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This paper addresses the problem of disseminating multiple live videos to mobile users by using a hybrid cellular and ad hoc network. Specifically, we develop techniques to optimize the overall quality of video delivery by: (a) exploiting the flexibility of layered videos for in-network adaptation to reduce the gap between video coding rate and network capacity, and (b) alleviating the load of individually handling a large number of flows at the cell tower by using device-to-device ad hoc connectivity to deliver videos. We study the problem of optimally choosing the mobile devices that will serve as gateways from the cellular to the ad hoc network, the ad hoc routes from the gateway to individual devices, and the layers to deliver on these ad hoc routes. We develop a Mixed Integer Linear Program (MILP) based solution to the considered problem. We also develop a heuristic algorithm to select the devices, routes, and layers more efficiently than the ideal, but potentially time-consuming MILP-based algorithm. We evaluate the proposed techniques via through simulations. The simulation results show that the proposed algorithms significantly outperform the current solution in terms of overall video quality, transmission latency, delivery ratio, and missed frame ratio. For example, compared to the current cellular network, the MILP-based and the heuristic algorithms result in up to 20 dB higher video quality. Furthermore, the heuristic algorithm runs efficiently yet achieves near-optimal quality: at most 2.3 dB gap across all experiments.