Android Native C++ 层中使用AudioRecord录制PCM音频

    Android应用程序很少会用到Android Native C++ 层中AudioRecord来录制PCM，但也不是完全没有需求，至少这么做可以在不懂C++的程序员面前装装逼！
直接在Native C++层录制和处理PCM数据可以避免数据拷贝到虚拟机，再由虚拟机拷回到Native C++层；虽然这个消耗笔者认为应该不大，但是没有具体分析过虚拟机，不清楚，有知道的朋友请告诉一下。
    本文描述了在Android Native C++ 层中使用AudioRecord录制PCM音频的一般方法，希望对有此需求的童鞋有所帮助。

    C++层的AudioRecord类位于源码目录\frameworks\av\include\media\AudioRecord.h中，定义如下：

namespace android {class audio_track_cblk_t;// ----------------------------------------------------------------------------class AudioRecord : virtual public RefBase{public:    static const int DEFAULT_SAMPLE_RATE = 8000;        ...} //end of calss} //end of namespace android

    可以看到AudioRecord位于android名字空间中，继承于RefBase,这个基类是智能指针引用计数用的，而  

class AudioRecord : virtual public RefBase

虚继承是为了解决菱形继承问题，让从不同的路径继承过来的同一个类在子类内存中只有一个拷贝。

以下是具体代码：

#include <media/AudioRecord.h>//==============================================//Audio Record Defination//==============================================static pthread_tg_AudioRecordThread;static pthread_t *g_AudioRecordThreadPtr = NULL;volatile bool g_bQuitAudioRecordThread = false;volatile int g_iInSampleTime = 0;int g_iNotificationPeriodInFrames = 8000/10; // g_iNotificationPeriodInFrames should be change when sample rate changes.static void *AudioRecordThread( void *inArg );void StartAudioRecordThread();void StopAudioRecordThread();void AudioRecordCallback(int event, void* user, void *info){if(event == android::AudioRecord::EVENT_NEW_POS){g_iInSampleTime += g_iNotificationPeriodInFrames;//if(g_iInSampleTime > g_iNotificationPeriodInFrames*100) //g_bQuitAudioRecordThread = true;}else if (event == android::AudioRecord::EVENT_MORE_DATA){android::AudioRecord::Buffer* pBuff = (android::AudioRecord::Buffer*)info;        pBuff->size = 0;}else if (event == android::AudioRecord::EVENT_OVERRUN){LOGE(" EVENT_OVERRUN \n");}}static void *AudioRecordThread( void *inArg ){uint64_t  inHostTime = 0;void *inBuffer = NULL; audio_source_t inputSource = AUDIO_SOURCE_MIC;audio_format_t audioFormat = AUDIO_FORMAT_PCM_16_BIT;audio_channel_mask_t channelConfig = AUDIO_CHANNEL_IN_MONO; //AUDIO_CHANNEL_IN_STEREO;int bufferSizeInBytes = 1600;int sampleRateInHz = 8000;android::AudioRecord *pAudioRecord = NULL;FILE * g_pAudioRecordFile = NULL;char strAudioFile[] = "/mnt/sdcard/external_sd/AudioRecordFile.pcm";int iNbChannels = 1;// 1 channel for mono, 2 channel for streoint iBytesPerSample = 2; // 16bits pcm, 2Bytesint frameSize = 0;// frameSize = iNbChannels * iBytesPerSample  int minFrameCount = 0;// get from AudroRecord objectint iWriteDataCount = 0;// how many data are there write to file// log the thread id for debug infoLOGD("%s  Thread ID  = %d  \n", __FUNCTION__,  pthread_self());  g_iInSampleTime = 0;g_pAudioRecordFile = fopen(strAudioFile, "wb+");iNbChannels = (channelConfig == AUDIO_CHANNEL_IN_STEREO) ? 2 : 1;frameSize = iNbChannels * iBytesPerSample;android::status_t status = android::AudioRecord::getMinFrameCount(&minFrameCount, sampleRateInHz, audioFormat, channelConfig);if(status != android::NO_ERROR){LOGE("%s  AudioRecord.getMinFrameCount fail \n", __FUNCTION__);goto exit ;}LOGE("sampleRateInHz = %d minFrameCount = %d iNbChannels = %d frameSize = %d ", sampleRateInHz, minFrameCount, iNbChannels, frameSize);bufferSizeInBytes = minFrameCount * frameSize;inBuffer = malloc(bufferSizeInBytes); if(inBuffer == NULL){LOGE("%s  alloc mem failed \n", __FUNCTION__);goto exit ; }g_iNotificationPeriodInFrames = sampleRateInHz/10;pAudioRecord  = new android::AudioRecord();if(NULL == pAudioRecord){LOGE(" create native AudioRecord failed! ");goto exit;}pAudioRecord->set( inputSource,                                    sampleRateInHz,                                    audioFormat,                                    channelConfig,                                    0,                                    AudioRecordCallback,                                    NULL,                                    0,                                    true,                                    0); if(pAudioRecord->initCheck() != android::NO_ERROR)  {LOGE("AudioTrack initCheck error!");goto exit;}if(pAudioRecord->setPositionUpdatePeriod(g_iNotificationPeriodInFrames) != android::NO_ERROR){LOGE("AudioTrack setPositionUpdatePeriod error!");goto exit;}if(pAudioRecord->start()!= android::NO_ERROR){LOGE("AudioTrack start error!");goto exit;}while (!g_bQuitAudioRecordThread){inHostTime = UpTicks();int readLen = pAudioRecord->read(inBuffer, bufferSizeInBytes);int writeResult = -1;if(readLen > 0) {iWriteDataCount += readLen;if(NULL != g_pAudioRecordFile){writeResult = fwrite(inBuffer, 1, readLen, g_pAudioRecordFile);if(writeResult < readLen){LOGE("Write Audio Record Stream error");}}// write PCM data to file or other stream,implement it yourselfwriteResult = WriteAudioData(g_iInSampleTime, inHostTime, inBuffer, readLen);//LOGD("readLen = %d  writeResult = %d  iWriteDataCount = %d", readLen, writeResult, iWriteDataCount);}else {LOGE("pAudioRecord->read  readLen = 0");}}exit:if(NULL != g_pAudioRecordFile){fflush(g_pAudioRecordFile);fclose(g_pAudioRecordFile);g_pAudioRecordFile = NULL;}if(pAudioRecord){pAudioRecord->stop();delete pAudioRecord;pAudioRecord == NULL;}if(inBuffer){free(inBuffer);inBuffer = NULL;}LOGD("%s  Thread ID  = %d  quit\n", __FUNCTION__,  pthread_self());return NULL;}

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