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My colleague tells me that changing tab during the upload could cause problems.
We ll try to fix this ASAP. In the meantime, try to stay on the tab until the end of the upload.

I see... yeah maybe it's fixed for my next vid :)

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.