The work that happens after you say yes
Uploads arrive, you accept them immediately, and something behind the scenes does the expensive part. The user is told it worked before it has.
The processing step calls a third-party encoder that costs money on every call and has no idea when it is being asked the same question twice.
Twenty-five uploads a second. Every upload is encoded within a second of arriving, and the backlog never gets silly.
Before anything runs: which promise gives way first, and what is the mechanism?
Upload to encoded, the slowest in a hundred is under 1s
Nothing is ever more than 300 jobs behind
Every number appears here, on every change.