Record audio on Android in the background (even when screen is off)

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.myapp">

    <application android:allowBackup="true" android:icon="@mipmap/ic_launcher android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round" android:supportsRtl="true" android:theme="@style/AppTheme">

        <service android:name=".ForegroundService" android:enabled="true" android:exported="true"></service>

        <activity
            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale"
            android:name="com.myapp.MainActivity"
            android:label="@string/title_activity_main"
            android:theme="@style/AppTheme.NoActionBarLaunch"
            android:launchMode="singleTop">
            <!-- //android:launchMode="singleTask" -->

            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>

            <intent-filter>
                <action android:name="android.intent.action.VIEW" />
                <category android:name="android.intent.category.DEFAULT" />
                <category android:name="android.intent.category.BROWSABLE" />
                <data android:scheme="@string/custom_url_scheme" />
            </intent-filter>
        </activity>

        <provider
            android:name="android.support.v4.content.FileProvider"
            android:authorities="${applicationId}.fileprovider"
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/file_paths"></meta-data>
        </provider>
    </application>

    <!-- Permissions -->

    <uses-permission android:name="android.permission.INTERNET" />
    <!-- Camera, Photos, input file -->
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <!-- Geolocation API -->
    <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
    <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
    <uses-feature android:name="android.hardware.location.gps" />
    <!-- Network API -->
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <!-- Navigator.getUserMedia -->
    <!-- Video -->
    <uses-permission android:name="android.permission.CAMERA" />
    <!-- Audio -->
    <uses-permission android:name="android.permission.RECORD_AUDIO" />
    <uses-permission android:name="android.permission.MODIFY_AUDIO_SETTINGS"/>

    <!-- v-added -->
    <uses-permission android:name="android.permission.WAKE_LOCK" />
    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
</manifest>

ForegroundService.java

package com.myapp;

import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.PendingIntent;
import android.app.Service;
import android.content.Intent;
import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioRecord;
import android.media.AudioTrack;
import android.media.MediaRecorder;
import android.os.Build;
import android.os.IBinder;
import android.support.annotation.Nullable;
import android.support.v4.app.NotificationCompat;
import android.util.Log;

import com.getcapacitor.PluginCall;
import com.getcapacitor.PluginMethod;

public class ForegroundService extends Service {
	public static final String CHANNEL_ID = "ForegroundServiceChannel";

	@Override
	public void onCreate() {
		super.onCreate();
	}

	@Override
	public int onStartCommand(Intent intent, int flags, int startId) {
		String input = intent.getStringExtra("inputExtra");
		createNotificationChannel();
		Intent notificationIntent = new Intent(this, MainActivity.class);
		PendingIntent pendingIntent = PendingIntent.getActivity(this,
			0, notificationIntent, 0);

		Notification notification = new NotificationCompat.Builder(this, CHANNEL_ID)
			.setContentTitle("Foreground Service")
			.setContentText(input)
			.setSmallIcon(R.drawable.ic_launcher_foreground)
			.setContentIntent(pendingIntent)
			.build();

		startForeground(1, notification);

		// do heavy work on a background thread
		StartRecorder();

		//stopSelf();

		return START_NOT_STICKY;
	}

	@Override
	public void onDestroy() {
		super.onDestroy();
	}

	@Nullable
	@Override
	public IBinder onBind(Intent intent) {
		return null;
	}

	private void createNotificationChannel() {
		if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
			NotificationChannel serviceChannel = new NotificationChannel(
				CHANNEL_ID,
				"Foreground Service Channel",
				NotificationManager.IMPORTANCE_DEFAULT
			);

			NotificationManager manager = getSystemService(NotificationManager.class);
			manager.createNotificationChannel(serviceChannel);
		}
	}
































	private static String TAG = "ForegroundService";

	// the audio recording options
	private static final int RECORDING_RATE = 44100;
	private static final int CHANNEL = AudioFormat.CHANNEL_IN_MONO;
	private static final int FORMAT = AudioFormat.ENCODING_PCM_16BIT;

	// the audio recorder
	private AudioRecord recorder;
	// the minimum buffer size needed for audio recording
	private static int BUFFER_SIZE = AudioRecord.getMinBufferSize(RECORDING_RATE, CHANNEL, FORMAT);
	// are we currently sending audio data
	private boolean currentlySendingAudio = false;
	public void StartRecorder() {
		Log.i(TAG, "Starting the audio stream");
		currentlySendingAudio = true;
		startStreaming();
	}
	public void StopRecorder() {
		Log.i(TAG, "Stopping the audio stream");
		currentlySendingAudio = false;
		recorder.release();
	}

	private void startStreaming() {
		Log.i(TAG, "Starting the background thread (in this foreground service) to read the audio data");

