System Design Article

Design Video Conferencing (Zoom)

Difficulty: Hard

Design a real-time video conferencing system like Zoom that supports 1-on-1 calls and meetings of up to 1000 participants with sub-200ms glass-to-glass latency, adapts to user bandwidth, and runs reliably across mobile networks. The interview centerpiece is the choice of media topology: peer-to-peer mesh (small calls), MCU mixing (centralized, expensive), or SFU forwarding (the modern standard). We cover the WebRTC stack (signaling vs media planes, ICE/STUN/TURN), simulcast and SVC for adaptive quality, recording pipelines, and how to keep latency low when participants span multiple continents.