---
license: cc-by-4.0
tags:
  - animation
  - motion-in-betweening
  - onnx
  - 3d
  - qtmesheditor
library_name: onnx
pipeline_tag: other
---

# QtMeshEditor — RMIB Animation In-Betweening

A small transformer that fills the gap between two sparse keyframes with smooth,
plausible intermediate motion — **Robust Motion In-Betweening (RMIB)** style,
exported to **ONNX** for in-app inference via ONNX Runtime.

Built for **[QtMeshEditor](https://github.com/fernandotonon/QtMeshEditor)** (issue #409) — a free,
open-source 3D mesh & animation editor — and its companion **QtMesh Cloud**
asset service. The app downloads this model on first use and runs it locally
(offline) to power the dope-sheet **"AI in-between → Fill gap"** action, the
`qtmesh anim --in-between` CLI, and the `motion_in_between` MCP tool.

## Model

- **Input:** `pose_pair` `float32 [1, 2, 220]` — the start and end pose, each
  22 core-body joints × 10 DoF `[tx,ty,tz, qx,qy,qz,qw, sx,sy,sz]`.
- **Output:** `interior` `float32 [1, 8, 220]` — 8 predicted in-between poses.
- **Architecture:** a 4-layer Transformer encoder (start + end pose tokens +
  learnable interior-frame queries → per-frame pose). ~13 MB.
- **Skeleton:** the 22 CMU core-body joints (hips / spine / neck / head + both
  arms + both legs). QtMeshEditor maps arbitrary rig bone names (Mixamo,
  generic, CMU) onto these roles at runtime; rigs that don't map fall back to a
  deterministic spline.

## Training data & license

Trained **from scratch** on the **[CMU Graphics Lab Motion Capture Database](http://mocap.cs.cmu.edu)**
— permissively licensed (free to use/modify/redistribute, including in
commercial products; you may not resell the motion data itself; credit
mocap.cs.cmu.edu). This is what makes the weights redistributable under
QtMeshEditor's permissive (MIT) distribution — unlike the field-standard LAFAN1
(CC-BY-NC-ND), which we deliberately avoided.

On a held-out CMU split the model beats spherical-linear interpolation (the
shipped spline fallback) by **more than 2×** on rotation error.

Weights released under **CC-BY-4.0**; please credit *QtMeshEditor* and the CMU
Graphics Lab Motion Capture Database.

## Reproducing

`scripts/export-rmib-onnx.py` in the QtMeshEditor repo (one-time, offline; not
shipped with the app).

## Versions

- **v1.0.0** (current) — initial RMIB in-betweening model trained on CMU MoCap
  (22 core-body joints, ~421k windows; beats slerp by >2× on a held-out split).