Design YouTube/Netflix - Scaling Considerations

CDN Strategy

• Hit Rate: 95%+ for video content
• Edge Locations: 200+ globally
• Cache Duration: 7-30 days for videos
• Origin Shield: Reduce origin load

Transcoding at Scale

• Workers: 100,000 GPU servers
• Queue: SQS with priority queues
• Parallel Processing: Process multiple resolutions simultaneously
• Spot Instances: Use AWS Spot for cost savings

Adaptive Bitrate Streaming

• HLS/DASH: Industry standard protocols
• Multiple Resolutions: 360p, 480p, 720p, 1080p, 4K
• Client Selection: Client chooses quality based on bandwidth
• Smooth Transitions: Seamless quality switching

Recommendation System

• Collaborative Filtering: User-user similarity
• Content-Based: Video metadata similarity
• Neural Networks: Deep learning models
• Real-time: Update recommendations based on current session
• A/B Testing: Experiment with different algorithms

Storage Optimization

• Compression: H.265 for 50% size reduction
• Deduplication: Detect duplicate uploads
• Tiered Storage: Hot (S3), Cold (Glacier)
• Lifecycle Policies: Move old content to Glacier

Performance Optimization

• Preloading: Preload next video segment
• Prefetching: Prefetch recommended videos
• Lazy Loading: Load thumbnails on demand
• Image Optimization: WebP for thumbnails

Auto-Scaling

• Transcoding: Scale based on queue depth
• Streaming: Scale based on concurrent viewers
• Search: Scale based on query rate

Monitoring

• Playback Quality: Rebuffer rate, start time
• CDN Performance: Hit rate, latency
• Transcoding: Queue depth, processing time
• User Engagement: Watch time, completion rate

This scaling strategy ensures YouTube/Netflix can handle billions of video views globally.