diff --git a/RELEASENOTES.md b/RELEASENOTES.md
index 3ae194c223..87adaa8840 100644
--- a/RELEASENOTES.md
+++ b/RELEASENOTES.md
@@ -33,6 +33,8 @@
   ([#4385](https://github.com/google/ExoPlayer/issues/4385)).
 * Expose all internal ID3 data stored in MP4 udta boxes, and switch from using
   CommentFrame to InternalFrame for frames with gapless metadata in MP4.
+* Allow setting the `Looper`, which is used to access the player, in
+  `ExoPlayerFactory` ([#4278](https://github.com/google/ExoPlayer/issues/4278)).
 
 ### 2.8.2 ###
 
diff --git a/extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java b/extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java
index 4bafaa4326..e8758cd05b 100644
--- a/extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java
+++ b/extensions/mediasession/src/main/java/com/google/android/exoplayer2/ext/mediasession/MediaSessionConnector.java
@@ -19,7 +19,6 @@ import android.graphics.Bitmap;
 import android.net.Uri;
 import android.os.Bundle;
 import android.os.Handler;
-import android.os.Looper;
 import android.os.ResultReceiver;
 import android.os.SystemClock;
 import android.support.annotation.NonNull;
@@ -39,6 +38,7 @@ import com.google.android.exoplayer2.Player;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.util.ErrorMessageProvider;
 import com.google.android.exoplayer2.util.RepeatModeUtil;
+import com.google.android.exoplayer2.util.Util;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
@@ -323,7 +323,6 @@ public final class MediaSessionConnector {
   public final MediaSessionCompat mediaSession;
 
   private final MediaControllerCompat mediaController;
-  private final Handler handler;
   private final boolean doMaintainMetadata;
   private final ExoPlayerEventListener exoPlayerEventListener;
   private final MediaSessionCallback mediaSessionCallback;
@@ -341,10 +340,9 @@ public final class MediaSessionConnector {
   private RatingCallback ratingCallback;
 
   /**
-   * Creates an instance. Must be called on the same thread that is used to construct the player
-   * instances passed to {@link #setPlayer(Player, PlaybackPreparer, CustomActionProvider...)}.
-   * <p>
-   * Equivalent to {@code MediaSessionConnector(mediaSession, new DefaultPlaybackController())}.
+   * Creates an instance.
+   *
+   * <p>Equivalent to {@code MediaSessionConnector(mediaSession, new DefaultPlaybackController())}.
    *
    * @param mediaSession The {@link MediaSessionCompat} to connect to.
    */
@@ -353,8 +351,7 @@ public final class MediaSessionConnector {
   }
 
   /**
-   * Creates an instance. Must be called on the same thread that is used to construct the player
-   * instances passed to {@link #setPlayer(Player, PlaybackPreparer, CustomActionProvider...)}.
+   * Creates an instance.
    *
    * <p>Equivalent to {@code MediaSessionConnector(mediaSession, playbackController, true, null)}.
    *
@@ -367,8 +364,7 @@ public final class MediaSessionConnector {
   }
 
   /**
-   * Creates an instance. Must be called on the same thread that is used to construct the player
-   * instances passed to {@link #setPlayer(Player, PlaybackPreparer, CustomActionProvider...)}.
+   * Creates an instance.
    *
    * @param mediaSession The {@link MediaSessionCompat} to connect to.
    * @param playbackController A {@link PlaybackController} for handling playback actions, or {@code
@@ -388,8 +384,6 @@ public final class MediaSessionConnector {
     this.playbackController = playbackController != null ? playbackController
         : new DefaultPlaybackController();
     this.metadataExtrasPrefix = metadataExtrasPrefix != null ? metadataExtrasPrefix : "";
-    this.handler = new Handler(Looper.myLooper() != null ? Looper.myLooper()
-        : Looper.getMainLooper());
     this.doMaintainMetadata = doMaintainMetadata;
     mediaSession.setFlags(BASE_MEDIA_SESSION_FLAGS);
     mediaController = mediaSession.getController();
@@ -401,7 +395,8 @@ public final class MediaSessionConnector {
   }
 
