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.