The problem

A cooking school puts its lessons online. Teachers film a 20-minute lesson and upload the file from home in the evening.

Last week a teacher’s 3 GB upload reached 90% after 18 minutes. The Wi-Fi dropped for a moment, the upload started again from 0%, and the teacher gave up for the night.

Students watch on phones on the train and on TVs at home, so each lesson is needed in three sizes. The teachers ask for an upload that survives a drop, and a page that says how far along their video is.