   /**
-   * Sets the player to be connected to the media session.
+   * Sets the player to be connected to the media session. Must be called on the same thread that is
+   * used to access the player.
    *
    * <p>The order in which any {@link CustomActionProvider}s are passed determines the order of the
    * actions published with the playback state of the session.
@@ -428,6 +423,7 @@ public final class MediaSessionConnector {
     this.customActionProviders = (player != null && customActionProviders != null)
         ? customActionProviders : new CustomActionProvider[0];
     if (player != null) {
+      Handler handler = new Handler(Util.getLooper());
       mediaSession.setCallback(mediaSessionCallback, handler);
       player.addListener(exoPlayerEventListener);
     }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java
index b97790d5fb..ce43772d8d 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayer.java
@@ -89,12 +89,13 @@ import com.google.android.exoplayer2.video.MediaCodecVideoRenderer;
  * model">
  *
  * <ul>
- *   <li>ExoPlayer instances must be accessed from a single application thread. This must be the
- *       thread the player is created on if that thread has a {@link Looper}, or the application's
- *       main thread otherwise.
- *   <li>Registered listeners are called on the thread the player is created on if that thread has a
- *       {@link Looper}, or the application's main thread otherwise. Note that this means registered
- *       listeners are called on the same thread which must be used to access the player.
+ *   <li>ExoPlayer instances must be accessed from the thread associated with {@link
+ *       #getApplicationLooper()}. This Looper can be specified when creating the player, or this is
+ *       the Looper of the thread the player is created on, or the Looper of the application's main
+ *       thread if the player is created on a thread without Looper.
+ *   <li>Registered listeners are called on the thread thread associated with {@link
+ *       #getApplicationLooper()}. Note that this means registered listeners are called on the same
+ *       thread which must be used to access the player.
  *   <li>An internal playback thread is responsible for playback. Injected player components such as
  *       Renderers, MediaSources, TrackSelectors and LoadControls are called by the player on this
  *       thread.
@@ -178,13 +179,15 @@ public interface ExoPlayer extends Player {
   @Deprecated
   @RepeatMode int REPEAT_MODE_ALL = Player.REPEAT_MODE_ALL;
 
-  /**
-   * Gets the {@link Looper} associated with the playback thread.
-   *
-   * @return The {@link Looper} associated with the playback thread.
-   */
+  /** Returns the {@link Looper} associated with the playback thread. */
   Looper getPlaybackLooper();
 
+  /**
+   * Returns the {@link Looper} associated with the application thread that's used to access the
+   * player and on which player events are received.
+   */
+  Looper getApplicationLooper();
+
   /**
    * Prepares the player to play the provided {@link MediaSource}. Equivalent to
    * {@code prepare(mediaSource, true, true)}.
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java
index 8095ed9c64..e8bd8b34f6 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerFactory.java
@@ -16,12 +16,14 @@
 package com.google.android.exoplayer2;
 
 import android.content.Context;
+import android.os.Looper;
 import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.analytics.AnalyticsCollector;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
 import com.google.android.exoplayer2.drm.FrameworkMediaCrypto;
 import com.google.android.exoplayer2.trackselection.TrackSelector;
 import com.google.android.exoplayer2.util.Clock;
+import com.google.android.exoplayer2.util.Util;
 
 /**
  * A factory for {@link ExoPlayer} instances.
@@ -156,7 +158,11 @@ public final class ExoPlayerFactory {
   public static SimpleExoPlayer newSimpleInstance(RenderersFactory renderersFactory,
       TrackSelector trackSelector, LoadControl loadControl) {
     return new SimpleExoPlayer(
-        renderersFactory, trackSelector, loadControl, /* drmSessionManager= */ null);
+        renderersFactory,
+        trackSelector,
+        loadControl,
+        /* drmSessionManager= */ null,
+        Util.getLooper());
   }
 
   /**
@@ -173,7 +179,8 @@ public final class ExoPlayerFactory {
       TrackSelector trackSelector,
       LoadControl loadControl,
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager) {
-    return new SimpleExoPlayer(renderersFactory, trackSelector, loadControl, drmSessionManager);
+    return new SimpleExoPlayer(
+        renderersFactory, trackSelector, loadControl, drmSessionManager, Util.getLooper());
   }
 
