Design a live video broadcasting platform similar to Twitch that supports real-time streaming from broadcasters to millions of concurrent viewers with interactive features.
Scale requirements: - 30 million daily active users - 100,000 concurrent live streams at peak - Top streams have 500,000+ concurrent viewers - End-to-end latency under 5 seconds from broadcaster to viewer - Support real-time chat alongside streams
Areas to cover: 1. Ingest pipeline (broadcaster to platform) 2. Transcoding and packaging for multiple qualities 3. Distribution to viewers at scale 4. Live chat system with moderation 5. DVR / rewind and VOD conversion
Constraints: - Handle thundering herd when a popular streamer goes live - Support low-latency mode (sub-2-second) for interactive streams - Graceful degradation under load (drop quality before dropping viewers) - Record streams for later on-demand viewing
How to approach it
- Hint 1
Start with the ingest path: how does a broadcaster send video to your platform (RTMP/SRT), where does it land, and how do you transcode it into multiple adaptive bitrate renditions in real time?
- Hint 2
Think about the distribution fan-out problem: a single stream going to 500K viewers. How do you use a CDN, edge caching of live segments, and origin shielding to avoid overwhelming your origin servers?
- Hint 3
Consider the interplay between live and recorded content: how do you support DVR (rewinding a live stream), convert a finished stream to VOD, and handle the live chat system at scale with moderation tooling?
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