Rate control scheme using independent rate-distortion (R-D) model at the minimum coding unit (macroblock) level has been widely discussed in the literature where R-D optimization is performed without consideration of the inter-dependencies of different coding units. In this paper, we extend these techniques to the more general situations — rate control for inter-dependent video coding units. The interdependent distortion-quantization (D-Q) model and rate-quantization (R-Q) model are formulated separately based on the analysis of the relationship between the spatial-domain residual and the transform-domain residual. Then a window-based rate control scheme with frame bit allocation and video quality optimization is proposed, which uses the approximated R-D model to reduce the computational complexity. Simulation results demonstrate that the proposed algorithm shows excellent peak signal-to-noise ratio (PSNR) performance under the bit rate constraint. This one-pass rate control scheme is highly practical for the realtime video coding application.