Skilled Coder Blog
System Design

System Design: Video Streaming Service (Like Netflix)

1. What’s the Goal?

  • Stream videos smoothly (buffer-free), even on slow networks.
  • Support millions of users, devices, qualities, and recommendations.
  • Ensure videos load fast, resume where left off, and don’t kill your servers.

2. When a User Plays a Video…

  1. Client requests video: “Play movie123 at 720p”
  2. Backend:
    • Authenticates user
    • Checks subscription/license
    • Returns video stream URL from CDN
  3. Player starts streaming in chunks (HLS/DASH)

3. Video Storage & Encoding

  • Uploaded videos are transcoded into formats like 240p, 480p, 720p, 1080p, 4K
  • Split into small segments (2-10 sec) for smooth streaming
  • Stored in object storage (like AWS S3, GCS)
  • Distributed globally using CDNs (CloudFront, Akamai, etc.)

4. How Video Streaming Works (Simplified)

  1. User presses Play
    You open a movie or show and hit “Play.”

  2. App talks to the backend
    The app sends a request to the server saying:
    “User123 wants to watch MovieABC in 720p.”

  3. Backend checks everything

    • Is the user logged in?
    • Do they have permission (like subscription)?
    • Is the video available in the requested quality?

  4. Backend responds with a video URL
    It returns a special link that points to the video file-actually, a list of small video parts.

  5. Video plays in small pieces
    Your device starts downloading and playing short chunks of the video (like 2-10 seconds each), one by one.

  6. Video quality adjusts automatically
    If your internet slows down, the player quietly switches to lower quality (like 480p) so it doesn’t stop playing.

  7. Nothing is downloaded fully
    You’re not downloading the whole movie-just enough to stay a few seconds ahead, like buffering smartly.

5. Core Components

  • User Service → Manages user accounts & subscriptions
  • Video Catalog Service → Stores video metadata (titles, tags, genres)
  • Streaming Service → Handles playback requests, generates streaming URLs
  • Encoding Service → Converts uploaded videos into multiple resolutions/formats
  • CDN (Content Delivery Network) → Delivers video chunks close to user
  • Recommendation Engine → Suggests what to watch next
  • Analytics/Monitoring → Tracks playback, errors, usage

6. Video Streaming Protocols

Protocol How it Works Used By
HLS HTTP Live Streaming (Apple) Most iOS devices
DASH Dynamic Adaptive Streaming over HTTP Android, browsers

7. Scaling the System

  • Use CDNs: Video data is huge; CDNs cache video chunks near users to minimize latency
  • Sharded Metadata DBs: Split video info/user data by region/userID to scale
  • Microservices Architecture: Split services like encoding, auth, streaming, catalog
  • Async Transcoding: Use queues (Kafka/SQS) to process video uploads in background
  • Clever Load Balancers: Direct users to nearest/least-loaded servers
  • Segment Pre-fetching: Predict and preload next chunks to avoid buffering
  • Monitoring: Track play errors, bitrate switches, and CDN misses in real-time
  • Autoscaling: Stream and encode servers scale based on traffic patterns

Key Design Considerations

1. Content Management

  • Content ingestion pipeline for processing new videos
  • Metadata management for search and discovery
  • DRM (Digital Rights Management) for content protection

2. User Experience

  • Intelligent client-side buffering strategies
  • Adaptive bitrate selection based on network conditions
  • Seamless playback across devices (continue watching feature)

3. Global Distribution

  • Multi-region deployment for disaster recovery
  • Content availability based on licensing agreements by region
  • Edge caching strategies for popular content

4. Analytics and Personalization

  • Real-time viewing metrics to identify trending content
  • Personalized recommendations based on viewing history
  • A/B testing for UI and recommendation algorithms

Conclusion

Building a Netflix-like streaming service requires balancing many components including content delivery, video processing, user management, and recommendations. The architecture prioritizes low latency, high availability, and adaptive quality to provide a smooth viewing experience across diverse network conditions and devices. CDNs, microservices, and smart caching strategies are essential for handling the massive scale required for modern video streaming platforms.