Design a simulator to replay left-turn videos

Q: Design a simulator to replay left-turn videos

This question evaluates system design competency for building an end-to-end video replay and simulation service, including data modeling, event indexing, API design, storage/streaming choices, scalability, latency, and reliability considerations.

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Question

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Design a system to simulate and replay a car’s left-turn driving scenario using recorded video. The replay should support browsing a specific left-turn event and playing it back with appropriate metadata.

Cover the following:

Requirements & scope
- What user workflows are supported (e.g., list events, open an event, play/pause/seek)?
- Latency and scale assumptions.
Data model / schema
- How you represent a “drive”, an “event” (left-turn segment), and the associated video chunks/frames.
- What metadata you store (timestamps, vehicle ID, camera ID, geo, labels, etc.).
API design
- APIs to create/ingest recordings and event boundaries.
- APIs to query left-turn events and fetch/stream replay data.
- Seek/range requests and pagination.
Storage and retrieval
- Where raw video is stored (object store vs. database) and how it’s indexed.
- How you handle streaming (HLS/DASH/MP4 range), caching, and CDN.
System architecture
- Main services/components (ingestion, transcoding, metadata service, playback service, auth).
- Trade-offs, failure modes, and consistency considerations.

Design a simulator to replay left-turn videos

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