Server-side ad insertion
Design server-side ad insertion (SSAI) for an ad-supported streaming service that stitches personalized ads into the video stream at the manifest/segment level so the ads can't be blocked and play seamlessly (no buffering at the ad boundary). Each viewer gets different ads (targeting), so you can't serve one shared manifest; you must decide ad breaks, call an ad decisioning service per viewer, splice ad segments into the content timeline, and track that ads were actually watched — for live and VOD, at millions of concurrent streams.
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.