Exploring Scalability of Self-Training for Open-Vocabulary Temporal Action Localization

The vocabulary size in temporal action localization (TAL) is limited by the scarcity of large-scale annotated datasets. To overcome this recent works integrate vision-language models (VLMs) such as CLIP for open-vocabulary TAL (OV-TAL). However despite the success of VLMs trained on extensive datasets existing OV-TAL methods still rely on human-labeled TAL datasets of limited size to train action localizers limiting their generalizability. In this paper we explore the scalability of self-training with unlabeled YouTube videos for OV-TAL. Our approach consists of two stages: (1) a class-agnostic action localizer is trained on a human-labeled TAL dataset to generate pseudo-labels for unlabeled videos and (2) the large-scale pseudo-labeled dataset is then used to train the localizer. Extensive experiments demonstrate that leveraging web-scale videos in self-training significantly enhances the generalizability of an action localizer. Additionally we identify limitations in existing OV-TAL evaluation schemes and propose a new benchmark for thorough assessment. Finally we showcase the TAL performance of the large multimodal model Gemini-1.5 on our new benchmark. Code is released at https://github.com/HYUNJS/STOV-TAL.