Prohibit duplicate TrackGroups in TrackGroupArray

Allowing duplicate groups caused some other code working with the
array to use reference equality comparison. This is error-prone,
easily forgotten (e.g. when using the TrackGroups in a map) and
causes bugs when TrackGroups are serialized to disk or to another
process.

All TrackGroups created by ExoPlayer are already unique and custom
code creating TrackGroupArrays with identical groups can easily
distringuish them by adding an id to each group.

Issue: google/ExoPlayer#9718
PiperOrigin-RevId: 413617005

RELEASENOTES.md

@@ -9,6 +9,11 @@
         track matching system Locale language) over technical track selection
         constraints (for example, preferred MIME type, or maximum channel
         count).
+    *   Prohibit duplicate `TrackGroup`s in a `TrackGroupArray`. `TrackGroup`s
+        can always be made distinguishable by setting an `id` in the
+        `TrackGroup` constructor. This fixes a crash when resuming playback
+        after backgrounding the app with an active track override
+        ((#9718)[https://github.com/google/ExoPlayer/issues/9718]).
 *   Extractors:
     *   Fix inconsistency with spec in H.265 SPS nal units parsing
         ((#9719)[https://github.com/google/ExoPlayer/issues/9719]).

library/common/src/main/java/com/google/android/exoplayer2/source/TrackGroupArray.java

@@ -21,32 +21,38 @@ import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.Bundleable;
 import com.google.android.exoplayer2.C;
 import com.google.android.exoplayer2.util.BundleableUtil;
+import com.google.android.exoplayer2.util.Log;
 import com.google.common.collect.ImmutableList;
-import com.google.common.collect.Lists;
 import java.lang.annotation.Documented;
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
-import java.util.Arrays;
 import java.util.List;
 
 /** An immutable array of {@link TrackGroup}s. */
 public final class TrackGroupArray implements Bundleable {
 
+  private static final String TAG = "TrackGroupArray";
+
   /** The empty array. */
   public static final TrackGroupArray EMPTY = new TrackGroupArray();
 
   /** The number of groups in the array. Greater than or equal to zero. */
   public final int length;
 
-  private final TrackGroup[] trackGroups;
+  private final ImmutableList<TrackGroup> trackGroups;
 
   // Lazily initialized hashcode.
   private int hashCode;
 
-  /** Construct a {@code TrackGroupArray} from an array of (possibly empty) trackGroups. */
+  /**
+   * Construct a {@code TrackGroupArray} from an array of {@link TrackGroup TrackGroups}.
+   *
+   * <p>The groups must not contain duplicates.
+   */
   public TrackGroupArray(TrackGroup... trackGroups) {
-    this.trackGroups = trackGroups;
+    this.trackGroups = ImmutableList.copyOf(trackGroups);
     this.length = trackGroups.length;
+    verifyCorrectness();
   }
 
   /**
@@ -56,7 +62,7 @@ public final class TrackGroupArray implements Bundleable {
    * @return The group.
    */
   public TrackGroup get(int index) {
-    return trackGroups[index];
+    return trackGroups.get(index);
   }
 
   /**
@@ -65,16 +71,9 @@ public final class TrackGroupArray implements Bundleable {
    * @param group The group.
    * @return The index of the group, or {@link C#INDEX_UNSET} if no such group exists.
    */
-  @SuppressWarnings("ReferenceEquality")
   public int indexOf(TrackGroup group) {
-    for (int i = 0; i < length; i++) {
-      // Suppressed reference equality warning because this is looking for the index of a specific
-      // TrackGroup object, not the index of a potential equal TrackGroup.
-      if (trackGroups[i] == group) {
-        return i;
-      }
-    }
-    return C.INDEX_UNSET;
+    int index = trackGroups.indexOf(group);
+    return index >= 0 ? index : C.INDEX_UNSET;
   }
 
   /** Returns whether this track group array is empty. */
@@ -85,7 +84,7 @@ public final class TrackGroupArray implements Bundleable {
   @Override
   public int hashCode() {
     if (hashCode == 0) {
-      hashCode = Arrays.hashCode(trackGroups);
+      hashCode = trackGroups.hashCode();
     }
     return hashCode;
   }
@@ -99,7 +98,7 @@ public final class TrackGroupArray implements Bundleable {
       return false;
     }
     TrackGroupArray other = (TrackGroupArray) obj;
-    return length == other.length && Arrays.equals(trackGroups, other.trackGroups);
+    return length == other.length && trackGroups.equals(other.trackGroups);
   }
 
