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Ok I checked for 20mn and whatever I do it s working but it s very slow when lots of videos in the queue. I guess you were just unlucky and tried to upload when the queue was too long, the Sprite Creation can also take a while.
You said it worked on DTube, but my guess is that if you d have done it on DTube at that moment, it would have taken the same time, since our process is exactly the same.