Fix playback of postrolls with multiple ads

At the point of starting to play a postroll, source info refreshes for future
postroll ads in the same ad group would cause a seek that incorrectly identified
the media period to play as the content media period. Fix the logic in
getAdGroupIndexForPositionUs to address this.

Also handle empty postroll ad breaks by resetting the expected ad group index
when we send content complete.

Issue: #4710
Issue: #4681

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=210071054

RELEASENOTES.md

@@ -118,6 +118,14 @@
 * Add option to show buffering view when playWhenReady is false
   ([#4304](https://github.com/google/ExoPlayer/issues/4304)).
 * Allow any `Drawable` to be used as `PlayerView` default artwork.
+* IMA:
+  * Refine the previous fix for empty ad groups to avoid discarding ad breaks
+    unnecessarily ([#4030](https://github.com/google/ExoPlayer/issues/4030)),
+    ([#4280](https://github.com/google/ExoPlayer/issues/4280)).
+  * Fix handling of empty postrolls
+    ([#4681](https://github.com/google/ExoPlayer/issues/4681).
+  * Fix handling of postrolls with multiple ads
+    ([#4710](https://github.com/google/ExoPlayer/issues/4710).
 
 ### 2.8.4 ###
 

extensions/ima/src/main/java/com/google/android/exoplayer2/ext/ima/ImaAdsLoader.java

@@ -864,8 +864,6 @@ public final class ImaAdsLoader
         && playWhenReady) {
       checkForContentComplete();
     } else if (imaAdState != IMA_AD_STATE_NONE && playbackState == Player.STATE_ENDED) {
-      // IMA is waiting for the ad playback to finish so invoke the callback now.
-      // Either CONTENT_RESUME_REQUESTED will be passed next, or playAd will be called again.
       for (int i = 0; i < adCallbacks.size(); i++) {
         adCallbacks.get(i).onEnded();
       }
@@ -1041,26 +1039,24 @@ public final class ImaAdsLoader
     int oldPlayingAdIndexInAdGroup = playingAdIndexInAdGroup;
     playingAd = player.isPlayingAd();
     playingAdIndexInAdGroup = playingAd ? player.getCurrentAdIndexInAdGroup() : C.INDEX_UNSET;
-    if (!sentContentComplete) {
-      boolean adFinished = wasPlayingAd && playingAdIndexInAdGroup != oldPlayingAdIndexInAdGroup;
-      if (adFinished) {
-        // IMA is waiting for the ad playback to finish so invoke the callback now.
-        // Either CONTENT_RESUME_REQUESTED will be passed next, or playAd will be called again.
-        for (int i = 0; i < adCallbacks.size(); i++) {
-          adCallbacks.get(i).onEnded();
-        }
-        if (DEBUG) {
-          Log.d(TAG, "VideoAdPlayerCallback.onEnded in onTimelineChanged/onPositionDiscontinuity");
-        }
+    boolean adFinished = wasPlayingAd && playingAdIndexInAdGroup != oldPlayingAdIndexInAdGroup;
+    if (adFinished) {
+      // IMA is waiting for the ad playback to finish so invoke the callback now.
+      // Either CONTENT_RESUME_REQUESTED will be passed next, or playAd will be called again.
+      for (int i = 0; i < adCallbacks.size(); i++) {
+        adCallbacks.get(i).onEnded();
       }
-      if (!wasPlayingAd && playingAd && imaAdState == IMA_AD_STATE_NONE) {
-        int adGroupIndex = player.getCurrentAdGroupIndex();
-        // IMA hasn't called playAd yet, so fake the content position.
-        fakeContentProgressElapsedRealtimeMs = SystemClock.elapsedRealtime();
-        fakeContentProgressOffsetMs = C.usToMs(adPlaybackState.adGroupTimesUs[adGroupIndex]);
-        if (fakeContentProgressOffsetMs == C.TIME_END_OF_SOURCE) {
-          fakeContentProgressOffsetMs = contentDurationMs;
-        }
+      if (DEBUG) {
+        Log.d(TAG, "VideoAdPlayerCallback.onEnded in onTimelineChanged/onPositionDiscontinuity");
+      }
+    }
+    if (!sentContentComplete && !wasPlayingAd && playingAd && imaAdState == IMA_AD_STATE_NONE) {
+      int adGroupIndex = player.getCurrentAdGroupIndex();
+      // IMA hasn't called playAd yet, so fake the content position.
+      fakeContentProgressElapsedRealtimeMs = SystemClock.elapsedRealtime();
+      fakeContentProgressOffsetMs = C.usToMs(adPlaybackState.adGroupTimesUs[adGroupIndex]);
+      if (fakeContentProgressOffsetMs == C.TIME_END_OF_SOURCE) {
+        fakeContentProgressOffsetMs = contentDurationMs;
       }
     }
   }
@@ -1125,6 +1121,7 @@ public final class ImaAdsLoader
       pendingAdLoadError = AdLoadException.createForAdGroup(error, adGroupIndex);
     }
     pendingContentPositionMs = C.TIME_UNSET;
+    fakeContentProgressElapsedRealtimeMs = C.TIME_UNSET;
   }
 
   private void handleAdPrepareError(int adGroupIndex, int adIndexInAdGroup, Exception exception) {
@@ -1172,6 +1169,10 @@ public final class ImaAdsLoader
         Log.d(TAG, "adsLoader.contentComplete");
       }
       sentContentComplete = true;
+      // After sending content complete IMA will not poll the content position, so set the expected
+      // ad group index.
+      expectedAdGroupIndex =
+          adPlaybackState.getAdGroupIndexForPositionUs(C.msToUs(contentDurationMs));
     }
   }
 

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

@@ -315,8 +315,7 @@ public final class AdPlaybackState {
     // Use a linear search as the array elements may not be increasing due to TIME_END_OF_SOURCE.
     // In practice we expect there to be few ad groups so the search shouldn't be expensive.
     int index = adGroupTimesUs.length - 1;
-    while (index >= 0
-        && (adGroupTimesUs[index] == C.TIME_END_OF_SOURCE || adGroupTimesUs[index] > positionUs)) {
+    while (index >= 0 && isPositionBeforeAdGroup(positionUs, index)) {
       index--;
     }
     return index >= 0 && adGroups[index].hasUnplayedAds() ? index : C.INDEX_UNSET;
@@ -454,4 +453,13 @@ public final class AdPlaybackState {
     result = 31 * result + Arrays.hashCode(adGroups);
     return result;
   }
+
+  private boolean isPositionBeforeAdGroup(long positionUs, int adGroupIndex) {
+    long adGroupPositionUs = adGroupTimesUs[adGroupIndex];
+    if (adGroupPositionUs == C.TIME_END_OF_SOURCE) {
+      return contentDurationUs == C.TIME_UNSET || positionUs < contentDurationUs;
+    } else {
+      return positionUs < adGroupPositionUs;
+    }
+  }
 }