Streaming video over wireless networks can be complicated by a highly varying link capacity. We present an approach that allows close-to-optimal utilization of the link bandwidth. We use a property of the medium access control (MAC) of the 802.11 standard to do instant detection of the bandwidth fluctuations by observing the transmission rate from the sending buffer. The specifics of a general MPEG stream allow classifying video-frames by their importance for the user-perceived quality. We build a scheduling mechanism that favors transmission of more important frames at the expense of the less important ones. We validate our approach by means of test-bed experiments and demonstrate a significant improvement of the end video quality.