In this TouchDesigner tutorial we look at how to set up a 3D "world" through which we can endlessy move through. You can use any 3D objects and are not limited to this example. There's a lot of small tricks so this is not only about the main technique as usual :)
Visit this link for demo of some real-time effects reacting to motion of talented dancers. Even though it shows pre-recorded footage, it would work the same way with any live video as only RGB data are used as input (no additional sensors were used).