A Dynamic Programming Solution for Energy-Optimal Video Playback on Mobile Devices

Abstract

Due to the development of mobile technology and wide availability of smartphones, the Internet of Things (IoT) starts to handle high volumes of video data to facilitate multimedia-based services, which requires energy-efficient video playback. In video playback, frames have to be decoded and rendered at high playback rate, increasing the computation cost on the CPU. To save the CPU power, dynamic voltage and frequency scaling (DVFS) dynamically adjusts the operating voltage of the processor along with frequency, in which appropriate selection of frequency on power could achieve a balance between performance and power. We present a decoding model that allows buffering frames to let the CPU run at low frequency and then propose an algorithm that determines the CPU frequency needed to decode each frame in a video, with the aim of minimizing power consumption while meeting buffer size and deadline constraints, using a dynamic programming technique. We finally extend this algorithm to optimize CPU frequencies over a short sequence of frames, producing a practical method of reducing the energy required for video decoding. Experimental results show a system-wide reduction in energy of27%, compared with a processor running at full speed.

Making Image More Energy Efficient for OLED Smart Devices

“…The capacity of lithium-ion batteries is still constrained by the size and weight due to smart devices' mobility; thus energy saving of smart devices has become an urgent concern. Many studies have been made to reduce energy consumption of smart devices from different aspects; particularly for OLED, there are mainly three ways for energy saving, namely, dynamic voltage scaling [7-9, 14, 15], color context aware dimming [10][11][12][16][17][18], and color remapping [13,15,[19][20][21][22][23]. Shin et al [7] first introduced dynamic driving voltage scaling (DVS) of OLED panel technique; the idea is to scale down the supply voltage and, in turn, dramatically reduce the wasted power caused by the voltage drop across the driver transistor as well as internal parasitic resistance; thus energy is saved on the OLED display panel with only minor changes in the color and luminance of the image; their experiment shows that their method saves up to 52.5% of the OLED energy while keeping the same image quality for the Lena image.…”

“…Their experimental results show that, compared to existing global DVS technique, FDVS technique can achieve 25.9%∼43.1% more OLED power saving while maintaining a high image quality measured by Structural Similarity Index (SSIM = 0.98). Also in [15], Song and Park presented a decoding model that allows buffering frames to let the CPU run at low frequency to reduce the energy required for video decoding. These two methods focus on the hardware structure of the OLED, which are compatible with our method, since our method focuses on the image.…”

“…Many attempts have proposed to reduce energy consumption of OLED displays from different aspects, mainly through dynamic voltage scaling of OLED displays [7-9, 14, 15], context-aware dimming [10][11][12][16][17][18], and color remapping Power (uw) Figure 1: Power consumption for the R, G, and B components of an OLED pixel by different intensity levels. [13,15,[19][20][21][22][23]. Among these techniques, dimming is a simple and effective method for energy saving, which reduces luminance of the pixels displayed on OLED, while color remapping is implemented by replacing the energy-saving color schemes with the energy-hungry color schemes.…”