implemented stage 1 ultra-basic background play of videos; see https://github.com/theScrabi/NewPipe/wiki/Background-Playback-Mini-Roadmap

app/src/main/AndroidManifest.xml

@@ -71,6 +71,9 @@
             android:parentActivityName=".VideoItemDetailActivity"
             >
         </activity>
+        <service android:name=".BackgroundPlayer"
+            android:exported="false" >
+        </service>
         <activity
             android:name=".SettingsActivity"
             android:label="@string/title_activity_settings" >

app/src/main/java/org/schabi/newpipe/ActionBarHandler.java

@@ -287,13 +287,26 @@ public class ActionBarHandler {
     }
 
     public void playAudio() {
-        Intent intent = new Intent();
+        boolean b = true;//todo: replace with preference
+        Intent intent;
+        if (b)//internal (background) music player: explicit intent
+        {
+            intent = new Intent(activity, BackgroundPlayer.class);
+            intent.setAction(Intent.ACTION_VIEW);
+            intent.setDataAndType(Uri.parse(audioStream.url),
+                    MediaFormat.getMimeById(audioStream.format));
+            intent.putExtra(Intent.EXTRA_TITLE, videoTitle);
+            intent.putExtra("title", videoTitle);
+            activity.startService(intent);
+        }
+        /*Intent intent = new Intent();
         try {
             intent.setAction(Intent.ACTION_VIEW);
             intent.setDataAndType(Uri.parse(audioStream.url),
                     MediaFormat.getMimeById(audioStream.format));
             intent.putExtra(Intent.EXTRA_TITLE, videoTitle);
             intent.putExtra("title", videoTitle);
+
             activity.startActivity(intent);      // HERE !!!
         } catch (Exception e) {
             e.printStackTrace();
@@ -317,6 +330,6 @@ public class ActionBarHandler {
             builder.create().show();
             Log.e(TAG, "Either no Streaming player for audio was installed, or something important crashed:");
             e.printStackTrace();
-        }
+        }*/
     }
 }

app/src/main/java/org/schabi/newpipe/BackgroundPlayer.java

@@ -0,0 +1,73 @@
+package org.schabi.newpipe;
+
+import android.app.IntentService;
+import android.app.Notification;
+import android.app.PendingIntent;
+import android.content.Intent;
+import android.media.AudioManager;
+import android.media.MediaPlayer;
+import android.os.PowerManager;
+
+import java.io.IOException;
+
+/**
+ * Created by Adam Howard on 08/11/15.
+ *
+ * Copyright (c) Adam Howard <achdisposable1@gmail.com> 2015
+ *
+ * BackgroundPlayer.java is part of NewPipe.
+ *
+ * NewPipe is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * NewPipe is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with NewPipe.  If not, see <http://www.gnu.org/licenses/>.
+ */
+public class BackgroundPlayer extends IntentService /*implements MediaPlayer.OnPreparedListener*/ {
+
+    private static final String TAG = BackgroundPlayer.class.toString();
+    /**
+     * Creates an IntentService.  Invoked by your subclass's constructor.
+     */
+    public BackgroundPlayer() {
+        super(TAG);
+    }
+
+    @Override
+    protected void onHandleIntent(Intent intent) {
+        String source = intent.getDataString();
+
+        MediaPlayer mediaPlayer = new MediaPlayer();
+        //mediaPlayer.setWakeMode(getApplicationContext(), PowerManager.PARTIAL_WAKE_LOCK);//cpu lock apparently
+        mediaPlayer.setAudioStreamType(AudioManager.STREAM_MUSIC);
+        try {
+            mediaPlayer.setDataSource(source);
+            mediaPlayer.prepare(); // IntentService already puts us in a separate worker thread,
+            //so calling the blocking prepare() method should be ok
+        } catch (IOException ioe) {
+            ioe.printStackTrace();
+            //can't really do anything useful without a file to play; exit early
+            return;
+        }
+        //mediaPlayer.setOnPreparedListener(this);
+        mediaPlayer.start();
+/*
+        PendingIntent pi = PendingIntent.getActivity(getApplicationContext(), 0,
+                new Intent(getApplicationContext(), MainActivity.class),
+                PendingIntent.FLAG_UPDATE_CURRENT);
+        Notification notification = new Notification();
+        notification.tickerText = text;
+        notification.icon = R.drawable.play0;
+        notification.flags |= Notification.FLAG_ONGOING_EVENT;
+        notification.setLatestEventInfo(getApplicationContext(), "MusicPlayerSample",
+                "Playing: " + songName, pi);
+        startForeground(NOTIFICATION_ID, notification);*/
+    }
+}