We decided we wanted to try motion-capturing the marine animations in NS2 because there are tons of them to make and because they are very time-consuming to create (because the human eye is so familiar with how humans move). Colin Knueppel is one of two animators on NS2 and has done motion-capture before (unlike the rest of us). He wrote up with this set of guidelines to help us get started. We thought this might be helpful for other game developers and interesting for everyone.

Check with the mocap studio

Motion capture most often uses a myriad of cameras to catch reflective balls sticky taped or velcroed to an actor's body. If you bring something similarly reflective.. well, it can cause issues. Discuss what you'd like to bring with you to the studio with the studio. Ask them what you can do to minimize any conflicts your props may cause.

Have some masking tape

Hopefully they'll have it there, but if they don't, have your own tape. Putting down a target from start to finish helps. We animators can dampen or ramp up motion to make a target move X far or turn Y more, but the closer to the mark they get, the less work we animators will need to do.

Send the actor lots of Marine concept work with notes

The better the actor understands what his character is wearing and what restrictions he may have, the better the performance will be.

Bring the material with you

Unfortunately many actors have been disappointingly unwilling to read material sent to them, preferring to "wing it." Setting aside 45 minutes before you're on the mocap clock with the actor to make sure they understand what they'll be doing is preferable to arguing it out while the machines are running. If you can set aside an afternoon to plan through moves with him or her before the mocap, even better. Inside the mocap studio your on an expensive clock. A parking lot with coworkers to get down the gist of motions is a great start. Getting time with the actor to convey what you learned will cost you the actors wages, but the motion capture session will go many times smoother.

Proper weight

A marine tends to carry something akin to 60 lbs of gear, ammo and armor. Weighting the mocaper down correctly will keep him from doing unrealistic motion, give his foot steps proper weight and dampen the slight dancey tendencies that come with mocapers. It's not their fault, usually. It's human nature. When you don't properly weight a character, the actor often hams it up to "act" bigger or more impressive. It may work on film, but the cruel eye of the motion capture cameras will make every odd mannerism twice as goofy. Ask the motion capture studio what you may be able to use to properly weight the character. A belt with some sand bags attached to it, a shoulder straps with some weights, some ankle or wrist weights. Get or make a well-weighted weapon. Find out if there's a color you should use that wont throw off the capture.

With each of these, we don't necessary want to go realistic but light of realistic. Ask the actor what he'd be comfortable with. Test it ahead of time when practicing with the actor, if you can.

Recoil

An innovative approach to motion capture was tested by my lead at Bioware, Shane Welbourn, and it worked fairly well. Gun recoil comes from the gun, not the marine shrugging spasticaly. When the actor is "firing" have someone strike the rifle's end. This makes the motion driven by the gun, not by muscle contractions in the actor.

Make it as realistic as you can

Ultimately the less the actor has to guess, the more realistic the motion will likely be. If you can restrict his spine movement, he'll compensate for the marine's rigid outfit. If you tape a mocap friendly ruler to his forearm, he wont have to guess where the pad will be. If you give him a nicely weighted weapon that's approximately the right size, he'll wield it right.

Experience

Find someone that has "been" what you want to mocap. Finding an actor who was a marine, he'll bring his experience to the session. When you get someone that isn't familiar with appropriate motions, they sometimes bring their other non-related experiences to play. We had a martial artist being dual-booked for our sci-fi game that could not, if his life depended on it, make a kick that didn't go at least a foot and a half off the ground by the time it was finished. That flourish took hours of animation and creative camera work to tone down.

Getting an appropriately experienced actor is not without pitfalls. Sometimes what actual marines do is less interesting then what we think they do, and even a hardened marine can come across with oddly consistent emotional gestures. Meeting the actor is a good way to pick up on problematic gestures, and practicing and discussing the moves ahead of time is a good way to avoid uninteresting motions.

Do what looks right, not what is right

This is a huge, but sadly not well known, rule of animation. The human mind has expectations, some of which are not always true. When confronted with whether to do what looks right or what is right, always go with what looks right, because an audience is not going to have the benefit of an explanation. They will cock their head and say, "that's odd." We want to keep the player in the game focused, not educate them.

We hope you found this interesting and helpful and we're hoping to share with you some footage of our motion-capture session!