Long battery life and high performance multimedia decoding are
competing design goals for portable appliances. For a target level of
QoS, the achievable battery life can be increased by dynamically
adjusting the supply voltage throughout execution. In this paper, an
efficient offline scheduling algorithm is proposed for preprocessing
stored MPEG audio and video streams. It computes the order and
voltage settings at which the appliance's CPU decodes the frames,
reducing energy consumption without violating timing or buffering
constraints. Our experimental results elucidate the tradeoff of QoS
and energy consumption. They demonstrate that the scheduler reduces
CPU energy consumption by 19%, without any sacrifice of quality, and
by nearly 50%, with only slightly reduced quality. The results also
explore how the QoS/energy tradeoff is affected by buffering and
processor speed.
