1. Introduction
There has been a recent emergence of multimedia streaming applications over sensor networks, such as multimedia surveillance, storage of potentially relevant activities from networked cameras, traffic conditions and collision avoidance. However, wireless sensor networks (WSNs) have restrictions in supporting these video/audio streaming applications because of the lack of raw bandwidth, poor link characteristics and limited power supply. Recent advances of multimedia source coding techniques such as Multiple Description Coding and inexpensive hardware, such as CMOS cameras and microphones, have made multimedia transmission over WSNs possible. In many applications, not all video data need to be transmitted to the end-users.