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Clarify requirements before you design — kept separate from your stage notes.

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Video Conferencing System Design

Visual Problem Diagram

Scenario

Standup with 40 participants and two users on 3G—SFU must forward selective streams without melting CPU, while screen share needs crisp text at higher bitrate than camera. SFU vs MCU, signaling, and TURN for NAT are the interview center.

Design a video conferencing system supporting multi-party calls with screen sharing and acceptable quality on poor networks. Separate signaling from media plane and prefer SFU architecture for scale.

You should support room join/leave, A/V streams, screen share, mute, and NAT traversal. Be ready to explain WebRTC, SFU vs MCU, and TURN costs.

Constraints

Functional

Create/join room, A/V streams, screen share, mute, participant list, optional recording

Non-functional

< 150 ms one-way latency target, 99.9% availability, adapt to packet loss, 50+ participant modes

Scale

100M meeting minutes/day, thousands concurrent rooms, regional SFU clusters

Stages ahead

1Requirement Analysis

2API Design

3High-Level Design

4HLD Extensions

5Trade-offs

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