Unsupervised domain adaptation which aims to adapt models trained on a labeled source domain to a completely unlabeled target domain has attracted much attention in recent years. While many domain adaptation techniques have been proposed for images, the problem of unsupervised domain adaptation in videos remains largely underexplored. In this paper, we introduce Contrast and Mix (CoMix), a new contrastive learning framework that aims to learn discriminative invariant feature representations for unsupervised video domain adaptation. First, unlike existing methods that rely on adversarial learning for feature alignment, we utilize temporal contrastive learning to bridge the domain gap by maximizing the similarity between encoded representations of an unlabeled video at two different speeds as well as minimizing the similarity between different videos played at different speeds. Second, we propose a novel extension to the temporal contrastive loss by using background mixing that allows additional positives per anchor, thus adapting contrastive learning to leverage action semantics shared across both domains. Moreover, we also integrate a supervised contrastive learning objective using target pseudo-labels to enhance discriminability of the latent space for video domain adaptation. Extensive experiments on several benchmark datasets demonstrate the superiority of our proposed approach over state-of-the-art methods. Project page: https://cvir.github.io/projects/comix

本文介绍了Contrast and Mix（CoMix）的新对比学习框架，旨在为无监督的视频领域适应学习具有判别不变性的特征表示。与现有方法依靠对抗学习进行特征对齐不同，我们利用时间对比学习通过最大化未标记视频在两个不同速度下的编码表示的相似性以及最小化不同速度下播放的不同视频的相似性来弥合领域差距，还利用背景混合提出了一种用于时间对比性损失的新型扩展，从而允许每个锚点附加附加正物，增加视频领域适应的语义分享。此外，我们还使用目标伪标签集成了有监督的对比性学习目标，以增强视频领域适应的潜在空间的可区分性。在几个基准数据集上进行的广泛实验验证了我们所提出的方法的优越性。

对比和混合：利用背景混合的时间对比视频域自适应