The Design And Realization Of HE-AAC V2 Decoding Based On SH-Mobile

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.