This document discusses human action detection in stored videos using support vector machines. It describes the major steps in activity detection as feature detection, feature description, video representation, and classification. It explains that supervised learning uses labeled training samples to build models for normal and abnormal behavior detection, but it is limited by the need for sufficient training data for less defined events. Unsupervised learning builds models of normal behavior but classifies any samples not fitting a model as abnormal. The document reviews various approaches to human activity detection and outlines challenges, such as dealing with limited or low-quality video data.