In wireless video streaming, it is desirable to minimize the energy consumption of mobile devices while achieving target video quality. For this purpose, it is essential to model (i.e., estimate) the energy cost of the streaming system, including both video encoder and wireless transmission energy, under different system settings. In this paper, an energy consumption model is proposed for a MPEG-4 simple profile encoder implemented in ASIC. Our proposed model consists of three major steps: 1) compute the encoder energy consumption through power simulations; 2) empirically model the impact of configuration parameters through curve fitting; and 3) online updating of model coefficients. Experimental results show that our proposed model works well for different types of video, and the average estimation error is below 6%.1. INTRODUCTION With the fast development of video coding, hardware, and wireless communication technologies, wireless video streaming is expected to be one of the killer applications in the coming era. Due to the increased energy requirements of signal processing and wireless transmission, the limited battery capacity of mobile devices has become a major bottleneck.When streaming live video across wireless links, two main sources of energy consumption are video coding and wireless transmission. In most of the state-of-the-art video encoders and wireless transmitters, it is possible to adjust the configuration parameters (i.e., "knobs") based on varying channel conditions and/or video content to improve system performance. For instance, in a bad channel state, to reduce the effect of bit errors on the received video quality, many options are available, including (but not limited to): 1) increasing the INTRA refresh rate, 2) using specific error resilience tools such as resynchronization markers and data partitioning, 3) increasing channel coding rate, and 4) increasing the transmission power of the antenna, etc. This enables system performance optimization, such as minimizing the energy consumption of the entire system (including both video coding and wireless transmission), while satisfying end-users' requirement on the perceived video quality.To this end, it is essential to model (i.e., make an estimation of) the energy consumption under different system settings, so that the optimal operation point can be chosen given the system state. Although the modelling of wireless transmission energy has been extensively studied in the literature, the work on video encoder is rather limited.In [1], a H.263 encoder with eight encoding modes is used. It is assumed that the encoder is running on a TI DSP, and the power consumption of each mode is estimated using the "iprof" software [1]. Since only one test sequence is used in the experiment, it is not clear whether the video content has an impact on the encoder's energy consumption.In [2], two "knobs" are considered for a H.263 encoder: bitrate and the INTRA refresh rate. The power consumption is measured on a laptop computer running the software H.263 encoder...