		Thread streamThread = new Thread(() -> {
			try {
				Log.d(TAG, "Creating the buffer of size " + BUFFER_SIZE);
				//byte[] buffer = new byte[BUFFER_SIZE];
				int rate = AudioTrack.getNativeOutputSampleRate(AudioManager.STREAM_SYSTEM);
				int bufferSize = AudioRecord.getMinBufferSize(rate, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT);
				short[] buffer = new short[bufferSize];

				android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_AUDIO);

				Log.d(TAG, "Creating the AudioRecord");
				//recorder = new AudioRecord(MediaRecorder.AudioSource.MIC, RECORDING_RATE, CHANNEL, FORMAT, BUFFER_SIZE * 10);
				recorder = new AudioRecord(MediaRecorder.AudioSource.MIC, rate, AudioFormat.CHANNEL_IN_MONO, AudioFormat.ENCODING_PCM_16BIT, bufferSize);

				Log.d(TAG, "AudioRecord recording...");
				recorder.startRecording();

				while (currentlySendingAudio == true) {
					// read the data into the buffer
					int readSize = recorder.read(buffer, 0, buffer.length);

					double maxAmplitude = 0;
					for (int i = 0; i < readSize; i++) {
						if (Math.abs(buffer[i]) > maxAmplitude) {
							maxAmplitude = Math.abs(buffer[i]);
						}
					}

					double db = 0;
					if (maxAmplitude != 0) {
						db = 20.0 * Math.log10(maxAmplitude / 32767.0) + 90;
					}

					Log.d(TAG, "Max amplitude: " + maxAmplitude + " ; DB: " + db);
				}

				Log.d(TAG, "AudioRecord finished recording");
			} catch (Exception e) {
				Log.e(TAG, "Exception: " + e);
			}
		});

		// start the thread
		streamThread.start();
	}
}

General.java (place that launches service)

package com.myapp;

import android.content.Context;
import android.content.Intent;
import android.media.AudioFormat;
import android.media.AudioManager;
import android.media.AudioRecord;
import android.media.AudioTrack;
import android.media.MediaRecorder;
import android.net.wifi.WifiManager;
import android.nfc.Tag;
import android.os.PowerManager;
import android.support.v4.content.ContextCompat;
import android.util.Log;
import android.widget.Button;

import com.getcapacitor.JSObject;
import com.getcapacitor.NativePlugin;
import com.getcapacitor.Plugin;
import com.getcapacitor.PluginCall;
import com.getcapacitor.PluginMethod;
import com.getcapacitor.PluginResult;

import java.net.DatagramSocket;

@NativePlugin()
public class General extends Plugin {



	private static String TAG = "V.General";
	@PluginMethod
	public void StartRecorder(PluginCall call) {
		Log.i(TAG, "Starting the foreground-thread");

		Intent serviceIntent = new Intent(getActivity().getApplicationContext(), ForegroundService.class);
		serviceIntent.putExtra("inputExtra", "Foreground Service Example in Android");
		ContextCompat.startForegroundService(getActivity(), serviceIntent);

		call.resolve();
	}
	@PluginMethod
	public void StopRecorder(PluginCall call) {
		Log.i(TAG, "Stopping the foreground-thread");

		Intent serviceIntent = new Intent(getActivity().getApplicationContext(), ForegroundService.class);
		getActivity().getApplicationContext().stopService(serviceIntent);

		call.resolve();
	}




  // From what I've seen you don't need the wake-lock or wifi-lock below for the audio-recorder to persist through screen-off.
  // However, to be on the safe side you might want to activate them anyway. (and/or if you have other functions that need them)



	private PowerManager.WakeLock wakeLock_partial = null;
	public void StartPartialWakeLock() {
		if (wakeLock_partial != null && wakeLock_partial.isHeld()) return;
		Log.i("vmain", "Starting partial wake-lock.");
		final PowerManager pm = (PowerManager) getActivity().getApplicationContext().getSystemService(Context.POWER_SERVICE);
		wakeLock_partial = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "com.myapp:partial_wake_lock");
		wakeLock_partial.acquire();
	}
	public void StopPartialWakeLock() {
		if (wakeLock_partial != null && wakeLock_partial.isHeld()) {
			Log.i("vmain", "Stopping partial wake-lock.");
			wakeLock_partial.release();
		}
	}

	private WifiManager.WifiLock wifiLock = null;
	public void StartWifiLock() {
		WifiManager wifiManager = (WifiManager) getActivity().getApplicationContext().getSystemService(Context.WIFI_SERVICE);
		wifiLock = wifiManager.createWifiLock(WifiManager.WIFI_MODE_FULL, "LockTag");
		wifiLock.acquire();
	}
	public void StopWifiLock() {
		wifiLock.release();
	}
}