System Design – Video streaming platform

Objective: Design a video streaming platform like YouTube

Infographic

Capacity Estimation

Before diving into the architecture, let’s establish baseline requirements to understand the scale we’re designing for:

User Scale

  • Daily Active Users (DAU): 100 million users
  • Monthly Active Users (MAU): 2 billion users
  • Peak concurrent users: 20 million (during prime time)

Video Upload Requirements

  • Videos uploaded per day: 500,000 videos
  • Average video size: 100 MB (after compression)
  • Peak upload rate: 1,000 videos/minute during busy hours
  • Video formats supported: Multiple resolutions (360p, 720p, 1080p, 4K)

Storage Requirements

  • Daily storage needs: 500,000 videos × 100 MB = 50 TB/day
  • Annual storage growth: ~18 PB/year
  • Total storage (5 years): ~90 PB
  • Redundancy factor: 3x (considering backups and CDN replication)
  • Total storage with redundancy: ~270 PB

Bandwidth Requirements

  • Average concurrent viewers: 10 million
  • Average video bitrate: 2 Mbps (mixed resolutions)
  • Peak bandwidth: 10M users × 2 Mbps = 20 Tbps
  • Monthly data transfer: ~500 PB

Database Scale

  • Video metadata records: Growing by 500K/day = 180M/year
  • Comments per day: ~50 million
  • User interactions: ~500 million/day (likes, views, subscriptions)

** These numbers justify our architectural decisions around horizontal scaling, CDN usage, and distributed storage systems.

Data Model (Abstract Example)

Entities:

User: represents an account (username, email, password etc.)
Video: stores metadata about uploaded videos (title, uploader_id, upload_time, visibility, resolution, duration etc.)
Comment: user comments tied to videos (video_id, user_id, comment_text, created_date)

Note:
This is entity-level modeling — not schema-level.

API Endpoints (High-Level View)

Core API Endpoints:

POST /videos/upload — Upload a new video
GET /videos/{id} — Get video metadata
DELETE /videos/{id} – Delete a video (if uploader)
GET /videos/{id}/stream — Stream the actual video
POST /videos/{id}/like — Like a video
POST /videos/{id}/comments — Post a comment
GET /videos/{id}/comments – Fetch comments
GET /videos/search?q=query – Search videos by keyword

Proposed design diagram:

Process flow:

** Breakdown **

  • User Upload → HTTP POST request
  • Load Balancer → Traffic distribution
  • API Gateway → Request routing
  • Upload Service → Handles the upload
  • Object Storage (Raw) → Stores original video
  • Queue → Triggers transcoding job
  • Transcoding Service → Processes video into multiple formats
  • Object Storage (Multiple Formats) → Stores all video qualities
  • Metadata Service → Updates video information
  • Metadata DB → Saves video metadata
  • CDN Cache Invalidation → Refreshes cache for new content
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