在可伸缩视频编码系统中，原始码流经过裁剪可以提取出多个子码流。为了联合优化原始码流和子码流的编码质量，提出了基于部分解码的率失真优化算法。首先，在增强层的率失真计算中，通过对离散余弦变换(DCT)系数进行有选择截断来估计子码流对编码的影响，并建立误差扩散失真图对部分解码引起的误差扩散进行预测。在基本层的率失真计算中，针对编码层之间在模式选择上的限制，使用多层联合编码方法来计算率失真代价。为了降低算法引入的计算量，对部分解码条件下的重建过程和基本层模式选择进行复杂度优化。最后，对参数选择进行了讨论，利用每个宏块的误差扩散敏感度来动态估计算法参数。实验结果表明，本方法能使子码流的峰值信噪比提高0.03~0.53 dB，可以满足可伸缩编码系统对编码效率和码率提取点的要求。

In scalable video coding, the original bit-stream can be cropped and generate multiple sub-bit-streams. In order to optimize coding efficiency of both the original bit-stream and the sub-bit-streams, partial decoding based on a Rate Distortion Optimization (RDO) algorithm is proposed. In the enhancement layer’s RDO process, the influence of sub-bit-streams on coding efficiency is predicted by selectively truncating Discrete Cosine Transform(DCT) coefficients.The propagation distortion map is then used to estimate the drift error. In the base layer’s RDO process, the multi-layer coding method is employed to cope with the constraint between the layers’ mode choice. In order to reduce the computational complexity of the algorithm, both the partially decoded reconstruction process and the base layer’s mode decision are optimized. Finally, the configuration of parameters is discussed and chosen adaptively based on the error propagation sensitivity on a macroblock basis. From experimental results, the proposed algorithm improves the sub-bit-streams’ Peak Signal to Noise Ratio(PSNR) by 0.03-0.53 dB. For the scalable video system, the proposal can meet the needs of high coding efficiency and flexible sub-bit-rate extraction.