In the modern society, mobile is gradually going to become all about video streaming. The main reasons of video growth are mobile devices such as smartphones and tablets which enable people to have access to videos they would like to watch at anywhere and anytime. However, due to the large video data size and intensive computation, video processing leads to a huge power consumption. Mobile system designers typically focus on hardware-level power optimization techniques without considering how hardware performance interfaces with viewer experience. In my research, I investigated how viewing context factors affect mobile viewing experience. Furthermore, a viewer-aware intelligent mobile video system was designed to optimize power efficiency automatically in real-time according to the viewing context and maintain the same viewing experience. Our research opened a door for developments of future viewer-aware mobile system design, accelerating low-cost mobile devices with longer battery life.