We present PolemicTweet a system with an encompassing, economic, and engaging approach to video tagging and analysis. Annotating and tag- ging videos manually is a boring and time-consuming process. Yet, in the last couple of years the audiences of events—such as academic conferences—have begun to produce unexploited metadata in the form of micropost activities. With PolemicTweet we explore the use of tagged microposts for both video annotation and browsing aid. PolemicTweet is a system 1) to crowd source conference video tagging with structured sentiment metadata, 2) to engage audiences in a tagging process, and 3) to visualize these annotations for browsing and analyzing a video. We describe the the system and its components as well as the results from a one-year live deployment in 27 different events.