Reze Rig

Convert humanoid skeletal animations into MMD VMD files in the browser. Upload a motion, watch it play on a PMX model, and download the VMD.

One piece of the Reze MMD family, covering the whole MMD workflow on the web:

reze-engine	The WebGPU foundation — anime-character rendering and physics, dependency-free
reze-design	Scene design, rendering and sharing platform
reze-studio	Animation editing on a professional timeline and curve editor
MiKaPo	Real-time motion capture in the browser, exporting straight to VMD
reze-rig	This repo — retarget FBX animations to MMD VMD format

How it works

Each source bone's animation is expressed as a world-orientation delta from its own bind pose, aligned onto the MMD skeleton, and written as parent-local rotations for MMD's hierarchy (センター / 上半身 / 左腕 / …). Every calibration below happens automatically, per file — there is nothing to configure.

• Rig detection. Mixamo, UE-Mannequin / Unity Humanoid, 3ds Max Biped and Character Creator names resolve to MMD's Japanese bone names, with the hierarchy taken from the file's own connections.
• Any bind pose. Each bone is aligned by measuring the same anatomical segment on both skeletons, so T-pose, A-pose and relaxed binds convert alike — arms, legs, feet, spine and fingers.
• The true bind, wherever it lives. FBX records it in the skin or a BindPose node; exporters that overwrite the rest pose with the current frame no longer break the conversion. A file authored Z-up is stood upright first. When nothing supplies a bind, the tool says so instead of converting silently.
• The target model is measured, not assumed. Bone positions come from the loaded PMX, so alignment, proportions and translation scale adapt to whatever model is in the viewport — centimetre, metre and inch exports all land correctly. Upload your own model as a zip and the motion re-retargets to it on the spot.
• Feet are placed, not derived. The VMD drives 左足ＩＫ / 右足ＩＫ from the source's own foot positions, so a proportion difference between the two skeletons doesn't turn into sliding, and the motion adapts to other models.
• In Place removes horizontal travel while keeping the vertical, so jumps and crouches survive.

Preview and download share one code path: the converted clip plays in the engine directly, and exportVmd serializes exactly what you watched.

Supported source rigs

Rig	Bone names	Status
Mixamo	mixamorig:Hips, mixamorig:LeftArm	Tested
UE-Mannequin / Unity Humanoid	pelvis, upperarm_l, thigh_l	Tested
Reallusion Character Creator	CC_Base_Hip, CC_Base_L_Upperarm	Mapped, lightly tested
3ds Max Biped	Bip001 Pelvis, Bip01 L Thigh	Mapped, lightly tested

Any other humanoid rig is worth a try: the retarget is rig-agnostic and only the naming table is rig-specific. The corner panel shows the skeleton as parsed — rig profile, bones mapped, measured scale, with unmapped bones dimmed. If a rig converts badly, open an issue with that line and the file if you can share it.

Batch conversion

scripts/fbx2vmd.ts converts folders of FBX without a browser:

npx esbuild scripts/fbx2vmd.ts --bundle --platform=node --format=esm --outfile=/tmp/fbx2vmd.mjs
node /tmp/fbx2vmd.mjs <files-or-dirs...> [options]

Directories are scanned recursively; each clip writes <out>/<basename>.vmd.

Option
--out <dir>	Output directory
--target-pmx <file>	Measure this model as the retarget target
--in-place	Strip horizontal root motion
--no-foot-ik	Drive the legs by FK instead of exporting foot-IK targets
--bind-ref <file>	Anchor per-pose exports to this clip's bind (defaults to an Idle.fbx among the inputs)
--no-bind-ref	Use each clip's own rest pose

scripts/regression.ts pins every verified conversion — profile, bone counts, scale and a checksum over all exported keys — so a change to the retarget can't quietly alter motions that already work.