The MNM File: The Bridge Between Your BVH Animations and Biped
When you try to apply a .bvh animation to a Biped system in 3ds Max and the bones seem to speak different languages, it's not that you're cursed (although it feels that way). What's missing is an interpreter: the .mnm file (Marker Name Map), a fairly unknown but essential tool for aligning bones from a BVH file with those expected by Biped. The good news is that you don't need an arcane ritual to create it… just patience, and a good dose of technical knowledge that I'm sharing with you right now.
What is an MNM File and What is it Used For?
An .mnm file acts as a dictionary that relates the bone names from your .bvh animation with the internal names of the Biped system. For example, if your BVH says RightArm but Biped expects RUpperArm, the MNM file tells the system, when you see RightArm, use it as if it were RUpperArm.
This becomes essential when working with motion capture data (mocap), whether from Mixamo, homemade systems, or free libraries like CMU or Carnegie Mellon.
How to Create an MNM File from Scratch
Creating an MNM file doesn't require extra software. It's simply a plain text file (.txt) renamed with the .mnm extension. The structure is simple:
RightArm = RUpperArm LeftArm = LUpperArm RightForeArm = RForearm LeftForeArm = LForearm RightLeg = RThigh LeftLeg = LThigh RightUpLeg = RCalf LeftUpLeg = LCalf Hips = Pelvis Spine = Spine Head = Head
Each line represents a mapping: BVH bone name = Biped bone name. Save it with the .mnm extension, for example: mixamo_to_biped.mnm.
How to Apply the MNM File When Importing BVH
Once you've created your MNM file:
- Open 3ds Max.
- Go to Motion > Biped > Motion Capture.
- In the window, select the .bvh file you want to import.
- Check the Use Marker Name Map box.
- Load the .mnm file you just created.
Click OK. If the mapping is correct, you'll see that Biped accepts the animation without errors. It's important that the MNM file covers all relevant names; if any are missing, the animation may be incomplete or mispositioned.
Modern Alternative? Forget Biped and Use CAT or Direct FBX
If you're getting into mocap animation and see that Biped and MNM are draining your soul, it might be time to look to the future. The CAT (Character Animation Toolkit) system and modern FBX retargeting tools in 3ds Max 2025 and other software like MotionBuilder or Cascadeur allow retargeting animations with much less pain. Plus, the FBX format is more flexible, preserves hierarchy and clean rotations, and doesn't require MNM files.
Because of course, you thought the bones moved on their own… and it turns out they need someone to tell them who they are.