1. A composite masking system for improving invisibility of high-definition video watermarking, comprising: a watermark generation module for generating a basic watermark pattern using a private key and generating a watermark pattern by repeatedly extending the basic watermark pattern in order to improve the robustness against scaling attacks as well as general video processing attacks; a mask generation module for generating a Noise Visibility Function (NVF) mask using NVF masking means, an adaptive dithering mask using adaptive dithering masking means, and a contour mask using contour masking means; and watermark embedment means for generating a composite mask by multiplying the NVF mask, the adaptive dithering mask and the contour mask together, multiplying the composite mask and the extended watermark pattern together, and embedding a result of the second multiplication in a luminance channel of an original image.