Temporal Sentiment Localization: Listen and Look in Untrimmed Videos

Video sentiment analysis aims to uncover the underlying attitudes of viewers, which has a wide range of applications in real world. Existing works simply classify a video into a single sentimental category, ignoring the fact that sentiment in untrimmed videos may appear in multiple segments with varying lengths and unknown locations. To address this, we propose a challenging task, i.e., Temporal Sentiment Localization (TSL), to find which parts of the video convey sentiment. To systematically investigate fully- and weakly-supervised settings for TSL, we first build a benchmark dataset named TSL-300, which is consisting of 300 videos with a total length of 1,291 minutes. Each video is labeled in two ways, one of which is frame-by-frame annotation for the fully-supervised setting, and the other is single-frame annotation, i.e., only a single frame with strong sentiment is labeled per segment for the weakly-supervised setting. Due to the high cost of labeling a densely annotated dataset, we propose TSL-Net in this work, employing single-frame supervision to localize sentiment in videos. In detail, we generate the pseudo labels for unlabeled frames using a greedy search strategy, and fuse the affective features of both visual and audio modalities to predict the temporal sentiment distribution. Here, a reverse mapping strategy is designed for feature fusion, and a contrastive loss is utilized to maintain the consistency between the original feature and the reverse prediction. Extensive experiments show the superiority of our method against the state-of-the-art approaches.