Training-free Video Corpus Moment Retrieval via Synergistic Collaboration and Adaptive Calibration.

Video Corpus Moment Retrieval (VCMR) is pivotal to multimodal understanding. However, existing methods rely heavily on large-scale annotated data, which limits their generalization and scalability. To address this issue, we propose a training-free VCMR framework, termed Synergistic Collaboration and Adaptive Calibration (SCAC), enabling effective semantic parsing and precise temporal localization without parameter updates. SCAC introduces a Query Event Chain Generation module that leverages large language models to transform complex textual queries into structured event chains, while a Video Event Chain Generation module represents videos as semantically coherent event chains through subtitle segmentation and keyframe aggregation. Built on these structured representations, SCAC performs Event-Chain-Based Cross-Modal Retrieval with mean-variance joint scoring to suppress local mismatches and reinforce global consistency. During localization, a Synergy-Calibration Mechanism dynamically refines temporal boundaries via profit-setback feedback. Extensive experiments show that SCAC achieves comparable or superior results to supervised counterparts under training-free conditions, demonstrating strong cross-modal generalization and adaptive capability. The code of our method is available at https://github.com/cyanlll/SCAC.