Most model based rate control solutions have the generally questionable assumption that video sequence is stationary, and also suffer from the fundamental problems of model parameter mis-estimation. In this paper, we propose a sequence based bit allocation solution with the capability of tracking the nonstationary characteristics in the video source without look-ahead encoding and thus stationarity assumption is no longer needed. In addition, a new model parameter estimation approach is provided to solve the problems in the existing model parameter estimation schemes. Moreover, a general concept of bit allocation guarantee is presented to achieve the allocated bits in a deterministic way. The proposed rate control solution can achieve constant quality video with less quality flicker and motion jerkiness.