AAC音频格式分析

/**

 *

 * 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;

    }

}