Add optional id to TrackGroup.

This allows to give TrackGroups an identifier. The underlying goal is
to provide a way to make otherwise identical TrackGroups
distinguishable.

Also set this id in all internal sources that may produce identical
TrackGroups in certain edge cases.

Issue: google/ExoPlayer#9718
PiperOrigin-RevId: 413430719

extensions/cast/src/main/java/com/google/android/exoplayer2/ext/cast/CastPlayer.java

@@ -1058,7 +1058,8 @@ public final class CastPlayer extends BasePlayer {
         new TracksInfo.TrackGroupInfo[castMediaTracks.size()];
     for (int i = 0; i < castMediaTracks.size(); i++) {
       MediaTrack mediaTrack = castMediaTracks.get(i);
-      trackGroups[i] = new TrackGroup(CastUtils.mediaTrackToFormat(mediaTrack));
+      trackGroups[i] =
+          new TrackGroup(/* id= */ Integer.toString(i), CastUtils.mediaTrackToFormat(mediaTrack));
 
       long id = mediaTrack.getId();
       @C.TrackType int trackType = MimeTypes.getTrackType(mediaTrack.getContentType());

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

@@ -18,6 +18,7 @@ package com.google.android.exoplayer2.source;
 import static com.google.android.exoplayer2.util.Assertions.checkArgument;
 
 import android.os.Bundle;
+import androidx.annotation.CheckResult;
 import androidx.annotation.IntDef;
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.Bundleable;
@@ -40,6 +41,8 @@ public final class TrackGroup implements Bundleable {
 
   /** The number of tracks in the group. */
   public final int length;
+  /** An identifier for the track group. */
+  public final String id;
 
   private final Format[] formats;
 
@@ -47,18 +50,40 @@ public final class TrackGroup implements Bundleable {
   private int hashCode;
 
   /**
-   * Constructs an instance {@code TrackGroup} containing the provided {@code formats}.
+   * Constructs a track group containing the provided {@code formats}.
    *
-   * @param formats Non empty array of format.
+   * @param formats The list of {@link Format Formats}. Must not be empty.
    */
   public TrackGroup(Format... formats) {
+    this(/* id= */ "", formats);
+  }
+
+  /**
+   * Constructs a track group with the provided {@code id} and {@code formats}.
+   *
+   * @param id The identifier of the track group. May be an empty string.
+   * @param formats The list of {@link Format Formats}. Must not be empty.
+   */
+  public TrackGroup(String id, Format... formats) {
     checkArgument(formats.length > 0);
+    this.id = id;
     this.formats = formats;
     this.length = formats.length;
     verifyCorrectness();
   }
 
   /**
+   * Returns a copy of this track group with the specified {@code id}.
+   *
+   * @param id The identifier for the copy of the track group.
+   * @return The copied track group.
+   */
+  @CheckResult
+  public TrackGroup copyWithId(String id) {
+    return new TrackGroup(id, formats);
+  }
+
+  /**
    * Returns the format of the track at a given index.
    *
    * @param index The index of the track.
@@ -90,6 +115,7 @@ public final class TrackGroup implements Bundleable {
   public int hashCode() {
     if (hashCode == 0) {
       int result = 17;
+      result = 31 * result + id.hashCode();
       result = 31 * result + Arrays.hashCode(formats);
       hashCode = result;
     }
@@ -105,25 +131,25 @@ public final class TrackGroup implements Bundleable {
       return false;
     }
     TrackGroup other = (TrackGroup) obj;
-    return length == other.length && Arrays.equals(formats, other.formats);
+    return length == other.length && id.equals(other.id) && Arrays.equals(formats, other.formats);
   }
 
   // Bundleable implementation.
 
