Enhanced aacPlus音频编解码器的研究及其解码器在XScale上的高效实现

【作者】 高磊；

【导师】 张长明；

【作者基本信息】 电子科技大学 ， 电路与系统， 2008， 硕士

【摘要】 Enhanced aacPlus是目前最完美的开放式低码率音频编解码方案。作为MPEG-4和3GPP标准它必然在未来的无线通信、网络流媒体、数字广播等领域拥有广泛的应用前景。基于Intel XScale架构的处理器PXA272具有强大的多媒体处理能力,同时采用了独特的节电技术,适用于各类便携式设备。CMMB(China Mobile Multimedia Broadcasting)标准是广电总局最近颁布的运用于移动电视业务的行业标准,今后将在我国的广播电视领域扮演重要的角色。本文对Enhanced aacPlus编解码器的原理和实现方法作了深入的研究,并针对手机电视终端的应用,详细论述了基于XScale处理器的Enhanced aacPlus解码器的高效实现方法。全文首先从数字音频技术的发展及基本原理出发,讨论Enhanced aacPlus编解码器的结构框架和主要算法模块,重点分析它的三个主要功能单元:AAC_LC(核心编解码器)、SBR(频带扩展工具)、PS(参数立体声工具)。接着介绍Enhanced aacPlus解码器的一个应用——手机电视业务。并以此为背景详细论述在尽量不降低音频质量的前提下,为提高解码性能,对Enhanced aacPlus解码器的部分算法和程序所进行的改进措施和优化方法。在算法层主要包括:滤波器组模块的快速IMDCT算法改进,反量化解码模块中的快速查表算法改进,以及Huffman解码模块中的快速实现算法。在代码层则依次讨论了基本操作优化、C level优化和汇编level优化。最后完成Enhanced aacPlus解码器在XScale处理器上的高效实现,并分析了解码器的各项性能。从最终的测试数据和结论中可以看出,课题成功实现了XScale平台上Enhanced aacPlus解码器的改进优化,解码音质达到商用标准,解码效率接近业界先进水平。更多还原

【Abstract】 Enhanced aacPlus is the state-of-the art low bit rate open standards audio codec. As the standard of MPEG-4 and 3GPP, the application prospect of Enhanced aacPlus is very widely in the markets of mobile, Internet streaming and digital broadcasting.Processor PXA272 based on Intel XScale architecture has powerful multimedia process ability,and meanwhile adopts unique power saving technology. It is suitable for portable apparatus. CMMB(China Mobile Multimedia Broadcasting)is the standard of the digital mobile TV which is published by the state administration of radio film and television. It will be the key role in Chinese digital mobile TV for the future. This thesis investigates the principle and implementation method of Enhanced aacPlus codec ,and discusses the method of decoding efficiently based on the XScale processor for the application of mobile TV terminals.Firstly, based on the brief introduction to the development and the fundamental principle of audio coding technology, the standard structure and algorithm techniques of Enhanced aacPlus are discussed in detail. In all of them, it focuses on the three function blocks: AAC_LC, SBR and PS.Subsequently, based on the introduction of application of Mobile TV, the thesis investigates some important algorithmic modifications and code optimizations for the improvement of decoding performance and speed without reducing the audio quality. In the algorithm level it includes the use of fast IMDCT, the modification in the blocks of inverse scaled and Huffman decoding; in the code level it includes basic operation optimizations, C code optimizations and ASM code optimizations.Finally, after the finishing of efficient implementation of Enhanced aacPlus decodec based on the XScale processor, this thesis analyzes the capability of the decodec.It can be seen from the final test data and conclusion that, this thesis successfully realizes the mendings and optimizations of Enhanced aacPlus on XScale. The timbre of decoding accords with the commercial demand and the efficiency approachs the best in the field.更多还原