Real-time camera effects
Design the real-time camera-filter / AR-effects system for a social app where users apply face-tracking lenses and effects live in the camera preview at 30fps on a wide range of phones, and the same effect must render consistently when applied to a captured photo/video server-side (for users on devices too weak to run it live). Effect creators publish new lenses constantly. Design the runtime, the effect distribution, and how you reconcile on-device real-time with server-side rendering.
What a strong answer looks like
Clarify scale and constraints first. Propose a clean component breakdown, then go deep on the hard parts (data model, bottlenecks, consistency, failure modes) and name the trade-offs you are making.
Clarify5:00 left
Estimate5:00 planned
Design15:00 planned
Deep dive12:00 planned
Failure8:00 planned
Which questions mattered is sealed until you submit. Telling you now would just be handing over the edge cases.
Run or narrate your approach, then ask the coach.