YouTube developed a 3D interface last year. The “3D” menu at the bottom of the video is there to choose between the various 3D flavors. Now, instead of choosing your preferences each time in a scroll-down list, you get a sleecker interface which keeps your preferences in memory for the next time. The menu is smaller and friendlier, too.
Check by yourseilf here with the 3D 4K video “Miniature Mega Cities”. You may also use www.keepvid.com to store the video in 4K 3D for later replay with StereoscopicPlayer!
source: http://stereoscopynews.com/hotnews/history/digital/1058-youtube-3d-new-3d-interface.html