Pretty good, but i think it needs a couple more tweaks/features to be truly great imho.

- more "compact" ui, the current layout has a lot of useless whitespace and at the same time the control buttons are tiny. maybe add an option to disable the thumbnail?
- when you click a video-element it should select the tab
- a "pause all videos" button

- the mute/unmute button could change icon on click
- could use the badge to show number of opened/playing videos

good job