Multimodal Deepfake Detection for Digital Forensics: A Robust Audio-Visual Inconsistency Approach for Evidence Integrity

The rapid proliferation of Generative AI (GenAI) has democratized the creation of hyper-realistic multimedia forgeries, posing severe threats to electronic Know Your Customer (eKYC) systems and digital forensic investigations. While visual synthesis has reached near-perfection, maintaining precise synchronization between lip movements (visemes) and speech signals (phonemes) remains a formidable challenge. To address this, we propose a novel Multimodal Deep Learning framework designed to detect high-fidelity Deepfakes by exploiting audio visual temporal inconsistencies. Beyond traditional feature fusion, our architecture integrates a Contrastive Synchronization Loss with a Transformer based Cross-Modal Attention mechanism. This hybrid objective explicitly enforces intra-class compactness for authentic pairs while amplifying the distance for asynchronous forgeries. Extensive experiments on FaceForensics++, DFDC, and a custom Vietnamese dataset (Vn-eKYC-Aug) demonstrate that our model achieves state-of-the-art performance, maintaining high robustness against video compression and environmental noise, though operational efficacy remains sensitive to extreme low-light conditions and diverse regional dialects. This research provides a resilient forensic layer for digital identity verification, ensuring evidence integrity in the GenAI era.