On Raspbian OS, Epiphany browser, the video plays fine, even the sound is in sync, on a Pi 2, however that nasty play button (centered on the screen in white & red )never disappears.
I've seen this myself. If I'm not mistaken, Epiphany uses a hack behind the scenes to get the YouTube video to play. It is part of this hack and not the YouTube player itself that causes that play button to sit there forever.
right after the
this.playArea.style.opacity = 0;
line or something similar to have it disappear ("playArea" is the element for the play button). It looks like it tries to use some opacity effects to hide it, and probably if those don't work, it ends up just staying there.
Let me know how it goes.