Loading Optitrack Motions onto Character Studio Avatars
Optitrack Arena Software enables you to export captured and trajectorized animation files in the BVH format.
Such files can be loaded onto character studio bipeds for animation.
However, the animations need to be converted to match the biped skeleton first. This can be achieved as follows:

Choose the biped to activate the character studio panel. This can be
done by pressning the "H" key and selecting the first element in the
biped hierarchy:

Choose figure mode to save the biped structure of the avatar:

Save the skeletal structure of your Avatar in for example AMan0004-CS.fig file.

Remove the character by selecting all and pressing delete.
Create a new Biped


Accept Mocap Dialog by pressing OK.

Test the motion on the biped

Go to Figure Mode

Once you have pressed Load Max will adapt the existing animation to the
structure of the original avatar that is contained in the .fig file.
Now we can leave the figure mode and save the biped and the animation that was loaded onto it.

Save the biped with the whole motion sequence:

Remove the bipead and create a new scene.
Load the original Avatar that we used to save the .fig file for the skeletal structure.
Go into the character studio panel and load the prepared .bip file.

Thats it. Now the motion can be adapted by using layers or by segmenting it into pieces for looping and blending.