There are several methods for generating the Avar values to obtain realistic motion. Traditionally, animators manipulate the Avars directly. Rather than set Avars for every frame, they usually set Avars at strategic points (frames) in time and let the computer interpolate or tween between them in a process called keyframing. Keyframing puts control in the hands of the animator and has roots in hand-drawn traditional animation.
In contrast, a newer method called motion capture makes use of live action footage. When computer animation is driven by motion capture, a real performer acts out the scene as if they were the character to be animated. His/her motion is recorded to a computer using video cameras and markers and that performance is then applied to the animated character.