We present a cross-modal Transformer-based framework, which jointly encodes video data and text labels for zero-shot action recognition (ZSAR). Our model employs a conceptually new pipeline by which visual representations are learned in conjunction with visual-semantic associations in an end-to-end manner. The model design provides a natural mechanism for visual and semantic representations to be learned in a shared knowledge space, whereby it encourages the learned visual embedding to be discriminative and more semantically consistent. In zero-shot inference, we devise a simple semantic transfer scheme that embeds semantic relatedness information between seen and unseen classes to composite unseen visual prototypes. Accordingly, the discriminative features in the visual structure could be preserved and exploited to alleviate the typical zero-shot issues of information loss, semantic gap, and the hubness problem. Under a rigorous zero-shot setting of not pre-training on additional datasets, the experiment results show our model considerably improves upon the state of the arts in ZSAR, reaching encouraging top-1 accuracy on UCF101, HMDB51, and ActivityNet benchmark datasets. Code will be made available.

本篇研究提出了一种基于跨模态Transformer的框架，用于零样本动作识别，其将视频数据和文本标签进行联合编码，并通过一个新的管道来构建视觉和语义表示之间的共享知识空间，其中包括了一个语义传递的策略，通过将已有和未见的课程联合在一起，提高了在UCF101、HMDB51和ActivityNet基准数据集中的顶级准确度。

跨模态表示学习用于零样本动作识别