Component-Aware Spatio-Temporal Adaptation of Frozen Foundation Models for Video Deepfake Detection

The advancement of deep generative models facilitates realistic synthetic facial videos, threatening social trust and digital security. Existing detection methods achieve strong in-domain performance but suffer from cross-dataset degradation, primarily due to overfitting to dataset-specific spatial artifacts. To address these challenges, we propose a parameter-efficient, video-based deepfake detection framework that leverages a frozen foundation model encoder coupled with a lightweight spatio-temporal decoder. First, we introduce a Component-Aware Spatial Enhancement (CASE) module that selectively accentuates manipulation-prone facial regions, such as the eyes, mouth and nose, while capturing global-local structural inconsistencies, thereby enabling the detection of subtle artifacts. Second, it is complemented by a Bidirectional Spatio-Temporal (Bi-ST) decoder that models local temporal transitions and bidirectional temporal dependencies across sampled frames, enabling robust temporal reasoning within each video clip. Without fine-tuning the backbone network, our framework achieves robust cross-dataset generalization by jointly reasoning about spatial and temporal anomalies. Finally, extensive experiments demonstrate that the proposed method performs competitively against strong baselines, particularly under cross-dataset evaluation.