Este é o meu código: eu uso esse código para gravar o áudio de saída do iPhone usando a Unidade de áudio e salvando a saída em output.caf, mas o arquivo output.caf está vazio, qualquer corpo tem idéia sobre o que devo fazer? o arquivo de áudio de saída está vazio

isto está inicializando a unidade de áudio

-(void) initializaeOutputUnit
{
    OSStatus status;

    // Describe audio component
    AudioComponentDescription desc;
    desc.componentType = kAudioUnitType_Output;
    desc.componentSubType = kAudioUnitSubType_RemoteIO;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;

    // Get component
    AudioComponent inputComponent = AudioComponentFindNext(NULL, &desc);

    // Get audio units
    status = AudioComponentInstanceNew(inputComponent, &audioUnit);

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

    // Enable IO for playback
    status = AudioUnitSetProperty(audioUnit, 
                                  kAudioOutputUnitProperty_EnableIO, 
                                  kAudioUnitScope_Output, 
                                  kOutputBus,
                                  &flag, 
                                  sizeof(flag));

    // Describe format
    AudioStreamBasicDescription audioFormat={0};
    audioFormat.mSampleRate         = 44100.00;
    audioFormat.mFormatID           = kAudioFormatLinearPCM;
    audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    audioFormat.mFramesPerPacket    = 1;
    audioFormat.mChannelsPerFrame   = 1;
    audioFormat.mBitsPerChannel     = 16;
    audioFormat.mBytesPerPacket     = 2;
    audioFormat.mBytesPerFrame      = 2;

    // Apply format
    status = AudioUnitSetProperty(audioUnit, 
                                  kAudioUnitProperty_StreamFormat, 
                                  kAudioUnitScope_Output, 
                                  kInputBus, 
                                  &audioFormat, 
                                  sizeof(audioFormat));
    status = AudioUnitSetProperty(audioUnit, 
                                  kAudioUnitProperty_StreamFormat, 
                                  kAudioUnitScope_Input, 
                                  kOutputBus, 
                                  &audioFormat, 
                                  sizeof(audioFormat));


    // Set input callback
    AURenderCallbackStruct callbackStruct;
    callbackStruct.inputProc = recordingCallback;
    callbackStruct.inputProcRefCon = self;
    status = AudioUnitSetProperty(audioUnit, 
                                  kAudioOutputUnitProperty_SetInputCallback, 
                                  kAudioUnitScope_Global, 
                                  kInputBus, 
                                  &callbackStruct, 
                                  sizeof(callbackStruct));

    // Set output callback
    callbackStruct.inputProc = playbackCallback;
    callbackStruct.inputProcRefCon = self;
    status = AudioUnitSetProperty(audioUnit, 
                                  kAudioUnitProperty_SetRenderCallback, 
                                  kAudioUnitScope_Global, 
                                  kOutputBus,
                                  &callbackStruct, 
                                  sizeof(callbackStruct));

    // Disable buffer allocation for the recorder (optional - do this if we want to pass in our own)
    flag = 0;
    status = AudioUnitSetProperty(audioUnit, 
                                  kAudioUnitProperty_ShouldAllocateBuffer,
                                  kAudioUnitScope_Output, 
                                  kInputBus,
                                  &flag, 
                                  sizeof(flag));


    AudioUnitInitialize(audioUnit);
    AudioOutputUnitStart(audioUnit);


    // On initialise le fichier audio
    NSArray  *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *destinationFilePath = [[[NSString alloc] initWithFormat: @"%@/output.caf", documentsDirectory] autorelease];
    NSLog(@">>> %@", destinationFilePath);
    CFURLRef destinationURL = CFURLCreateWithFileSystemPath(kCFAllocatorDefault, (CFStringRef)destinationFilePath, kCFURLPOSIXPathStyle, false);

    OSStatus setupErr = ExtAudioFileCreateWithURL(destinationURL, kAudioFileWAVEType, &audioFormat, NULL, kAudioFileFlags_EraseFile, &effectState.audioFileRef);  
    CFRelease(destinationURL);
    NSAssert(setupErr == noErr, @"Couldn't create file for writing");

    setupErr = ExtAudioFileSetProperty(effectState.audioFileRef, kExtAudioFileProperty_ClientDataFormat, sizeof(AudioStreamBasicDescription), &audioFormat);
    NSAssert(setupErr == noErr, @"Couldn't create file for format");

    setupErr =  ExtAudioFileWriteAsync(effectState.audioFileRef, 0, NULL);
    NSAssert(setupErr == noErr, @"Couldn't initialize write buffers for audio file");

   }

a chamada de gravação de volta

static OSStatus recordingCallback       (void *                         inRefCon,
                                         AudioUnitRenderActionFlags *      ioActionFlags,
                                         const AudioTimeStamp *            inTimeStamp,
                                         UInt32                            inBusNumber,
                                         UInt32                            inNumberFrames,
                                         AudioBufferList *                 ioData) {
    NSLog(@"callback");
   if (*ioActionFlags == kAudioUnitRenderAction_PostRender&&inBusNumber==0) 
   {
        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 =[(MixerHostAudio*)inRefCon getAudioUnit];

        OSStatus status;
        NSLog(@"de5eal el call back ");
        // 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;     
}




// then stop Recording 
- (void) stopRecord
{

    AudioOutputUnitStop(audioUnit);
    AudioUnitUninitialize(audioUnit);
}