使用音频单元录制我的 iPhone 应用程序播放的声音

我今天有很多有趣的事情iOS 和音频单元并发现了很多有用的资源（包括在内）。

首先，我对某些事情感到困惑：是否真的有必要创建一个音频图 with 混合器单元录制应用程序播放的声音？

或者播放声音就足够了ObjectAL https://github.com/kstenerud/ObjectAL-for-iPhone（或者更简单地说 AVAudioPlayer 调用）并创建一个远程IO单元通过录音回调寻址到正确的总线上？

Second，一个更加编程化的问题！ 因为我还不太适应音频单元概念，我尝试适应苹果混音器主机项目 http://developer.apple.com/library/ios/#samplecode/MixerHost/Introduction/Intro.html能够记录最终的混音。显然，我尝试用迈克尔·泰森 RemoteIO 帖子 http://atastypixel.com/blog/using-remoteio-audio-unit/.

我的回调函数上收到 EXC_BAD_ACCESS ：

static OSStatus recordingCallback       (void *inRefCon,
                                  AudioUnitRenderActionFlags *ioActionFlags,
                                  const AudioTimeStamp *inTimeStamp,
                                  UInt32        inBusNumber,
                                  UInt32        inNumberFrames,
                                  AudioBufferList *ioData) {

    AudioBufferList *bufferList; // <- Fill this up with buffers (you will want to malloc it, as it's a dynamic-length list)

    EffectState *effectState = (EffectState *)inRefCon;
    AudioUnit rioUnit = effectState->rioUnit;

    OSStatus status;

    // BELOW I GET THE ERROR
    status = AudioUnitRender(rioUnit,      
                             ioActionFlags, 
                             inTimeStamp, 
                             inBusNumber, 
                             inNumberFrames, 
                             bufferList);

    if (noErr != status) { NSLog(@"AudioUnitRender error"); return noErr;}

    // Now, we have the samples we just read sitting in buffers in bufferList
    //ExtAudioFileWriteAsync(effectState->audioFileRef, inNumberFrames, bufferList);

    return noErr;
}

在使用回调函数之前我做了MixerHostAudio.h

typedef struct {
    AudioUnit rioUnit;
    ExtAudioFileRef audioFileRef;
} EffectState;

并在界面中创建：

AudioUnit                       iOUnit;
EffectState effectState;
AudioStreamBasicDescription     iOStreamFormat;
...
@property                       AudioUnit           iOUnit;
@property (readwrite)           AudioStreamBasicDescription iOStreamFormat;

然后在实现文件中MixerHostAudio.h :

#define kOutputBus 0
#define kInputBus 1
...
@synthesize iOUnit;                    // the Remote IO unit
...
result =    AUGraphNodeInfo (
                             processingGraph,
                             iONode,
                             NULL,
                             &iOUnit
                             );

if (noErr != result) {[self printErrorMessage: @"AUGraphNodeInfo" withStatus: result]; return;}

// Enable IO for recording
UInt32 flag = 1;
result = AudioUnitSetProperty(iOUnit, 
                              kAudioOutputUnitProperty_EnableIO, 
                              kAudioUnitScope_Input, 
                              kInputBus,
                              &flag, 
                              sizeof(flag));

if (noErr != result) {[self printErrorMessage: @"AudioUnitSetProperty" withStatus: result]; return;}
// Describe format
iOStreamFormat.mSampleRate          = 44100.00;
iOStreamFormat.mFormatID            = kAudioFormatLinearPCM;
iOStreamFormat.mFormatFlags     = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
iOStreamFormat.mFramesPerPacket = 1;
iOStreamFormat.mChannelsPerFrame    = 1;
iOStreamFormat.mBitsPerChannel      = 16;
iOStreamFormat.mBytesPerPacket      = 2;
iOStreamFormat.mBytesPerFrame       = 2;

// Apply format
result = AudioUnitSetProperty(iOUnit, 
                              kAudioUnitProperty_StreamFormat, 
                              kAudioUnitScope_Output, 
                              kInputBus, 
                              &iOStreamFormat, 
                              sizeof(iOStreamFormat));

if (noErr != result) {[self printErrorMessage: @"AudioUnitSetProperty" withStatus: result]; return;}

result = AudioUnitSetProperty(iOUnit, 
                              kAudioUnitProperty_StreamFormat, 
                              kAudioUnitScope_Input, 
                              kOutputBus, 
                              &iOStreamFormat, 
                              sizeof(iOStreamFormat));

if (noErr != result) {[self printErrorMessage: @"AudioUnitSetProperty" withStatus: result]; return;}

effectState.rioUnit = iOUnit;

// Set input callback ----> RECORDING
AURenderCallbackStruct callbackStruct;
callbackStruct.inputProc = recordingCallback;
callbackStruct.inputProcRefCon = self;
result = AudioUnitSetProperty(iOUnit, 
                              kAudioOutputUnitProperty_SetInputCallback, 
                              kAudioUnitScope_Global, 
                              kInputBus, 
                              &callbackStruct, 
                              sizeof(callbackStruct));

if (noErr != result) {[self printErrorMessage: @"AudioUnitSetProperty" withStatus: result]; return;}

但我不知道出了什么问题，也不知道如何挖掘。 注：效果状态结构存在是因为我也尝试集成生物音频项目 https://github.com/brennon/BioAudio从缓冲区写入文件的能力。

还有第三，我想知道是否有更简单的方法来录制我的iPhone应用程序播放的声音（即排除麦克风）？

我自己发现的。我忘记像这样链接：

callbackStruct.inputProcRefCon = &effectState;

这是代码部分。现在我又遇到了概念问题......