4. The method of claim 1 , wherein tracking the non-rigid motion of the user comprises performing an optimization, using the animation prior and the expression parameters, to determine the animation parameters.
4. The method of claim 1 , wherein tracking the non-rigid motion of the user comprises performing an optimization, using the animation prior and the expression parameters, to determine the animation parameters. 5. The method of claim 4 , wherein tracking the non-rigid motion of the user comprises avoiding an unrealistic facial expression by regularizing the expression parameters with a dynamic expression prior, the dynamic expression prior based on a set of blendshape animations.