视频加密对于保护视频数据的安全具有重要作用。将已有的几种典型MPEG视频加密算法，根据加密过程与压缩编码过程的关系不同，分为4类：完全加密算法，部分加密算法，DCT系数加密算法和熵编码过程加密算法，并从算法的安全性、压缩比、计算复杂度和可操作性几个方面对算法的性能分别做了评价，给出了理论分析和实验结果；结合各类算法的特点，指出了它们各自适应的应用场合。

Video encryption is a suitable method to protect video data. In this paper, the existed MPEG video encryption algorithms are classified into four types according to the relationship between encryption process and compression process. They are complete encryption algorithm, partial encryption algorithm, DCT coefficient encryption algorithm and entropy encoding encryption algorithm. Each of them is evaluated from the four aspects: security, compression ratio, computing complexity and operationality. Theoretical analyses and experimental results are presented to compare these algorithms. And their application fields are given, which are consistent with their properties. According to the development direction of video application, the encryption algorithms combining with encoding process will be studied deeply in the future, such as DCT coefficient encryption algorithm, entropy encoding encryption algorithm or novel algorithm combining with error correcting code and so on.