Match MergingMediaPeriod track selection by period index in id

MergingMediaPeriod creates its track groups with ids concatenating position in its periods array and the underlying child track group id. The ids can be used in selectTracks for matching to periods list.

Issue: google/ExoPlayer#10930
PiperOrigin-RevId: 505074653
(cherry picked from commit 542a1ef)

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

@@ -118,17 +118,13 @@ public long selectTracks(
     for (int i = 0; i < selections.length; i++) {
       Integer streamChildIndex = streams[i] == null ? null : streamPeriodIndices.get(streams[i]);
       streamChildIndices[i] = streamChildIndex == null ? C.INDEX_UNSET : streamChildIndex;
-      selectionChildIndices[i] = C.INDEX_UNSET;
       if (selections[i] != null) {
         TrackGroup mergedTrackGroup = selections[i].getTrackGroup();
-        TrackGroup childTrackGroup =
-            checkNotNull(childTrackGroupByMergedTrackGroup.get(mergedTrackGroup));
-        for (int j = 0; j < periods.length; j++) {
-          if (periods[j].getTrackGroups().indexOf(childTrackGroup) != C.INDEX_UNSET) {
-            selectionChildIndices[i] = j;
-            break;
-          }
-        }
+        // mergedTrackGroup.id is 'periods array index' + ":" + childTrackGroup.id
+        selectionChildIndices[i] =
+            Integer.parseInt(mergedTrackGroup.id.substring(0, mergedTrackGroup.id.indexOf(":")));
+      } else {
+        selectionChildIndices[i] = C.INDEX_UNSET;
       }
     }
     streamPeriodIndices.clear();

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

@@ -198,6 +198,39 @@ public void selectTracks_withSameArguments_forwardsEqualSelectionsToChildSources
     assertThat(firstSelectionChild2).isEqualTo(secondSelectionChild2);
   }
 
+  // https://github.com/google/ExoPlayer/issues/10930
+  @Test
+  public void selectTracks_withIdenticalFormats_selectsMatchingPeriod() throws Exception {
+    MergingMediaPeriod mergingMediaPeriod =
+        prepareMergingPeriod(
+            new MergingPeriodDefinition(
+                /* timeOffsetUs= */ 0, /* singleSampleTimeUs= */ 123_000, childFormat11),
+            new MergingPeriodDefinition(
+                /* timeOffsetUs= */ -3000, /* singleSampleTimeUs= */ 456_000, childFormat11));
+
+    ExoTrackSelection[] selectionArray = {
+      new FixedTrackSelection(mergingMediaPeriod.getTrackGroups().get(1), /* track= */ 0)
+    };
+
+    SampleStream[] streams = new SampleStream[1];
+    mergingMediaPeriod.selectTracks(
+        selectionArray,
+        /* mayRetainStreamFlags= */ new boolean[2],
+        streams,
+        /* streamResetFlags= */ new boolean[2],
+        /* positionUs= */ 0);
+    mergingMediaPeriod.continueLoading(/* positionUs= */ 0);
+
+    FormatHolder formatHolder = new FormatHolder();
+    DecoderInputBuffer inputBuffer =
+        new DecoderInputBuffer(DecoderInputBuffer.BUFFER_REPLACEMENT_MODE_NORMAL);
+    streams[0].readData(formatHolder, inputBuffer, FLAG_REQUIRE_FORMAT);
+
+    assertThat(streams[0].readData(formatHolder, inputBuffer, /* readFlags= */ 0))
+        .isEqualTo(C.RESULT_BUFFER_READ);
+    assertThat(inputBuffer.timeUs).isEqualTo(456_000 - 3000);
+  }
+
   private MergingMediaPeriod prepareMergingPeriod(MergingPeriodDefinition... definitions)
       throws Exception {
     MediaPeriod[] mediaPeriods = new MediaPeriod[definitions.length];