   /**
@@ -194,7 +201,62 @@ public final class ExoPlayerFactory {
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
       AnalyticsCollector.Factory analyticsCollectorFactory) {
     return new SimpleExoPlayer(
-        renderersFactory, trackSelector, loadControl, drmSessionManager, analyticsCollectorFactory);
+        renderersFactory,
+        trackSelector,
+        loadControl,
+        drmSessionManager,
+        analyticsCollectorFactory,
+        Util.getLooper());
+  }
+
+  /**
+   * Creates a {@link SimpleExoPlayer} instance.
+   *
+   * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
+   * @param trackSelector The {@link TrackSelector} that will be used by the instance.
+   * @param loadControl The {@link LoadControl} that will be used by the instance.
+   * @param drmSessionManager An optional {@link DrmSessionManager}. May be null if the instance
+   *     will not be used for DRM protected playbacks.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
+   */
+  public static SimpleExoPlayer newSimpleInstance(
+      RenderersFactory renderersFactory,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
+      Looper looper) {
+    return new SimpleExoPlayer(
+        renderersFactory, trackSelector, loadControl, drmSessionManager, looper);
+  }
+
+  /**
+   * Creates a {@link SimpleExoPlayer} instance.
+   *
+   * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
+   * @param trackSelector The {@link TrackSelector} that will be used by the instance.
+   * @param loadControl The {@link LoadControl} that will be used by the instance.
+   * @param drmSessionManager An optional {@link DrmSessionManager}. May be null if the instance
+   *     will not be used for DRM protected playbacks.
+   * @param analyticsCollectorFactory A factory for creating the {@link AnalyticsCollector} that
+   *     will collect and forward all player events.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
+   */
+  public static SimpleExoPlayer newSimpleInstance(
+      RenderersFactory renderersFactory,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
+      AnalyticsCollector.Factory analyticsCollectorFactory,
+      Looper looper) {
+    return new SimpleExoPlayer(
+        renderersFactory,
+        trackSelector,
+        loadControl,
+        drmSessionManager,
+        analyticsCollectorFactory,
+        looper);
   }
 
   /**
@@ -216,7 +278,20 @@ public final class ExoPlayerFactory {
    */
   public static ExoPlayer newInstance(Renderer[] renderers, TrackSelector trackSelector,
       LoadControl loadControl) {
-    return new ExoPlayerImpl(renderers, trackSelector, loadControl, Clock.DEFAULT);
+    return newInstance(renderers, trackSelector, loadControl, Util.getLooper());
   }
 
+  /**
+   * Creates an {@link ExoPlayer} instance.
+   *
+   * @param renderers The {@link Renderer}s that will be used by the instance.
+   * @param trackSelector The {@link TrackSelector} that will be used by the instance.
+   * @param loadControl The {@link LoadControl} that will be used by the instance.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
+   */
+  public static ExoPlayer newInstance(
+      Renderer[] renderers, TrackSelector trackSelector, LoadControl loadControl, Looper looper) {
+    return new ExoPlayerImpl(renderers, trackSelector, loadControl, Clock.DEFAULT, looper);
+  }
 }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java
index 390f8b59a5..e803fb30ee 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/ExoPlayerImpl.java
@@ -81,10 +81,16 @@ import java.util.concurrent.CopyOnWriteArraySet;
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
    * @param loadControl The {@link LoadControl} that will be used by the instance.
    * @param clock The {@link Clock} that will be used by the instance.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    */
   @SuppressLint("HandlerLeak")
   public ExoPlayerImpl(
-      Renderer[] renderers, TrackSelector trackSelector, LoadControl loadControl, Clock clock) {
+      Renderer[] renderers,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      Clock clock,
+      Looper looper) {
     Log.i(TAG, "Init " + Integer.toHexString(System.identityHashCode(this)) + " ["
         + ExoPlayerLibraryInfo.VERSION_SLASHY + "] [" + Util.DEVICE_DEBUG_INFO + "]");
     Assertions.checkState(renderers.length > 0);
@@ -102,13 +108,13 @@ import java.util.concurrent.CopyOnWriteArraySet;
     window = new Timeline.Window();
     period = new Timeline.Period();
     playbackParameters = PlaybackParameters.DEFAULT;
-    Looper eventLooper = Looper.myLooper() != null ? Looper.myLooper() : Looper.getMainLooper();
-    eventHandler = new Handler(eventLooper) {
-      @Override
-      public void handleMessage(Message msg) {
-        ExoPlayerImpl.this.handleEvent(msg);
-      }
-    };
+    eventHandler =
+        new Handler(looper) {
+          @Override
+          public void handleMessage(Message msg) {
+            ExoPlayerImpl.this.handleEvent(msg);
+          }
+        };
     playbackInfo =
         new PlaybackInfo(
             Timeline.EMPTY,
@@ -146,6 +152,11 @@ import java.util.concurrent.CopyOnWriteArraySet;
     return internalPlayer.getPlaybackLooper();
   }
 
