Like my last thread, this video is kind of long, but the wow factor is definitely there.
TL;DR
People in charge of graphics for the movie were able to get enough data on Brad Pitts face that they could essentially put his head in as many movies they want for life. Using a new technique they developed there were able to capture over 1 million points of data on Pitt's face. Pitt made every facial movement/expression he could and they took this data and were able to translate it into different faces. So basically, they have enough data on Pitt that he could act in movies forever.
Also, Brad Pitt's head in the first half of the film is computer generated
