1. A method of categorizing a motion event candidate, comprising: forming one or more clusters comprising respective pluralities of motion vectors, the motion vectors corresponding to respective motion event candidates previously detected in a live video stream, and the one or more clusters being associated with a respective event category and having a respective cluster creation time at which the respective cluster was formed; in accordance with a determination that a first cluster of the one or more clusters has included fewer than a threshold number of motion vectors for at least a threshold amount of time since a respective cluster creation time of the first cluster: deleting the first cluster including all motion vectors currently in the first cluster; and removing the motion event candidates corresponding to the deleted motion vectors from a first event category associated with the first cluster.