+  @Override
+  public Looper getApplicationLooper() {
+    return eventHandler.getLooper();
+  }
+
   @Override
   public void addListener(Player.EventListener listener) {
     listeners.add(listener);
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java b/library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java
index 7fa13338ad..0fa7279079 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/SimpleExoPlayer.java
@@ -98,23 +98,40 @@ public class SimpleExoPlayer implements ExoPlayer, Player.VideoComponent, Player
   private List<Cue> currentCues;
 
   /**
-   * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
-   * @param trackSelector The {@link TrackSelector} that will be used by the instance.
-   * @param loadControl The {@link LoadControl} that will be used by the instance.
-   * @param drmSessionManager An optional {@link DrmSessionManager}. May be null if the instance
-   *     will not be used for DRM protected playbacks.
+   * @deprecated Use {@link #SimpleExoPlayer(RenderersFactory, TrackSelector, LoadControl,
+   *     DrmSessionManager, Looper)}.
    */
+  @Deprecated
   protected SimpleExoPlayer(
       RenderersFactory renderersFactory,
       TrackSelector trackSelector,
       LoadControl loadControl,
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager) {
+    this(renderersFactory, trackSelector, loadControl, drmSessionManager, Util.getLooper());
+  }
+
+  /**
+   * @param renderersFactory A factory for creating {@link Renderer}s to be used by the instance.
+   * @param trackSelector The {@link TrackSelector} that will be used by the instance.
+   * @param loadControl The {@link LoadControl} that will be used by the instance.
+   * @param drmSessionManager An optional {@link DrmSessionManager}. May be null if the instance
+   *     will not be used for DRM protected playbacks.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
+   */
+  protected SimpleExoPlayer(
+      RenderersFactory renderersFactory,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
+      Looper looper) {
     this(
         renderersFactory,
         trackSelector,
         loadControl,
         drmSessionManager,
-        new AnalyticsCollector.Factory());
+        new AnalyticsCollector.Factory(),
+        looper);
   }
 
   /**
@@ -125,20 +142,24 @@ public class SimpleExoPlayer implements ExoPlayer, Player.VideoComponent, Player
    *     will not be used for DRM protected playbacks.
    * @param analyticsCollectorFactory A factory for creating the {@link AnalyticsCollector} that
    *     will collect and forward all player events.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    */
   protected SimpleExoPlayer(
       RenderersFactory renderersFactory,
       TrackSelector trackSelector,
       LoadControl loadControl,
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
-      AnalyticsCollector.Factory analyticsCollectorFactory) {
+      AnalyticsCollector.Factory analyticsCollectorFactory,
+      Looper looper) {
     this(
         renderersFactory,
         trackSelector,
         loadControl,
         drmSessionManager,
         analyticsCollectorFactory,
-        Clock.DEFAULT);
+        Clock.DEFAULT,
+        looper);
   }
 
