AudioRecord - writing PCM file

Question

I' m trying to record some voice using AudioRecord class and then write it to output .pcm file. I want my program to keep recording until the stop button is pressed. Unfortunatelly no matter how long I' m recording, output file size is always 3528 bytes and it lasts for about 20 ms. Also according to Toolsoft Audio Tools, properies of that file are: 44100Hz, 16 bits, stereo, even if I' m using mono with completely different sampling frequency.

Thread recordingThread;
boolean isRecording = false;


int audioSource = AudioSource.MIC;
int sampleRateInHz = 44100;
int channelConfig = AudioFormat.CHANNEL_IN_MONO;
int audioFormat = AudioFormat.ENCODING_PCM_16BIT;
int bufferSizeInBytes = AudioRecord.getMinBufferSize(sampleRateInHz, channelConfig, audioFormat);

byte Data[] = new byte[bufferSizeInBytes];

AudioRecord audioRecorder = new AudioRecord(audioSource,
                                            sampleRateInHz, 
                                            channelConfig, 
                                            audioFormat, 
                                            bufferSizeInBytes);
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);   
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    getMenuInflater().inflate(R.menu.activity_main, menu);
    return true;
}    

public void startRecording(View arg0) {
    audioRecorder.startRecording();
    isRecording = true;
    recordingThread = new Thread(new Runnable() {
        public void run() {
            String filepath = Environment.getExternalStorageDirectory().getPath();
            FileOutputStream os = null;
            try {
                os = new FileOutputStream(filepath+"/record.pcm");
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
            while(isRecording) {
                audioRecorder.read(Data, 0, Data.length);
                try {
                    os.write(Data, 0, bufferSizeInBytes);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                try {
                    os.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    });
    recordingThread.start();
}

public void stopRecording(View arg0) {
    if (null != audioRecorder) {
        isRecording = false;
        audioRecorder.stop();
        audioRecorder.release();
        audioRecorder = null;
        recordingThread = null;
    }
}

May I kindly ask you to tell me what's wrong? I'm hoping the answer won't be 'everything' :)

Answer 1

try {
                os.write(Data, 0, bufferSizeInBytes);
            } catch (IOException e) {
                e.printStackTrace();
            }
            try {
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }

This is the issue. You are closing the FileOutputStream (os.close()) after just a single write. Move it out of the while loop:

while(isRecording) {
            audioRecorder.read(Data, 0, Data.length);
            try {
                os.write(Data, 0, bufferSizeInBytes);
            } catch (IOException e) {
                e.printStackTrace();
            }

        }
      try {
                os.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
    }

Answer 2

Change your sample rate to 8000, because in emulator you cant test with 44100 sample rate.

use AudioRecord source as shown to play in emulator

private static final int RECORDER_SAMPLERATE = 8000;
private static final int RECORDER_CHANNELS = AudioFormat.CHANNEL_IN_MONO;
private static final int RECORDER_AUDIO_ENCODING = AudioFormat.ENCODING_PCM_16BIT;

AudioRecord audio_record = new AudioRecord(MediaRecorder.AudioSource.MIC,
            RECORDER_SAMPLERATE, RECORDER_CHANNELS,
            RECORDER_AUDIO_ENCODING, BufferElements2Rec * BytesPerElement);


int BufferElements2Play = 1024; // want to play 2048 (2K) since 2 bytes we use only 1024
int BytesPerElement = 2; // 2 bytes in 16bit format

If it din't get worked, then go to this blog. It will work fine for recording and storing the data in .pcm file.