Injecting Text Clues for Improving Anomalous Event Detection from Weakly Labeled Videos

Video anomaly detection (VAD) aims at localizing the snippets containing anomalous events in long unconstrained videos. The weakly supervised (WS) setting, where solely video-level labels are available during training, has attracted considerable attention, owing to its satisfactory trade-off between the detection performance and annotation cost. However, due to lack of snippet-level dense labels, the existing WS-VAD methods still get easily stuck on the detection errors, caused by false alarms and incomplete localization. To address this dilemma, in this paper, we propose to inject text clues of anomaly-event categories for improving WS-VAD, via a dedicated dual-branch framework. For suppressing the response of confusing normal contexts, we first present a text-guided anomaly discovering (TAG) branch based on a hierarchical matching scheme, which utilizes the label-text queries to search the discriminative anomalous snippets in a global-to-local fashion. To facilitate the completeness of anomaly-instance localization, an anomaly-conditioned text completion (ATC) branch is further designed to perform an auxiliary generative task, which intrinsically forces the model to gather sufficient event semantics from all the relevant anomalous snippets for completely reconstructing the masked description sentence. Furthermore, to encourage the cross-branch knowledge sharing, a mutual learning strategy is introduced by imposing a consistency constraint on the anomaly scores of these two branches. Extensive experimental results on two public benchmarks validate that the proposed method achieves superior performance over the competing methods.