Abstract: A category overlay infrastructure for Peer-to-Peer (P2P) content search and a cost-effective large-scale on-demand media streaming are described. Based on a novel hierarchical P2P model, the category overlay infrastructure can provide good load balancing and efficient keyword search services for large-scale networks. The category overlay search services may be applied for locating video segments. The on-demand media streaming architecture can apply an efficient media segment scheduling algorithm and aggregate concurrent media streaming from multiple sources to allow users to play high-quality video or other media.