Can anybody help me in recording iPhone output sound through Audio Unit

Question

this is my code : i use this code to record the iPhone output audio by using Audio Unit then saving the output in output.caf but the output.caf file is empty any body have idea about what shall i do ? the output audio file is empty

this is intializing the audio unit

-(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");

   }

the recording call back

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);
}

Answer 1

In initializaeOutputUnit you only created your audio file:

OSStatus setupErr = ExtAudioFileCreateWithURL(destinationURL, kAudioFileWAVEType, &audioFormat, NULL, kAudioFileFlags_EraseFile, &effectState.audioFileRef);

by passing 0 (frames) and NULL (audiobuffer) is just for init internal buffers:

setupErr =  ExtAudioFileWriteAsync(effectState.audioFileRef, 0, NULL);

That's what's going wrong in recordingCallback:

1) ioActionFlags are always 0 and inBusNumber are always 1, because thats how you setup your callback (kInputBus = 1):

if (*ioActionFlags == kAudioUnitRenderAction_PostRender&&inBusNumber==0)

so just remove the if statement.

2) From AudioUnitRender you will receive -50 error, which is defined in CoreAudioTypes.h as an kAudio_ParamError error. This happens by bufferList is not defined and NULL!

 OSStatus status; 
 status = AudioUnitRender(THIS->mAudioUnit,     
                          ioActionFlags, 
                          inTimeStamp, 
                          kInputBus, 
                          inNumberFrames, 
                          &bufferList);

 if (noErr != status) {
      printf("AudioUnitRender error: %ld", status);   
      return noErr; 
 }

You just need to define an valid AudioBuffer and pass it to AudioUnitRender, this is my working RenderCallback:

  static OSStatus recordingCallback       (void *                      inRefCon,
                                           AudioUnitRenderActionFlags *      ioActionFlags,
                                           const AudioTimeStamp *            inTimeStamp,
                                           UInt32                            inBusNumber,
                                           UInt32                            inNumberFrames,
                                           AudioBufferList *                 ioData)  {
      double timeInSeconds = inTimeStamp->mSampleTime / kSampleRate;
      printf("\n%fs inBusNumber: %lu inNumberFrames: %lu ", timeInSeconds, inBusNumber, inNumberFrames);
      //printAudioUnitRenderActionFlags(ioActionFlags);

      AudioBufferList bufferList;

      SInt16 samples[inNumberFrames]; // A large enough size to not have to worry about buffer overrun
      memset (&samples, 0, sizeof (samples));

      bufferList.mNumberBuffers = 1;
      bufferList.mBuffers[0].mData = samples;
      bufferList.mBuffers[0].mNumberChannels = 1;
      bufferList.mBuffers[0].mDataByteSize = inNumberFrames*sizeof(SInt16);

      ViewController* THIS = THIS = (__bridge ViewController *)inRefCon;

      OSStatus status;
      status = AudioUnitRender(THIS->mAudioUnit,     
                               ioActionFlags, 
                               inTimeStamp, 
                               kInputBus, 
                               inNumberFrames, 
                               &bufferList);

      if (noErr != status) {

          printf("AudioUnitRender error: %ld", status); 
          return noErr;
      }

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

      return noErr;      
 }

In stopRecord you should close the audio file with ExtAudioFileDispose:

  - (void)stopRecording:(NSTimer*)theTimer {
      printf("\nstopRecording\n");
      AudioOutputUnitStop(mAudioUnit);
      AudioUnitUninitialize(mAudioUnit);

      OSStatus status = ExtAudioFileDispose(mAudioFileRef);
      printf("OSStatus(ExtAudioFileDispose): %ld\n", status); 
 }

Full source code: http://pastebin.com/92Fyjaye

Answer 2

The RemoteIO Audio Unit does not record audio output, only input from the microphone. The output is not connected to the mic input.

If you use RemoteIO for playing audio, you can copy the copy the same buffers you feed the output callback for playing audio to a file writer as well. But that's only for raw audio content you play via RemoteIO.