A method and system for invisible marking directly into compressed video stream
Original Publication Date: 2002-Jan-01
Included in the Prior Art Database: 2003-Jun-20
Disclosed is a method and system to embed additional information (watermark) invisibly into compressed digital video stream in (MPEG) compressed domain, by modifying (DCT) coefficients of AC component, while preserving the length of the compressed video stream after embedded. This invention has following advantages: 1. The watermark operation is done in the compressed domain. So, high cost operations such as frequency transformation are not necessary and the computation cost of embedding is very low, thus,the embedder can be achieved with low cost chip. 2. The stream length is preserved after embedding. So, the embedding system can be implemented to such device as DVD drives or Set To Box (STB) and also conduct watermark embedding to packetized stream in which bit stream length cannot be changed. 3. The AC components are is used for embedding, and more coefficients become available for embedding. Therefore, it's robust for various post-processing and has large data payload. This invention consists of following points: 1. A method and system to embed watermark into AC components by modifying Variable Length Code (VLC). 2. A method and system to embed watermark by keeping the total length of the VLC unchanged in each macroblock or intra block unit after embedded by controlling the embedding amount of each DCT coefficient automatically. Following is an example of the workflow of the embedding system of this invention to achieve this invention(Figure). In this example, watermark is embedded into MPEG2 video stream, using only AC coefficients in Luminance intra block. Length of bitstream is kept unchanged in macroblock unit. Embedding is achieved by slightly changing the luminance value of each block, i.e., by adding a 16pixel x 16pixel pattern Pi to Luminance array Mi of the original stream, where i is the macroblock address (MBA). Watermark is embedded by the following sequence: Each Pi is DCT transferred prior to embedding.