Audio Queue Playback Callback

audioPlayback.m

typedef struct FCAudioPlayer {
  AudioStreamBasicDescription asbd;
  AudioBuffer fileBuffer;
  UInt32 playbackPosition;
  UInt32 totalFrames;
} FCAudioPlayer;

static void FCAudioOutputCallback(void *inUserData, AudioQueueRef inAudioQueue, AudioQueueBufferRef inCompleteAudioQueueBuffer)
{
  FCAudioPlayer *audioPlayer = (FCAudioPlayer *)inUserData;
  UInt32 queueBufferFrameCapacity = inCompleteAudioQueueBuffer->mAudioDataBytesCapacity / audioPlayer->asbd.mBytesPerFrame;
  UInt32 framesLeftInFile = audioPlayer->totalFrames - audioPlayer->playbackPosition;
  UInt32 numberOfFramesToCopy = MIN(queueBufferFrameCapacity, framesLeftInFile);
  
  if (numberOfFramesToCopy > 0)
  {
    UInt32 sizeOfDataToCopy = numberOfFramesToCopy * audioPlayer->asbd.mBytesPerFrame;
    UInt32 offset = audioPlayer->playbackPosition * audioPlayer->asbd.mBytesPerFrame;
    memcpy(inCompleteAudioQueueBuffer->mAudioData, &audioPlayer->fileBuffer.mData[0] + offset, sizeOfDataToCopy);
    inCompleteAudioQueueBuffer->mAudioDataByteSize = sizeOfDataToCopy;
    
    audioPlayer->playbackPosition += numberOfFramesToCopy;
    
    OSStatus anErr = AudioQueueEnqueueBuffer(inAudioQueue, inCompleteAudioQueueBuffer, 0, 0);
    assert(anErr == noErr);
  }
  else
  {
    OSStatus anErr = AudioQueueStop(inAudioQueue, false);
    assert(anErr == noErr);
    return;
  }
}