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Watermarking H.264 video

Posted: 29 Oct 2008     Print Version  Bookmark and Share

Keywords:watermarking  H.264  video codecs 

Internet and video coding technologies have grown significantly. With Internet-based multimedia applications, digital rights management and security are extremely important for authentication and copyright management. So a variety of watermarking techniques have come to market, and at the same time many attacks have been developed to destroy any hidden information in terms of watermarking embedded into the video stream.

Among different video codecs, H.264 has proven to be one of the best because of its reduced bandwidth, better image quality and network friendliness. In this article we shall discuss a novel technique for adding watermarking to H.264 video that resists attacks.

To be able to report the quality of a watermarking scheme in terms of its robustness against attacks, we have also developed a measurement system that can evaluate an attack by comparing the attacked video with the original watermarked video stream. At the conclusion of this article we present the results of this watermarking evaluation for the different attacks performed against this H.264 based watermarking scheme.

What is watermarking?
Watermarking is a process that embeds data, called a watermark or digital signature, into a multimedia object so that the watermark can be detected or extracted at later times to make an assertion about the object.

Information that can be included in the Watermark
- A serial number or pseudo random number sequence
- Ownership identifiers
- Copyright messages
- Control signals
- Transaction dates
- Information about the creators of the work
- Bi-level or gray level images
- Text or other digital data formats

Requirements of digital watermark
- Should convey as much information as possible
- be secret and accessible by authorized parties only
- Should withstand any signal processing and hostile attacks, i.e. robustness
- Should be imperceptible

Proposed watermarking algorithm
A basic description of the watermark module and its interaction with the H.264 codec is described in the block diagram. The overall process of H.264 codec is shown in Figure 1. Here the gray colored blocks are the addition for embedding the watermark.

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Figure 1: Process of H.264 codec.

In the proposed watermarking method, watermarking in the H.264 encoder is achieved in two folds: in even numbered Independent Decoder Refresh (IDR) frames, three different messages are embedded; and in odd numbered frames the bitstream is obtained by hashing the last Group of Picture (GOP) to ensure integrity. The process is described in details as follows:

The algorithm for watermark embedding is described below. It is also depicted pictorially in Figure 2.

Is the frame an even numbered IDR?
If Yes,
embed logo, timestamp and IP address or key.

Hash the last GOP and embed the number.

image name

Figure 2: Sub-blocks of the algorithm

The various sub-blocks of the algorithm in Figure 2 are described in detail below.

Test for watermarking message size:
This process of checking the size is depicted in Figure 3.

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Figure 3: Process of checking the size.

Find the location for embedding Watermark:
Selection of the position of DCT coefficient to be modified is based on our following observations:
- DCT coefficients are zero in most cases
- Most significant information lies in top and left
- Modification of diagonal elements at right and bottom results in insignificant artifacts
- Coefficients in diagonal positions are more stable than the others.

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