In this paper, we present an algorithm for Real-time Iterative Spectrogram Inversion (RTISI) with Look-Ahead (RTISI-LA). RTISI-LA reconstructs a time-domain signal from a given sequence of short-time Fourier transform magnitude (STFTM) spectra without phase information. Whereas RTISI [1] reconstructs the current frame using only magnitude spectra information for previous frames and the current frame, RTISI-LA also uses magnitude spectra for a small number future frames. This allows RTISI-LA to achieve substantially higher signal-to-noise (SNR) performance than either RTISI or the Griffin & Lim method [2][3] with an equivalent computational load, while retaining the real-time properties of RTISI.
Content-dependent watermarking (CDWM) has been proposed as a solution to overcome the potential estimation attack aiming to recover and remove the watermark from the host signal. It has also been used for the application of content authentication. In this work, we first present an analysis on why some prior work on CDWM pose potential security problems due to their inherent cryptographic weakness. With the aim of achieving cryptographic level of security, we then propose a novel CDWM scheme based on homomorphic encryption and dirty paper precoding. The general idea is to introduce a decryption module before watermark detection to create some nonlinearity and thereby inhibit conventional watermark attacks based on linear operations. We conclude this paper by bringing up some thoughts on the integration of watermarking and cryptography.
In most existing Wyner-Ziv video coding schemes, a feedback channel (FC) is expected at the decoder in order to allocate a proper bit rate for each Wyner-Ziv frame. However, FC not only results in additional latency but also increases decoding complexity due to the several feedback-decoding iterations. Moreover, FC may be unavailable in many practical video applications. In this paper, we propose a novel feedback-free rate-allocation scheme for transform domain Wyner-Ziv video coding (TD-WZVC), which predicts the rate for each Wyner-Ziv frame at the encoder without significantly increasing the complexity of the encoder. First, a correlation estimation model is presented to characterize the relationship between the source frame and the reference frame estimated at the encoder in TD-WZVC. Then, an efficient FC-free rateallocation algorithm is proposed and a linear model is built to avoid both overestimation and underestimation of the real rate and obtain an optimal rate-distortion performance. Experimental results show that the proposed scheme is able to achieve a good encoder rate allocation while still maintaining consistent coding efficiency.
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