   @Documented
   @Retention(RetentionPolicy.SOURCE)
-  @IntDef({
-    FIELD_FORMATS,
-  })
+  @IntDef({FIELD_FORMATS, FIELD_ID})
   private @interface FieldNumber {}
 
   private static final int FIELD_FORMATS = 0;
+  private static final int FIELD_ID = 1;
 
   @Override
   public Bundle toBundle() {
     Bundle bundle = new Bundle();
     bundle.putParcelableArrayList(
         keyForField(FIELD_FORMATS), BundleableUtil.toBundleArrayList(Lists.newArrayList(formats)));
+    bundle.putString(keyForField(FIELD_ID), id);
     return bundle;
   }
 
@@ -135,7 +161,8 @@ public final class TrackGroup implements Bundleable {
                 Format.CREATOR,
                 bundle.getParcelableArrayList(keyForField(FIELD_FORMATS)),
                 ImmutableList.of());
-        return new TrackGroup(formats.toArray(new Format[0]));
+        String id = bundle.getString(keyForField(FIELD_ID), /* defaultValue= */ "");
+        return new TrackGroup(id, formats.toArray(new Format[0]));
       };
 
   private static String keyForField(@FieldNumber int field) {

library/common/src/test/java/com/google/android/exoplayer2/source/TrackGroupTest.java

@@ -32,8 +32,9 @@ public final class TrackGroupTest {
     Format.Builder formatBuilder = new Format.Builder();
     Format format1 = formatBuilder.setSampleMimeType(MimeTypes.VIDEO_H264).build();
     Format format2 = formatBuilder.setSampleMimeType(MimeTypes.AUDIO_AAC).build();
+    String id = "abc";
 
-    TrackGroup trackGroupToBundle = new TrackGroup(format1, format2);
+    TrackGroup trackGroupToBundle = new TrackGroup(id, format1, format2);
 
     TrackGroup trackGroupFromBundle = TrackGroup.CREATOR.fromBundle(trackGroupToBundle.toBundle());
 

library/core/src/main/java/com/google/android/exoplayer2/source/MergingMediaPeriod.java

@@ -15,19 +15,25 @@
  */
 package com.google.android.exoplayer2.source;
 
+import static com.google.android.exoplayer2.util.Assertions.checkNotNull;
 import static java.lang.Math.max;
 
 import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.C;
+import com.google.android.exoplayer2.Format;
 import com.google.android.exoplayer2.FormatHolder;
 import com.google.android.exoplayer2.SeekParameters;
 import com.google.android.exoplayer2.decoder.DecoderInputBuffer;
 import com.google.android.exoplayer2.offline.StreamKey;
+import com.google.android.exoplayer2.source.chunk.Chunk;
+import com.google.android.exoplayer2.source.chunk.MediaChunk;
+import com.google.android.exoplayer2.source.chunk.MediaChunkIterator;
 import com.google.android.exoplayer2.trackselection.ExoTrackSelection;
 import com.google.android.exoplayer2.util.Assertions;
 import java.io.IOException;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.HashMap;
 import java.util.IdentityHashMap;
 import java.util.List;
 import org.checkerframework.checker.nullness.compatqual.NullableType;
@@ -40,6 +46,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
   private final IdentityHashMap<SampleStream, Integer> streamPeriodIndices;
   private final CompositeSequenceableLoaderFactory compositeSequenceableLoaderFactory;
   private final ArrayList<MediaPeriod> childrenPendingPreparation;
+  private final HashMap<TrackGroup, TrackGroup> childTrackGroupByMergedTrackGroup;
 
