Audio Recording and Streaming in Android

Question

I an developing an android app. I want to accomplish below feature. I will use my phone's built-in mic to record and at the same time i want the recorded audio to be played through either phone's speakers or headphones. Is it feasible? If yes, please help me in this.

Answer 1

Here is a simple Recording and Playback application.
Uses Android AudioRecord and AudioTrack,

Design:

The recorded audio is written to a buffer and played back from the same buffer, This mechanism runs in a loop (using Android thread) controlled by buttons.

---

Code

private String TAG = "AUDIO_RECORD_PLAYBACK";
private boolean isRunning = true;
private Thread m_thread;               /* Thread for running the Loop */

private AudioRecord recorder = null;
private AudioTrack track = null;

int bufferSize = 320;                  /* Buffer for recording data */
byte buffer[] = new byte[bufferSize];

/* Method to Enable/Disable Buttons */
private void enableButton(int id,boolean isEnable){
    ((Button)findViewById(id)).setEnabled(isEnable);
}

---

The GUI has two Buttons START and STOP.
Enable the Button:

enableButton(R.id.StartButton,true);
enableButton(R.id.StopButton,false);

/* Assign Button Click Handlers */
((Button)findViewById(R.id.StartButton)).setOnClickListener(btnClick);
((Button)findViewById(R.id.StopButton)).setOnClickListener(btnClick);

---

Mapping START and STOP Button for OnClickListener

private View.OnClickListener btnClick = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        switch(v.getId()){
        case R.id.StartButton:
        {
            Log.d(TAG, "======== Start Button Pressed ==========");
            isRunning = true;
            do_loopback(isRunning);
            enableButton(R.id.StartButton,false);
            enableButton(R.id.StopButton,true);
            break;
        }
        case R.id.StopButton:
        {
            Log.d(TAG, "======== Stop Button Pressed ==========");
            isRunning = false;
            do_loopback(isRunning);
            enableButton(R.id.StopButton,false);
            enableButton(R.id.StartButton,true);
            break;
        }
    }
}

---

Start the Thread:

private void do_loopback(final boolean flag) 
{
    m_thread = new Thread(new Runnable() {
        public void run() {
            run_loop(flag);
        }
    });
    m_thread.start();
}

---

Method for Initializing AudioRecord and AudioTrack:

public AudioTrack findAudioTrack (AudioTrack track)
{
    Log.d(TAG, "===== Initializing AudioTrack API ====");
    int m_bufferSize = AudioTrack.getMinBufferSize(8000, 
            AudioFormat.CHANNEL_OUT_MONO, 
            AudioFormat.ENCODING_PCM_16BIT);

    if (m_bufferSize != AudioTrack.ERROR_BAD_VALUE) 
    {
        track = new AudioTrack(AudioManager.STREAM_MUSIC, 8000, 
                AudioFormat.CHANNEL_OUT_MONO, 
                AudioFormat.ENCODING_PCM_16BIT, m_bufferSize, 
                AudioTrack.MODE_STREAM);

        if (track.getState() == AudioTrack.STATE_UNINITIALIZED) {
            Log.e(TAG, "===== AudioTrack Uninitialized =====");
            return null;
        }
    }
    return track;
}

public AudioRecord findAudioRecord (AudioRecord recorder)
{
    Log.d(TAG, "===== Initializing AudioRecord API =====");     
    int m_bufferSize = AudioRecord.getMinBufferSize(8000,
            AudioFormat.CHANNEL_IN_MONO,
            AudioFormat.ENCODING_PCM_16BIT);

    if (m_bufferSize != AudioRecord.ERROR_BAD_VALUE) 
    {
        recorder = new AudioRecord(MediaRecorder.AudioSource.MIC, 8000, 
                AudioFormat.CHANNEL_IN_MONO,
                AudioFormat.ENCODING_PCM_16BIT, m_bufferSize);

        if (recorder.getState() == AudioRecord.STATE_UNINITIALIZED) {
            Log.e(TAG, "====== AudioRecord UnInitilaised ====== ");
            return null;
        }
    }
    return recorder;
}

The Values for findAudioRecord or findAudioTrack can change based on device.
Please refer this question.

---

Code for Running the loop:

public void run_loop (boolean isRunning)
{

    /** == If Stop Button is pressed == **/
    if (isRunning == false) {
        Log.d(TAG, "=====  Stop Button is pressed ===== ");
        
        if (AudioRecord.STATE_INITIALIZED == recorder.getState()){
            recorder.stop();
            recorder.release();
        }
        if (AudioTrack.STATE_INITIALIZED == track.getState()){
            track.stop();
            track.release();
        }
        return;
    }
    

    /** ======= Initialize AudioRecord and AudioTrack ======== **/
    recorder = findAudioRecord(recorder);
    if (recorder == null) {
        Log.e(TAG, "======== findAudioRecord : Returned Error! =========== ");
        return;
    }

    track = findAudioTrack(track);
    if (track == null) {
        Log.e(TAG, "======== findAudioTrack : Returned Error! ========== ");
        return;
    }

    if ((AudioRecord.STATE_INITIALIZED == recorder.getState()) &&
            (AudioTrack.STATE_INITIALIZED == track.getState()))
    {
        recorder.startRecording();
        Log.d(TAG, "========= Recorder Started... =========");
        track.play();
        Log.d(TAG, "========= Track Started... =========");
    } 
    else 
    {
        Log.d(TAG, "==== Initilazation failed for AudioRecord or AudioTrack =====");
        return;
    }

    /** ------------------------------------------------------ **/

    /* Recording and Playing in chunks of 320 bytes */
    bufferSize = 320;
    
    while (isRunning == true) 
    {
        /* Read & Write to the Device */
        recorder.read(buffer, 0, bufferSize);
        track.write(buffer, 0, bufferSize);

    }
    Log.i(TAG, "Loopback exit");
    return;
}

---

Please include the following in AndroidManifest.xml

<uses-permission android:name="android.permission.RECORD_AUDIO" >  </uses-permission>

This above procedure is also possible by Writing/Reading from a file using the same APIs.
Why use audioRecord over mediaRecorder - See here.

The Code is tested (on Google Nexus 5) and working perfectly.

Note: Please add some error-checking code for recorder.read and track.write, in case you fail. Same applies for findAudioRecord and findAudioTrack.