Entropy coding is a new technology used in the H.264 video standard.In the video security communications

entropy-coding encryption is one of the important encryption algorithms. Commonly

the H.264 entropy-coding encryption is a fusion of encryption and entropy encoding video security algorithm

which is fast and the data format can remain unchanged. It is a compatibility encryption scheme

but needs to deal with all of the data frames. To deal with the problem of the entropy coding encryption process

we propose a video encryption method based on key frames selection combined with entropy coding

by capturing all 8×8 sub-macroblock motion vectors in one frame and

constructing the vector to represent the change of the content of each frame. Then the Euclidean norm is compared with the threshold ; if greater than or equal to the threshold

the current frame is the key frame. Then encrypts the next frame when the coding motion-vector and the coefficient of the residual value

otherwise it does not participate in any encryption arithmetic. By controlling the threshold value to determine the key frame selection

combines with the chaotic sequence to guarantee the security of videos. Compared with the entropy coding encryption algorithm

the encryption data is reduced about 39.78%. The experiments show that the encryption method maintains the total data

obtains a good encryption effect with a smaller time cost

and significantly reduces the amount of the encrypted data. The operation only changes the entropy encoding data

and it has nothing to do with the other processes of video coding. Therefores

the encryption system has no effect on the encoded data quantity. This algorithm is a compatibility video encryption.