An Introduction to WebRTC Simulcast

Simulcast is a feature in WebRTC that allows conferences to scale despite participants with unpredictable network connectivity. It works by enabling WebRTC clients to publish multiple versions of the same source track, with different encodings (i.e., spatial layers). In LiveKit, participants can publish high, medium, and low-resolution versions of the same video, encoded at different bitrates. Simulcast is designed to work with an SFU, where the SFU receives all three layers for the track and makes a decision on which layer to forward to each subscriber.