This special issue contains extended versions of the five best papers presented at the 10-th International Workshop on Multimedia Systems (MIS04), organized by Prof. V S. Subrahmanian at University of Maryland, College Park, between August 25th and August 27th 2004. The aim of MIS workshop is to bring together experts in all aspects of multimedia information systems. A special theme of the 10th edition was multimedia sensor systems, an emerging area which involves a confluence of multimedia systems, operating systems, databases, networking, computer vision, and information retrieval. As the editors of this special issue, we invited top rated papers that covered the range of research issues discussed at the workshop. Six papers were invited, five of which were accepted for publication after going though a separate review process. Each accepted paper has been significantly enhanced from its initial workshop version. The first paper, ”Optimization of Media Processing Workflows with Adaptive Operator Behaviors” by Lina Peng, K. Selcuk Candan, Christopher Mayer, Kyung D. Ryu, and Karamvir S. Chatha from Arizona State University has been chosen as the representative of this year special theme. The authors present the qStream media workflow architecture that processes, filters, and fuses sensory inputs and actuates responses in real time. The components of the architecture are programmable and adaptable: the delay, size, and quality/precision characteristics of individual operators can be controlled by means of specific parameter values. The second paper ”Flexible Integration of Multimedia Sub-Queries with Qualitative Preferences” by Ilaria Bartolini and Paolo Ciaccia from University of Bologna, Vincent Oria from New Jersey Institute of Technology, and M. Tamer Ozsu from University of Waterloo, proposes a novel approach to subquery integration in multimedia databases. The method, based on qualitative preferences, includes scoring functions as