diff --git a/demo/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java b/demo/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java
index d1224a7dfb..7edc4457bc 100644
--- a/demo/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java
+++ b/demo/src/main/java/com/google/android/exoplayer2/demo/PlayerActivity.java
@@ -43,7 +43,6 @@ import com.google.android.exoplayer2.ExoPlayerFactory;
 import com.google.android.exoplayer2.SimpleExoPlayer;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.drm.DrmSessionManager;
-import com.google.android.exoplayer2.drm.FrameworkMediaCrypto;
 import com.google.android.exoplayer2.drm.FrameworkMediaDrm;
 import com.google.android.exoplayer2.drm.HttpMediaDrmCallback;
 import com.google.android.exoplayer2.drm.StreamingDrmSessionManager;
@@ -364,7 +363,7 @@ public class PlayerActivity extends Activity implements OnKeyListener, OnTouchLi
     }
     HttpMediaDrmCallback drmCallback = new HttpMediaDrmCallback(licenseUrl,
         buildHttpDataSourceFactory(false));
-    return new StreamingDrmSessionManager<FrameworkMediaCrypto>(uuid,
+    return new StreamingDrmSessionManager<>(uuid,
         FrameworkMediaDrm.newInstance(uuid), drmCallback, null, mainHandler, eventLogger);
   }
 
@@ -404,7 +403,9 @@ public class PlayerActivity extends Activity implements OnKeyListener, OnTouchLi
 
   /**
    * Build a HttpDataSource factory.
-   * @param useBandwidthMeter
+   *
+   * @param useBandwidthMeter Whether to set {@link #BANDWIDTH_METER} as a listener to the new
+   *     DataSource factory.
    */
   private HttpDataSource.Factory buildHttpDataSourceFactory(boolean useBandwidthMeter) {
     return new DefaultHttpDataSourceFactory(userAgent, useBandwidthMeter ? BANDWIDTH_METER : null);
diff --git a/library/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java b/library/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
index 5aad9e259e..90af3936a4 100644
--- a/library/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
+++ b/library/src/main/java/com/google/android/exoplayer2/source/ConcatenatingMediaSource.java
@@ -23,10 +23,12 @@ import com.google.android.exoplayer2.upstream.Allocator;
 import com.google.android.exoplayer2.util.Util;
 import java.io.IOException;
 import java.util.HashMap;
+import java.util.IdentityHashMap;
 import java.util.Map;
 
 /**
- * Concatenates multiple {@link MediaSource}s.
+ * Concatenates multiple {@link MediaSource}s. It is valid for the same {@link MediaSource} instance
+ * to be present more than once in the concatenation.
  */
 public final class ConcatenatingMediaSource implements MediaSource {
 
@@ -34,47 +36,45 @@ public final class ConcatenatingMediaSource implements MediaSource {
   private final Timeline[] timelines;
   private final Object[] manifests;
   private final Map<MediaPeriod, Integer> sourceIndexByMediaPeriod;
+  private final boolean[] duplicateFlags;
 
+  private Listener listener;
   private ConcatenatedTimeline timeline;
 
   /**
-   * @param mediaSources The {@link MediaSource}s to concatenate.
+   * @param mediaSources The {@link MediaSource}s to concatenate. It is valid for the same
+   *     {@link MediaSource} instance to be present more than once in the array.
    */
   public ConcatenatingMediaSource(MediaSource... mediaSources) {
     this.mediaSources = mediaSources;
     timelines = new Timeline[mediaSources.length];
     manifests = new Object[mediaSources.length];
     sourceIndexByMediaPeriod = new HashMap<>();
+    duplicateFlags = buildDuplicateFlags(mediaSources);
   }
 
   @Override
-  public void prepareSource(final Listener listener) {
+  public void prepareSource(Listener listener) {
+    this.listener = listener;
     for (int i = 0; i < mediaSources.length; i++) {
-      final int index = i;
-      mediaSources[i].prepareSource(new Listener() {
-
-        @Override
-        public void onSourceInfoRefreshed(Timeline sourceTimeline, Object manifest) {
-          timelines[index] = sourceTimeline;
-          manifests[index] = manifest;
-          for (Timeline timeline : timelines) {
-            if (timeline == null) {
-              // Don't invoke the listener until all sources have timelines.
-              return;
-            }
+      if (!duplicateFlags[i]) {
+        final int index = i;
+        mediaSources[i].prepareSource(new Listener() {
+          @Override
+          public void onSourceInfoRefreshed(Timeline timeline, Object manifest) {
+            handleSourceInfoRefreshed(index, timeline, manifest);
           }
-          timeline = new ConcatenatedTimeline(timelines.clone());
-          listener.onSourceInfoRefreshed(timeline, manifests.clone());
-        }
-
-      });
+        });
+      }
     }
   }
 
   @Override
   public void maybeThrowSourceInfoRefreshError() throws IOException {
-    for (MediaSource mediaSource : mediaSources) {
-      mediaSource.maybeThrowSourceInfoRefreshError();
+    for (int i = 0; i < mediaSources.length; i++) {
+      if (!duplicateFlags[i]) {
+        mediaSources[i].maybeThrowSourceInfoRefreshError();
+      }
     }
   }
 
@@ -98,11 +98,49 @@ public final class ConcatenatingMediaSource implements MediaSource {
 
   @Override
   public void releaseSource() {
-    for (MediaSource mediaSource : mediaSources) {
-      mediaSource.releaseSource();
+    for (int i = 0; i < mediaSources.length; i++) {
+      if (!duplicateFlags[i]) {
+        mediaSources[i].releaseSource();
+      }
     }
   }
 
+  private void handleSourceInfoRefreshed(int sourceFirstIndex, Timeline sourceTimeline,
+      Object sourceManifest) {
+    // Set the timeline and manifest.
+    timelines[sourceFirstIndex] = sourceTimeline;
+    manifests[sourceFirstIndex] = sourceManifest;
+    // Also set the timeline and manifest for any duplicate entries of the same source.
+    for (int i = sourceFirstIndex + 1; i < mediaSources.length; i++) {
+      if (mediaSources[i] == mediaSources[sourceFirstIndex]) {
+        timelines[i] = sourceTimeline;
+        manifests[i] = sourceManifest;
+      }
+    }
+    for (Timeline timeline : timelines) {
+      if (timeline == null) {
+        // Don't invoke the listener until all sources have timelines.
+        return;
+      }
+    }
+    timeline = new ConcatenatedTimeline(timelines.clone());
+    listener.onSourceInfoRefreshed(timeline, manifests.clone());
+  }
+
+  private static boolean[] buildDuplicateFlags(MediaSource[] mediaSources) {
+    boolean[] duplicateFlags = new boolean[mediaSources.length];
+    IdentityHashMap<MediaSource, Void> sources = new IdentityHashMap<>(mediaSources.length);
+    for (int i = 0; i < mediaSources.length; i++) {
+      MediaSource source = mediaSources[i];
+      if (!sources.containsKey(source)) {
+        sources.put(source, null);
+      } else {
+        duplicateFlags[i] = true;
+      }
+    }
+    return duplicateFlags;
+  }
+
   /**
    * A {@link Timeline} that is the concatenation of one or more {@link Timeline}s.
    */