Design a simulator to replay left-turn videos
Company: Applied
Role: Software Engineer
Category: System Design
Difficulty: medium
Interview Round: Onsite
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:
1. **Requirements & scope**
- What user workflows are supported (e.g., list events, open an event, play/pause/seek)?
- Latency and scale assumptions.
2. **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.).
3. **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.
4. **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.
5. **System architecture**
- Main services/components (ingestion, transcoding, metadata service, playback service, auth).
- Trade-offs, failure modes, and consistency considerations.
Quick Answer: 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.