簡單說，ADTS可以在任意幀解碼，也就是說它每一幀都有頭信息。ADIF只有一個統一的頭，所以必須得到所有的數據后解碼。且這兩種的header的格式也是不同的，目前一般編碼后的和抽取出的都是ADTS格式的音頻流。
/**
*
* filename: MyAACDecoder.h
* summary: convert aac to wave
* author: caosiyang
* email: csy3228@gmail.com
*
*/
#ifndef __MYAACDECODER_H__
#define __MYAACDECODER_H__
#include "Buffer.h"
#include "mytools.h"
#include "WaveFormat.h"
#include "faad.h"
#include <iostream>
using namespace std;
class MyAACDecoder {public:
MyAACDecoder();
~MyAACDecoder();
int32_t Decode(char *aacbuf, uint32_t aacbuflen);
const char* WavBodyData() const {return _mybuffer.Data();
}
uint32_t WavBodyLength() const {return _mybuffer.Length();
}
const char* WavHeaderData() const {return _wave_format.getHeaderData();
}
uint32_t WavHeaderLength() const {return _wave_format.getHeaderLength();
}
private:
MyAACDecoder(const MyAACDecoder &dec);
MyAACDecoder& operator=(const MyAACDecoder &rhs);
//init AAC decoder
int32_t _init_aac_decoder(char *aacbuf, int32_t aacbuflen);
//destroy aac decoder
void _destroy_aac_decoder();
//parse AAC ADTS header, get frame length
uint32_t _get_frame_length(const char *aac_header) const;
//AAC decoder properties
NeAACDecHandle _handle;
unsigned long _samplerate;
unsigned char _channel;
Buffer _mybuffer;
WaveFormat _wave_format;
};
#endif /*__MYAACDECODER_H__*/
#include "MyAACDecoder.h"
MyAACDecoder::MyAACDecoder(): _handle(NULL), _samplerate(44100), _channel(2), _mybuffer(4096, 4096) {}
MyAACDecoder::~MyAACDecoder() {_destroy_aac_decoder();
}
int32_t MyAACDecoder::Decode(char *aacbuf, uint32_t aacbuflen) {int32_t res = 0;
if (!_handle) {if (_init_aac_decoder(aacbuf, aacbuflen) != 0) {ERR1(":::: init aac decoder failed ::::");return -1;
}
}
//clean _mybuffer
_mybuffer.Clean();
uint32_t donelen = 0;
uint32_t wav_data_len = 0;
while (donelen < aacbuflen) {uint32_t framelen = _get_frame_length(aacbuf + donelen);
if (donelen + framelen > aacbuflen) {break;
}
//decode
NeAACDecFrameInfo info;
void *buf = NeAACDecDecode(_handle, &info, (unsigned char*)aacbuf + donelen, framelen);
if (buf && info.error == 0) {if (info.samplerate == 44100) {//44100Hz
//src: 2048 samples, 4096 bytes
//dst: 2048 samples, 4096 bytes
uint32_t tmplen = info.samples * 16 / 8;
_mybuffer.Fill((const char*)buf, tmplen);
wav_data_len += tmplen;
} else if (info.samplerate == 22050) {//22050Hz
//src: 1024 samples, 2048 bytes
//dst: 2048 samples, 4096 bytes
short *ori = (short*)buf;
short tmpbuf[info.samples * 2];
uint32_t tmplen = info.samples * 16 / 8 * 2;
for (int32_t i = 0, j = 0; i < info.samples; i += 2) {tmpbuf[j++] = ori[i];
tmpbuf[j++] = ori[i + 1];
tmpbuf[j++] = ori[i];
tmpbuf[j++] = ori[i + 1];
}
_mybuffer.Fill((const char*)tmpbuf, tmplen);
wav_data_len += tmplen;
}
} else {ERR1("NeAACDecDecode() failed");}
donelen += framelen;
}
//generate Wave header
_wave_format.setSampleRate(_samplerate);
_wave_format.setChannel(_channel);
_wave_format.setSampleBit(16);
_wave_format.setBandWidth(_samplerate * 16 * _channel / 8);
_wave_format.setDataLength(wav_data_len);
_wave_format.setTotalLength(wav_data_len + 44);
_wave_format.GenerateHeader();
return 0;
}
uint32_t MyAACDecoder::_get_frame_length(const char *aac_header) const {uint32_t len = *(uint32_t *)(aac_header + 3);
len = ntohl(len); //Little Endian
len = len << 6;
len = len >> 19;
return len;
}
int32_t MyAACDecoder::_init_aac_decoder(char* aacbuf, int32_t aacbuflen) {unsigned long cap = NeAACDecGetCapabilities();
_handle = NeAACDecOpen();
if (!_handle) {ERR1("NeAACDecOpen() failed");_destroy_aac_decoder();
return -1;
}
NeAACDecConfigurationPtr conf = NeAACDecGetCurrentConfiguration(_handle);
if (!conf) {ERR1("NeAACDecGetCurrentConfiguration() failed");_destroy_aac_decoder();
return -1;
}
NeAACDecSetConfiguration(_handle, conf);
long res = NeAACDecInit(_handle, (unsigned char *)aacbuf, aacbuflen, &_samplerate, &_channel);
if (res < 0) {ERR1("NeAACDecInit() failed");_destroy_aac_decoder();
return -1;
}
//fprintf(stdout, "SampleRate = %d\n", _samplerate);
//fprintf(stdout, "Channel = %d\n", _channel);
//fprintf(stdout, ":::: init aac decoder done ::::\n");
return 0;
}
void MyAACDecoder::_destroy_aac_decoder() {if (_handle) {NeAACDecClose(_handle);
_handle = NULL;
}
}