   /**
@@ -151,6 +172,8 @@ public class SimpleExoPlayer implements ExoPlayer, Player.VideoComponent, Player
    *     will collect and forward all player events.
    * @param clock The {@link Clock} that will be used by the instance. Should always be {@link
    *     Clock#DEFAULT}, unless the player is being used from a test.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    */
   protected SimpleExoPlayer(
       RenderersFactory renderersFactory,
@@ -158,15 +181,15 @@ public class SimpleExoPlayer implements ExoPlayer, Player.VideoComponent, Player
       LoadControl loadControl,
       @Nullable DrmSessionManager<FrameworkMediaCrypto> drmSessionManager,
       AnalyticsCollector.Factory analyticsCollectorFactory,
-      Clock clock) {
+      Clock clock,
+      Looper looper) {
     componentListener = new ComponentListener();
     videoListeners = new CopyOnWriteArraySet<>();
     textOutputs = new CopyOnWriteArraySet<>();
     metadataOutputs = new CopyOnWriteArraySet<>();
     videoDebugListeners = new CopyOnWriteArraySet<>();
     audioDebugListeners = new CopyOnWriteArraySet<>();
-    Looper eventLooper = Looper.myLooper() != null ? Looper.myLooper() : Looper.getMainLooper();
-    eventHandler = new Handler(eventLooper);
+    eventHandler = new Handler(looper);
     renderers =
         renderersFactory.createRenderers(
             eventHandler,
@@ -184,7 +207,7 @@ public class SimpleExoPlayer implements ExoPlayer, Player.VideoComponent, Player
     currentCues = Collections.emptyList();
 
     // Build the player and associated objects.
-    player = createExoPlayerImpl(renderers, trackSelector, loadControl, clock);
+    player = createExoPlayerImpl(renderers, trackSelector, loadControl, clock, looper);
     analyticsCollector = analyticsCollectorFactory.createAnalyticsCollector(player, clock);
     addListener(analyticsCollector);
     videoDebugListeners.add(analyticsCollector);
@@ -671,6 +694,11 @@ public class SimpleExoPlayer implements ExoPlayer, Player.VideoComponent, Player
     return player.getPlaybackLooper();
   }
 
+  @Override
+  public Looper getApplicationLooper() {
+    return player.getApplicationLooper();
+  }
+
   @Override
   public void addListener(Player.EventListener listener) {
     player.addListener(listener);
@@ -954,11 +982,17 @@ public class SimpleExoPlayer implements ExoPlayer, Player.VideoComponent, Player
    * @param trackSelector The {@link TrackSelector} that will be used by the instance.
    * @param loadControl The {@link LoadControl} that will be used by the instance.
    * @param clock The {@link Clock} that will be used by this instance.
+   * @param looper The {@link Looper} which must be used for all calls to the player and which is
+   *     used to call listeners on.
    * @return A new {@link ExoPlayer} instance.
    */
   protected ExoPlayer createExoPlayerImpl(
-      Renderer[] renderers, TrackSelector trackSelector, LoadControl loadControl, Clock clock) {
-    return new ExoPlayerImpl(renderers, trackSelector, loadControl, clock);
+      Renderer[] renderers,
+      TrackSelector trackSelector,
+      LoadControl loadControl,
+      Clock clock,
+      Looper looper) {
+    return new ExoPlayerImpl(renderers, trackSelector, loadControl, clock, looper);
   }
 
   private void removeSurfaceCallbacks() {
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java b/library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
index 52e44c3a4b..680eea6a3e 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
@@ -16,7 +16,6 @@
 package com.google.android.exoplayer2.source;
 
 import android.os.Handler;
-import android.os.Looper;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.C;
@@ -61,13 +60,14 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
   private final List<MediaSourceHolder> mediaSourceHolders;
   private final MediaSourceHolder query;
   private final Map<MediaPeriod, MediaSourceHolder> mediaSourceByMediaPeriod;
-  private final List<EventDispatcher> pendingOnCompletionActions;
+  private final List<Runnable> pendingOnCompletionActions;
   private final boolean isAtomic;
   private final boolean useLazyPreparation;
   private final Timeline.Window window;
   private final Timeline.Period period;
 
