed, TV can be watched without modifying the playlist, and what is interesting is that when watching, the stream goes only to the port where it is really needed, i.e. where they look. How is it implemented?
PS: in case I screwed up with the terms.
We are talking about Open TV of Rostelecom, the UDP protocol is used to transmit the stream. Channel addresses look like this:
udp://@233.3.2.1:5000

Answer 1

in managed switches, this is called igmp snooping
when multicast is distributed only to those ports that requested it.
I think that the same technology is used in the router.

Answer 2

How is it implemented there? It's no secret that most routers basically have a Linux kernel. Hardware manufacturers write their own?

Answer 3

Seems to have figured it out.
IGMP Snooping is an option in kernels starting from 2.6.34, when enabled, IGMP traffic starts running between bridged network interfaces.
I think that in routers just all the ports and WiFi are combined into a bridge. Only in this case it turns out that the home network is perfectly accessible "from the outside", through the WAN interface.

Answer 4

For routers with Broadcom, this feature is called "efficient multicast forwarding".