Hi Ignacio,
thanks for the nice video. I hope you were able to completely unknot your antenna wire again 
I suspect that winding a 20m long wire in a figure of 8 on a single hand would become rather tedious, therefore I simply use my forearm as “winder”. I just position my forearm vertically and then wind the antenna wire in a figure of 8 fashion between my hand and the elbow. That’s quite a quick method even for longer wires.
Looking forward for your next tutorial video!
73 Stephan, DM1LE