围绕网络流媒体技术以及嵌入式环境的特点,为保障流媒体的服务质量,研究了基于客户端的缓冲区控制策略,以及具有流量控制机制的流媒体网络通信技术。在探讨嵌入式视频点播系统架构基础上,提出了利用平均传输速率、时延抖动、解码速率和辅助系数这四个参数进行网络缓冲区长度估算的简化算法;并提出在客户端按照数据的重要性或优先级的不同来实施主动抛弃策略;该系统也针对服务器端引入了流量控制算法。结果表明,应用上述策略明显节约了缓存,并且实现了流量控制功能,改善了系统的服务质量(Quality of Service,QoS)。
In this paper a blind image watermarking that can resist to rotation, scaling and translation （RST） attacks is proposed. Based on the spread spectrum, the watermark is modulated before embedding. The logpolar mapped discrete fourier transform （LPM-DFT） magnitude of a disk, a part of the origin image, constitutes the RST-invariant domain, where the origin of the LPM is the center of the disk and the sampling rates of the LPM are constant. After the middle frequency band of LPM-DFT magnitude, namely the watermark-embedding domain, is grouped according to the watermark length, the watermark is embedded by adjusting the difference between the two sub-region energy in each group. To improve the imperceptibility, the watermark-embedding domain is shuffled before embedding and the watermark is not embedded directly into the watermark-embedding domain. In watermark detection procedure, neither the original image nor any knowledge about the distortions is required. Experimental results show that the proposed scheme is very robust against RST distortion and common image processing attacks.