   private @Nullable ExoPlayer player;
+  private @Nullable Handler playerApplicationHandler;
   private boolean listenerNotificationScheduled;
   private ShuffleOrder shuffleOrder;
   private int windowCount;
@@ -351,11 +351,7 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
   public final synchronized void clear(@Nullable Runnable actionOnCompletion) {
     mediaSourcesPublic.clear();
     if (player != null) {
-      player
-          .createMessage(this)
-          .setType(MSG_CLEAR)
-          .setPayload(actionOnCompletion != null ? new EventDispatcher(actionOnCompletion) : null)
-          .send();
+      player.createMessage(this).setType(MSG_CLEAR).setPayload(actionOnCompletion).send();
     } else if (actionOnCompletion != null) {
       actionOnCompletion.run();
     }
@@ -380,6 +376,7 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
   public final synchronized void prepareSourceInternal(ExoPlayer player, boolean isTopLevelSource) {
     super.prepareSourceInternal(player, isTopLevelSource);
     this.player = player;
+    playerApplicationHandler = new Handler(player.getApplicationLooper());
     if (mediaSourcesPublic.isEmpty()) {
       notifyListener();
     } else {
@@ -424,6 +421,7 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
     super.releaseSourceInternal();
     mediaSourceHolders.clear();
     player = null;
+    playerApplicationHandler = null;
     shuffleOrder = shuffleOrder.cloneAndClear();
     windowCount = 0;
     periodCount = 0;
@@ -462,6 +460,10 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
   @Override
   @SuppressWarnings("unchecked")
   public final void handleMessage(int messageType, Object message) throws ExoPlaybackException {
+    if (player == null) {
+      // Stale event.
+      return;
+    }
     switch (messageType) {
       case MSG_ADD:
         MessageData<MediaSourceHolder> addMessage = (MessageData<MediaSourceHolder>) message;
@@ -493,15 +495,16 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
         break;
       case MSG_CLEAR:
         clearInternal();
-        scheduleListenerNotification((EventDispatcher) message);
+        scheduleListenerNotification((Runnable) message);
         break;
       case MSG_NOTIFY_LISTENER:
         notifyListener();
         break;
       case MSG_ON_COMPLETION:
-        List<EventDispatcher> actionsOnCompletion = ((List<EventDispatcher>) message);
+        List<Runnable> actionsOnCompletion = ((List<Runnable>) message);
+        Handler handler = Assertions.checkNotNull(playerApplicationHandler);
         for (int i = 0; i < actionsOnCompletion.size(); i++) {
-          actionsOnCompletion.get(i).dispatchEvent();
+          handler.post(actionsOnCompletion.get(i));
         }
         break;
       default:
@@ -509,7 +512,7 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
     }
   }
 
-  private void scheduleListenerNotification(@Nullable EventDispatcher actionOnCompletion) {
+  private void scheduleListenerNotification(@Nullable Runnable actionOnCompletion) {
     if (!listenerNotificationScheduled) {
       Assertions.checkNotNull(player).createMessage(this).setType(MSG_NOTIFY_LISTENER).send();
       listenerNotificationScheduled = true;
@@ -521,9 +524,9 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
 
   private void notifyListener() {
     listenerNotificationScheduled = false;
-    List<EventDispatcher> actionsOnCompletion =
+    List<Runnable> actionsOnCompletion =
         pendingOnCompletionActions.isEmpty()
-            ? Collections.<EventDispatcher>emptyList()
+            ? Collections.<Runnable>emptyList()
             : new ArrayList<>(pendingOnCompletionActions);
     pendingOnCompletionActions.clear();
     refreshSourceInfo(
@@ -698,34 +701,16 @@ public class ConcatenatingMediaSource extends CompositeMediaSource<MediaSourceHo
     }
   }
 
-  /** Can be used to dispatch a runnable on the thread the object was created on. */
-  private static final class EventDispatcher {
-
-    public final Handler eventHandler;
-    public final Runnable runnable;
-
-    public EventDispatcher(Runnable runnable) {
-      this.runnable = runnable;
-      this.eventHandler =
-          new Handler(Looper.myLooper() != null ? Looper.myLooper() : Looper.getMainLooper());
-    }
-
-    public void dispatchEvent() {
-      eventHandler.post(runnable);
-    }
-  }
-
   /** Message used to post actions from app thread to playback thread. */
   private static final class MessageData<T> {
 
     public final int index;
     public final T customData;
-    public final @Nullable EventDispatcher actionOnCompletion;
+    public final @Nullable Runnable actionOnCompletion;
 