   @Nullable private Callback callback;
   @Nullable private TrackGroupArray trackGroups;
@@ -53,6 +60,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     this.compositeSequenceableLoaderFactory = compositeSequenceableLoaderFactory;
     this.periods = periods;
     childrenPendingPreparation = new ArrayList<>();
+    childTrackGroupByMergedTrackGroup = new HashMap<>();
     compositeSequenceableLoader =
         compositeSequenceableLoaderFactory.createCompositeSequenceableLoader();
     streamPeriodIndices = new IdentityHashMap<>();
@@ -111,9 +119,11 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       streamChildIndices[i] = streamChildIndex == null ? C.INDEX_UNSET : streamChildIndex;
       selectionChildIndices[i] = C.INDEX_UNSET;
       if (selections[i] != null) {
-        TrackGroup trackGroup = selections[i].getTrackGroup();
+        TrackGroup mergedTrackGroup = selections[i].getTrackGroup();
+        TrackGroup childTrackGroup =
+            checkNotNull(childTrackGroupByMergedTrackGroup.get(mergedTrackGroup));
         for (int j = 0; j < periods.length; j++) {
-          if (periods[j].getTrackGroups().indexOf(trackGroup) != C.INDEX_UNSET) {
+          if (periods[j].getTrackGroups().indexOf(childTrackGroup) != C.INDEX_UNSET) {
             selectionChildIndices[i] = j;
             break;
           }
@@ -129,7 +139,15 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     for (int i = 0; i < periods.length; i++) {
       for (int j = 0; j < selections.length; j++) {
         childStreams[j] = streamChildIndices[j] == i ? streams[j] : null;
-        childSelections[j] = selectionChildIndices[j] == i ? selections[j] : null;
+        if (selectionChildIndices[j] == i) {
+          ExoTrackSelection mergedTrackSelection = checkNotNull(selections[j]);
+          TrackGroup mergedTrackGroup = mergedTrackSelection.getTrackGroup();
+          TrackGroup childTrackGroup =
+              checkNotNull(childTrackGroupByMergedTrackGroup.get(mergedTrackGroup));
+          childSelections[j] = new ForwardingTrackSelection(mergedTrackSelection, childTrackGroup);
+        } else {
+          childSelections[j] = null;
+        }
       }
       long selectPositionUs =
           periods[i].selectTracks(
@@ -268,11 +286,14 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     }
     TrackGroup[] trackGroupArray = new TrackGroup[totalTrackGroupCount];
     int trackGroupIndex = 0;
-    for (MediaPeriod period : periods) {
-      TrackGroupArray periodTrackGroups = period.getTrackGroups();
+    for (int i = 0; i < periods.length; i++) {
+      TrackGroupArray periodTrackGroups = periods[i].getTrackGroups();
       int periodTrackGroupCount = periodTrackGroups.length;
       for (int j = 0; j < periodTrackGroupCount; j++) {
-        trackGroupArray[trackGroupIndex++] = periodTrackGroups.get(j);
+        TrackGroup childTrackGroup = periodTrackGroups.get(j);
+        TrackGroup mergedTrackGroup = childTrackGroup.copyWithId(i + ":" + childTrackGroup.id);
+        childTrackGroupByMergedTrackGroup.put(mergedTrackGroup, childTrackGroup);
+        trackGroupArray[trackGroupIndex++] = mergedTrackGroup;
       }
     }
     trackGroups = new TrackGroupArray(trackGroupArray);
@@ -453,4 +474,138 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
       return sampleStream.skipData(positionUs - timeOffsetUs);
     }
   }
+
+  private static final class ForwardingTrackSelection implements ExoTrackSelection {
+
+    private final ExoTrackSelection trackSelection;
+    private final TrackGroup trackGroup;
+
+    public ForwardingTrackSelection(ExoTrackSelection trackSelection, TrackGroup trackGroup) {
+      this.trackSelection = trackSelection;
+      this.trackGroup = trackGroup;
+    }
+
+    @Override
+    public @Type int getType() {
+      return trackSelection.getType();
+    }
+
+    @Override
+    public TrackGroup getTrackGroup() {
+      return trackGroup;
+    }
+
+    @Override
+    public int length() {
+      return trackSelection.length();
+    }
+
+    @Override
+    public Format getFormat(int index) {
+      return trackSelection.getFormat(index);
+    }
+
+    @Override
+    public int getIndexInTrackGroup(int index) {
+      return trackSelection.getIndexInTrackGroup(index);
+    }
+
+    @Override
+    public int indexOf(Format format) {
+      return trackSelection.indexOf(format);
+    }
+
+    @Override
+    public int indexOf(int indexInTrackGroup) {
+      return trackSelection.indexOf(indexInTrackGroup);
+    }
+
+    @Override
+    public void enable() {
+      trackSelection.enable();
+    }
+
+    @Override
+    public void disable() {
+      trackSelection.disable();
+    }
+
+    @Override
+    public Format getSelectedFormat() {
+      return trackSelection.getSelectedFormat();
+    }
+
+    @Override
+    public int getSelectedIndexInTrackGroup() {
+      return trackSelection.getSelectedIndexInTrackGroup();
+    }
+
+    @Override
+    public int getSelectedIndex() {
+      return trackSelection.getSelectedIndex();
+    }
+
+    @Override
+    public int getSelectionReason() {
+      return trackSelection.getSelectionReason();
+    }
+
+    @Nullable
+    @Override
+    public Object getSelectionData() {
+      return trackSelection.getSelectionData();
+    }
+
+    @Override
+    public void onPlaybackSpeed(float playbackSpeed) {
+      trackSelection.onPlaybackSpeed(playbackSpeed);
+    }
+
+    @Override
+    public void onDiscontinuity() {
+      trackSelection.onDiscontinuity();
+    }
+
+    @Override
+    public void onRebuffer() {
+      trackSelection.onRebuffer();
+    }
+
+    @Override
+    public void onPlayWhenReadyChanged(boolean playWhenReady) {
+      trackSelection.onPlayWhenReadyChanged(playWhenReady);
+    }
+
+    @Override
+    public void updateSelectedTrack(
+        long playbackPositionUs,
+        long bufferedDurationUs,
+        long availableDurationUs,
+        List<? extends MediaChunk> queue,
+        MediaChunkIterator[] mediaChunkIterators) {
+      trackSelection.updateSelectedTrack(
+          playbackPositionUs, bufferedDurationUs, availableDurationUs, queue, mediaChunkIterators);
+    }
+
+    @Override
+    public int evaluateQueueSize(long playbackPositionUs, List<? extends MediaChunk> queue) {
+      return trackSelection.evaluateQueueSize(playbackPositionUs, queue);
+    }
+
+    @Override
+    public boolean shouldCancelChunkLoad(
+        long playbackPositionUs, Chunk loadingChunk, List<? extends MediaChunk> queue) {
+      return trackSelection.shouldCancelChunkLoad(playbackPositionUs, loadingChunk, queue);
+    }
+
+    @Override
+    public boolean blacklist(int index, long exclusionDurationMs) {
+      return trackSelection.blacklist(index, exclusionDurationMs);
+    }
+
+    @Override
+    public boolean isBlacklisted(int index, long nowMs) {
+      return trackSelection.isBlacklisted(index, nowMs);
+    }
+  }
 }

