Add missing equals to MergingMediaPeriod.ForwardingTrackSelection

This causes a bug where the forwarded selections are no longer
assumed equal and the child MediaPeriods will think they need
to reset streams even though the selection stayed the same.

Issue: Issue: google/ExoPlayer#10248
PiperOrigin-RevId: 449454038

RELEASENOTES.md

@@ -12,6 +12,10 @@
         by the user of the device. Apps can opt-out of contributing to platform
         diagnostics for ExoPlayer with
         `ExoPlayer.Builder.setUsePlatformDiagnostics(false)`.
+    *   Fix bug that tracks are reset too often when using `MergingMediaSource`,
+        for example when side-loading subtitles and changing the selected
+        subtitle mid-playback
+         ([#10248](https://github.com/google/ExoPlayer/issues/10248)).
 *   Track selection:
     *   Flatten `TrackSelectionOverrides` class into `TrackSelectionParameters`,
         and promote `TrackSelectionOverride` to a top level class.

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/source/MergingMediaPeriod.java

@@ -608,5 +608,25 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     public boolean isBlacklisted(int index, long nowMs) {
       return trackSelection.isBlacklisted(index, nowMs);
     }
+
+    @Override
+    public boolean equals(@Nullable Object o) {
+      if (this == o) {
+        return true;
+      }
+      if (!(o instanceof ForwardingTrackSelection)) {
+        return false;
+      }
+      ForwardingTrackSelection that = (ForwardingTrackSelection) o;
+      return trackSelection.equals(that.trackSelection) && trackGroup.equals(that.trackGroup);
+    }
+
+    @Override
+    public int hashCode() {
+      int result = 17;
+      result = 31 * result + trackGroup.hashCode();
+      result = 31 * result + trackSelection.hashCode();
+      return result;
+    }
   }
 }

libraries/exoplayer/src/test/java/androidx/media3/exoplayer/source/MergingMediaPeriodTest.java

@@ -35,6 +35,7 @@ import androidx.media3.exoplayer.upstream.DefaultAllocator;
 import androidx.media3.test.utils.FakeMediaPeriod;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import com.google.common.collect.ImmutableList;
+import java.util.Arrays;
 import java.util.concurrent.CountDownLatch;
 import org.checkerframework.checker.nullness.compatqual.NullableType;
 import org.junit.Test;
@@ -139,21 +140,64 @@ public final class MergingMediaPeriodTest {
     streams[0].readData(formatHolder, inputBuffer, FLAG_REQUIRE_FORMAT);
     streams[1].readData(formatHolder, inputBuffer, FLAG_REQUIRE_FORMAT);
 
-    FakeMediaPeriodWithSelectTracksPosition childMediaPeriod1 =
-        (FakeMediaPeriodWithSelectTracksPosition) mergingMediaPeriod.getChildPeriod(0);
+    FakeMediaPeriodWithSelectionParameters childMediaPeriod1 =
+        (FakeMediaPeriodWithSelectionParameters) mergingMediaPeriod.getChildPeriod(0);
     assertThat(childMediaPeriod1.selectTracksPositionUs).isEqualTo(0);
     assertThat(streams[0].readData(formatHolder, inputBuffer, /* readFlags= */ 0))
         .isEqualTo(C.RESULT_BUFFER_READ);
     assertThat(inputBuffer.timeUs).isEqualTo(123_000L);
 
-    FakeMediaPeriodWithSelectTracksPosition childMediaPeriod2 =
-        (FakeMediaPeriodWithSelectTracksPosition) mergingMediaPeriod.getChildPeriod(1);
+    FakeMediaPeriodWithSelectionParameters childMediaPeriod2 =
+        (FakeMediaPeriodWithSelectionParameters) mergingMediaPeriod.getChildPeriod(1);
     assertThat(childMediaPeriod2.selectTracksPositionUs).isEqualTo(3000L);
     assertThat(streams[1].readData(formatHolder, inputBuffer, /* readFlags= */ 0))
         .isEqualTo(C.RESULT_BUFFER_READ);
     assertThat(inputBuffer.timeUs).isEqualTo(456_000 - 3000);
   }
 
