Use microphone in multiple app simultaneously in Android

Question

We have an Android device on which we would like to use the microphone in 2 app simultaneously.

In fact, we have a vocal command service that is running in the background (we are using the CMU Sphinx library). The problem is when we start a video recorder (camera application), we can't start the recording as 2 applications can't access to the microphone at the same time.

Error

08-20 12:20:14.601: I/MediaRecorderJNI(7261): prepare: surface=0x59590668
08-20 12:20:15.916: E/MediaRecorder(7261): start failed: -38
08-20 12:20:15.916: E/com.example.CamcorderView(7261): Failed to start recorder.
08-20 12:20:15.916: E/com.example.CamcorderView(7261): java.lang.IllegalStateException
08-20 12:20:15.916: E/com.example.CamcorderView(7261):     at android.media.MediaRecorder.start(Native Method)

Note that the camera works well when the vocal service is off.

Moreover, I precise that I've already read this thread :

Android: Accessing the microphone simultaniously (RecognizerIntent + own app)

but the difference here is that we have a hand on the O/S and the kernel. So we can apply patch if needed.

Is it an SDK/OS/Kernel limitation? Is there any workaround ?

Answer 1

This scenario happens

for instance

when you want to record phone call. you can use the open source call recorder. see this and this

Here is a code sample

private MediaRecorder recorder = null;
public void onCreate()
{
    super.onCreate();
    recorder = new MediaRecorder();
    Log.i("CallRecorder", "onCreate created MediaRecorder object");
}

public void onStart(Intent intent, int startId) {

    if (isRecording) return;

    Context c = getApplicationContext();
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(c);

    Boolean shouldRecord = prefs.getBoolean(Preferences.PREF_RECORD_CALLS, false);
    if (!shouldRecord) {
        Log.i("CallRecord", "RecordService::onStartCommand with PREF_RECORD_CALLS false, not recording");
        return;
    }

    int audiosource = Integer.parseInt(prefs.getString(Preferences.PREF_AUDIO_SOURCE, "1"));
    int audioformat = Integer.parseInt(prefs.getString(Preferences.PREF_AUDIO_FORMAT, "1"));

    recording = makeOutputFile(prefs);
    if (recording == null) {
        recorder = null;
        return; //return 0;
    }

    Log.i("CallRecorder", "RecordService will config MediaRecorder with audiosource: " + audiosource + " audioformat: " + audioformat);
    try {
        // These calls will throw exceptions unless you set the 
        // android.permission.RECORD_AUDIO permission for your app
        recorder.reset();
        recorder.setAudioSource(audiosource);
        recorder.setOutputFormat(audioformat);
        recorder.setAudioEncoder(MediaRecorder.AudioEncoder.DEFAULT);
        recorder.setOutputFile(recording.getAbsolutePath());
        //recorder.setMaxDuration(msDuration); //1000); // 1 seconds
        //recorder.setMaxFileSize(bytesMax); //1024*1024); // 1KB

        recorder.setOnInfoListener(this);
        recorder.setOnErrorListener(this);

        try {
            recorder.prepare();
        } catch (java.io.IOException e) {
            Log.e("CallRecorder", "RecordService::onStart() IOException attempting recorder.prepare()\n");
            t.show();
            recorder = null;
            return;
        }
        Log.d("CallRecorder", "recorder.prepare() returned");

        recorder.start();
        isRecording = true;
        Log.i("CallRecorder", "recorder.start() returned");
        updateNotification(true);
    } catch (java.lang.Exception e) {
        Log.e("CallRecorder", "RecordService::onStart caught unexpected exception", e);
        recorder = null;
    }

    return;
}