Peer-to-peer video works for two. At ten, it needs 54 Mbps each.

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Peer-to-peer video. No media server. Beautiful for two people. Now your team of ten joins the call.

WebRTC sends video straight between browsers. In a group, that's a mesh. Everyone sends to everyone. Four people? You send 3 streams. And receive 3 more. Every person, at once.

At 1080p, four people need about 18 megabits a second each. Ten people: 18 streams each. About 27 megabits of that is upload. About 54 in total. Per person.

And your device encodes 9 outgoing streams at once. Many home connections can't sustain that upload. A 10-person mesh is impractical.

So put a server in the middle. A selective forwarding unit. An SFU. You upload your video once. It forwards to everyone else. No decoding, no re-encoding. So its CPU stays low. It scales to 50 or more people.

The rule of thumb. Four or fewer? A mesh is fine. Five to a hundred? Add an SFU. Over a hundred? Cascade the SFUs.

Google Meet and Discord route group media through their own servers. WebRTC doesn't mean serverless.

Full breakdown in the lecture.