Bugfix: Allow discontinuity on selectTracks

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=129987709

library/src/main/java/com/google/android/exoplayer2/ExoPlayerImplInternal.java

@@ -727,8 +727,13 @@ import java.io.IOException;
 
       // Update streams for the new selection, recreating all streams if reading ahead.
       boolean recreateStreams = readingPeriod != playingPeriod;
-      boolean[] streamResetFlags = playingPeriod.updatePeriodTrackSelection(playbackInfo.positionUs,
+      boolean[] streamResetFlags = new boolean[renderers.length];
-          loadControl, recreateStreams);
+      long positionUs = playingPeriod.updatePeriodTrackSelection(playbackInfo.positionUs,
+          loadControl, recreateStreams, streamResetFlags);
+      if (positionUs != playbackInfo.positionUs) {
+        playbackInfo.positionUs = positionUs;
+        resetInternalPosition(positionUs);
+      }
 
       int enabledRendererCount = 0;
       boolean[] rendererWasEnabledFlags = new boolean[renderers.length];
@@ -1156,12 +1161,12 @@ import java.io.IOException;
 
     public final MediaPeriod mediaPeriod;
     public final Object id;
-    public final long startPositionUs;
 
     public final SampleStream[] sampleStreams;
     public final boolean[] mayRetainStreamFlags;
 
     public int index;
+    public long startPositionUs;
     public boolean isLast;
     public boolean prepared;
     public boolean hasEnabledTracks;
@@ -1205,7 +1210,7 @@ import java.io.IOException;
         throws ExoPlaybackException {
       prepared = true;
       selectTracks();
-      updatePeriodTrackSelection(positionUs, loadControl, false);
+      startPositionUs = updatePeriodTrackSelection(positionUs, loadControl, false);
     }
 
     public boolean selectTracks() throws ExoPlaybackException {
@@ -1220,19 +1225,23 @@ import java.io.IOException;
       return true;
     }
 
-    public boolean[] updatePeriodTrackSelection(long positionUs, LoadControl loadControl,
+    public long updatePeriodTrackSelection(long positionUs, LoadControl loadControl,
         boolean forceRecreateStreams) throws ExoPlaybackException {
+      return updatePeriodTrackSelection(positionUs, loadControl, forceRecreateStreams,
+          new boolean[renderers.length]);
+    }
+
+    public long updatePeriodTrackSelection(long positionUs, LoadControl loadControl,
+        boolean forceRecreateStreams, boolean[] streamResetFlags) throws ExoPlaybackException {
       for (int i = 0; i < trackSelections.length; i++) {
         mayRetainStreamFlags[i] = !forceRecreateStreams
             && Util.areEqual(periodTrackSelections == null ? null : periodTrackSelections.get(i),
             trackSelections.get(i));
       }
 
-      boolean[] streamResetFlags = new boolean[renderers.length];
-
       // Disable streams on the period and get new streams for updated/newly-enabled tracks.
-      mediaPeriod.selectTracks(trackSelections.getAll(), mayRetainStreamFlags, sampleStreams,
+      positionUs = mediaPeriod.selectTracks(trackSelections.getAll(), mayRetainStreamFlags,
-          streamResetFlags, positionUs);
+          sampleStreams, streamResetFlags, positionUs);
       periodTrackSelections = trackSelections;
 
       hasEnabledTracks = false;
@@ -1245,8 +1254,7 @@ import java.io.IOException;
 
       // The track selection has changed.
       loadControl.onTrackSelections(renderers, mediaPeriod.getTrackGroups(), trackSelections);
-
+      return positionUs;
-      return streamResetFlags;
     }
 
     public void release() {

library/src/main/java/com/google/android/exoplayer2/source/ExtractorMediaSource.java

@@ -239,7 +239,7 @@ public final class ExtractorMediaSource implements MediaPeriod, MediaSource,
   }
 
   @Override
-  public void selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
+  public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
       SampleStream[] streams, boolean[] streamResetFlags, long positionUs) {
     Assertions.checkState(prepared);
     // Disable old tracks.
@@ -284,7 +284,7 @@ public final class ExtractorMediaSource implements MediaPeriod, MediaSource,
         loader.cancelLoading();
       }
     } else if (seenFirstTrackSelection ? selectedNewTracks : positionUs != 0) {
-      seekToUs(positionUs);
+      positionUs = seekToUs(positionUs);
       // We'll need to reset renderers consuming from all streams due to the seek.
       for (int i = 0; i < streams.length; i++) {
         if (streams[i] != null) {
@@ -293,6 +293,7 @@ public final class ExtractorMediaSource implements MediaPeriod, MediaSource,
       }
     }
     seenFirstTrackSelection = true;
+    return positionUs;
   }
 
