I have been looking for a way to convert *.bip files to *.bvh, but it seems nobody doing such conversion before. Therefore, I had to figure it out myself how to do that. And here the quick and dirty to do the conversion.

Software you need: 3DS Max, MotionBuilder, bvhhacker (optional)

As far as I know, 3DS Max is the only software that can read *.bip, so you will need it installed. In 3DS Max, create Biped.

Make sure the biped structure conform the bvh structure (e.g. only have one spine). Rename the bones so that no space in the bones name, since bvh does not allow space in joint name. To make renaming the bones easier, use the script that you can download here. The script is called UI rename floater. Unhide all, select all and run the script. Replace all spaces.

To ensure that BVH resulted from the conversion is useable, I suggest you to rename the bones/joints in accordance with BVH joint name convention.

Save the MAX file, so that you do not have to do the above steps all over again when you need to convert another bip file.

Load the bip file into the biped, edit or play the animation, then export it as FBX.

Fire up MotionBuilder then load the FBX.

Delete the fbx_root. You have to delete the fbx_root, because if you don't, your BVH will not move from its original position while performing the motion. When you delete the fbx_root, the figure will face or move toward the ground, but it is okay since we can rotate it in Blender.

Finally export the scene as BVH.

You can check the BVH in BVHhacker.

When the BVH is imported to Blender, it turned out that we do not have to rotate the BVH figure.

That is it.