Resend playback info update when skipping very short periods.

Skipping short periods in a while loop is conceptually a new operation
and thus we need to send out the updated playback info in between for
the listeners to receive multiple period transition discontinuities.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=179027334

library/core/src/androidTest/java/com/google/android/exoplayer2/ExoPlayerTest.java

@@ -35,6 +35,7 @@ import com.google.android.exoplayer2.testutil.FakeTrackSelection;
 import com.google.android.exoplayer2.testutil.FakeTrackSelector;
 import com.google.android.exoplayer2.testutil.FakeTrackSelector;
 import com.google.android.exoplayer2.upstream.Allocator;
 import com.google.android.exoplayer2.upstream.Allocator;
 import java.util.ArrayList;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import java.util.List;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.CountDownLatch;
 import junit.framework.TestCase;
 import junit.framework.TestCase;
@@ -111,6 +112,29 @@ public final class ExoPlayerTest extends TestCase {
     assertTrue(renderer.isEnded);
     assertTrue(renderer.isEnded);
   }
   }
 
 
+  /** Tests playback of periods with very short duration. */
+  public void testPlayShortDurationPeriods() throws Exception {
+    // TimelineWindowDefinition.DEFAULT_WINDOW_DURATION_US / 100 = 1000 us per period.
+    Timeline timeline =
+        new FakeTimeline(new TimelineWindowDefinition(/* periodCount= */ 100, /* id= */ 0));
+    FakeRenderer renderer = new FakeRenderer(Builder.VIDEO_FORMAT);
+    ExoPlayerTestRunner testRunner =
+        new ExoPlayerTestRunner.Builder()
+            .setTimeline(timeline)
+            .setRenderers(renderer)
+            .build()
+            .start()
+            .blockUntilEnded(TIMEOUT_MS);
+    int[] expectedReasons = new int[99];
+    Arrays.fill(expectedReasons, Player.DISCONTINUITY_REASON_PERIOD_TRANSITION);
+    testRunner.assertPositionDiscontinuityReasonsEqual(expectedReasons);
+    testRunner.assertTimelinesEqual(timeline);
+    testRunner.assertTimelineChangeReasonsEqual(Player.TIMELINE_CHANGE_REASON_PREPARED);
+    assertEquals(100, renderer.formatReadCount);
+    assertEquals(1, renderer.bufferReadCount);
+    assertTrue(renderer.isEnded);
+  }
+
   /**
   /**
    * Tests that the player does not unnecessarily reset renderers when playing a multi-period
    * Tests that the player does not unnecessarily reset renderers when playing a multi-period
    * source.
    * source.

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

@@ -1303,16 +1303,22 @@ import java.io.IOException;
     }
     }
 
 
     // Advance the playing period if necessary.
     // Advance the playing period if necessary.
+    boolean advancedPlayingPeriod = false;
     while (playWhenReady && playingPeriodHolder != readingPeriodHolder
     while (playWhenReady && playingPeriodHolder != readingPeriodHolder
         && rendererPositionUs >= playingPeriodHolder.next.rendererPositionOffsetUs) {
         && rendererPositionUs >= playingPeriodHolder.next.rendererPositionOffsetUs) {
       // All enabled renderers' streams have been read to the end, and the playback position reached
       // All enabled renderers' streams have been read to the end, and the playback position reached
       // the end of the playing period, so advance playback to the next period.
       // the end of the playing period, so advance playback to the next period.
+      if (advancedPlayingPeriod) {
+        // If we advance more than one period at a time, notify listeners after each update.
+        maybeNotifyPlaybackInfoChanged();
+      }
       playingPeriodHolder.release();
       playingPeriodHolder.release();
       setPlayingPeriodHolder(playingPeriodHolder.next);
       setPlayingPeriodHolder(playingPeriodHolder.next);
       playbackInfo = playbackInfo.fromNewPosition(playingPeriodHolder.info.id,
       playbackInfo = playbackInfo.fromNewPosition(playingPeriodHolder.info.id,
           playingPeriodHolder.info.startPositionUs, playingPeriodHolder.info.contentPositionUs);
           playingPeriodHolder.info.startPositionUs, playingPeriodHolder.info.contentPositionUs);
       playbackInfoUpdate.setPositionDiscontinuity(Player.DISCONTINUITY_REASON_PERIOD_TRANSITION);
       playbackInfoUpdate.setPositionDiscontinuity(Player.DISCONTINUITY_REASON_PERIOD_TRANSITION);
       updatePlaybackPositions();
       updatePlaybackPositions();
+      advancedPlayingPeriod = true;
     }
     }
 
 
     if (readingPeriodHolder.info.isFinal) {
     if (readingPeriodHolder.info.isFinal) {