Today, mass-scale electronic content distribution systems embed forensic tracking watermarks primarily at the distribution server. For limiting the bandwidth usage and server complexity and enhancing scalability, it is preferable to embed the watermark at the client. Embedding in these untrusted clients requires secure embedding methods that do not leak unmarked content or the watermarking secrets. In this work, we propose a secure watermark embedding scheme based on lookup tables for spread-spectrum watermarks, which are robust to noise and can be detected without comparison to the original content. We also develop fast detection mechanisms that make the watermark detection feasible for tracking systems with a large number of clients. Our fast detection algorithm improves detection speed of existing methods by six orders of magnitude in a typical system with millions of clients.

In a forensic watermarking architecture, a buyer-seller protocol protects the watermark secrets from the buyer and prevents false infringement accusations by the seller. Existing protocols encrypt the watermark and the content with a homomorphic public-key cipher and perform embedding under encryption. When used for multimedia data, these protocols create a large computation and bandwidth overhead. In this correspondence, we show that the same functionality can be achieved efficiently using recently proposed secure watermark embedding algorithms.

In an electronic content distribution system, it is preferable to embed forensic tracking watermarks at the client-side to limit bandwidth usage and server complexity. Embedding in these untrusted clients, however, requires secure embedding methods that do not leak unmarked contents or the watermarking secrets. In this work, we propose a look-up-table (LUT) based cipher, similar to Andersen's Chameleon cipher, for securely embedding spread-spectrum watermarks, which are noise robust and detectable without the original content. We also develop fast detection mechanisms that make the watermark detection feasible for tracking systems with large number of clients. Our fast detection algorithm improves detection speed six orders of magnitude in a typical system.

Unauthorized re-distribution remains a significant threat for emerging electronic movie distribution services. In this paper, we propose a forensic tracking watermark for MPEG-2 bit-streams that can be employed to complement Digital Rights Management and conditional access systems in electronic movie distribution. The watermark is embedded by modulating a subset of quantization matrix entries, which are periodically present in the MPEG-2 headers. When observed over time the watermark can be detected even after cropping, de-interlacing, resizing and DivX compression at 300 kbps or after being captured with a video camera from a flat-screen TV. As the method modifies only a small part of the bit-stream (ap100 bytes per second), it can be readily implemented in resource constrained environments like the current generation set-top boxes, without costly hardware upgrades.

We propose a method for embedding a robust forensic tracking watermark within the AAC decoder during audio playback. For predefined frequency bands, the method intercepts and modifies the scale-factors, which are present in the AAC bit-stream. It thereby modulates the short-time envelope of the band-limited audio and embeds a watermark which is robust to various attacks such as recompression and acoustic transmission. Due to its low complexity - a few additions per AAC frame - the method is suitable for implementation even in resource constrained devices such as portable players. Furthermore, decode-time embedding enables dynamic payload assignments which may be used to signal playback time and location.

In digital rights-management systems, forensic watermarking complements encryption and deters the capture and unauthorized redistribution of the rendered content. In this paper, we propose a novel watermarking method which is integrated into the advanced audio coding (AAC) standard's decoding process. For predefined frequency bands, the method intercepts and modifies the scale factors, which are utilized for dequantization of spectral coefficients. It thereby modulates the short-time envelope of the bandlimited audio and embeds a watermark which is robust to various attacks, such as capture with a microphone and recompression at lower bit rates. Inclusion of watermark embedding in the AAC decoder has practically no effect on the decoding complexity. As a result, the proposed method can be integrated even into resource-constrained devices, such as portable players without any additional hardware.

High-resolution parameter estimation techniques have been applied to jointly estimate multiple signal parameters. We consider the problem of determining the directions and center frequencies of a number of narrow-band sources in a certain frequency band of interest. We present a joint angle-frequency estimation method, based on the multidimensional ESPRIT algorithm. A perturbation error analysis gives bounds on the parameter estimates, and provides optimal values for the temporal and spatial smoothing parameters. The analysis is shown to be consistent with simulation results.

Multi-resolution ESPRIT is an extension of the ESPRIT direction finding algorithm to antenna arrays with multiple baselines. A short (half wavelength) baseline is necessary to avoid aliasing, a long baseline is preferred for accuracy. The MR-ESPRIT algorithm allows to combine both estimates. The same algorithm can be used for multi-resolution frequency estimation, by combining two different sampling frequencies. We show how this can be used to construct a joint angle-frequency estimator.

Using state space representations of biorthogonal time-varying filter banks, it is possible to derive conditions under which the transition between two time-invariant filter banks can be so controlled that both the decomposition filters and the reconstruction functions gently embrace. The transition interval can be made arbitrarily short. If it is zero, then the special case of instantaneous transition is reached.