Approaches to abnormality detection in crowded scene largely rely on supervised methods using discriminative models. In this paper, we presents a novel and efficient unsupervised learning method for video analysis. We start from visual saliency, which has been used in several vision tasks, e.g., image classification, object detection, and foreground segmentation. To detect saliency regions in video sequences, we propose a new approach for detecting spatiotemporal visual saliency based on the phase spectrum of the videos, which is easy to implement and computationally efficient. With the proposed algorithm, we also study how the spatiotemporal saliency can be used in two important vision tasks, saliency prediction and abnormality detection. The proposed algorithm is evaluated on several benchmark datasets with comparison to the state-of-the-art methods from the literature. The experiments demonstrate the effectiveness of the proposed approach to spatiotemporal visual saliency detection and its application to the above vision tasks.