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arXiv · 2509.17084

MoCLIP-Lite: Efficient Video Recognition by Fusing CLIP with Motion Vectors

Binhua Huang·Ni Wang·Arjun Pakrashi·Soumyabrata Dev
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Abstract

Video action recognition is a fundamental task in computer vision, but state-of-the-art models are often computationally expensive and rely on extensive video pre-training. In parallel, large-scale vision-language models like Contrastive Language-Image Pre-training (CLIP) offer powerful zero-shot capabilities on static images, while motion vectors (MV) provide highly efficient temporal information directly from compressed video streams. To synergize the strengths of these paradigms, we propose MoCLIP-Lite, a simple yet powerful two-stream late fusion framework for efficient video recognition. Our approach combines features from a frozen CLIP image encoder with features from a lightweight, supervised network trained on raw MV. During fusion, both backbones are frozen, and only a tiny Multi-Layer Perceptron (MLP) head is trained, ensuring extreme efficiency. Through comprehensive experiments on the UCF101 dataset, our method achieves a remarkable 89.2% Top-1 accuracy, significantly outperforming strong zero-shot (65.0%) and MV-only (66.5%) baselines. Our work provides a new, highly efficient baseline for video understanding that effectively bridges the gap between large static models and dynamic, low-cost motion cues. Our code and models are available at https://github.com/microa/MoCLIP-Lite.

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Binhua Huang, Ni Wang, Arjun Pakrashi, Soumyabrata Dev. 2025-09-25. MoCLIP-Lite: Efficient Video Recognition by Fusing CLIP with Motion Vectors. https://arxiv.org/abs/2509.17084

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