1. A device comprising: one or more computer-readable media; and one or more processors that are coupled to the computer-readable media and that are configured to cause the device to obtain frame-level feature sets of visual features that were extracted from respective frames of a video, wherein the respective frame-level feature set of a frame includes the respective visual features that were extracted from the frame, generate first-level feature sets, wherein each first-level feature set is generated by pooling the visual features from two or more frame-level feature sets, and wherein each first-level feature set includes pooled features, and generate second-level feature sets, wherein each second-level feature set is generated by pooling the pooled features in two or more first-level feature sets, wherein each second-level feature set includes pooled features.