Weakly-supervised action localization aims to recognize and localize action instancese in untrimmed videos with only video-level labels. Most existing models rely on multiple instance learning(MIL), where the predictions of unlabeled instances are supervised by classifying labeled bags. The MIL-based methods are relatively well studied with cogent performance achieved on classification but not on localization. Generally, they locate temporal regions by the video-level classification but overlook the temporal variations of feature semantics. To address this problem, we propose a novel attention-based hierarchically-structured latent model to learn the temporal variations of feature semantics. Specifically, our model entails two components, the first is an unsupervised change-points detection module that detects change-points by learning the latent representations of video features in a temporal hierarchy based on their rates of change, and the second is an attention-based classification model that selects the change-points of the foreground as the boundaries. To evaluate the effectiveness of our model, we conduct extensive experiments on two benchmark datasets, THUMOS-14 and ActivityNet-v1.3. The experiments show that our method outperforms current state-of-the-art methods, and even achieves comparable performance with fully-supervised methods.

本文提出了一种基于注意力机制的分层结构潜在模型，用于学习特征语义的时间变化，通过两个组件进行实现：第一个是无监督的变点检测模块，通过在时间层次中学习视频特征的变化率来检测变点；第二个是基于注意力的分类模型，将前景的变点作为边界来选择。通过在两个基准数据集THUMOS-14和ActivityNet-v1.3上进行广泛实验，结果表明我们的方法优于当前最先进的方法，并且甚至与全监督方法具有可比较的性能。

层次结构潜在注意力建模的弱监督动作定位