In this paper, we address the problem of privacy protection in video surveillance. We introduce two efficient approaches to conceal Regions of Interest (ROI) based on transform-domain or codestream-domain scrambling. In the first technique, the sign of selected transform coefficients is pseudo-randomly flipped during encoding. In the second method, some bits of the codestream are pseudo-randomly inverted. We address more specifically the cases of MPEG-4 as it is today the prevailing standard in video surveillance equipment. Simulations show that both techniques successfully hide private data in ROI while the scene remains comprehensible. Additionally, the amount of noise introduced by the scrambling process can be adjusted. Finally, the impact on coding efficiency performance is small and the required computational complexity is negligible.