YouTube had announced about this feature being rolled out soon a couple of months ago :

We’re expanding the width of the page to 960 pixels to better reflect the quality of the videos you create and the screens that you use to watch them. This new, wider player is in a widescreen aspect ratio which we hope will provide you with a cleaner, more powerful viewing experience. And don’t worry, your 4:3 aspect ratio videos will play just fine in this new player.

YouTube Has Implemented Widescreen Player Now.

All the old videos were of the standard 4:3 ratio, and these videos may appear inset. Where as the recent videos are of 16:9 ratio, and these videos are tailor made for current format.

So what’s behind this move from YouTube ? Few days ago it was reported on CNet News that YouTube was working closely with content producers to showcase feature films.

YouTube Has Implemented Widescreen Player Now.
YouTube Has Implemented Widescreen Player Now.

May be Hulu is the driving force behind this. Competition from such competitors is forcing YouTube to provide better user experience.

Not sure how this will affect all those sites that embed YouTube videos, as those sites may require a facelift …