Video synopsis is an activity-based video condensation approach to achieve efficient video browsing and retrieval for surveillance cameras. It is one of the most effective ways to reduce the inactive density of input video in order to provide fast and easy retrieval of the parts of interest. Unlike frame-based video summarization methods, the interested activities are shifted in the time domain to obtain video representation that is more compact. Although the number of studies on video synopsis has increased over the past years, there has still been no survey study on the subject. The aim in this article is to review state-of-the-art approaches in video synopsis studies and provide a comprehensive analysis. The methodology of video synopsis is described to provide an overview on the flow of the algorithm. Recent literature is investigated into different aspects such as optimization type, camera topology, input data domain, and activity clustering mechanisms. Commonly used performance evaluation techniques are also examined. Finally, the current situation of the literature and potential future research directions are discussed after an exhaustive analysis that covers most of the studies from early on to the present in this field. To the best of our knowledge, this study is the first review of published video synopsis approaches.