library/core/src/main/java/com/google/android/exoplayer2/source/ProgressiveMediaPeriod.java

@@ -781,7 +781,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
         }
       }
       trackFormat = trackFormat.copyWithCryptoType(drmSessionManager.getCryptoType(trackFormat));
-      trackArray[i] = new TrackGroup(trackFormat);
+      trackArray[i] = new TrackGroup(/* id= */ Integer.toString(i), trackFormat);
     }
     trackState = new TrackState(new TrackGroupArray(trackArray), trackIsAudioVideoFlags);
     prepared = true;

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

@@ -273,7 +273,7 @@ public class EventLogger implements AnalyticsListener {
                   trackGroup.length,
                   mappedTrackInfo.getAdaptiveSupport(
                       rendererIndex, groupIndex, /* includeCapabilitiesExceededTracks= */ false));
-          logd("    Group:" + groupIndex + ", adaptive_supported=" + adaptiveSupport + " [");
+          logd("    Group:" + trackGroup.id + ", adaptive_supported=" + adaptiveSupport + " [");
           for (int trackIndex = 0; trackIndex < trackGroup.length; trackIndex++) {
             String status = getTrackStatusString(trackSelection, trackGroup, trackIndex);
             String formatSupport =

library/dash/src/main/java/com/google/android/exoplayer2/source/dash/DashMediaPeriod.java

