YouTube test a stereoscopic player for watching videos in 3D. To enable the 3D player, you need to add the following tag to one of your videos: yt3d:enable=true. The current tags are provisional and may change or expand. They’re: yt3d:enable=true Enables the view mode – yt3d:aspect=3:4 Sets the aspect of the encoded video – yt3d:swap=true Swaps the left and right sources. You may need to add this to videos when the player with fixed anaglyph modes ships.