Much attention has been paid to the problem of optimally utilizing resources such as spectrum, power and time in order to achieve the best video delivery quality in wireless communications system, due to the fueling demand for such applications. In this work, we present a joint source coding and data adaptation scheme for downlink video transmission in a multi-user wireless network. We formulate a rate-distortion optimization problem, where the source coding and data rate are jointly designed according to the changing channel conditions. In addition, transmissions of video packets are optimally scheduled through exploiting the multi-user diversity. We solve the problem using a backward stochastic dynamical programming approach, and the simulation results have shown the advantage of the joint selection of source coding parameter and transmission rate coupled with optimal packet scheduling.