【作者】 陈茜；

【导师】 黄秋元；

【作者基本信息】 武汉理工大学 ， 通信与信息系统， 2008， 硕士

【摘要】 随着计算机技术的飞速发展,数字音频在消费电子、网络、广播、移动通信和数字影视等领域都有着广泛应用。互联网与无线通信协议的结合,移动终端的应用日益普及,使对更高效编解码系统的需求不断持续。本文中实现的HE-AAC v2解码器是手持数字电视终端需求的功能之一,旨在实现低比特率,高音质的完全解码,未来必将成为移动多媒体广泛应用的技术之一。本文首先分析了HE-AAC v2主要技术构成,及其编解码器的工作原理,深入分析了先进音频编码(AAC)、频带复制(SBR)和参数立体声(PS)中各算法模块的原理。按照两类不同的AAC文件格式——音频数据交换格式和音频数据传输比特流,分别分析了HE-AAC v2的各种比特流结构。对比特流中的原始数据块中的八类元素做了详细介绍。本文还着重了介绍了完成解码功能的HE-AAC v2解码中间件在软件设计中的作用,分析了其提供的应用函数接口(API),以及在使用这些API时所需的注意事项,根据两种不同的比特流结构,给出对两类比特流的解码流程。本文通过对HE-AAC v2技术的理论研究,比特流结构分析,借助瑞萨公司HE-AAC v2中间件,在基于SH-Mobile平台的地面数字多媒体广播(T-DMB)终端上,实现了对HE-AAC v2音频格式的文件的解码功能。所做的主要工作如下:(1)通过对T-DMB终端软件的结构和各功能的分析,提出了前后端共同驱动中间件解码的方案,即前端通过判断输入缓冲中的剩余数据量来不断从SD卡上读取文件,后端通过中断方式驱动中间件解码的不断进行。(2)结合T-DMB终端软件已有的模块和任务,从总体上设计了解码实现的流程。其中包括从SD卡读出文件,逐个数掘块的解码,解码后的PCM输出。创建多媒体音频解码控制任务,该任务利用中间件,与其他任务相互协作,控制解码的过程与状态。(3)根据总体设计,进一步详细设计了解码功能实现的任务构成,以及多媒体音频解码控制任务的三种状态(解码启动,解码过程中,解码停止)的实现流程。包括前后端共同驱动文件读取和解码不断进行的具体流程。(4)编写代码,调试,并设计测试用例、制作样本进行了测试。经过测试,本设计可支持采样率为16、22.05、24、32、44.1和48kHz,比特率为16～128kbps的各种HE-AAC v2音频文件。通过与适用于PC的同类解码器Nero AAC对比发现,解码性能更胜于它。更多还原

【Abstract】 As the rapid development of computer technology, digital audio has a wide range of applications in consumer electronics, networks, broadcasting, mobile communication and digital television etc. Internet combined with wireless communication and mobile terminal application growing popularity will make the need for more efficiency codec system continue. HE-AAC v2 decoder realized in the paper is one of the functions of portable digital TV. It means to realize the completed decode with high audio qualification at low bitrate. It will surely be one of the most popular technology applied in mobile multimedia area.Firstly, HE-AAC v2’s main technology and codec’s working principle are analyzed. The algorithm principles of compress tools in AAC, SBR and PS areanalyzed deeply. Then, according to two different types of AAC file------audio datainterchange format and andio data transmition stream, the bitestream structures of HE-AAC v2 are analyzed. Seven types element in raw data block in bitstream are introduced. The function of HE-AAC v2 middleware which completes the decoding is focused on. The API provided by middleware and the attension issues when use those application interface are introduced. At last, two types of bitstream’s decode process are given out according to their bitstream structures.Through the study of HE-AAC v2 theory and analysis of bitstream structure, the completed decoding of HE-AAC v2 compress format file on SH-mobile is realized successfully with HE-AAC v2 middleware provided by Renesas co..The major work done are:(1) Through the analysis of the structure and each functions of T-DMB terminal software, raise a programme which can co-drive decoding from front and end. Files are read from SD card continuously by judging the rest data size in input buffer in front. Continuous decoding is driven by interrupt in the end.(2) With the existed modual and task in T-DMB terminal software, design the decoding programme in whole. It includes reading files from SD card, decoding every data block and outputting the decoded PCM. Create a task named multimedia audio decode control task. The task controls the decoding process and status by cooperating with other tasks with HE-AAC v2 middleware.(3) Accoding to the whole designation, design the constructed tasks in the realization of decoding and the flow of realize three status(start decoding, decoding and stop decoding) in multimedia audio decode control task. It includes the specific flow of how to drive reading file and decoding.(4) Code in C language, debug, design testcase and make samples to test the function.By playing different HE-AAC v2 audio samples, the design in this paper can support kinds of HE-AAC v2 audio files whose sample rate is 16、22.05、24、32、44.1 or 48kHz, and bitrate is beteen 16 and 128kbps. And, through the compare of the decoder in this paper and Nero AAC which is a AAC decoder userd on PC, it can be found that the decode qualities are more well.更多还原