   // Bundleable implementation.
@@ -117,8 +116,7 @@ public final class TrackGroupArray implements Bundleable {
   public Bundle toBundle() {
     Bundle bundle = new Bundle();
     bundle.putParcelableArrayList(
-        keyForField(FIELD_TRACK_GROUPS),
-        BundleableUtil.toBundleArrayList(Lists.newArrayList(trackGroups)));
+        keyForField(FIELD_TRACK_GROUPS), BundleableUtil.toBundleArrayList(trackGroups));
     return bundle;
   }
 
@@ -133,6 +131,20 @@ public final class TrackGroupArray implements Bundleable {
         return new TrackGroupArray(trackGroups.toArray(new TrackGroup[0]));
       };
 
+  private void verifyCorrectness() {
+    for (int i = 0; i < trackGroups.size(); i++) {
+      for (int j = i + 1; j < trackGroups.size(); j++) {
+        if (trackGroups.get(i).equals(trackGroups.get(j))) {
+          Log.e(
+              TAG,
+              "",
+              new IllegalArgumentException(
+                  "Multiple identical TrackGroups added to one TrackGroupArray."));
+        }
+      }
+    }
+  }
+
   private static String keyForField(@FieldNumber int field) {
     return Integer.toString(field, Character.MAX_RADIX);
   }

library/core/src/main/java/com/google/android/exoplayer2/offline/DownloadHelper.java

@@ -832,8 +832,6 @@ public final class DownloadHelper {
    * Runs the track selection for a given period index with the current parameters. The selected
    * tracks will be added to {@link #trackSelectionsByPeriodAndRenderer}.
    */
-  // Intentional reference comparison of track group instances.
-  @SuppressWarnings("ReferenceEquality")
   @RequiresNonNull({
     "trackGroupArrays",
     "trackSelectionsByPeriodAndRenderer",
@@ -858,7 +856,7 @@ public final class DownloadHelper {
         boolean mergedWithExistingSelection = false;
         for (int j = 0; j < existingSelectionList.size(); j++) {
           ExoTrackSelection existingSelection = existingSelectionList.get(j);
-          if (existingSelection.getTrackGroup() == newSelection.getTrackGroup()) {
+          if (existingSelection.getTrackGroup().equals(newSelection.getTrackGroup())) {
             // Merge with existing selection.
             scratchSet.clear();
             for (int k = 0; k < existingSelection.length(); k++) {

library/core/src/main/java/com/google/android/exoplayer2/trackselection/MappingTrackSelector.java

@@ -560,13 +560,10 @@ public abstract class MappingTrackSelector extends TrackSelector {
         for (int trackIndex = 0; trackIndex < trackGroup.length; trackIndex++) {
           trackSupport[trackIndex] =
               mappedTrackInfo.getTrackSupport(rendererIndex, groupIndex, trackIndex);
-          // Suppressing reference equality warning because the track group stored in the track
-          // selection must point to the exact track group object to be considered part of it.
-          @SuppressWarnings("ReferenceEquality")
           boolean isTrackSelected =
-              (trackSelection != null)
-                  && (trackSelection.getTrackGroup() == trackGroup)
-                  && (trackSelection.indexOf(trackIndex) != C.INDEX_UNSET);
+              trackSelection != null
+                  && trackSelection.getTrackGroup().equals(trackGroup)
+                  && trackSelection.indexOf(trackIndex) != C.INDEX_UNSET;
           selected[trackIndex] = isTrackSelected;
         }
         @C.TrackType int trackGroupType = mappedTrackInfo.getRendererType(rendererIndex);

library/core/src/main/java/com/google/android/exoplayer2/util/EventLogger.java

@@ -651,14 +651,11 @@ public class EventLogger implements AnalyticsListener {
     }
   }
 