   @Override

library/src/main/java/com/google/android/exoplayer2/source/MediaPeriod.java

@@ -110,8 +110,9 @@ public interface MediaPeriod extends SequenceableLoader {
    * @param streamResetFlags Will be updated to indicate new sample streams, and sample streams that
    *     have been retained but with the requirement that the consuming renderer be reset.
    * @param positionUs The current playback position in microseconds.
+   * @return The actual position at which the tracks were enabled, in microseconds.
    */
-  void selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
+  long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
       SampleStream[] streams, boolean[] streamResetFlags, long positionUs);
 
   /**

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

@@ -70,7 +70,7 @@ public final class MergingMediaPeriod implements MediaPeriod, MediaPeriod.Callba
   }
 
   @Override
-  public void selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
+  public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
       SampleStream[] streams, boolean[] streamResetFlags, long positionUs) {
     // Map each selection and stream onto a child period index.
     int[] streamChildIndices = new int[selections.length];
@@ -98,8 +98,13 @@ public final class MergingMediaPeriod implements MediaPeriod, MediaPeriod.Callba
         childStreams[j] = streamChildIndices[j] == i ? streams[j] : null;
         childSelections[j] = selectionChildIndices[j] == i ? selections[j] : null;
       }
-      periods[i].selectTracks(childSelections, mayRetainStreamFlags, childStreams, streamResetFlags,
+      long selectPositionUs = periods[i].selectTracks(childSelections, mayRetainStreamFlags,
-          positionUs);
+          childStreams, streamResetFlags, positionUs);
+      if (i == 0) {
+        positionUs = selectPositionUs;
+      } else if (selectPositionUs != positionUs) {
+        throw new IllegalStateException("Children enabled at different positions");
+      }
       boolean periodEnabled = false;
       for (int j = 0; j < selections.length; j++) {
         if (selectionChildIndices[j] == i) {
@@ -118,6 +123,7 @@ public final class MergingMediaPeriod implements MediaPeriod, MediaPeriod.Callba
     enabledPeriods = new MediaPeriod[enabledPeriodsList.size()];
     enabledPeriodsList.toArray(enabledPeriods);
     sequenceableLoader = new CompositeSequenceableLoader(enabledPeriods);
+    return positionUs;
   }
 
   @Override

library/src/main/java/com/google/android/exoplayer2/source/SingleSampleMediaSource.java

@@ -158,7 +158,7 @@ public final class SingleSampleMediaSource implements MediaPeriod, MediaSource,
   }
 
   @Override
-  public void selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
+  public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
       SampleStream[] streams, boolean[] streamResetFlags, long positionUs) {
     for (int i = 0; i < selections.length; i++) {
       if (streams[i] != null && (selections[i] == null || !mayRetainStreamFlags[i])) {
@@ -172,6 +172,7 @@ public final class SingleSampleMediaSource implements MediaPeriod, MediaSource,
         streamResetFlags[i] = true;
       }
     }
+    return positionUs;
   }
 
   @Override

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

@@ -118,7 +118,7 @@ import java.util.List;
   }
 
   @Override
-  public void selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
+  public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
       SampleStream[] streams, boolean[] streamResetFlags, long positionUs) {
     ArrayList<ChunkSampleStream<DashChunkSource>> sampleStreamsList = new ArrayList<>();
     for (int i = 0; i < selections.length; i++) {
@@ -142,6 +142,7 @@ import java.util.List;
     sampleStreams = newSampleStreamArray(sampleStreamsList.size());
     sampleStreamsList.toArray(sampleStreams);
     sequenceableLoader = new CompositeSequenceableLoader(sampleStreams);
+    return positionUs;
   }
 
   @Override

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

@@ -171,7 +171,7 @@ public final class HlsMediaSource implements MediaPeriod, MediaSource,
   }
 
   @Override
-  public void selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
+  public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
       SampleStream[] streams, boolean[] streamResetFlags, long positionUs) {
     // Map each selection and stream onto a child period index.
     int[] streamChildIndices = new int[selections.length];
@@ -231,6 +231,7 @@ public final class HlsMediaSource implements MediaPeriod, MediaSource,
       }
     }
     seenFirstTrackSelection = true;
+    return positionUs;
   }
 
   @Override

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

@@ -109,7 +109,7 @@ import java.util.ArrayList;
   }
 
   @Override
-  public void selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
+  public long selectTracks(TrackSelection[] selections, boolean[] mayRetainStreamFlags,
       SampleStream[] streams, boolean[] streamResetFlags, long positionUs) {
     ArrayList<ChunkSampleStream<SsChunkSource>> sampleStreamsList = new ArrayList<>();
     for (int i = 0; i < selections.length; i++) {
@@ -133,6 +133,7 @@ import java.util.ArrayList;
     sampleStreams = newSampleStreamArray(sampleStreamsList.size());
     sampleStreamsList.toArray(sampleStreams);
     sequenceableLoader = new CompositeSequenceableLoader(sampleStreams);
+    return positionUs;
   }
 
   @Override