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Digital Video Watermarking

AlpVision does not have direct products for sale to protect video streams against fraudulent copies, but it licenses its technology to third parties. AlpVision filed US and EU registered patents, in cooperation with the Ecole Polytechnique Fédérale de Lausanne (EPFL), listed at the end of this page.

Digital video watermarking can be achieved by either applying still image technologies to each frame of the movie or using dedicated methods that exploit inherent features of the video sequence.

The table on the right provides a partial list of still and/or moving picture watermarking concepts.

One of the primary requirements of video watermarking schemes is their robustness to unintentional attacks while avoiding the introduction of disturbing artifacts. The most important unintentional attack on video is "lossy" compression. In the production chain, compression is usually applied before broadcasting or before transferring the video to other devices.

 
Still image watermarking
Video watermarking
Spread Spectrum (spatial domain and transform domain) X X
Motion Vector Modifications - X
Fractal Image Coding X X
Transform coefficient relationship (e.g. DCT) X X
Quantization Index Modulation X X
2D-Subband Spread Spectrum X X
3D-Subband Spread Spectrum - X

The following diagram shows the evaluation procedure we employ to test the robustness of video watermarking solutions against compression. Each frame of the video is first watermarked using a 64 bit signature. The resulting signed frames are then compressed using an MPEG-2 encoder at different bitrates.

To recover the embedded signature, the video bit stream is first decompressed and then each individual frame is passed through the watermark detection system. If the detection is perfect all the bits of the retrieved signature are correct and the same signature is found in each frame. This also means that only one single frame is required to recover the embedded information. However, practice has shown that in order to keep the watermark invisible, only very slight modifications of the frames are acceptable.

As a consequence, and depending on the compression bit rate, some of the signature bits may therefore be wrongly detected on individual frames. An additional step based on statistical analysis over several frames is therefore required in order to correct possible errors (see diagram below)..

Example  

The combination of the basic watermarking technology with adequate statistical processing over several frames provides an excellent solution for invisible video watermarking that is robust to MPEG-2 compression. The following results show an example of the performance achieved by this system (diagram on the right).

The first 100 frames of the "Mobile Calendar" standard CCIR-601 test sequence were watermarked and compressed using 4:2:0 YUV sub sampling and three different bit rates: 6 Mbit/s, 4 Mbit/s and 3 Mbit/s. The graph below shows the number of errors versus the number of frames processed by the statistical detection algorithm.

The graph shows that in order to recover the correct signature at 6, 4 and 3 Mbit/s, the required number of frames is 11, 21 and 60, respectively.

In other words, the signature is retrievable from less than 500 ms of video compressed at 6 Mbit/s and about 2.5 seconds of video compressed at 3 Mbit/s. It should be noted that 3 Mbit/s is a fairly low bit rate for a CCIR-601 sequence and that it creates compression artefacts that are substantially more visible than the watermark itself.

The picture below is the first frame of the signed sequence after Mpeg-2 compression: it clearly shows the artifacts caused by video compression (typical effect of DCT coefficient quantization).

As can be seen, the watermarking artifacts are very hard to detect.

The images above show the original (left) and watermarked (right) frames extracted from compressed bit stream.

To further illustrate this, some examples of the original and signed video sequences have been converted to the standard AVI format using the following scheme:

The Mpeg-2 bit streams "original.m2v" and "signed.m2v"as well as the AVI movies can be downloaded by clicking on the links below (you need a MPEG2 decoder to read the m2v files, which can be freely downloaded on the Internet):

Bit stream watermarking:

Motion vectors can also be modified without decoding the MPEG (or similar) compressed bit stream. This approach provides for a marking/detection technique that has very low computational power requirements. Details can be found in following document US patent US6785332.

Patents:

US (US6785332) and European (EP0997042) patents are already granted with no opposition filed (opposition time limit has now expired) and all fees have been duly paid. The priority date was July 1997. The patent is entitled "Method for marking a compressed digital video signal".

Starting January 2007, these patents are now available for licensing or acquisition. Please feel free to contact us for more information.

More scientific references are available in our Publications list.

 
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