@@ -675,13 +675,17 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
       }
 
       AdaptationSet firstAdaptationSet = adaptationSets.get(adaptationSetIndices[0]);
+      String trackGroupId =
+          firstAdaptationSet.id != AdaptationSet.ID_UNSET
+              ? Integer.toString(firstAdaptationSet.id)
+              : ("unset:" + i);
       int primaryTrackGroupIndex = trackGroupCount++;
       int eventMessageTrackGroupIndex =
           primaryGroupHasEventMessageTrackFlags[i] ? trackGroupCount++ : C.INDEX_UNSET;
       int closedCaptionTrackGroupIndex =
           primaryGroupClosedCaptionTrackFormats[i].length != 0 ? trackGroupCount++ : C.INDEX_UNSET;
 
-      trackGroups[primaryTrackGroupIndex] = new TrackGroup(formats);
+      trackGroups[primaryTrackGroupIndex] = new TrackGroup(trackGroupId, formats);
       trackGroupInfos[primaryTrackGroupIndex] =
           TrackGroupInfo.primaryTrack(
               firstAdaptationSet.type,
@@ -690,18 +694,20 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
               eventMessageTrackGroupIndex,
               closedCaptionTrackGroupIndex);
       if (eventMessageTrackGroupIndex != C.INDEX_UNSET) {
+        String eventMessageTrackGroupId = trackGroupId + ":emsg";
         Format format =
             new Format.Builder()
-                .setId(firstAdaptationSet.id + ":emsg")
+                .setId(eventMessageTrackGroupId)
                 .setSampleMimeType(MimeTypes.APPLICATION_EMSG)
                 .build();
-        trackGroups[eventMessageTrackGroupIndex] = new TrackGroup(format);
+        trackGroups[eventMessageTrackGroupIndex] = new TrackGroup(eventMessageTrackGroupId, format);
         trackGroupInfos[eventMessageTrackGroupIndex] =
             TrackGroupInfo.embeddedEmsgTrack(adaptationSetIndices, primaryTrackGroupIndex);
       }
       if (closedCaptionTrackGroupIndex != C.INDEX_UNSET) {
+        String closedCaptionTrackGroupId = trackGroupId + ":cc";
         trackGroups[closedCaptionTrackGroupIndex] =
-            new TrackGroup(primaryGroupClosedCaptionTrackFormats[i]);
+            new TrackGroup(closedCaptionTrackGroupId, primaryGroupClosedCaptionTrackFormats[i]);
         trackGroupInfos[closedCaptionTrackGroupIndex] =
             TrackGroupInfo.embeddedClosedCaptionTrack(adaptationSetIndices, primaryTrackGroupIndex);
       }
@@ -721,7 +727,8 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
               .setId(eventStream.id())
               .setSampleMimeType(MimeTypes.APPLICATION_EMSG)
               .build();
-      trackGroups[existingTrackGroupCount] = new TrackGroup(format);
+      String uniqueTrackGroupId = eventStream.id() + ":" + i;
+      trackGroups[existingTrackGroupCount] = new TrackGroup(uniqueTrackGroupId, format);
       trackGroupInfos[existingTrackGroupCount++] = TrackGroupInfo.mpdEventTrack(i);
     }
   }

library/dash/src/test/java/com/google/android/exoplayer2/source/dash/DashMediaPeriodTest.java

@@ -80,12 +80,13 @@ public final class DashMediaPeriodTest {
     TrackGroupArray expectedTrackGroups =
         new TrackGroupArray(
             new TrackGroup(
+                /* id= */ "0",
                 adaptationSets.get(0).representations.get(0).format,
                 adaptationSets.get(0).representations.get(1).format,
                 adaptationSets.get(2).representations.get(0).format,
                 adaptationSets.get(2).representations.get(1).format,
                 adaptationSets.get(3).representations.get(0).format),
-            new TrackGroup(adaptationSets.get(1).representations.get(0).format));
+            new TrackGroup(/* id= */ "3", adaptationSets.get(1).representations.get(0).format));
 
