iOS實現麥克風捕獲和AAC編碼

轉載地址：http://blog.csdn.net/shenyi0106/article/details/47004039

在Ios中，實現打開和捕獲麥克風大多是用的AVCaptureSession這個組件來實現的，它可以不僅可以實現音頻捕獲，還可以實現視頻的捕獲。本文將主要實現麥克風音頻的捕獲和編碼。

針對打開麥克風和捕獲音頻的代碼，網上也有一些，我就簡單的整理了一下：

首先，我們需要定義一個AVCaptureSession類型的變量，它是架起在麥克風設備和數據輸出上的一座橋，通過它可以方便的得到麥克風的實時原始數據。

AVCaptureSession *m_capture

同時，定義一組函數，用來打開和關閉麥克風；爲了能使數據順利的導出，你還需要實現AVCaptureAudioDataOutputSampleBufferDelegate這個協議

-(void)open;
-(void)close;
-(BOOL)isOpen;

下面我們將分別實現上述參數函數，來完成數據的捕獲。

-(void)open {
    NSError *error;
    m_capture = [[AVCaptureSession alloc]init];
    AVCaptureDevice *audioDev = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
    if (audioDev == nil)
    {
        CKPrint("Couldn't create audio capture device");
        return ;
    }

    // create mic device
    AVCaptureDeviceInput *audioIn = [AVCaptureDeviceInput deviceInputWithDevice:audioDev error:&error];
    if (error != nil)
    {
        CKPrint("Couldn't create audio input");
        return ;
    }


    // add mic device in capture object
    if ([m_capture canAddInput:audioIn] == NO)
    {
        CKPrint("Couldn't add audio input")
        return ;
    }
    [m_capture addInput:audioIn];
    // export audio data
    AVCaptureAudioDataOutput *audioOutput = [[AVCaptureAudioDataOutput alloc] init];
    [audioOutput setSampleBufferDelegate:self queue:dispatch_get_main_queue()];
    if ([m_capture canAddOutput:audioOutput] == NO)
    {
        CKPrint("Couldn't add audio output");
        return ;
    }
    [m_capture addOutput:audioOutput];
    [audioOutput connectionWithMediaType:AVMediaTypeAudio];
    [m_capture startRunning];
    return ;
}

-(void)close {
    if (m_capture != nil && [m_capture isRunning])
    {
        [m_capture stopRunning];
    }

    return;
}
-(BOOL)isOpen {
    if (m_capture == nil)
    {
        return NO;
    }

    return [m_capture isRunning];
}

通過上面三個函數，即可完成所有麥克風捕獲的準備工作，現在我們就等着數據主動送上門了。要想數據主動送上門，我們還需要實現一個協議接口：

- (void)captureOutput:(AVCaptureOutput *)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection *)connection {
    char szBuf[4096];
    int  nSize = sizeof(szBuf);

#if SUPPORT_AAC_ENCODER
    if ([self encoderAAC:sampleBuffer aacData:szBuf aacLen:&nSize] == YES)
    {
        [g_pViewController sendAudioData:szBuf len:nSize channel:0];
    }
#else //#if SUPPORT_AAC_ENCODER
    AudioStreamBasicDescription outputFormat = *(CMAudioFormatDescriptionGetStreamBasicDescription(CMSampleBufferGetFormatDescription(sampleBuffer)));
    nSize = CMSampleBufferGetTotalSampleSize(sampleBuffer);
    CMBlockBufferRef databuf = CMSampleBufferGetDataBuffer(sampleBuffer);
    if (CMBlockBufferCopyDataBytes(databuf, 0, nSize, szBuf) == kCMBlockBufferNoErr)
    {
        [g_pViewController sendAudioData:szBuf len:nSize channel:outputFormat.mChannelsPerFrame];
    }
#endif
}

到這裏，我們的工作也就差不多做完了，所捕獲出來的數據是原始的PCM數據。

當然，由於PCM數據本身比較大，不利於網絡傳輸，所以如果需要進行網絡傳輸時，就需要對數據進行編碼；Ios系統本身支持多種音頻編碼格式，這裏我們就以AAC爲例來實現一個PCM編碼AAC的函數。

在Ios系統中，PCM編碼AAC的例子，在網上也是一找一大片，但是大多都是不太完整的，而且相當一部分都是E文的，對於某些童鞋而言，這些都是深惡痛絕的。我這裏就做做好人，把它們整理了一下，寫成了一個函數，方便使用。

在編碼前，需要先創建一個編碼轉換對象

AVAudioConverterRef m_converter;

#if SUPPORT_AAC_ENCODER
-(BOOL)createAudioConvert:(CMSampleBufferRef)sampleBuffer { //根據輸入樣本初始化一個編碼轉換器
    if (m_converter != nil)
    {
        return TRUE;
    }

