Animator Tim Borrelli tweeted this article of an interview with Joe Letteri, Weta’s senior visual effects supervisor:
It’s still a work in progress because figuring out how facial muscles work is not easily understood because they don’t behave like the other muscles in the body. They are not so bound by the skeleton. But there’s enough of it working for the animators to drive the performance, whether it comes from the capture or the animation or the combination of the two.
there’s a big interpretive effort that goes into that. But then it comes back full-circle: You go through this whole process of tracking and analyzing the data, interpreting it through these FACS poses and then putting it back on the face through all the combination muscle shapes. And then you just look at it side by side with the performance from the actor and say, ‘Does that look like the right performance or not?’ If not, why not?”
I personally feel this article settles the recent debate as to whether Andy Serkis deserves recognition over the hundreds of talented VFX artist who painstakingly made the character Caesar come to life.