Twitch / YouTube Live System Design | Live Streaming, LL-HLS, CDN, Chat at Scale with Animation

Streamer apne room se game khel raha hai aur kuch hi seconds mein duniya bhar ke lakhs log use dekh rahe hain, chat kar rahe hain aur Super Chat bhej rahe hain — ye kaise hota hai? Is video mein animation ke saath Twitch / YouTube Live jaisa live broadcasting platform design karenge: requirements, capacity estimation, high-level architecture, ingest (RTMP / SRT / WebRTC, stream keys, stream health), real-time transcoding + bitrate ladder, segments + latency (HLS, Low-Latency HLS, WebRTC), CDN fan-out + request collapsing, player ABR + latency modes, chat at scale (pub/sub, batching), moderation, Super Chat / Bits payments, DVR + VOD + clips, discovery + viewer counts, failover aur datastore choices. Note: traffic numbers are interview-style assumptions, not real company data. CHAPTERS: 00:00 Twitch + YouTube Live 00:36 Step 1: Requirements 01:25 Step 2: Capacity Estimation 02:16 Step 3: High Level Architecture 03:01 Deep Dive: Ingest 03:54 Deep Dive: Real-time Transcoding 04:48 Deep Dive: Segments and Latency 05:46 Deep Dive: CDN Fan-out 06:36 Player: ABR and Latency Modes 07:19 Deep Dive: Chat at Scale 08:13 Chat Moderation and Safety 08:52 Super Chat, Bits and Subscriptions 09:28 VOD, DVR and Clips 10:07 Discovery and Viewer Counts 10:53 Reliability and Failover 11:33 Choosing the Datastores 12:04 Summary