This experiment uses HTML5 and CSS3 to rescale proportionally, resize and center a .png image overlayed on top of an embedded video. It was based on this CSS3 background-clip experiment.
It should work in most modern browsers including Chrome, Safari and Firefox.
If you have a wide monitor, it may be advised to reduce your browser's window to reduce lag.
Many thanks to Onur Senturk for letting me use his really cool abstract video.