just to conclude an old thread here.
This thread requirement can be met with tools such as "mps-youtube" and mplayer. You also need "Python" installed from the tcl app store and also maybe "git" so you can install things easily
As far as i can see, this idea works very well for youtube and is low on hunger for resources.
You can make a new mplayer "config file" with just 2 lines (ontop=true AND zoom=true).
When a video is playing you just hit the "F" key for full screen and it should be fine if you have Xorg video driver running
(even without Xorg too)
Vin