Video processing

An upload finishing is only the file arriving. YouTube then re-encodes it into the ladder of resolutions it serves, working from the bottom up, so the low ones become available before the high ones. That is why a freshly published upload can look soft for a while and then sharpen without anyone touching it. Long files and high resolutions take longer, and a 4K master can sit in processing for hours. Scheduling is the practical consequence. Get the file up well before you intend to publish, so the good version exists by the time the notification goes out and the first viewers are not judging a blurry one.