Fix freezing playing multi-period DASH with EventStreams

EventSampleStream.readData required eventStreamUpdatable to be
false for END_OF_STREAM to be returned, but it was only being
set to false when the manifest became static. This change also
sets it to false if the period is not the last one in a dynamic
manifest. It also renames it the parameter to appendable, since
that's what it really represents. Events may still be removed
from the start of the EventStream as the period starts moving
out of the live window.

Issue: #4492

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=207517265

RELEASENOTES.md

@@ -99,8 +99,11 @@
     ([#4491](https://github.com/google/ExoPlayer/issues/4491)).
   * CEA-608: Improve handling of embedded styles
     ([#4321](https://github.com/google/ExoPlayer/issues/4321)).
-* DASH: Exclude text streams from duration calculations
-  ([#4029](https://github.com/google/ExoPlayer/issues/4029)).
+* DASH:
+  * Exclude text streams from duration calculations
+    ([#4029](https://github.com/google/ExoPlayer/issues/4029)).
+  * Fix freezing when playing multi-period manifests with `EventStream`s
+    ([#4492](https://github.com/google/ExoPlayer/issues/4492)).
 * DRM: Allow DrmInitData to carry a license server URL
   ([#3393](https://github.com/google/ExoPlayer/issues/3393)).
 * MPEG-TS: Fix bug preventing SCTE-35 cues from being output

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

@@ -149,7 +149,10 @@ import java.util.List;
     for (EventSampleStream eventSampleStream : eventSampleStreams) {
       for (EventStream eventStream : eventStreams) {
         if (eventStream.id().equals(eventSampleStream.eventStreamId())) {
-          eventSampleStream.updateEventStream(eventStream, manifest.dynamic);
+          int lastPeriodIndex = manifest.getPeriodCount() - 1;
+          eventSampleStream.updateEventStream(
+              eventStream,
+              /* eventStreamAppendable= */ manifest.dynamic && periodIndex == lastPeriodIndex);
           break;
         }
       }

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

@@ -36,37 +36,53 @@ import java.io.IOException;
   private final EventMessageEncoder eventMessageEncoder;
 
   private long[] eventTimesUs;
-  private boolean eventStreamUpdatable;
+  private boolean eventStreamAppendable;
   private EventStream eventStream;
 
   private boolean isFormatSentDownstream;
   private int currentIndex;
   private long pendingSeekPositionUs;
 
-  EventSampleStream(EventStream eventStream, Format upstreamFormat, boolean eventStreamUpdatable) {
+  public EventSampleStream(
+      EventStream eventStream, Format upstreamFormat, boolean eventStreamAppendable) {
     this.upstreamFormat = upstreamFormat;
     this.eventStream = eventStream;
     eventMessageEncoder = new EventMessageEncoder();
     pendingSeekPositionUs = C.TIME_UNSET;
     eventTimesUs = eventStream.presentationTimesUs;
-    updateEventStream(eventStream, eventStreamUpdatable);
+    updateEventStream(eventStream, eventStreamAppendable);
   }
 
-  void updateEventStream(EventStream eventStream, boolean eventStreamUpdatable) {
+  public String eventStreamId() {
+    return eventStream.id();
+  }
+
+  public void updateEventStream(EventStream eventStream, boolean eventStreamAppendable) {
     long lastReadPositionUs = currentIndex == 0 ? C.TIME_UNSET : eventTimesUs[currentIndex - 1];
 
-    this.eventStreamUpdatable = eventStreamUpdatable;
+    this.eventStreamAppendable = eventStreamAppendable;
     this.eventStream = eventStream;
     this.eventTimesUs = eventStream.presentationTimesUs;
     if (pendingSeekPositionUs != C.TIME_UNSET) {
       seekToUs(pendingSeekPositionUs);
     } else if (lastReadPositionUs != C.TIME_UNSET) {
-      currentIndex = Util.binarySearchCeil(eventTimesUs, lastReadPositionUs, false, false);
+      currentIndex =
+          Util.binarySearchCeil(
+              eventTimesUs, lastReadPositionUs, /* inclusive= */ false, /* stayInBounds= */ false);
     }
   }
 
-  String eventStreamId() {
-    return eventStream.id();
+  /**
+   * Seeks to the specified position in microseconds.
+   *
+   * @param positionUs The seek position in microseconds.
+   */
+  public void seekToUs(long positionUs) {
+    currentIndex =
+        Util.binarySearchCeil(
+            eventTimesUs, positionUs, /* inclusive= */ true, /* stayInBounds= */ false);
+    boolean isPendingSeek = eventStreamAppendable && currentIndex == eventTimesUs.length;
+    pendingSeekPositionUs = isPendingSeek ? positionUs : C.TIME_UNSET;
   }
 
   @Override
@@ -88,7 +104,7 @@ import java.io.IOException;
       return C.RESULT_FORMAT_READ;
     }
     if (currentIndex == eventTimesUs.length) {
-      if (!eventStreamUpdatable) {
+      if (!eventStreamAppendable) {
         buffer.setFlags(C.BUFFER_FLAG_END_OF_STREAM);
         return C.RESULT_BUFFER_READ;
       } else {
@@ -118,15 +134,4 @@ import java.io.IOException;
     return skipped;
   }
 
-  /**
-   * Seeks to the specified position in microseconds.
-   *
-   * @param positionUs The seek position in microseconds.
-   */
-  public void seekToUs(long positionUs) {
-    currentIndex = Util.binarySearchCeil(eventTimesUs, positionUs, true, false);
-    boolean isPendingSeek = eventStreamUpdatable && currentIndex == eventTimesUs.length;
-    pendingSeekPositionUs = isPendingSeek ? positionUs : C.TIME_UNSET;
-  }
-
 }