Capping Off The Week
AUTHOR: Emily
This week, Phinney, Reid, Kevin, and Scott (who you’ll get to meet soon) piled into a car and took a trip to Vancouver, Canada. Their destination? Animatrik, a company that specializes in motion capture animation. If you’ve ever seen behind the scenes footage of people running around in tights with little reflective balls all over them, that’s mocap, and it’s been used in movies for years. As it’s evolved over the past fifteen or so years, though, it’s also become an important tool for game developers.
To give you guys some insight into what motion capture is, how it works, and how it’s going to apply to Class3, I sat down with Reid to learn more about what our recent session was like. Read on to see what he had to say!
What is mocap and how is it different than traditional animation?
Motion capture records the movements of a live actor onto a set of controls called a rig. The rig controls the movement of the character model. You know those tight suits the actors wear, covered with a series of markers? The markers are what actually gets recorded and through a lot of crazy math, gets translated on to the rig.
Mocap is a great way to get realistic motion in a short amount of time. While hand-created keyframe animation can create realistic movement, the process is really consuming, and you still wouldn’t capture all the subtleties that you can get from mocap.
Traditional keyframe animation is very good for stylized movement and stylized characters, and for the “realistic” motion of fantastic creatures like dragons. Obviously, you can’t mocap something that doesn’t exist!
A lot of people recognize the mocap suits that actors wear, but how does the process actually work?
A bunch of cameras track the position of the little white markers on the actors’ mocap suits, which are used to triangulate the position of the actor’s actual joints. The data is then converted into rotational joint information that’s put on the skeleton. (A lot of markers and a lot of math are involved because they haven’t figured out a way to put the markers inside the actors yet. 
) Once this motion is on the skeleton, we translate it again to the character’s animation controls (which we refer to as the “rig”).
In the end, the animation ends up on the character in the same format as it does when I keyframe it. The only difference is that mocap data puts a key on every frame (that’s 30 keys per second of animation), which requires different animation techniques and tools to edit the dense amount of data that motion capture gives you.
For cinematics, if you plan correctly, get a good performance from the actors, and get good motion from the mocap studio, the animator shouldn’t have to edit much. Gameplay motion is a whole different thing — that requires a lot of editing.
What do you look for in a motion capture actor?
Since we were shooting both cinematic and gameplay styles for this session, we were looking for people that were both good actors and had strong physical and athletic skills.
For our cinematic shoot, the actors just ran through the scenes like they would if they were on stage performing a play, and we captured their motion in large chunks. For these sequences we’re primarily looking for acting ability.
On the other hand, the gameplay part of the shoot required the actors to perform specific actions in small pieces, which can feel pretty counterintuitive or unnatural. For example, if a character picks up an object and then throws it, the acting sequence might be broken up like this: the character is standing still (one shot), the character picks up an object (second shot), the character stands with the object in their hands (third shot), the character throws the object (fourth shot), and finally, the characters returns to a casual standing state (fifth and final shot). For an actor who’s used to following typical stage directions to just pick something up and throw it, that can be a jarring experience!
It sounds like mocap is pretty specialized. How do you go about finding the right actors?
Well, in our case, one of the actors we used was highly recommended by Animatrik and the other was recommended to Animatrik by someone who had worked with him in the past. Most mocap studios will know talented local actors from past projects, and they’re usually happy to recommend them. When that approach doesn’t work, you can hold casting calls where actors and their agents can send you resumes, demo reels, and things like that.
Once you find someone that looks good, you typically hold auditions to make sure they’re a good fit for what you need. (Since our guys came highly recommended from people we trusted, we actually skipped this step.)
What’s a mocap session like? Tell us what you guys did when you were up there!
The session started out with breakfast provided by the studio. While we ate, we got acquainted with the team and the actors. We also went over some of the scripts for the acting portion and some of the action for the gameplay portion. Once the actors had their suits on and everything was calibrated, we had them go right into the acting.
Phinney and Kevin took turns directing the storyline scenes. Before each scene was recorded, they prepped the actors on things like where to be on stage, how the characters they were playing should behave, what their personality and state of mind should be during the scene, and how intense or subtle the scene should be. I chimed in a little bit on some logistical things, like the placement of the objects they were interacting with. The actors also had some great ideas and added a lot of personality on their own.
After the acting section of the session was complete, it was my turn to direct gameplay stuff. I coached the actors on the speed and strength in which they should perform an action, judging the motion on if I thought it I could easily make it loop or not. I also tried to get them to start out in an idle pose, do an action in place, and then end the motion in the same idle pose. That will make the animations blend much more smoothly when you actually put them in the game.
How long do mocap sessions usually take?
Our day consisted of two 3 to 4 hour blocks. In both cases, we started with cinematic scenes and moved on to action sequences.
The morning session started with breakfast, paperwork, and studio and actor set-up at 8:00 am. We started shooting at 9:30, then broke for lunch at 12:30. After talking zombie games, guns, and Skyrim with cast and crew, we went back into shooting at 1:30 and were scheduled to start wrapping up at 5:30. Things went quicker than we’d expected, though, so we finished our full list — plus some bonus recording — around 4:30.
Since we have a lot to do back at the Lab, we drove back to Seattle the same night. We were a bunch of zombies the next day, but hey. It fits, I guess. 
When we get back mocap data, what format is it in? How do you get the finished characters into the game?
We get video first so we can choose the takes we like best. Once we’ve picked these, we send the details back to Animatrik, who cleans up the files we requested and sends them to us as skeletons with the motion attached to them.
The animations we get back are in a lot of different pieces, so to get them ready to use, Scott translates the motion from the skeleton to the rig. When he’s done, he sends them to me to do the necessary edits and get the pieces organized and exported. Once we’re finished, they are usable for the designers to put into the game.
Thanks for giving details about your trip, Reid!
I hope you guys liked this inside view of how our characters are being built! Next week, we have more game information coming your way — Phinney is preparing a design article on multiplayer in Class3 to close out 2011, so be sure to check back in on Friday.
Have a great weekend, everyone!
Emily
Zombies do not simply seek to kill you. They want to consume you. If you fight a zombie, you’d better destroy it, find a way to escape, or pray to god someone will rescue you before it is too late. Defeat can only end in two ways: you’re torn apart and eaten alive, or you’re infected and turn into a zombie yourself. Not pretty. You must learn to cope with being hunted if you want to live. Humans aren’t used to having predators — especially ones that look like us or worse, used to be our friends and loved ones.
