Actually the gradient is good for userexperience so far that it shows that the player responds to the users hovering, but it´s disturbing when the user just wants to jump from time to time or set the volume, or even hovers accidentially.
The actual video is still the most important content on a video-page. ;)
My personal opinion is that the gradient on top is most disturbing, the one at the bottom is okay since it anyway underlays the controls.