All currently published models for addressing this problem can be categorized into two types: (i) top-down approach: it does classification and regression for a set of pre-cut video segment candidates; (ii) bottom-up approach: it directly predicts probabilities for each video frame as the temporal boundaries (i.e., start and end time point).
both two approaches suffer several limitations: the former is computationintensive for densely placed candidates, while the latter has trailed the performance of the top-down counterpart thus far.