Abstract: Rate control plays a dominant role in getting the higher video reconstruction quality in given bandwidth.In order to improve the rate control performance of H.264，a novel rate control algorithm is presented in this paper.First，the Quantization Parameter（QP） of the I-frame is determined by using a linear PSNR-QP model.Then，the QP of the P-frame is calculated from H.264’s quadratic R-Q model.Different from H.264，the predicted MAD is calculated by a combined space-time model，i.e.，the combination of linear prediction model and the weighted model，and adaptively corrected according to prediction errors.Experimental results have shown that the reconstructed frames by the proposed algorithm can achieve better reconstruction performance and less fluctuation than by JM10.2 in terms of PSNR.

Key words: H.264, rate control, Mean Absolute Difference（MAD）, Basic Unit（BU）

摘要： 为了在网络带宽受限的情况下获得更好的重建图像质量，码率控制成为视频编码不可缺少的重要组成部分。针对H.264/AVC码率控制算法的不足，提出了改进方法。首先通过PSNR-QP线性关系确定I帧的QP；其次，在采用二次R-Q模型来确定P帧的QP时，采用时间线性预测模型和时空加权预测模型相结合的方法取代H.264的时间线性预测模型来预测P帧基本单元的MAD值，并根据前一单元的预测误差对MAD值进行修正。实验结果表明，与JM10.2参考软件的码率控制算法相比，该算法的码率控制精度更高，输出视频序列的平均PSNR更高、波动更小。

关键词: H.264, 码率控制, 平均绝对差, 基本单元