Question

I’m trying to develop an application which about VOIP,

is there any high level audio queue service library for iOS ?

because I’m not very good at for working on extension filename “.mm”,

using an open source would be a better option.

or someone could give me some hints for how to fetch the buffer from AudioQueueBufferRef ?

the ideal way is like a delegate :

- (void)audioRecorderDidReceivedBuffer:(Buffer) {
    do something for other operations
}

---

• Update
  I found an article which about Using RemoteIO audio unit

  maybe the input callback is what I need.

Overvier

1. Identify the audio component (kAudioUnitType_Output/ kAudioUnitSubType_RemoteIO/ kAudioUnitManufacturerApple)
2. Use AudioComponentFindNext(NULL, &descriptionOfAudioComponent) to obtain the AudioComponent, which is like the factory with which you
   obtain the audio unit
3. Use AudioComponentInstanceNew(ourComponent, &audioUnit) to make an instance of the audio unit
4. Enable IO for recording and possibly playback with AudioUnitSetProperty
5. Describe the audio format in an AudioStreamBasicDescription structure, and apply the format using AudioUnitSetProperty
6. Provide a callback for recording, and possibly playback, again using AudioUnitSetProperty
7. Allocate some buffers
8. Initialise the audio unit
9. Start the audio unit
10. Rejoice

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



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



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

// TODO: Use inRefCon to access our interface object to do stuff
// Then, use inNumberFrames to figure out how much data is available, and make
// that much space available in buffers in an AudioBufferList.

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

// Then:
// Obtain recorded samples

OSStatus status;

status = AudioUnitRender([audioInterface audioUnit], 
                         ioActionFlags, 
                         inTimeStamp, 
                         inBusNumber, 
                         inNumberFrames, 
                         bufferList);
checkStatus(status);

// Now, we have the samples we just read sitting in buffers in bufferList
DoStuffWithTheRecordedAudio(bufferList);
return noErr;
}

Answer 1

Here is the method that how to fetch Audio Buffer from recording

( reference from: http://atastypixel.com/blog/using-remoteio-audio-unit/ )

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

    // TODO: Use inRefCon to access our interface object to do stuff
    // Then, use inNumberFrames to figure out how much data is available, and make
    // that much space available in buffers in an AudioBufferList.

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

    // Then:
    // Obtain recorded samples

    OSStatus status;

    status = AudioUnitRender([audioInterface audioUnit], 
                             ioActionFlags, 
                             inTimeStamp, 
                             inBusNumber, 
                             inNumberFrames, 
                             bufferList);
    checkStatus(status);

    // Now, we have the samples we just read sitting in buffers in bufferList
    DoStuffWithTheRecordedAudio(bufferList);
    return noErr;
}