Video streaming over wireless networks is challenged with the time-varying nature of the underlying channels and the stringent requirements of video applications. In this paper, we propose a new scheme for streaming video over wireless channels. The scheme is designed to prevent potential playback discontinuities that may result due to quality variations of the wireless link while gracefully degrading the rendered video quality. We approximate the frame delay statistics and playback process by a simple queueing model. In this queueing system, the rates at which frames are received and played back are occupancy-dependent. This allows us to compute the steady-state probability of the playback buffer occupancy. This in turn, allows us to obtain an expression for the probability of starvation which we use to determine a threshold occupancy and hence the optimal source and channel rates for the upcoming frames. Simulation and numerical investigations are carried out to study the interactions among various key parameters and verify the adequacy of the analysis.