It appears that some time over the weekend, YouTube began experimenting with 3D videos. Peter, the developer, said the project is extremely new and has several bugs.
Peter also gave us various ways to view such videos:
- yt3d:enable=true Enables the view mode. (obviously you've already discovered this)
- 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. Apologies for the inconvenience.
- yt3d:left=0_0.1_0.5_0.9 and yt3d:right=0.5_0.1_1_0.9 These tags are very provisional and most useful for fixing up old videos. They set the source area for each eye as pairs of coordinates x1_y1_x2_y2. The scale of these coordinates is 0,0 for the the top left down to 1,1 for the bottom right.
All of the information above makes no sense to me but, someone may have a clue.