CacheFlow: Fast Human Motion Prediction by Cached Normalizing Flow

TL;DR

CacheFlow introduces a fast, cache-based flow model for 3D human motion prediction, significantly reducing inference time while maintaining high accuracy, outperforming existing methods in speed and density estimation.

Contribution

The paper proposes CacheFlow, a novel two-stage flow-based model that precomputes and caches flow computations, enabling rapid conditional human motion prediction without sacrificing accuracy.

Findings

Inference time reduced to approximately one millisecond.

Outperforms previous VAE and diffusion-based methods in speed.

Maintains comparable or improved prediction and density estimation accuracy.

Abstract

Many density estimation techniques for 3D human motion prediction require a significant amount of inference time, often exceeding the duration of the predicted time horizon. To address the need for faster density estimation for 3D human motion prediction, we introduce a novel flow-based method for human motion prediction called CacheFlow. Unlike previous conditional generative models that suffer from poor time efficiency, CacheFlow takes advantage of an unconditional flow-based generative model that transforms a Gaussian mixture into the density of future motions. The results of the computation of the flow-based generative model can be precomputed and cached. Then, for conditional prediction, we seek a mapping from historical trajectories to samples in the Gaussian mixture. This mapping can be done by a much more lightweight model, thus saving significant computation overhead compared to a typical conditional flow model. In such a two-stage fashion and by caching results from the slow flow model computation, we build our CacheFlow without loss of prediction accuracy and model expressiveness. This inference process is completed in approximately one millisecond, making it 4 times faster than previous VAE methods and 30 times faster than previous diffusion-based methods on standard benchmarks such as Human3.6M and AMASS datasets. Furthermore, our method demonstrates improved density estimation accuracy and comparable prediction accuracy to a SOTA method on Human3.6M. Our code and models are available at https://github.com/meaten/CacheFlow.