ArrayIndexOutOfBoundsException in guessMediaTimeBasedOnElapsedRealTime

We recently started using PlaybackStatsListener in our app, and we’re seeing low-medium volume crashes that we haven’t been able to reproduce locally:

java.lang.ArrayIndexOutOfBoundsException: length=0; index=-1
        at java.util.ArrayList.get(ArrayList.java:439)
        at e.d.a.a.a.l(Unknown:5)
        at com.google.android.exoplayer2.analytics.PlaybackStatsListener$PlaybackStatsTracker.guessMediaTimeBasedOnElapsedRealtime(PlaybackStatsListener:775)
        at com.google.android.exoplayer2.analytics.PlaybackStatsListener$PlaybackStatsTracker.maybeUpdateMediaTimeHistory(PlaybackStatsListener:770)
        at com.google.android.exoplayer2.analytics.PlaybackStatsListener$PlaybackStatsTracker.onEvents(PlaybackStatsListener:577)
        at com.google.android.exoplayer2.analytics.PlaybackStatsListener.onEvents(PlaybackStatsListener:257)
        at com.google.android.exoplayer2.analytics.AnalyticsCollector.lambda$setPlayer$1(AnalyticsCollector:137)
        at com.google.android.exoplayer2.analytics.AnalyticsCollector.lambda$setPlayer$1$AnalyticsCollector(AnalyticsCollector:1)
        at com.google.android.exoplayer2.analytics.-$$Lambda$AnalyticsCollector$4Pupd4CGdtbqprZwT2MGLeu1J-0.invoke(-:1)
        at com.google.android.exoplayer2.util.ListenerSet$ListenerHolder.iterationFinished(ListenerSet:294)
        at com.google.android.exoplayer2.util.ListenerSet.handleMessage(ListenerSet:239)
        at com.google.android.exoplayer2.util.ListenerSet.lambda$eEvjP-IE0x3J2lRvKfFbbjRFRvc(ListenerSet:9)
        at com.google.android.exoplayer2.util.-$$Lambda$ListenerSet$eEvjP-IE0x3J2lRvKfFbbjRFRvc.handleMessage(-:9)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7094)
        at java.lang.reflect.Method.invoke(Method.java:-2)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:494)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:975)

Examining the code, you can see how entering maybeUpdateMediaTimeHistory in a playback state other than PLAYBACK_STATE_PLAYING could lead to this crash:

private void maybeUpdateMediaTimeHistory(long realtimeMs, long mediaTimeMs) {
      if (!keepHistory) {
        return;
      }
      if (currentPlaybackState != PlaybackStats.PLAYBACK_STATE_PLAYING) {
        if (mediaTimeMs == C.TIME_UNSET) {
          return;
        }
        if (!mediaTimeHistory.isEmpty()) {
          long previousMediaTimeMs = mediaTimeHistory.get(mediaTimeHistory.size() - 1)[1];
          if (previousMediaTimeMs != mediaTimeMs) {
            mediaTimeHistory.add(new long[] {realtimeMs, previousMediaTimeMs});
          }
        }
      }
      mediaTimeHistory.add(
          mediaTimeMs == C.TIME_UNSET
              ? guessMediaTimeBasedOnElapsedRealtime(realtimeMs)
              : new long[] {realtimeMs, mediaTimeMs});
    }

private long[] guessMediaTimeBasedOnElapsedRealtime(long realtimeMs) {
      long[] previousKnownMediaTimeHistory = mediaTimeHistory.get(mediaTimeHistory.size() - 1);
      long previousRealtimeMs = previousKnownMediaTimeHistory[0];
      long previousMediaTimeMs = previousKnownMediaTimeHistory[1];
      long elapsedMediaTimeEstimateMs =
          (long) ((realtimeMs - previousRealtimeMs) * currentPlaybackSpeed);
      long mediaTimeEstimateMs = previousMediaTimeMs + elapsedMediaTimeEstimateMs;
      return new long[] {realtimeMs, mediaTimeEstimateMs};
    }

I’m happy to put up a PR to make the code more robust, but I’m wondering if this instead points to us using the analytics improperly in our app since I couldn’t find any other reports of this same crash.

• ExoPlayer version number: 2.14.0
• Android version: All (our minSDK is 19)
• Android device: Various

[christosts]

We added a check in maybeUpdateMediaTimeHistory to avoid the error - see the linked commit above. We haven’t been able to repro locally to verify under what circumstances this error can be raised. Per my comment above, avoid using the same listener instance on two players in parallel (in case that happens).

Closing the issue as a fix is submitted. Thanks.

[greyski]

Thank you, we’ll add an assert for this.