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In video-on-demand systems, users expect to watch a film right after its selection. Nonetheless, such a short response time is feasible only if there is available bandwidth. In line with that, several techniques have been proposed to reduce the huge bandwidth demand on video servers. In this paper, we introduce the Piggybacking policy S2, which adds a second level of optimization to the Snapshot policy. Moreover, we introduce a heuristic to reduce the complexity to generate the tree of superimposed video streams.