The objective of this chapter introduces an advanced encryption of MP3 and MPEG-4 coder with a quality degradation-based security model. For the MP3 audio, the magnitude, and phase information of modified discrete cosine transform (MDCT) coefficients is encrypted. DCT coefficients and motion vectors (MVs) are used for the scrambling of the MPEG-4 video. This encryption scheme has a level of security, secures in perception, keeps format compliance, and obtains high time efficiency though reducing the encrypted the volumes of multimedia contents. These properties make it practical to incorporate encryption and decryption process into compression and decompression process, and thus suitable for secure A/V transmission or sharing.
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