Nowadays it is easy and fast to deliver and communicate the digital video contents. Therefore, security problem reveals followed in applications such as video-on-demand, videoconference and video chatting system. In this paper, a scrambling scheme employing novel grouping strategy is proposed to encrypt the compressed video data. In new scheme, the scrambling and descrambling operations are embedded into the video encoding and decoding processes. DCT coefficients are divided into 64 groups according to their positions in 8×8 size blocks, and scrambled inside each group. Besides, motion vectors are also grouped and permuted in term of their modes. Thus the influence on statistical property of the video data is reduced furthest. Experimental results show that the proposed method has less bitstream overhead and no any image quality degradation. It is also indicated that the security is enhanced considerably via extending the scrambling range. A content-based dynamic secret key method is also presented to withstand the known-plaintext attack.