     MediaPeriodAsserts.assertTrackGroups(dashMediaPeriod, expectedTrackGroups);
   }
@@ -101,10 +102,12 @@ public final class DashMediaPeriodTest {
     TrackGroupArray expectedTrackGroups =
         new TrackGroupArray(
             new TrackGroup(
+                /* id= */ "0",
                 adaptationSets.get(0).representations.get(0).format,
                 adaptationSets.get(0).representations.get(1).format,
                 adaptationSets.get(1).representations.get(0).format),
             new TrackGroup(
+                /* id= */ "2",
                 adaptationSets.get(2).representations.get(0).format,
                 adaptationSets.get(2).representations.get(1).format,
                 adaptationSets.get(3).representations.get(0).format));
@@ -124,6 +127,7 @@ public final class DashMediaPeriodTest {
     TrackGroupArray expectedTrackGroups =
         new TrackGroupArray(
             new TrackGroup(
+                /* id= */ "0",
                 adaptationSets.get(0).representations.get(0).format,
                 adaptationSets.get(0).representations.get(1).format,
                 adaptationSets.get(1).representations.get(0).format,
@@ -147,9 +151,11 @@ public final class DashMediaPeriodTest {
     TrackGroupArray expectedTrackGroups =
         new TrackGroupArray(
             new TrackGroup(
+                /* id= */ "123",
                 adaptationSets.get(0).representations.get(0).format,
                 adaptationSets.get(0).representations.get(1).format),
             new TrackGroup(
+                /* id= */ "123:cc",
                 cea608FormatBuilder
                     .setId("123:cea608:1")
                     .setLanguage("eng")
@@ -177,9 +183,11 @@ public final class DashMediaPeriodTest {
     TrackGroupArray expectedTrackGroups =
         new TrackGroupArray(
             new TrackGroup(
+                /* id= */ "123",
                 adaptationSets.get(0).representations.get(0).format,
                 adaptationSets.get(0).representations.get(1).format),
             new TrackGroup(
+                /* id= */ "123:cc",
                 cea608FormatBuilder
                     .setId("123:cea708:1")
                     .setLanguage("eng")

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/HlsMediaPeriod.java

@@ -526,8 +526,10 @@ public final class HlsMediaPeriod
     // Subtitle stream wrappers. We can always use master playlist information to prepare these.
     for (int i = 0; i < subtitleRenditions.size(); i++) {
       Rendition subtitleRendition = subtitleRenditions.get(i);
+      String sampleStreamWrapperUid = "subtitle:" + i + ":" + subtitleRendition.name;
       HlsSampleStreamWrapper sampleStreamWrapper =
           buildSampleStreamWrapper(
+              sampleStreamWrapperUid,
               C.TRACK_TYPE_TEXT,
               new Uri[] {subtitleRendition.url},
               new Format[] {subtitleRendition.format},
@@ -538,7 +540,7 @@ public final class HlsMediaPeriod
       manifestUrlIndicesPerWrapper.add(new int[] {i});
       sampleStreamWrappers.add(sampleStreamWrapper);
       sampleStreamWrapper.prepareWithMasterPlaylistInfo(
-          new TrackGroup[] {new TrackGroup(subtitleRendition.format)},
+          new TrackGroup[] {new TrackGroup(sampleStreamWrapperUid, subtitleRendition.format)},
           /* primaryTrackGroupIndex= */ 0);
     }
 
