Proceedings of ICCT2003
A New Method of MPEG Video Watermarking Technology Yuanjun Dai Lihe Zhang
Yixian Yang
BeiJing University of Posts and Telecommunications Tel: +86 10 62383783; Fax: +86 10 62283779; E-mail:
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Abstract-In this paper, we propose a video Watermarking technology to hide copyright information by a slight modification of the motion vector, in MPEG2 video bitstream. In this method, watermark is embedded in the motion residual of large value motion vector, then the motion residual are regularized into a modified bitstream, from which the watermark information can be retrieved easily and exactly. From the experimental results, this technology has the advantage of little influence on the MPEG decoding speed ,little degrading the perceptive effect, capability to embed watermark in a short video sequence, and can be used to watermark directly on compressed and uncompressedvideo sequence. Keywords-watermark; MPEG; motion vector I.
INTRODUCTION
With the rapid spread of computer networks and the further development of multimedia technologies, the copyright protection of digital contents such as audio. image and video, has been one of the most serious problems because digital copies can be identical to the original. The digital watermark technology is now drawing the attention as a new method of protecting copyrights of digital contents. Digital watermark is realized by embedding information data directly into digital contents with an imperceptible form for human audiohrisual systems, and should satisfy the following requirements. The embedded watermark does not spoil the quality of the original contents and should not be perceptible. It must be difficult for an attacker to remove the watermark and should be robust to signal processing and geometric distortions. In video watermarking, the challenge is to mark a group of images which are strongly correlated and often manipulated in a compressed form , e.g. MPEG . H w g et&[ 11 proposed to mark only the DCT coefficients of the intra-frames(1-frames).They use a s p ~ a dspectrum signal containing the copyright information which is added to the non-zero DCT coefficients under the condition of not increasing the bit rate. Mobasseri proposed a video watermark scheme by applying a direct sequence spectrum model [2]. Video signal is modeled as a sequence of bit planes arranged along the time axis. Watermarking of this sequence is a 2 layers operation. A controlling m-sequence establishes a pseudorandom order in the bitplane stream. The watermarked video is robust to video editing attempts such as subsampling, frame recording etc, and also identifiable from very short segments of video. In contrast with the video watermarking where each frame was marked separately, Deguillaume et al. proposed the video watennarking scheme which is based on DFT of the 3
dimensional chucks of video scene[3]. Two kinds of information are hidden in the video: a watermark and a template. Other researchers do watermarking on modifcation with some parameters, like MPEG-4 facial animation parameters[4]. In this paper, we explore a new way to embed watermark in motion vector by modlfying the corresponding motion residual. 11. THE PRINCIPLE FOR WATERMARK EMBEDDING In the MPEG compression algorithms, Motion compensation prediction is a powerful tool to reduce temporal dundancies between frames and is used extensively in MPEG video coding standards as a prediction technique for temporal DPCM coding. Most of the frames in MPEG video sequence are in this coding scheme except the intra frame(I frame) . Consequently, to hide watermark information in motion vectors for copyright protection can more efficiently exploit the information in video bitstream. According to the bitstream of copyright watermark information, Kutter et al. Select the inter frames in MPEG video sequence and xegularize the motion vectors inside into a modified data sequence for easily watermark retrieving[5]. In this paper, we do some improvements on the watermarking scheme in MPEG motion vector. The larger motion vector magnitude indicates the faster physical moving of the macroblocks. In this case, to change the motion vector will be less perceivable by comparing to change the same value in motion vector when the macroblocks are in lower motion vector magnitude. Here, we should embed the watermark information into the motion vector which is large enough for little degrading the perceptive effect. In the process of decoding MPEG ,given r-size =f-code[sJ[t] - 1 (1) wheref_code[s][[t] is a 4 bit unsigned integer taking values 1 through 9, or 15. It is used in the decoding of motion vectors; See Table 1for the meaning of the indices: s and t. so given
f= 1
