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.
Source youtube blog.
For 2-3 years we heard more and more about wide. Hardware (as in laptops, monitors and teleisions) is going widescreen. Many online tvs are talking and imprementing the wide format. DVD Movies are wide. Even Adobe Premiere is working with wide formats! :-)
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