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Human Motion Diffusion as a Generative Prior
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Shows that a pretrained text-to-motion diffusion model (MDM) can be reused as a frozen prior via three composition methods (DoubleTake for long sequences, ComMDM for two-person motion, DiffusionBlending for joint/trajectory control) that need little or no new data.
Problem
Human motion diffusion models are limited by scarce annotated motion data, focus on short single-person clips, and offer coarse control; the paper asks how a pretrained motion prior can enable long sequences, two-person interaction, and fine-grained control with little data.
Approach
Compose frozen or lightly fine-tuned diffusion priors: DoubleTake generates overlapping intervals in one batch with handshake averaging and soft-masked second-take refinement (zero-shot); ComMDM adds a small transformer communication block between two frozen MDMs (few-shot); DiffusionBlending interpolates the noise predictions of models fine-tuned for different joint controls, generalizing classif
Key results
- On BABEL, DoubleTake transition FID 1.88 (70-frame margin) vs TEACH 3.86, and motion FID 1.04 vs TEACH 1.12.
- On HumanML3D trajectory control, fine-tuned MDM reaches FID 0.54 vs 0.98 for inpainted MDM; DiffusionBlending for left wrist+trajectory reaches FID 0.22 vs 1.18.
- In a 30-participant user study, ComMDM was preferred over MRT and MDM for two-person prefix completion, though MRT had lower L2 error (0.146 vs 0.176 joints at 3s).
Measured effects reported in the paper
| What was changed | Where | Measured | Effect |
|---|---|---|---|
| Add the second take to refine transitions (ablation) | DoubleTake · HumanML3D test | FID: 1.00 -> 0.60 | Helped |
| Use the first take before the second take (ablation) | DoubleTake · HumanML3D test | FID: 1.09 -> 0.60 | Helped |
| Set transition mask ramp length b to 20 instead of the default (ablation) | DoubleTake · HumanML3D test | FID: 0.60 -> 0.84 | Hurt |
| Set handshake size h to 30 instead of the default (ablation) | DoubleTake · HumanML3D test | FID: 0.60 -> 1.03 | Hurt |
| Set handshake size h to 40 instead of the default (ablation) | DoubleTake · HumanML3D test | FID: 0.60 -> 1.16 | Hurt |
| Set soft mask M_soft to 0.0 instead of the default (ablation) | DoubleTake · HumanML3D test | FID: 0.60 -> 0.85 | Hurt |
| Set soft mask M_soft to 0.2 instead of the default (ablation) | DoubleTake · HumanML3D test | FID: 0.60 -> 0.90 | Hurt |
| Add the ComMDM communication block to the fixed MDM priors (ablation) | ComMDM · 3DPW prefix completion, 3s | Root error [m]: 0.54 -> 0.30 | Helped |
| Use 2 or 4 ComMDM layers instead of 1 (ablation) | ComMDM · 3DPW prefix completion, 3s | Root error [m]: 0.30 -> 0.31; 0.30 -> 0.32 | Hurt |
| Place the communication block at a lower transformer layer instead of layer 8 (ablation) | ComMDM · 3DPW prefix completion, 3s | Root error [m]: 0.30 -> 0.33; 0.30 -> 0.36; 0.30 -> 0.45; 0.30 -> 0.47 | Hurt |
| Fine-tune MDM for trajectory control rather than using original inpainting | MDM · HumanML3D test, trajectory control | FID: 0.98 -> 0.54 | Helped |
| Fine-tune MDM for left wrist control rather than using original inpainting | MDM · HumanML3D test, left wrist control | FID: 0.82 -> 0.34 | Helped |
Surprising findings
- MRT achieves lower L2 prefix-completion error than ComMDM, yet produces static, unrealistic motion, so the authors argue L2 metrics are misleading here.
- DoubleTake produces coherent long motions (~10 minutes) from a prior trained only on clips up to ~10 seconds, with transitions never annotated in training data.
Limitations
- ComMDM generalizes only to interaction types seen during training and was trained on very few examples.
- Long-sequence quality is bounded by the base MDM and motion may be inconsistent between distant intervals.
- Two-person generation does not model valid contacts between people.
Experimental setup
Datasets: HumanML3D BABEL 3DPW AMASS
Benchmarks: HumanML3D BABEL 3DPW
Metrics: R-precision FID diversity multimodal distance L2 joint and root error user study preference
Baselines: TEACH MRT MDM inpainting MDM (no Com) Com only
Builds on: Motion Diffusion Model (MDM) classifier-free guidance DDPM MRT
Closest papers by meaning
- MixerMDM: Learnable Composition of Human Motion Diffusion Models (CVPR 2025 · similarity 0.92)
- MotionMix: Weakly-Supervised Diffusion for Controllable Motion Generation (AAAI 2024 · similarity 0.91)
- AMD: Autoregressive Motion Diffusion (AAAI 2024 · similarity 0.90)
- Rethinking Diffusion for Text-Driven Human Motion Generation: Redundant Representations, Evaluation, and Masked Autoregression (CVPR 2025 · similarity 0.90)
- Optimizing Diffusion Noise Can Serve As Universal Motion Priors (CVPR 2024 · similarity 0.89)
- Towards Detailed Text-to-Motion Synthesis via Basic-to-Advanced Hierarchical Diffusion Model (AAAI 2024 · similarity 0.89)
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