Abstract
In this paper, we propose Spatio-TEmporal Progressive
(STEP) action detector—a progressive learning framework
for spatio-temporal action detection in videos. Starting
from a handful of coarse-scale proposal cuboids, our approach progressively refines the proposals towards actions
over a few steps. In this way, high-quality proposals (i.e.,
adhere to action movements) can be gradually obtained at
later steps by leveraging the regression outputs from previous steps. At each step, we adaptively extend the proposals in time to incorporate more related temporal context. Compared to the prior work that performs action detection in one run, our progressive learning framework is
able to naturally handle the spatial displacement within action tubes and therefore provides a more effective way for
spatio-temporal modeling. We extensively evaluate our approach on UCF101 and AVA, and demonstrate superior detection results. Remarkably, we achieve mAP of 75.0% and
18.6% on the two datasets with 3 progressive steps and using respectively only 11 and 34 initial proposals.