[00:01] back-end after user clicks upload? Well, first, the client splits the file into to blob storage via what's called a pre-signed URL. This way, any dropped connection will retry just that one chunk, not the whole 10 GB file. Once
[00:16] uploaded, the pipeline then fans out into a DAG. The heaviest branch in this DAG is transcoding, where the video is put into segments and a job is queued for each segment at every target resolution, all the way from 360p up to
[00:28] 4K. Workers then pull off the queue and process the transcoding in parallel. branches are doing things like integrity checks, extracting metadata, generating content for copyright matches. There's also a central jobs table that tracks
[00:44] the completion across every branch. When all that processing finishes, the video pushed out to CDN edge nodes all over the world. This is so that a viewer in Tokyo isn't having to pull bytes all the way from a data center in Virginia. Read
[00:58] our full breakdown on how to design YouTube at hellointerview.com.