Online Action Detection

TL;DR

This paper introduces a new dataset and evaluation protocol for online action detection in videos, analyzes baseline methods, and highlights the challenges posed by real-world variability and partial observations.

Contribution

It provides a realistic dataset, compares baseline methods, and analyzes factors affecting performance, advancing research in online action detection.

Findings

Baseline methods perform poorly on the new dataset.

Performance drops with viewpoint, occlusion, and truncation variations.

The dataset and evaluation protocol facilitate future research.

Abstract

In online action detection, the goal is to detect the start of an action in a video stream as soon as it happens. For instance, if a child is chasing a ball, an autonomous car should recognize what is going on and respond immediately. This is a very challenging problem for four reasons. First, only partial actions are observed. Second, there is a large variability in negative data. Third, the start of the action is unknown, so it is unclear over what time window the information should be integrated. Finally, in real world data, large within-class variability exists. This problem has been addressed before, but only to some extent. Our contributions to online action detection are threefold. First, we introduce a realistic dataset composed of 27 episodes from 6 popular TV series. The dataset spans over 16 hours of footage annotated with 30 action classes, totaling 6,231 action instances. Second, we analyze and compare various baseline methods, showing this is a challenging problem for which none of the methods provides a good solution. Third, we analyze the change in performance when there is a variation in viewpoint, occlusion, truncation, etc. We introduce an evaluation protocol for fair comparison. The dataset, the baselines and the models will all be made publicly available to encourage (much needed) further research on online action detection on realistic data.