A STUDY ON VIDEO SCRAMBLING CONSIDERING INTER-FRAME PREDICTION(International Workshop on Advanced Image Technology 2006)

This paper considers the scrambling method for MPEG-2 and other similar video codecs that exploit the inter-frame prediction feature. Usually this kind of methods scrambles the data (e.g., DCT coefficients) in I-frames, and other frames (P-/B-frames) can be automatically scrambled due to the inter-frame prediction. This is efficient in reducing the computational complexity. However, it is known that intra-encoded macroblock (intra-MB) may exist in Pframes, which de-scrambles the MB and weakens the scrambling strength. In this paper we investigate the relationship between the number of intra-MBs and the scrambling effects in Pframes, and based on it, we propose a scrambling scheme which scrambles several frames instead of all frames.It is justified through analysis of distribution of local PSNR and its relation to subjective picture quality.