+  @Test
+  public void selectTracks_withSameArguments_forwardsEqualSelectionsToChildSources()
+      throws Exception {
+    MergingMediaPeriod mergingMediaPeriod =
+        prepareMergingPeriod(
+            new MergingPeriodDefinition(
+                /* timeOffsetUs= */ 0, /* singleSampleTimeUs= */ 0, childFormat11),
+            new MergingPeriodDefinition(
+                /* timeOffsetUs= */ 0, /* singleSampleTimeUs= */ 0, childFormat22));
+    FakeMediaPeriodWithSelectionParameters childMediaPeriod1 =
+        (FakeMediaPeriodWithSelectionParameters) mergingMediaPeriod.getChildPeriod(0);
+    FakeMediaPeriodWithSelectionParameters childMediaPeriod2 =
+        (FakeMediaPeriodWithSelectionParameters) mergingMediaPeriod.getChildPeriod(1);
+
+    TrackGroupArray mergedTrackGroups = mergingMediaPeriod.getTrackGroups();
+    ExoTrackSelection[] selectionArray =
+        new ExoTrackSelection[] {
+          new FixedTrackSelection(mergedTrackGroups.get(0), /* track= */ 0),
+          new FixedTrackSelection(mergedTrackGroups.get(1), /* track= */ 0)
+        };
+
+    mergingMediaPeriod.selectTracks(
+        selectionArray,
+        /* mayRetainStreamFlags= */ new boolean[2],
+        /* streams= */ new SampleStream[2],
+        /* streamResetFlags= */ new boolean[2],
+        /* positionUs= */ 0);
+    ExoTrackSelection firstSelectionChild1 = childMediaPeriod1.selectTracksSelections[0];
+    ExoTrackSelection firstSelectionChild2 = childMediaPeriod2.selectTracksSelections[1];
+
+    mergingMediaPeriod.selectTracks(
+        selectionArray,
+        /* mayRetainStreamFlags= */ new boolean[2],
+        /* streams= */ new SampleStream[2],
+        /* streamResetFlags= */ new boolean[2],
+        /* positionUs= */ 0);
+    ExoTrackSelection secondSelectionChild1 = childMediaPeriod1.selectTracksSelections[0];
+    ExoTrackSelection secondSelectionChild2 = childMediaPeriod2.selectTracksSelections[1];
+
+    assertThat(firstSelectionChild1).isEqualTo(secondSelectionChild1);
+    assertThat(firstSelectionChild2).isEqualTo(secondSelectionChild2);
+  }
+
   private MergingMediaPeriod prepareMergingPeriod(MergingPeriodDefinition... definitions)
       throws Exception {
     MediaPeriod[] mediaPeriods = new MediaPeriod[definitions.length];
@@ -166,7 +210,7 @@ public final class MergingMediaPeriodTest {
         trackGroups[j] = new TrackGroup(definition.formats[j]);
       }
       mediaPeriods[i] =
-          new FakeMediaPeriodWithSelectTracksPosition(
+          new FakeMediaPeriodWithSelectionParameters(
               new TrackGroupArray(trackGroups),
               new EventDispatcher()
                   .withParameters(
@@ -201,11 +245,12 @@ public final class MergingMediaPeriodTest {
     return mergingMediaPeriod;
   }
 
-  private static final class FakeMediaPeriodWithSelectTracksPosition extends FakeMediaPeriod {
+  private static final class FakeMediaPeriodWithSelectionParameters extends FakeMediaPeriod {
 
+    public @NullableType ExoTrackSelection[] selectTracksSelections;
     public long selectTracksPositionUs;
 
-    public FakeMediaPeriodWithSelectTracksPosition(
+    public FakeMediaPeriodWithSelectionParameters(
         TrackGroupArray trackGroupArray,
         EventDispatcher mediaSourceEventDispatcher,
         TrackDataFactory trackDataFactory) {
@@ -217,6 +262,7 @@ public final class MergingMediaPeriodTest {
           DrmSessionManager.DRM_UNSUPPORTED,
           new DrmSessionEventListener.EventDispatcher(),
           /* deferOnPrepared= */ false);
+      selectTracksSelections = new ExoTrackSelection[trackGroupArray.length];
       selectTracksPositionUs = C.TIME_UNSET;
     }
 
@@ -227,6 +273,7 @@ public final class MergingMediaPeriodTest {
         @NullableType SampleStream[] streams,
         boolean[] streamResetFlags,
         long positionUs) {
+      selectTracksSelections = Arrays.copyOf(selections, selections.length);
       selectTracksPositionUs = positionUs;
       return super.selectTracks(
           selections, mayRetainStreamFlags, streams, streamResetFlags, positionUs);