In video streaming applications over the Internet, TCP-friendly rate control schemes are useful for improving network stability and inter-protocol fairness. However, they do not always guarantee a smooth video streaming. To simultaneously satisfy both the network and user requirements, video streaming applications should be quality-adaptive. In this paper, we propose a new quality adaptation mechanism to adjust the quality of congestion-controlled video stream by controlling the frame rate. Based on the current network condition, it controls the frame rate of video stream and the sending rate in a TCP-friendly manner. Through a simulation, we prove that our adaptation mechanism appropriately adjusts the quality of video stream while improving network stability.