@@ -644,8 +646,10 @@ public final class HlsMediaPeriod
         !useVideoVariantsOnly && numberOfAudioCodecs > 0
             ? C.TRACK_TYPE_AUDIO
             : C.TRACK_TYPE_DEFAULT;
+    String sampleStreamWrapperUid = "main";
     HlsSampleStreamWrapper sampleStreamWrapper =
         buildSampleStreamWrapper(
+            sampleStreamWrapperUid,
             trackType,
             selectedPlaylistUrls,
             selectedPlaylistFormats,
@@ -662,12 +666,13 @@ public final class HlsMediaPeriod
         for (int i = 0; i < videoFormats.length; i++) {
           videoFormats[i] = deriveVideoFormat(selectedPlaylistFormats[i]);
         }
-        muxedTrackGroups.add(new TrackGroup(videoFormats));
+        muxedTrackGroups.add(new TrackGroup(sampleStreamWrapperUid, videoFormats));
 
         if (numberOfAudioCodecs > 0
             && (masterPlaylist.muxedAudioFormat != null || masterPlaylist.audios.isEmpty())) {
           muxedTrackGroups.add(
               new TrackGroup(
+                  /* id= */ sampleStreamWrapperUid + ":audio",
                   deriveAudioFormat(
                       selectedPlaylistFormats[0],
                       masterPlaylist.muxedAudioFormat,
@@ -676,7 +681,8 @@ public final class HlsMediaPeriod
         List<Format> ccFormats = masterPlaylist.muxedCaptionFormats;
         if (ccFormats != null) {
           for (int i = 0; i < ccFormats.size(); i++) {
-            muxedTrackGroups.add(new TrackGroup(ccFormats.get(i)));
+            String ccId = sampleStreamWrapperUid + ":cc:" + i;
+            muxedTrackGroups.add(new TrackGroup(ccId, ccFormats.get(i)));
           }
         }
       } else /* numberOfAudioCodecs > 0 */ {
@@ -689,11 +695,12 @@ public final class HlsMediaPeriod
                   masterPlaylist.muxedAudioFormat,
                   /* isPrimaryTrackInVariant= */ true);
         }
-        muxedTrackGroups.add(new TrackGroup(audioFormats));
+        muxedTrackGroups.add(new TrackGroup(sampleStreamWrapperUid, audioFormats));
       }
 
       TrackGroup id3TrackGroup =
           new TrackGroup(
+              /* id= */ sampleStreamWrapperUid + ":id3",
               new Format.Builder()
                   .setId("ID3")
                   .setSampleMimeType(MimeTypes.APPLICATION_ID3)
@@ -745,8 +752,10 @@ public final class HlsMediaPeriod
         }
       }
 
+      String sampleStreamWrapperUid = "audio:" + name;
       HlsSampleStreamWrapper sampleStreamWrapper =
           buildSampleStreamWrapper(
+              sampleStreamWrapperUid,
               C.TRACK_TYPE_AUDIO,
               scratchPlaylistUrls.toArray(Util.castNonNullTypeArray(new Uri[0])),
               scratchPlaylistFormats.toArray(new Format[0]),
@@ -760,12 +769,14 @@ public final class HlsMediaPeriod
       if (allowChunklessPreparation && codecStringsAllowChunklessPreparation) {
         Format[] renditionFormats = scratchPlaylistFormats.toArray(new Format[0]);
         sampleStreamWrapper.prepareWithMasterPlaylistInfo(
-            new TrackGroup[] {new TrackGroup(renditionFormats)}, /* primaryTrackGroupIndex= */ 0);
+            new TrackGroup[] {new TrackGroup(sampleStreamWrapperUid, renditionFormats)},
+            /* primaryTrackGroupIndex= */ 0);
       }
     }
   }
 
   private HlsSampleStreamWrapper buildSampleStreamWrapper(
+      String uid,
       @C.TrackType int trackType,
       Uri[] playlistUrls,
       Format[] playlistFormats,
@@ -785,6 +796,7 @@ public final class HlsMediaPeriod
             muxedCaptionFormats,
             playerId);
     return new HlsSampleStreamWrapper(
+        uid,
         trackType,
         /* callback= */ this,
         defaultChunkSource,

library/hls/src/main/java/com/google/android/exoplayer2/source/hls/HlsSampleStreamWrapper.java

