BVH in animation Master is rather simple:
-get yourself some BVH files to work with.
-Make a new action for your rigged character. I like to make sure my characters arms and legs are in full FK.
-Make sure you are in Animate mode for the loading of the BVH.(red 'A' in top toolbar.)
-Right Click on the action and select New/Motion Capture/ Biovision BVH
-Select a BVH file from your HD. You will see it loading. You will then see a 'bones' character in your action, and you can scrub to view the action-make sure it is a workable file.
-Scale the BVH to relative size of your character, you can rotate the BVH to face the same direction as well.
-Starting at the feet working upwards- apply 'Orient Like' and 'Translate To' constraints to each foot, the hips and chest, then the hands. 'Aim At' constraints can also be used, like for the upper legs- aim at knees... You will need to set the offsets for the bones as well... usually zero-out the values in the constraints offset X,Y,Zs. Do not worry about individual fingers, face, or toes info unless it is in the file and you want to.
Once done... hit play and watch your character move with motion-captured nuances! Most BVH capture files have trouble with 'flipping hands' or 'feet thru floor' or 'jump frames'... you can correct these as you see them in the action by keyframing correction or deleting bad keyframes from the BVH. Many BVH files are captured during a 'session' and share similar orientation attributes, you can easily import a new BVH from a like session without the need for re-constraining everything.
HERE is something I worked on for Mr.Bones recently- showcasing his actions on my character with A:M's dynamic hair. BVH's are fun and can be mixed with custom animation. Hope this helps!