Thanks Klaus, unfortunately I don't think the problem comes from the video. Indeed, it's doing it with every videos encoded by different ways.
Moreover, with the same videos, if I use the interface published
here I have no problem anymore. So you'll say I have to use this interface, but I prefer the look of yours

. So you'll say I have to fix the problem comparing the scripts of the 2 interfaces, but I tried and I haven't managed to do it

.
So I'm crying in your forum, hoping someone will help me.