Motion Editing With Spacetime Constraints
Yes. This really was all in real-time on a circa 1996 Macintosh. I have no idea how I made it go so fast.
This video is from the 1997 Interactive 3D Symposium Paper. An earlier version of the paper actually appeared as a 1998 journal paper. The journal paper mainly has 2D examples, and focuses on the non-interactive cases.