@@ -125,6 +125,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
           new HashSet<>(
               Arrays.asList(C.TRACK_TYPE_AUDIO, C.TRACK_TYPE_VIDEO, C.TRACK_TYPE_METADATA)));
 
+  private final String uid;
   private final @C.TrackType int trackType;
   private final Callback callback;
   private final HlsChunkSource chunkSource;
@@ -185,6 +186,8 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
   @Nullable private HlsMediaChunk sourceChunk;
 
   /**
+   * @param uid A identifier for this sample stream wrapper. Identifiers must be unique within the
+   *     period.
    * @param trackType The {@link C.TrackType track type}.
    * @param callback A callback for the wrapper.
    * @param chunkSource A {@link HlsChunkSource} from which chunks to load are obtained.
@@ -203,6 +206,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
    *     events.
    */
   public HlsSampleStreamWrapper(
+      String uid,
       @C.TrackType int trackType,
       Callback callback,
       HlsChunkSource chunkSource,
@@ -215,6 +219,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
       LoadErrorHandlingPolicy loadErrorHandlingPolicy,
       MediaSourceEventListener.EventDispatcher mediaSourceEventDispatcher,
       @HlsMediaSource.MetadataType int metadataType) {
+    this.uid = uid;
     this.trackType = trackType;
     this.callback = callback;
     this.chunkSource = chunkSource;
@@ -1416,7 +1421,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
                   ? sampleFormat.withManifestFormatInfo(playlistFormat)
                   : deriveFormat(playlistFormat, sampleFormat, /* propagateBitrates= */ true);
         }
-        trackGroups[i] = new TrackGroup(formats);
+        trackGroups[i] = new TrackGroup(uid, formats);
         primaryTrackGroupIndex = i;
       } else {
         @Nullable
@@ -1425,8 +1430,10 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
                     && MimeTypes.isAudio(sampleFormat.sampleMimeType)
                 ? muxedAudioFormat
                 : null;
+        String muxedTrackGroupId = uid + ":muxed:" + (i < primaryExtractorTrackIndex ? i : i - 1);
         trackGroups[i] =
             new TrackGroup(
+                muxedTrackGroupId,
                 deriveFormat(playlistFormat, sampleFormat, /* propagateBitrates= */ false));
       }
     }
@@ -1443,7 +1450,7 @@ import org.checkerframework.checker.nullness.qual.RequiresNonNull;
         Format format = trackGroup.getFormat(j);
         exposedFormats[j] = format.copyWithCryptoType(drmSessionManager.getCryptoType(format));
       }
-      trackGroups[i] = new TrackGroup(exposedFormats);
+      trackGroups[i] = new TrackGroup(trackGroup.id, exposedFormats);
     }
     return new TrackGroupArray(trackGroups);
   }

library/rtsp/src/main/java/com/google/android/exoplayer2/source/rtsp/RtspMediaPeriod.java

@@ -400,7 +400,9 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
     SampleQueue sampleQueue;
     for (int i = 0; i < rtspLoaderWrappers.size(); i++) {
       sampleQueue = rtspLoaderWrappers.get(i).sampleQueue;
-      listBuilder.add(new TrackGroup(checkNotNull(sampleQueue.getUpstreamFormat())));
+      listBuilder.add(
+          new TrackGroup(
+              /* id= */ Integer.toString(i), checkNotNull(sampleQueue.getUpstreamFormat())));
     }
     return listBuilder.build();
   }

library/smoothstreaming/src/main/java/com/google/android/exoplayer2/source/smoothstreaming/SsMediaPeriod.java

@@ -263,7 +263,7 @@ import org.checkerframework.checker.nullness.compatqual.NullableType;
         exposedFormats[j] =
             manifestFormat.copyWithCryptoType(drmSessionManager.getCryptoType(manifestFormat));
       }
-      trackGroups[i] = new TrackGroup(exposedFormats);
+      trackGroups[i] = new TrackGroup(/* id= */ Integer.toString(i), exposedFormats);
     }
     return new TrackGroupArray(trackGroups);
   }