AudioToolbox.m

// Step 2: Calculate the buffer size
    UInt32 size = sizeof(maxPacketSize);
    AudioFileGetProperty(
                         audioFileID,
                         kAudioFilePropertyPacketSizeUpperBound,
                         &size,
                         &maxPacketSize);
    if (status != noErr) NSLog(@"kAudioFilePropertyPacketSizeUpperBound failed %d", status);

    if (dataFormat.mFramesPerPacket != 0) {
        Float64 numPacketsPersecond = dataFormat.mSampleRate / dataFormat.mFramesPerPacket;
        outBufferSize = numPacketsPersecond * maxPacketSize;

    } else {
        outBufferSize = (maxBufferSize > maxPacketSize) ? maxBufferSize : maxPacketSize;
    }

    if (outBufferSize > maxBufferSize &&
        outBufferSize > maxPacketSize) {
        outBufferSize = maxBufferSize;

    } else {
        if (outBufferSize < minBufferSize) {
            outBufferSize = minBufferSize;
        }
    }

    // Step 3: Calculate the package count
    numPacketsToRead = outBufferSize / maxPacketSize;

    // Step 4: Alloc AudioStreamPacketDescription buffers
    packetDescs = (AudioStreamPacketDescription *)malloc(numPacketsToRead * sizeof(AudioStreamPacketDescription));

    // Step 5: Reset the packet index
    packetIndex = 0;