A perceptual-based video coding method provides a perceptual-based rate-distortion (R-D) curve as a predictive R-D curve. The Lagrange multiplier for a current frame is then determined by deciding a slope, with sign reversed, of a tangent to the predictive R-D curve at a current point that is on the predictive R-D curve and closest to a previous R-D point of a previous encoded frame. The current frame is then encoded according to the determined Lagrange multiplier.