This paper presents an attractive rate control scheme for the new MPEG-4 Scalable Video Coding standard. Our scheme enables us to control the bitrate at the output of the encoder on each video layer with great accuracy. Each frame is encoded only once, so that the computational complexity of the whole scheme is very low. The three spatial, temporal and quality scalabilities are handled correctly, as well as inter layer prediction and hierarchical B frames. A linear bitrate model is used to predict the output bitrate for a frame, based on a simple and effective framework called rho-domain. A coding-complexity measure is also introduced to dispatch the available bits among the frames, in order to reach a constant quality throughout the encoded video stream. To attest the performances of our rate control scheme, we present comprehensive results on some representative scalable video set-ups.