Motion capture systems typically require subjects to wear loads of sensors to be able to follow their movements. Disney wants to simplify the process, so its research lab has designed a physics-based system that needs much fewer sensors to work. A human actor can, say, wear sensors on both hands, both feet and the head only -- as you can see above, five sensors are comparably few. The physics-based system then predicts how the rest of the body moves, looking for limb and joint positions that are physically plausible based on the activities of the subject's hands and feet.
Disney Research has a more detailed, but highly technical, explanation of its creation:
"An inverse dynamics solver and physics-based body model are used, ensuring physical plausibility by computing joint torques and contact forces. A prior model is also used to give an improved estimate of motion of internal joints."
Since the system allows real-time motion tracking with but a few accessories, it could make animated movies easier to create and full-body VR experiences common. Think about it: this system could allow companies to create truly immersive VR games and experiences for the masses, since users wouldn't need to wear full-body suits or to slap on over a dozen sensors.
You can see the system in action in the video below. Keep a close eye on the green man in middle, since that's the result of the physics-based system's computations. The yellow guy with the crazy dance steps? That's what the computer had to work with.