Record/capture system sound from visualizer

Question

I'm trying to capture internal sound from visualizer. I couldn't notice how to capture sound from visualizer and save it to a file. I used onWaveFormDataCapture's waveform byte array in audioRecord.read and writeShort functions and app crashed. any help would be appreciated

private void MyVisualizer() {
        audioOutput = new Visualizer(0); 

        audioOutput.setDataCaptureListener(new Visualizer.OnDataCaptureListener() {
            @Override
            public void onWaveFormDataCapture(Visualizer visualizer, byte[] waveform, int samplingRate) {
                try {
                    while (isRecording) {
                        int bufferReadResult = audioRecord.read(waveform, 0, bufferSize);
                        for (int i = 0; i < bufferReadResult; i++)
                            dos.writeShort(waveform[i]);
                    }}catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
            @Override
            public void onFftDataCapture(Visualizer visualizer, byte[] fft, int samplingRate) {

            }
        }, Visualizer.getMaxCaptureRate(), true, false);
    }