-  // Suppressing reference equality warning because the track group stored in the track selection
-  // must point to the exact track group object to be considered part of it.
-  @SuppressWarnings("ReferenceEquality")
   private static String getTrackStatusString(
       @Nullable TrackSelection selection, TrackGroup group, int trackIndex) {
     return getTrackStatusString(
         selection != null
-            && selection.getTrackGroup() == group
+            && selection.getTrackGroup().equals(group)
             && selection.indexOf(trackIndex) != C.INDEX_UNSET);
   }
 

library/core/src/test/java/com/google/android/exoplayer2/trackselection/DefaultTrackSelectorTest.java

@@ -248,6 +248,8 @@ public final class DefaultTrackSelectorTest {
   @Test
   public void selectTracks_withEmptyTrackOverrideForDifferentTracks_hasNoEffect()
       throws ExoPlaybackException {
+    TrackGroup videoGroup0 = VIDEO_TRACK_GROUP.copyWithId("0");
+    TrackGroup videoGroup1 = VIDEO_TRACK_GROUP.copyWithId("1");
     trackSelector.setParameters(
         trackSelector
             .buildUponParameters()
@@ -261,11 +263,16 @@ public final class DefaultTrackSelectorTest {
     TrackSelectorResult result =
         trackSelector.selectTracks(
             RENDERER_CAPABILITIES,
-            new TrackGroupArray(VIDEO_TRACK_GROUP, AUDIO_TRACK_GROUP, VIDEO_TRACK_GROUP),
+            new TrackGroupArray(videoGroup0, AUDIO_TRACK_GROUP, videoGroup1),
             periodId,
             TIMELINE);
 
-    assertThat(result.selections).asList().containsExactlyElementsIn(TRACK_SELECTIONS).inOrder();
+    assertThat(result.selections)
+        .asList()
+        .containsExactly(
+            new FixedTrackSelection(videoGroup0, /* track= */ 0),
+            new FixedTrackSelection(AUDIO_TRACK_GROUP, /* track= */ 0))
+        .inOrder();
     assertThat(result.rendererConfigurations)
         .isEqualTo(new RendererConfiguration[] {DEFAULT, DEFAULT});
   }
@@ -364,17 +371,24 @@ public final class DefaultTrackSelectorTest {
   /** Tests that an override is not applied for a different set of available track groups. */
   @Test
   public void selectTracksWithNullOverrideForDifferentTracks() throws ExoPlaybackException {
+    TrackGroup videoGroup0 = VIDEO_TRACK_GROUP.copyWithId("0");
+    TrackGroup videoGroup1 = VIDEO_TRACK_GROUP.copyWithId("1");
     trackSelector.setParameters(
         trackSelector
             .buildUponParameters()
-            .setSelectionOverride(0, new TrackGroupArray(VIDEO_TRACK_GROUP), null));
+            .setSelectionOverride(0, new TrackGroupArray(VIDEO_TRACK_GROUP.copyWithId("2")), null));
     TrackSelectorResult result =
         trackSelector.selectTracks(
             RENDERER_CAPABILITIES,
-            new TrackGroupArray(VIDEO_TRACK_GROUP, AUDIO_TRACK_GROUP, VIDEO_TRACK_GROUP),
+            new TrackGroupArray(videoGroup0, AUDIO_TRACK_GROUP, videoGroup1),
             periodId,
             TIMELINE);
-    assertSelections(result, TRACK_SELECTIONS);
+    assertThat(result.selections)
+        .asList()
+        .containsExactly(
+            new FixedTrackSelection(videoGroup0, /* track= */ 0),
+            new FixedTrackSelection(AUDIO_TRACK_GROUP, /* track= */ 0))
+        .inOrder();
     assertThat(result.rendererConfigurations)
         .isEqualTo(new RendererConfiguration[] {DEFAULT, DEFAULT});
   }

library/core/src/test/java/com/google/android/exoplayer2/trackselection/MappingTrackSelectorTest.java

