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Twitch / Live Streaming — Simple#

Problem statement (interviewer prompt)

Design Twitch (or YouTube Live): streamers ingest via RTMP/SRT, live transcode into multiple bitrates, deliver to viewers via LL-HLS at 2–5s glass-to-glass, support 100k concurrent streams + 10M concurrent viewers per event, plus real-time chat with mod tooling.

flowchart LR
  S([Streamer])
  ING([RTMP / SRT Ingest])
  TR([Live Transcoder])
  PKG[HLS / LL-HLS Packager]
  CDN
  V([Viewer])
  CHAT[Chat - IRC-like]
  S --> ING --> TR --> PKG --> CDN --> V
  V <--> CHAT

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class S,V client;
    class PKG,CHAT service;
    class ING,TR compute;