The Polar Express, the Lord of the Rings, or played most any video game, you’ve seen motion cap­ture. Actors dress up in funny body suits with lit­tle white balls over them. Filmmakers run the cam­eras through a com­puter, using the actors’ move­ments to ani­mate a com­puter gen­er­ated char­ac­ter. It’s a quick and easy way to record com­plex, real­is­tic char­ac­ter move­ments with­out hav­ing an ani­ma­tor labor over it for weeks. Some say that most films will be made this way in the future.
I don’t think so. We all know the say­ing that the eyes are the door­way to the soul. The eyes and face allow us to read the feel­ings of a char­ac­ter. Audiences see those expres­sions, and when they are played well to match the moment, we become engaged in the char­ac­ters. We know what they’re feel­ing. We care. That’s the magic of act­ing.
Mocap will never be able to show such expres­sive­ness on its own. Right now, mocap has a hard time cap­tur­ing eye and face move­ments, but that’s just a tech­ni­cal prob­lem. They’ll fix that. Even if the motion cap­ture per­fectly cap­tures every­thing, you still need actors that can act on a green screen, with actors green suits, and objects don’t exist.

Actors are all about emo­tion. They’re not automa­tons used merely to record their move­ments. They are humans and need human inter­ac­tion. They need the same emo­tive respon­sive­ness from their co-stars that they’re try­ing to por­tray on screen. There are few peo­ple who can per­form well clad in a rub­ber suit oppo­site a sim­i­larly clad actor with dots glued all over his face. Dave McKean, for exam­ple, learned this les­son while film­ing Mirrormask.
This is where ani­ma­tors step in. Animators can take the cap­tured data and tune the emo­tional per­for­mance on close­ups. In fact, work­ing with the actor, they can cre­ate an awe­some per­for­mance. This is exactly how they made Gollum, the best char­ac­ter in the Lord of the Rings movies (It’s a crime that Gollum wasn’t nom­i­nated for Best Supporting Actor).
I think the best approach is in Sin City.

Let actors be peo­ple in real cos­tumes, and give them real look­ing props — even to the point of hav­ing a car mockup on set. The rest of the room is green. They can act & react, and the direc­tor can still do crazy visu­als. The whole thing can be done in a large (though some­what pricey) garage exactly as Rodriguez did. In fact, the mocap advances may help here — give the actor a real gun that hap­pens to have a lit­tle flu­o­res­cent ball on each end so the com­puter can pick it up, and that 9mm pis­tol becomes a badass alien Zap-O-Ray.
Mocap is great. The work the TVD peo­ple are doing is awe­some, and I am excited that this may bring mocap within reach of aspir­ing inde­pen­dent film­mak­ers. It’s just another tool, though; not an end in itself. A movie still needs a well struc­tured, inter­est­ing story, and a per­for­mance that we will draw us in. In other words, don’t for­get the per­for­mance in all the technology.