视频编码中DCT系数基于重量化的数据分割

数据分割技术将视频流分成不同的部分进行传输。传统的数据分割算法是采用基于DCT系数的频率域分层技术。文章提出的算法对DCT系数进行重量化，量化后的系数作为基本层的数据，而量化后的余值作为增强层的数据。实验证明，与频率域分层技术相比，该算法提供了较好的图像质量。     

Quantizer offset selection for improved requantization transcoding

In this paper, we provide an analysis of the requantization problem in order to improve the requantization process. This analysis is based on theoretical R-D results of requantized Laplacian sources instead of minimizing requantization errors as commonly found in the literature. We derive the effective quantizer characteristic by applying superposition to the quantizer characteristics of encoder and transcoder. Further investigation shows that the effective quantizer has a periodic property. Using the memoryless property of the probability distribution function and the periodic property of the effective quantizer characteristic, we derive expressions for entropy and distortion. Based on the theoretical R-D model, requantization for fine and coarse quantized signals is investigated. The analysis of the R-D behavior shows that a heuristic can be derived which improves the requantization process. Finally, the results from the R-D analysis are verified for requantization transcoding of H.264/AVC video streams. We show that the transcoding process for H.264/AVC video streams, which corresponds to coarse quantization, is improved with gains up to 1 dB.     

一种DCT域MPEG-2码率变换技术

文中根据MPEG-2编程算法，提出了一种DCT域的MPEG-2码率变换技术，由于这种技术的复杂度较低，此技术特别适合被应用于数字信号处理器（DSP）或计算机上，通过软件来实现MPEG-2码率变换。     

Perfect requantization for video transcoding

Bit rate adaptation is one of the most important types of video transcoding. In this paper, we investigate certain critical points in the spectrum of rate shaping requests. We show that the selection of quantization step sizes may not have monotonic effects on rate-distortion characteristics in the transcoding sense. In other words, rate-distortion tradeoff for transcoding which operates on an already-compressed source can be different than that for regular encoding which operates on an original source. We show in a generic form that careful selections of the step size can lead to much improved performance for transcoding, especially when comparing to what would have been produced through a direct encoding. We demonstrate this unique rate-distortion characteristic through simulations as well as real transcoding scenario with H.264 sequences.

抗重量化转码的H.264/AVC视频水印算法

根据H.264/AVC特定的编解码架构,该文提出一种基于残差系数符号编码的新水印方案.在重量化转码分析的基础上,结合纹理复杂度和率失真开销差距选择嵌入水印的宏块,解决了重量化转码过程中宏块模式变化引起水印不同步问题.水印嵌入不是直接对系数进行叠加,而是结合DCT残差系数特点,通过特定的符号编码方式对系数进行轻微调制.实验结果表明,该算法可以抵抗重量化转码、加性白高斯噪声、亮度与对比度调节等攻击,并且能很好地保持视频感知质量.     

Mixed architectures for H.264/AVC digital video transrating

In this paper, we investigate transrating architectures for H.264/AVC video streams. Basic architectures are presented with their strengths and weaknesses. None of the existing architectures provide an appropriate solution for H.264/AVC transrating with an optimal balance between visual quality and complexity. In order to find such an appropriate solution, we propose the use of mixed transrating architectures. These architectures combine different transrating techniques which are applied depending on the picture/macroblock type. The intra-predicted pictures are decoded and re-encoded, while open-loop transrating or transrating with compensation is applied to motion-compensated pictures. Performance results show that the mixed architecture which applies spatial compensation to motion-compensated pictures gives rate-distortion results which approach the cascade of decoder and re-encoder with a complexity only slightly higher than the open-loop transrater. Adding temporal compensation for motion-compensated pictures further improves the visual quality, albeit to a lower extent, at the expense of increased complexity.