### 📝 Feature: Generate Edited Video for Client Download

🎯 Goal

Allow clients to download a fully edited video of their recorded session by merging all individual participant recordings, using backend session metadata (e.g. join/leave times).

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📦 Context

Each participant's local video/audio is recorded in chunks and uploaded to cloud storage. The backend already tracks:

• Session ID
• Participant IDs
• When each participant joined and left the session

All this info is stored in:

• sessions table
• participants table
• participant_sessions table (contains joined_at and left_at)

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✅ Acceptance Criteria

• Create a backend job/process that:

  • Fetches all uploaded chunks for a session
  • Uses backend metadata to determine layout timeline (who was visible when)
  • Merges participant videos into one final .webm or .mp4
  • Stores the final video in cloud storage
  • Generates a public or signed URL for the user to download

• Expose an endpoint or UI link:
  GET /sessions/:id/download → triggers or fetches the final video.

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💡 Notes

• Backend should generate a layout manifest based on joined_at / left_at
• Use ffmpeg (or similar) to merge and render the final output
• Add retry/failure handling if any chunk is missing

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🔗 Related

• Chunk upload handling
• Participant session tracking
• Manifest generation logic