Question

I am using below code to init my audio components.

-(void) startListeningWithCoreAudio
{
     NSError *error = nil;

     [[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategoryPlayAndRecord error:&error];
     if (error) 
          NSLog(@"error setting up audio session: %@", [error localizedDescription]);

     [[AVAudioSession sharedInstance] setDelegate:self];

     OSStatus status = AudioSessionSetActive(YES);
     checkStatus(status);

          // Find the apple mic
    AudioComponentDescription desc;
    desc.componentType = kAudioUnitType_Output;
    desc.componentSubType = kAudioUnitSubType_VoiceProcessingIO;
    desc.componentFlags = 0;
    desc.componentFlagsMask = 0;
    desc.componentManufacturer = kAudioUnitManufacturer_Apple;

    AudioComponent inputComponent = AudioComponentFindNext( NULL, &desc );
    status = AudioComponentInstanceNew( inputComponent, &kAudioUnit );
    checkStatus( status );

          // enable mic output as our input
    UInt32 flag = 1;
    status = AudioUnitSetProperty( kAudioUnit, kAudioOutputUnitProperty_EnableIO, kAudioUnitScope_Input, kInputBus, &flag, sizeof(flag) );
    checkStatus(status);


          // Define mic output audio format
    AudioStreamBasicDescription audioFormat;
    audioFormat.mSampleRate         = 16000.0;
    audioFormat.mFormatID           = kAudioFormatLinearPCM;
    audioFormat.mFormatFlags        = kAudioFormatFlagIsSignedInteger | kAudioFormatFlagIsPacked;
    audioFormat.mFramesPerPacket    = 1;
    audioFormat.mChannelsPerFrame   = 1;
    audioFormat.mBitsPerChannel     = 16;
    audioFormat.mBytesPerPacket     = 2;
    audioFormat.mBytesPerFrame      = 2;

    status = AudioUnitSetProperty( kAudioUnit, kAudioUnitProperty_StreamFormat, kAudioUnitScope_Output, kInputBus, &audioFormat, sizeof(audioFormat) );
    checkStatus(status);

          // Define our callback methods
    AURenderCallbackStruct callbackStruct;
    callbackStruct.inputProc = recordingCallback;
    callbackStruct.inputProcRefCon = self;
    status = AudioUnitSetProperty( kAudioUnit, kAudioOutputUnitProperty_SetInputCallback, kAudioUnitScope_Global, kInputBus, &callbackStruct, sizeof(callbackStruct) );
    checkStatus(status);

          // By pass voice processing
     UInt32 audiobypassProcessing = [[NSUserDefaults standardUserDefaults] boolForKey:VOICE_BY_PASS_PROCESSING];
     status = AudioUnitSetProperty(kAudioUnit, kAUVoiceIOProperty_BypassVoiceProcessing, 
                                   kAudioUnitScope_Global, kInputBus, &audiobypassProcessing, sizeof(audiobypassProcessing));
     checkStatus(status);

          // Automatic Gain Control
     UInt32 audioAGC = [[NSUserDefaults standardUserDefaults]boolForKey:VOICE_AGC];
     status = AudioUnitSetProperty(kAudioUnit, kAUVoiceIOProperty_VoiceProcessingEnableAGC, 
                                   kAudioUnitScope_Global, kInputBus, &audioAGC, sizeof(audioAGC));
     checkStatus(status);

          //Non Audio Voice Ducking
     UInt32 audioDucking = [[NSUserDefaults standardUserDefaults]boolForKey:VOICE_DUCKING];
     status = AudioUnitSetProperty(kAudioUnit, kAUVoiceIOProperty_DuckNonVoiceAudio, 
                                   kAudioUnitScope_Global, kInputBus, &audioDucking, sizeof(audioDucking));
     checkStatus(status);

          //Audio Quality
     UInt32 quality = [[NSUserDefaults standardUserDefaults]integerForKey:VOICE_QUALITY];
     status = AudioUnitSetProperty(kAudioUnit, kAUVoiceIOProperty_VoiceProcessingQuality, 
                                   kAudioUnitScope_Global, kInputBus, &quality, sizeof(quality));
     checkStatus(status);

     status = AudioUnitInitialize(kAudioUnit);
     checkStatus(status);

    status = AudioOutputUnitStart( kAudioUnit );
    checkStatus(status);

    UInt32 audioRoute = (UInt32)kAudioSessionOverrideAudioRoute_Speaker;
    status = AudioSessionSetProperty(kAudioSessionProperty_OverrideAudioRoute, sizeof (audioRoute), &audioRoute);
    checkStatus(status);     
}


-(void) stopListeningWithCoreAudio
{ 
    OSStatus     status = AudioUnitUninitialize( kAudioUnit );
     checkStatus(status);

     status = AudioOutputUnitStop( kAudioUnit );
    checkStatus( status );

//     if(kAudioUnit)
//     {
//          status = AudioComponentInstanceDispose(kAudioUnit);
//          checkStatus(status);
//          kAudioUnit = nil;
//     }

    status = AudioSessionSetActive(NO);
     checkStatus(status);

     NSError *error = nil;
    [[AVAudioSession sharedInstance] setCategory: AVAudioSessionCategorySoloAmbient error:&error];
    if (error)
          NSLog(@"error setting up audio session: %@", [error localizedDescription]);
}

It works fine for first time. I mean startListeningWithCoreAudio is called by a button pressed event. It could record/process audio well. On other event I am calling stopListeningWithCoreAudio to stop record/process audio.

The problem is coming when I am again trying to call the function startListeningWithCoreAudio. It throws error for two functions. AudioUnitInitialize and AudioOutputUnitStart which are called from startListeningWithCoreAudio.

Can anyone please help me what is the problem?

Answer 1

I found the solution.
If we call below functions back to back, it creates problem.

extern OSStatus AudioUnitUninitialize(AudioUnit inUnit)                     
extern OSStatus AudioComponentInstanceDispose(AudioComponentInstance inInstance)

So, I called dispose method on main thread by below way.

[self performSelectorOnMainThread:@selector(disposeCoreAudio) withObject:nil waitUntilDone:NO];

-(void) disposeCoreAudio
{
     OSStatus status = AudioComponentInstanceDispose(kAudioUnit);
     kAudioUnit = nil;
}

It solved the problem. So, the correct sequence is Stop recording, uninitialize recorder and dispose recorder on main thread.