Rapid development of mobile computing technology has led to sufficient computing and communication power to support multimedia application such as video streaming, 3D games, video conferencing and mobile TV. However, most existing mobile devices are lacking in battery life. There have been many projects focused on energy-aware content adaptation that have been designed with different goals and approaches. This paper analyzes the functional aspects on solutions that have been proposed during the last few years, to improve the energy efficiency of wireless multimedia streaming in mobile devices via content adaptation. We categorize the research work according to different classification of multimedia content adaptation based on energy-aware requirements. In addition, we discuss the research spectrum of energy-aware multimedia delivery and some challenges in energy-aware content adaptation systems.