     public MessageData(int index, T customData, @Nullable Runnable actionOnCompletion) {
       this.index = index;
-      this.actionOnCompletion =
-          actionOnCompletion != null ? new EventDispatcher(actionOnCompletion) : null;
+      this.actionOnCompletion = actionOnCompletion;
       this.customData = customData;
     }
   }
diff --git a/library/core/src/main/java/com/google/android/exoplayer2/util/Util.java b/library/core/src/main/java/com/google/android/exoplayer2/util/Util.java
index 0e12964dfb..7a38350563 100644
--- a/library/core/src/main/java/com/google/android/exoplayer2/util/Util.java
+++ b/library/core/src/main/java/com/google/android/exoplayer2/util/Util.java
@@ -252,11 +252,14 @@ public final class Util {
    * assumption that the Handler won't be used to send messages until the callback is fully
    * initialized.
    *
+   * <p>If the current thread doesn't have a {@link Looper}, the application's main thread {@link
+   * Looper} is used.
+   *
    * @param callback A {@link Handler.Callback}. May be a partially initialized class.
    * @return A {@link Handler} with the specified callback on the current {@link Looper} thread.
    */
   public static Handler createHandler(Handler.@UnknownInitialization Callback callback) {
-    return createHandler(Looper.myLooper(), callback);
+    return createHandler(getLooper(), callback);
   }
 
   /**
@@ -275,6 +278,15 @@ public final class Util {
     return new Handler(looper, callback);
   }
 
+  /**
+   * Returns the {@link Looper} associated with the current thread, or the {@link Looper} of the
+   * application's main thread if the current thread doesn't have a {@link Looper}.
+   */
+  public static Looper getLooper() {
+    Looper myLooper = Looper.myLooper();
+    return myLooper != null ? myLooper : Looper.getMainLooper();
+  }
+
   /**
    * Instantiates a new single threaded executor whose thread has the specified name.
    *
diff --git a/testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoPlayerTestRunner.java b/testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoPlayerTestRunner.java
index cf7470b80a..b47ab16db6 100644
--- a/testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoPlayerTestRunner.java
+++ b/testutils/src/main/java/com/google/android/exoplayer2/testutil/ExoPlayerTestRunner.java
@@ -18,6 +18,7 @@ package com.google.android.exoplayer2.testutil;
 import static com.google.common.truth.Truth.assertThat;
 
 import android.os.HandlerThread;
+import android.os.Looper;
 import android.support.annotation.Nullable;
 import com.google.android.exoplayer2.DefaultLoadControl;
 import com.google.android.exoplayer2.ExoPlaybackException;
@@ -663,7 +664,8 @@ public final class ExoPlayerTestRunner extends Player.DefaultEventListener
           loadControl,
           /* drmSessionManager= */ null,
           new AnalyticsCollector.Factory(),
-          clock);
+          clock,
+          Looper.myLooper());
     }
   }
 }
diff --git a/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/MediaSourceTestRunner.java b/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/MediaSourceTestRunner.java
index ee3a3a2d32..5062b5c005 100644
--- a/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/MediaSourceTestRunner.java
+++ b/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/MediaSourceTestRunner.java
@@ -442,6 +442,11 @@ public class MediaSourceTestRunner {
       this.handler = new Handler(looper, this);
     }
 
+    @Override
+    public Looper getApplicationLooper() {
+      return handler.getLooper();
+    }
+
     @Override
     public PlayerMessage createMessage(PlayerMessage.Target target) {
       return new PlayerMessage(
diff --git a/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java b/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java
index b8ad949f4a..214c2b6a5e 100644
--- a/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java
+++ b/testutils_robolectric/src/main/java/com/google/android/exoplayer2/testutil/StubExoPlayer.java
@@ -49,6 +49,11 @@ public abstract class StubExoPlayer implements ExoPlayer {
     throw new UnsupportedOperationException();
   }
 
+  @Override
+  public Looper getApplicationLooper() {
+    throw new UnsupportedOperationException();
+  }
+
   @Override
   public void addListener(Player.EventListener listener) {
     throw new UnsupportedOperationException();