@@ -95,10 +95,13 @@ public final class MappingTrackSelectorTest {
   @Test
   public void selectTracks_multipleVideoAndAudioTracks_mappedToSameRenderer()
       throws ExoPlaybackException {
+    TrackGroup videoGroup0 = VIDEO_TRACK_GROUP.copyWithId("0");
+    TrackGroup videoGroup1 = VIDEO_TRACK_GROUP.copyWithId("1");
+    TrackGroup audioGroup0 = AUDIO_TRACK_GROUP.copyWithId("0");
+    TrackGroup audioGroup1 = AUDIO_TRACK_GROUP.copyWithId("1");
     FakeMappingTrackSelector trackSelector = new FakeMappingTrackSelector();
     TrackGroupArray trackGroups =
-        new TrackGroupArray(
-            VIDEO_TRACK_GROUP, AUDIO_TRACK_GROUP, AUDIO_TRACK_GROUP, VIDEO_TRACK_GROUP);
+        new TrackGroupArray(videoGroup0, audioGroup0, audioGroup1, videoGroup1);
     RendererCapabilities[] rendererCapabilities =
         new RendererCapabilities[] {
           VIDEO_CAPABILITIES, AUDIO_CAPABILITIES, VIDEO_CAPABILITIES, AUDIO_CAPABILITIES
@@ -106,16 +109,18 @@ public final class MappingTrackSelectorTest {
 
     trackSelector.selectTracks(rendererCapabilities, trackGroups, periodId, TIMELINE);
 
-    trackSelector.assertMappedTrackGroups(0, VIDEO_TRACK_GROUP, VIDEO_TRACK_GROUP);
-    trackSelector.assertMappedTrackGroups(1, AUDIO_TRACK_GROUP, AUDIO_TRACK_GROUP);
+    trackSelector.assertMappedTrackGroups(0, videoGroup0, videoGroup1);
+    trackSelector.assertMappedTrackGroups(1, audioGroup0, audioGroup1);
   }
 
   @Test
   public void selectTracks_multipleMetadataTracks_mappedToDifferentRenderers()
       throws ExoPlaybackException {
+    TrackGroup metadataGroup0 = METADATA_TRACK_GROUP.copyWithId("0");
+    TrackGroup metadataGroup1 = METADATA_TRACK_GROUP.copyWithId("1");
     FakeMappingTrackSelector trackSelector = new FakeMappingTrackSelector();
     TrackGroupArray trackGroups =
-        new TrackGroupArray(VIDEO_TRACK_GROUP, METADATA_TRACK_GROUP, METADATA_TRACK_GROUP);
+        new TrackGroupArray(VIDEO_TRACK_GROUP, metadataGroup0, metadataGroup1);
     RendererCapabilities[] rendererCapabilities =
         new RendererCapabilities[] {
           VIDEO_CAPABILITIES, METADATA_CAPABILITIES, METADATA_CAPABILITIES
@@ -124,8 +129,8 @@ public final class MappingTrackSelectorTest {
     trackSelector.selectTracks(rendererCapabilities, trackGroups, periodId, TIMELINE);
 
     trackSelector.assertMappedTrackGroups(0, VIDEO_TRACK_GROUP);
-    trackSelector.assertMappedTrackGroups(1, METADATA_TRACK_GROUP);
-    trackSelector.assertMappedTrackGroups(2, METADATA_TRACK_GROUP);
+    trackSelector.assertMappedTrackGroups(1, metadataGroup0);
+    trackSelector.assertMappedTrackGroups(2, metadataGroup1);
   }
 
   private static TrackGroup buildTrackGroup(String sampleMimeType) {
@@ -140,10 +145,10 @@ public final class MappingTrackSelectorTest {
             new int[] {C.TRACK_TYPE_AUDIO, C.TRACK_TYPE_VIDEO},
             new TrackGroupArray[] {
               new TrackGroupArray(
-                  new TrackGroup(new Format.Builder().build()),
-                  new TrackGroup(new Format.Builder().build())),
+                  new TrackGroup("0", new Format.Builder().build()),
+                  new TrackGroup("1", new Format.Builder().build())),
               new TrackGroupArray(
-                  new TrackGroup(new Format.Builder().build(), new Format.Builder().build()))
+                  new TrackGroup("2", new Format.Builder().build(), new Format.Builder().build()))
             },
             new int[] {
               RendererCapabilities.ADAPTIVE_SEAMLESS, RendererCapabilities.ADAPTIVE_NOT_SUPPORTED