Graph-based Dense Event Grounding with relative positional encoding

Temporal Sentence Grounding (TSG) in videos aims to localize a temporal moment from an untrimmed video that is relevant to a given query sentence. Most existing methods focus on addressing the problem of single sentence grounding. Recently, researchers proposed a new Dense Event Grounding (DEG) problem by extending the single event localization to a multi-event localization, where the temporal moments of multiple events described by multiple sentences are retrieved. In this paper, we introduce an effective proposal-based approach to solve the DEG problem. A Relative Sentence Interaction (RSI) module using graph neural network is proposed to model the event relationship by introducing a temporal relative positional encoding to learn the relative temporal order information between sentences in a dense multi-sentence query. In addition, we design an Event-contextualized Cross-modal Interaction (ECI) module to tackle the lack of global information from other related events when fusing visual and sentence features. Finally, we construct an Event Graph (EG) with intra-event edges and inter-event edges to model the relationship between proposals in the same event and proposals in different events to further refine their representations for final localizations. Extensive experiments on ActivityNet-Captions and TACoS datasets show the effectiveness of our solution.