Motion/Performance capture usually happens fairly early during development, because animators need time to take the captured data and turn it into actual performances. Despite what some actors might suggest, there's a huge amount of work, skill, and artistry necessary in order to convert a recorded motion and turn it into a performance that reads well from the viewer's perspective. Here's an example:
The raw motion capture looks rather generic but it isn't immediately clear exactly what is happening from a first viewing. The edited animation reads a lot better - the motions are more exaggerated, the struggles of the victim are a lot more readable, the attacker's stab is more pronounced, and so on - the entire action is clearer, more readable, and even a bit faster than the raw mocap. Much of what animators do during production is this performance capture cleanup and modification/adjustment.
We usually try to schedule performance capture sessions as early as we can because they involve aligning many separate schedules - the capture studio, the actors, and the developers who need to oversee all of the action. Usually we aim for around the end of pre-production, but it all depends on the availability of the studio, the actors, and the developers. The performance capture session is usually fairly quick - it usually takes a week or less to capture all of the necessary movements - but expensive because of the scheduling, number of people, equipment, and traveling involved. It normally costs tens of thousands of dollars per hour to pay for all of the time, equipment, and labor for all of the people involved, and everyone has a busy schedule - actors have other jobs lined up, the capture studio has other customers hoping to do their own recording sessions, and the developers have a whole game to build.
Because of the difficulty in scheduling and expense of recording, the art and animation team must put together a move list of all the actions they need to capture before the recording session. They can modify, update, and change the list up until the deadline, but it's pencils down once the session begins. Reshoots are extremely expensive for all of those reasons - aligning the schedules of the recording studio, all of the needed actors, and the developer representatives can be a nightmare in terms of scheduling. For DLC/expansion content, we usually try to reuse as many assets as we can, and schedule any new recording sessions as soon as we get the green light.
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