Spent 6 HOURS uploading a video onto @Youtube, and when it finally got to 100%, it dropped back down to 74%... AND on a different page telling me that the upload has failed. 6 HOURS! Help... 
It finally got uploaded after around 5hrs today! I've not changed the file format (same as before) and I've uploaded longer videos before, so it's probably down to my wifi now being much slower... But thanks for letting me know there's this troubleshooter! :)