Learning to recognize actions from only a handful of labeled videos is a
challenging problem due to the scarcity of tediously collected activity labels.
We approach this problem by learning a two-pathway temporal contrastive model
using unlabeled videos at two different speeds leveraging the fact that
changing video speed does not change an action. Specifically, we propose to
maximize the similarity between encoded representations of the same video at
two different speeds as well as minimize the similarity between different
videos played at different speeds. This way we use the rich supervisory
information in terms of `time' that is present in otherwise unsupervised pool
of videos. With this simple yet effective strategy of manipulating video
playback rates, we considerably outperform video extensions of sophisticated
state-of-the-art semi-supervised image recognition methods across multiple
diverse benchmark datasets and network architectures. Interestingly, our
proposed approach benefits from out-of-domain unlabeled videos showing
generalization and robustness. We also perform rigorous ablations and analysis
to validate our approach. Project page: this https URL

通过利用不同视频播放速度下不改变动作的特性，利用未标记的视频，学习两通道时间对比模型，提取时间信息并在多个基准数据集和网络架构上实现优异的半监督图像识别效果。