MPEG-2 AAC解码器的优化算法

作为新一代的音频编码国际标准,先进音频编码(AAC)提供了良好的压缩性能,具有广阔的发展和应用前景。但是由于AAC标准给出的算法比较复杂,按照标准算法进行测试时发现其并不能满足实时解码的要求,因此,必须对标准算法进行优化以达到实时解码的要求。在叙述了MPEG-2 AAC解码器的模块组成和原理的基础上,针对各个模块的特点采用优化算法,对MPEG-2 AAC解码器的部分模块进行了优化设计,较大程度地提高了解码速度。     

DRA算法及其实时解码器设计

DRA是一种新的音频编解码标准,其在每声道64 Kbit/s时重建的音质达到ITU-R规定的"人耳不可识别损伤"的主观音质评定.研究了DRA的编码与解码原理,在对解码算法进行了优化的基础上.设计并实现了基于PXA270平台的DRA实时解码器.主观听音测试结果表明.该解码器音质良好.满足实时解码应用的要求.     

多制式音频解码系统中IMDCT算法优化与硬件实现

逆改良型离散余弦变换(IMDCT)是高质量音频解码器的基本处理单元,其运算中大量的乘法是实现高效IMDCT的一个瓶颈.通过优化IMDCT的算法,实现了一个高效的IMDCT硬件加速器,具有很好的可配置功能,可支持12点,36点及2的幂次点数的IMDCT.通过蝶形拆分运算加快了解码速度,同时通过一个乘法器的复用,大大地降低了解码器的面积.     

音频工作站MPEG-Ⅰ Layer-Ⅱ码流快速解码混音

为了能实时完成数字音频工作站中多路MPEG-Ⅰ Layer-Ⅱ音频压缩码流的快速解码混音,在分析MPEG-Ⅰ解码器中的多相滤波器组这个核心算法的基础上,提出了多路MPEG-Ⅰ Layer-Ⅱ码流的快速解码混音算法.此算法在进行混音计算时,只需做一次在解码中较为费时的子带综合滤波计算,大大提高了多路混音的速度.实验表明,用该算法进行8路MPEG-Ⅰ Layer-Ⅱ解码混音时,在PI-Ⅱ 600MHz的PC机达到了0.25倍实时的解码速度,完全满足了专业数字音频工作站的要求.     

一种适用于高清视频解码的反离散余弦变换的VLSI实现

提出了一种面向视频处理应用的二维8X8IDCT(反离散余弦变换)处理器结构.该处理器设计利用了IDCT算法中的对称性,采用基于并行的乘累加器的结构加快处理速度.设计过程中对于有限位宽对运算结果误差及精度的影响进行了仿真与分析,并根据要求确定了运算位宽的优化值,在满足精度的条件下使芯片的面积开销最小.该处理器核的面积为48K逻辑门,能够在0.64μs内完成对一个数据块的运算,可以满足对高清晰度视频实时解码的性能需求.     

自适应计算为MPEG—4注入新的动力

下一代无线和便携式通信产品将广泛应用MPEG-4标准的流式视频和音频。相比基于DSP的设计,采用自适应算法能够更加有效地实现高质量流式视频所要求的强大处理能力。 比如,一个由编码通道和解码通道(全彩色、分辨率为352×288像素)所组成的双通道流式30fps MPEG-4视频信号要求的运算速度为1400000000次/秒。MPEG-4编码包括离散余弦变换(DCT)和运动估计等计算密集型算法(如图)。     

MPEG4编码器二维DCT变换的FPGA实现及优化

本文提出了一种适用于MPEG4视频编码系统的二维DCT的FPGA设计方案，该方案具有实时、高精度、易于FPGA实现的特点。在设计中，分别对DCT的算法及实现方法进行了分析和选择；在此基础上，对系统的结构进行了优化，提出了一种不同于传统二维DCT系统的新结构。最后对IDCT单元的运算精度进行了验证。     

