@ Daorus
gaab wrote:
Thank you very much for the detailed process.
I will make a test with a difficult video and report my findings.
Sorry, it took me more than I anticipated to do this test.
I uploaded two videos in 4K to Youtube. Quite a long process to discover that they have been converted to 1080P 
The result is not noticiably better, but the videos are really challenging !
I am mounting a private video of a 7 days horse ride in Africa, captured with a GoPro... So, they are VERY, VERY shaky !
So, for me, it is not worth to upload everything to Youtube.
In the future, another solution to consider could be this https://www.kickstar...ion/description
Much lighter than the device you displayed !
Thanks for sharing your knowledge !
Gérard