Your 4G dies in a cab. Nobody else's video gets worse.

transcript

Arjun's cab goes under a flyover. His 4G collapses mid-meeting. Thirteen others are on that call. Their video doesn't get any worse.

Here's the trick. Kavya is speaking. Her laptop encodes her camera three times. 180p, small. 360p, medium. And 720p, at about 1 point 5 megabits. That's called simulcast.

All three go to the router. It never decodes them. Rahul has 20 megabits. He gets 720p. Arjun drops to 600 kilobits. The router just switches him to 360p. Small gallery tiles get 180p. Everyone else stays on 720p.

But how does the router know? Arjun's phone reports when each packet arrived. Rising delay means a queue is building. Before a single packet is lost.

About 3 megabits, until the flyover. It falls within a second. Downgrade fast. A frozen picture is worse than a soft one. Then climb slowly. Probe the higher rate with padding first. Back to 720p only if delay stays flat. Otherwise his tile would flicker.

And if nobody wants 720p at all? The router tells Kavya to stop sending it.

Senders send layers. The router picks one for every receiver. One slow receiver never slows the sender.

Full breakdown in the lecture.