先进音频编码中MDCT的新型递归结构及其FPGA设计

文章以新型的MDCT递归算法为基础，首先给出了一种主要模块分时共享、数据流同步多路处理的改进型并行处理结构，其可以高效地应用于国际音频标准MPEG-2以及MPEG-4的先进音频编码（AAC）当中。另外，针对递归实现结构高度模块化和较强规则性的特点，进行了FPGA的设计和仿真，结果表明：改进后的处理结构在增加少量硬件模块的条件下．大大提高了运算速度。     

MP3音频解码速度优化

MP3采用MPEG-1 LayerIII层标准压缩编码格式,压缩率很高,失真也较小,算法也较为复杂.就MP3解码过程中,针对各解码模块的特点,通过浮点转定点运算、分段拟合、查找表等方法,对解码复杂度较高的模块进行算法优化,并且在16位定点DSP芯片实现,优化后解码每帧音频格式的指令数降到最初的1/ 20.     

MPEG-4 AAC解码器在NIOS Ⅱ平台上的实现和优化

给出了MEPG-4AAC实时解码器在NIOSⅡ平台的实现方案，介绍了MPEG-4AAC—LC解码算法及各关键模块优化算法。在完成实时解码要求下，结合NIOSⅡ平台特性，对解码器在软件代码与处理器上进行优化。实验结果表明CPU时钟为80MHz时能达到实时解码要求。     

Robust Video Watermarking Using a Hybrid DCT-DWT Approach

In order to solve the limitations of the digital video watermarking algorithm, this paper proposes a new robust video watermarking algorithm using combining discrete cosine transform (DCT) and discrete wavelet transform (DWT) techniques. First of all, the video frames are randomly selected and then the DCT algorithm is applied to the selected video frames. After that, the first column of the selected video frames is scrambled using the Arnold algorithm. Furthermore, every column with 4 direct current (DC) coefficients is reshaped and transformed into four different sub-bands using the DWT technique. Next, the watermark is embedded into the approximation (LL) sub-band. The proposed algorithm is easy to carry out because it provides random frames with no special requirements for video frames. The experiment results indicate that this algorithm can resist against different kinds of watermarking attacks, such as the Gaussian filter attack and sharpen attack. In addition, it also illustrates that the proposed algorithm has a better result than some other watermarking algorithms.     

Generalized fast mixed-radix algorithm for the computation of forward and inverse MDCTs

This paper presents a generalized mixed-radix decimation-in-time (DIT) fast algorithm for computing the modified discrete cosine transform (MDCT) of the composite lengths N=2×q^m, m≥2, where q is an odd positive integer. The proposed algorithm not only has the merits of parallelism and numerical stability, but also needs less multiplications than that of type-IV discrete cosine transform (DCT-IV) and type-II discrete cosine transform (DCT-II) based MDCT algorithms due to the optimized efficient length-(N/q) modules. The computation of MDCT for composite lengths N=q^m×2ⁿ, m≥2, n≥2, can then be realized by combining the proposed algorithm with fast radix-2 MDCT algorithm developed for N=2ⁿ. The combined algorithm can be used for the computation of length-12/36 MDCT used in MPEG-1/-2 layer III audio coding as well as the recently established wideband speech and audio coding standards such as G.729.1, where length-640 MDCT is used. The realization of the inverse MDCT (IMDCT) can be obtained by transposing the signal flow graph of the MDCT.     

基于小波变换的双水印算法

数字音频水印是水印技术中重要的组成部分。而近年来对音频水印的研究远远少于图像水印,双水印的研究则更加少。因此提出了一种基于小波变换的双水印算法,在音频信号的小波变换域嵌入两个不同作用的水印,对一些音频处理有很好的鲁棒性的同时又能有效地判别音频信号的真实性和完整性。实验证明本算法的两水印分别具有很好的鲁棒性和敏感性,并实现了水印的盲提取。     

A survey of efficient MDCT implementations in MP3 audio coding standard: Retrospective and state-of-the-art

