How the interviewer opens it
“Design an on-demand video service for a licensed film and television catalog. Subscribers watch on different devices, including during peak demand.”
The prompt is vague on purpose. The first minutes are for you. Reduce the prompt to the core features and agree on the numbers before you draw.
What to clarify first
- Audience
- Catalog and source files
- Devices and video quality
- Read-to-write mix
- Delivered bitrate
- Latency and playback quality
- Availability and consistency
- Rights and access
- External systems
- Scope limits
The interviewer has the answers. In a SysRound round, Alex gives these answers, as a real interviewer does.
Scope of a strong answer
Core requirements
- Browse films, series, and episodes
- Prepare licensed source files for supported devices
- Play, pause, and seek while network speed changes
- Restrict playback to eligible subscribers within licensed countries and rights windows
Usually out of scope
- Live broadcasts
- Offline downloads
- Recommendations and advertisements
- Account creation and payment processing
- Implementation of a DRM system
What interviewers ask about
- Playback on different devices
- Devices support different formats. Network speed changes during playback. An incomplete release can break playback for only some viewers.
- Traffic during popular releases
- A popular release concentrates traffic on a few titles. Empty caches and synchronized retries can overload the origin despite a high average cache hit rate.
- Access to licensed titles
- Rights depend on country and time. Shared media caches must not grant access. Revocation must stop playback without a control request for every segment.
Common mistakes
- The design treats video delivery as a database scale problem and ignores bandwidth.
- The design stores several resolutions but does not explain how the player changes quality.
- The design publishes a title before all required device formats are ready.
- The design checks access only in the application and leaves cached media or origin files unrestricted.
- The design assumes one manifest, codec, and DRM format serves every device.
- The design assumes a high average cache hit rate protects the origin during every release.
The bar by level
- Senior (L5/E5)
- Explains aligned variants, atomic publication, and device compatibility. Sizes delivery and origin capacity. Handles cold releases, access renewal, revocation, and dependency failures.
- Staff (L6+/E6+)
- Defines authority boundaries and availability trade-offs for rights checks. Quantifies delivery cost and renewal load. Plans staged provider failover. Verifies device-specific revocation guarantees.