MotionLLM: Understanding Human Behaviors from Human Motions and Videos
Authors: name: Ling-Hao Chen, name: Shunlin Lu, name: Ailing Zeng, name: Hao Zhang, name: Benyou Wang, name: Ruimao Zhang, name: Lei Zhang

This study delves into the realm of multi-modality (i.e., video and motion
modalities) human behavior understanding by leveraging the powerful
capabilities of Large Language Models (LLMs). Diverging from recent LLMs
designed for video-only or motion-only understanding, we argue that
understanding human behavior necessitates joint modeling from both videos and
motion sequences (e.g., SMPL sequences) to capture nuanced body part dynamics
and semantics effectively. In light of this, we present MotionLLM, a
straightforward yet effective framework for human motion understanding,
captioning, and reasoning. Specifically, MotionLLM adopts a unified
video-motion training strategy that leverages the complementary advantages of
existing coarse video-text data and fine-grained motion-text data to glean rich
spatial-temporal insights. Furthermore, we collect a substantial dataset,
MoVid, comprising diverse videos, motions, captions, and instructions.
Additionally, we propose the MoVid-Bench, with carefully manual annotations,
for better evaluation of human behavior understanding on video and motion.
Extensive experiments show the superiority of MotionLLM in the caption,
spatial-temporal comprehension, and reasoning ability.