These animations are done using a GPU based vertex shader.  This allows for fast performance for per vertex calculation.

This is necessary to transform each vertex into the new position for a given animation. This system starts by pre-calculating the transformation matrix for each limb.  These matrices are then passed into the GPU and applied per vertex depending on their position.  Which limb a particular vertex is a part of is also pre-calculated and passed to the GPU at the time of the vertex call.  Many animations can be created with this interface. 

It is a simple matter of defining a few time based calls to set rotations for the different limbs.  With these timed based rotations set it is then possible to make a call that will cause the character to walk, jump, or stand.