Code to play a buffer of ADPCM IMA4 data

PCMPlay.m

    OSStatus s;
    if (!self.aq) {
        AudioStreamBasicDescription asbd;
        asbd.mSampleRate = 8000;
        asbd.mFormatID = kAudioFormatAppleIMA4;
        asbd.mFormatFlags = 0; 
        asbd.mBytesPerPacket = 0;
        asbd.mFramesPerPacket = 0; 
        asbd.mBytesPerFrame = 0;
        asbd.mChannelsPerFrame = 1;
        asbd.mBitsPerChannel = 0;
        asbd.mReserved = 0;
        
        s = AudioQueueNewOutput(&asbd, aq_callback, NULL, CFRunLoopGetCurrent(), kCFRunLoopCommonModes, 0, &_aq);
        s = AudioQueueStart(self.aq, NULL);
    }
    
    int bufferSizeBytes = [audioData length];
    // Go over each object in the audio buffer and queue it up
    for (NSMutableData *audioPacket in self.audioBuffer) {
        AudioQueueBufferRef aq_buffer;
        s = AudioQueueAllocateBuffer(self.aq, bufferSizeBytes, &aq_buffer);
        aq_buffer->mAudioDataByteSize = bufferSizeBytes;
        [audioPacket getBytes:aq_buffer->mAudioData length:bufferSizeBytes];
        s = AudioQueueEnqueueBuffer(self.aq, aq_buffer, 0, NULL);
    }
    
    // Then clear it out for the next run
    [self.audioBuffer removeAllObjects];

FYI self.audioBuffer is simply an NSMutableArray containing a buffer of up to 5 data packets.