YouTube

How this question breaks down

1. 1Upload and transcodingWrite path6 minTake a raw file from the creator over a flaky connection, store it once, and encode it into every resolution viewers will ask for.
2. 2StreamingRead path28 minGet the first frame on screen in under a second and keep playing without stalls, by cutting video into small cacheable segments and serving them from caches as close to the viewer as possible.
3. 3Metadata and viewsRead path22 minServe every watch page's title, counts and comments from cache, and count billions of views a day without letting one viral video melt a database row.
4. 4SearchRead path19 minTurn a few typed words into the right twenty videos out of a billion, and make a new upload findable within a minute (typically in seconds).

Work through the parts in order and you’ve covered the full design. Each part is one topic.