YouTube said in it's Official blog post:
Creating 3D videos was pretty tough before. You had to set up two cameras, combine the footage from each, and use special software to make the effect look just right. Today we're launching 2D to 3D conversion. Once you've uploaded your 2D videos to YouTube, you can convert them to 3D with the click of a button. Converted videos will be viewable by everyone in 3D. You'll still get best results with a 3D camera, but it's a great new way to let people enjoy your finest moments. You'll find this feature by selecting "Edit Info", then "3D Video" on a video you've uploaded. (Note, you'll still need glasses to watch on most devices.)Once you convert your video into 3D, it will take sometime to convert., maybe an hour or so. I have converted one of my video into 3D and it's taking quite long. Why don't you go ahead and experiment with your uploaded videos?