Requirements & scope
- Functional: upload videos, watch with adaptive quality, search, like/comment/subscribe, get recommendations.
- Non-functional: fast upload + processing, low startup latency, high availability, massive scale.
- Scale: ~500 hours uploaded/minute, ~2B users, ~1B hours watched/day.
- Consistency: view/like counts can be eventually consistent (sampled counters); a video must be playable once processed.
Out of scope (covered in detail below)
Live streaming, Shorts, the ads auction, comments moderation at scale, and Content ID — deferred and discussed in the dedicated section.
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