CRNet: Centroid Radiation Network for Temporal Action Localization

Temporal action localization aims to localize segments in an untrimmed video that contains different actions. Since contexts at boundaries between action instances and backgrounds are similar, how to separate the action instances from their surrounding is a challenge to be solved. In fact, the similar or dissimilar contents in actions play an important role in accomplishing the task. Intuitively, the instances with the same class label are affinitive while those with different labels are divergent. In this paper, we propose a novel method to model the relations between pairs of frames and generate precise action boundaries based on the relations, namely Centroid Radiation Network (CRNet). Specifically, we propose a Relation Network (RelNet) to represent the relations between sampled pairs of frames by employing an affinity matrix. To generate action boundaries, we use an Offset Network (OffNet) to estimate centroids of each action segments and their corresponding class labels. Based on the assumption that a centroid and its propagating areas have the same action label, we obtain action boundaries by adopting random walk to propagate a centroid to its related areas. Our proposed method is an one-stage method and can be trained in an end-to-end fashion. Experimental results show that our approach outperforms the state-of-the-art methods on THUMOS14 and ActivityNet.