    AudioStreamBasicDescription inputFormat = *(CMAudioFormatDescriptionGetStreamBasicDescription(CMSampleBufferGetFormatDescription(sampleBuffer))); // 輸入音頻格式
    AudioStreamBasicDescription outputFormat; // 這裏開始是輸出音頻格式
    memset(&outputFormat, 0, sizeof(outputFormat));
    outputFormat.mSampleRate       = inputFormat.mSampleRate; // 採樣率保持一致
    outputFormat.mFormatID         = kAudioFormatMPEG4AAC;    // AAC編碼
    outputFormat.mChannelsPerFrame = 2;
    outputFormat.mFramesPerPacket  = 1024;                    // AAC一幀是1024個字節

    AudioClassDescription *desc = [self getAudioClassDescriptionWithType:kAudioFormatMPEG4AAC fromManufacturer:kAppleSoftwareAudioCodecManufacturer];
    if (AudioConverterNewSpecific(&inputFormat, &outputFormat, 1, desc, &m_converter) != noErr)
    {
        CKPrint(@"AudioConverterNewSpecific failed");
        return NO;
    }

    return YES;
}
-(BOOL)encoderAAC:(CMSampleBufferRef)sampleBuffer aacData:(char*)aacData aacLen:(int*)aacLen { // 編碼PCM成AAC
    if ([self createAudioConvert:sampleBuffer] != YES)
    {
        return NO;
    }

    CMBlockBufferRef blockBuffer = nil;
    AudioBufferList  inBufferList;
    if (CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(sampleBuffer, NULL, &inBufferList, sizeof(inBufferList), NULL, NULL, 0, &blockBuffer) != noErr)
    {
        CKPrint(@"CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer failed");
        return NO;
    }
    // 初始化一個輸出緩衝列表
    AudioBufferList outBufferList;
    outBufferList.mNumberBuffers              = 1;
    outBufferList.mBuffers[0].mNumberChannels = 2;
    outBufferList.mBuffers[0].mDataByteSize   = *aacLen; // 設置緩衝區大小
    outBufferList.mBuffers[0].mData           = aacData; // 設置AAC緩衝區
    UInt32 outputDataPacketSize               = 1;
    if (AudioConverterFillComplexBuffer(m_converter, inputDataProc, &inBufferList, &outputDataPacketSize, &outBufferList, NULL) != noErr)
    {
        CKPrint(@"AudioConverterFillComplexBuffer failed");
        return NO;
    }

    *aacLen = outBufferList.mBuffers[0].mDataByteSize; //設置編碼後的AAC大小
    CFRelease(blockBuffer);
    return YES;
}
-(AudioClassDescription*)getAudioClassDescriptionWithType:(UInt32)type fromManufacturer:(UInt32)manufacturer { // 獲得相應的編碼器
    static AudioClassDescription audioDesc;

    UInt32 encoderSpecifier = type, size = 0;
    OSStatus status;

    memset(&audioDesc, 0, sizeof(audioDesc));
    status = AudioFormatGetPropertyInfo(kAudioFormatProperty_Encoders, sizeof(encoderSpecifier), &encoderSpecifier, &size);
    if (status)
    {
        return nil;
    }

    uint32_t count = size / sizeof(AudioClassDescription);
    AudioClassDescription descs[count];
    status = AudioFormatGetProperty(kAudioFormatProperty_Encoders, sizeof(encoderSpecifier), &encoderSpecifier, &size, descs);
    for (uint32_t i = 0; i < count; i++)
    {
        if ((type == descs[i].mSubType) && (manufacturer == descs[i].mManufacturer))
        {
            memcpy(&audioDesc, &descs[i], sizeof(audioDesc));
            break;
        }
    }
    return &audioDesc;
}
OSStatus inputDataProc(AudioConverterRef inConverter, UInt32 *ioNumberDataPackets, AudioBufferList *ioData,AudioStreamPacketDescription **outDataPacketDescription, voidvoid *inUserData) { //<span style="font-family: Arial, Helvetica, sans-serif;">AudioConverterFillComplexBuffer 編碼過程中，會要求這個函數來填充輸入數據，也就是原始PCM數據</span>
    AudioBufferList bufferList = *(AudioBufferList*)inUserData;
    ioData->mBuffers[0].mNumberChannels = 1;
    ioData->mBuffers[0].mData           = bufferList.mBuffers[0].mData;
    ioData->mBuffers[0].mDataByteSize   = bufferList.mBuffers[0].mDataByteSize;
    return noErr;
}
#endif

好了，世界是那麼美好，一個函數即可所有的事情搞定了。當你需要進行AAC編碼時，調用encoderAAC這個函數就可以了（在上面有完整的代碼）

char szBuf[4096];
int  nSize = sizeof(szBuf);
if ([self encoderAAC:sampleBuffer aacData:szBuf aacLen:&nSize] == YES)
{
    // do something
}