This tutorial paper describes various efficient implementations (published and new unpublished) of the forward and backward modified discrete cosine transform (MDCT) in the MPEG layer III (MP3) audio coding standard developed in the time period 1990-2010, including the efficient implementation of polyphase filter banks for completeness. The efficient MDCT implementations are discussed in the context of (fast) complete analysis/synthesis MDCT filter banks in the MP3 encoder and decoder. In general, for each efficient forward/backward MDCT block transforms implementation are presented: complete formulas or sparse matrix factorizations of the algorithm, the corresponding signal flow graph for the short audio block and the total arithmetic complexity as well as the useful comments related to improving the arithmetic complexity and a possible structural simplification of the algorithm. Finally, all efficient forward/backward MDCT implementations are compared both in terms of the arithmetic complexity and structural simplicity. It is important to note that almost all presented algorithms can be also used for the 2ⁿ-length data blocks in others MPEG audio coding standards and proprietary audio compression algorithms.     

An Efficient IDCT Processor Design for HDTV Applications

This paper proposes a high performance and low cost inverse discrete cosine transform (IDCT) processor for high definition Television (HDTV) applications by using cyclic convolution and hardwired multipliers. By properly arranging the input sequence, we formulate the one-dimensional (1-D) IDCT into cyclic convolution that is regular and suitable for VLSI implementation. The hardwired multiplier that implements multiplication with IDCT coefficients are first scaled and optimized by using the common sub-expression techniques. Based on these techniques, the data-path in the proposed two-dimensional (2-D) IDCT design costs 7504 gates plus 1024 bits of memory with 100 M pixels/sec throughput according to the cost estimation based on the cell library of COMPASS 0.6 m SPDM CMOS technology. Also, we have verified that the precision analysis of the proposed 2-D 8 × 8 IDCT meets the demands of IEEE Std. 1180-1990. Due to the good performance in the computing speed as well as the hardware cost, the proposed design is compact and suitable for HDTV applications. This design methodology can be applied to forward DCT as well as other transforms like discrete sine transform (DST), discrete Fourier transform (DFT), and discrete Hartley transform (DHT).     

一种基于CORDIC算法改进的高速低功耗DCT协处理器设计

介绍了一种支持MPEG2压缩协议,应用于ARM9内核、高速低功耗的二维DCT协处理设计研究.该协处理器利用行列分解法,并行优化实现二维DCT数据结构,明显提高了8×8数据块的处理速度.与此同时,应用改进的CORDIC算法——移位代替乘法并优化移位算法实现一维DCT.仿真结果表明,对于此种一维DCT算法硬件实现,在符合MPEG2精度和ARM9数据传输频率的前提下比文献[2]速度提高了30%,面积却减少了50%.这种协处理器可以在移动多媒体设备的编解码模块中得到广泛应用.     

改进的层式DCT编码

在对几种具有多分辨率特性的DCT分析基础上提出了一种层式DCT的改进算法.与原始的层式DCT相比,该算法在同样的压缩比,尤其是较低压缩比下可以获得更高的峰值信噪比.     

基于DSP的H.264/AVC解码器运动补偿模块的优化

针对H.264/AVC解码器中运动补偿模块存取密集、计算复杂度高的特点,对参考数据读取方式和亚像素插值计算进行了一系列优化,提出了运动补偿参考数据读入的并行机制和亚像素插值的优化算法.在不降低图像质量的前提下,大大提高了解码速度,TI DM642DSP平台下仿真结果表明优化后的运动补偿模块的计算速度提高为原来的19倍.     

基于WinCE6.0系统的无损音乐播放插件的开发

分析了FLAC解码的流程,进行了架构上的优化以及相应结构体和接口的封装.在此基础上开发了基于DirectShow架构的播放插件,在PC机上测试通过后移植到WinCE6.0操作系统中,使用系统自带的媒体播放器可以流畅播放FLAC格式的音频文件.     

数字音频压缩中的变换编码算法

变换编码是音频压缩中的一个重要部分,文中叙述ＭＰＥＧ音频编码标准中的变换编码技术,包括改进余弦变换和反变换（ＭＤＣＴ和ＩＭＤＣＴ）时域混叠抵消与自适应窗选择,详细推导了ＭＤＣＴ和ＩＭＤＣＴ的快速算法。