Make use of position discontinuity changes.

The extended onPositionDiscontinuity callback can be used to improve some
listener classes:
 - Listening to onTimelineChanged to detect discontinuities is no longer needed.
 - Listening to onSeekStarted is no longer needed as the start position is part
   of the onPositionDiscontinuty callback.
 - The exact old position is also useful for media time history logging.

As a side effect, removing onSeekStarted handling from PlaybackStatsListener
fixes Issue: #8675 that was caused by the special EventTime handling for
onSeekStarted.

PiperOrigin-RevId: 365558959

library/core/src/main/java/com/google/android/exoplayer2/analytics/DefaultPlaybackSessionManager.java

@@ -33,6 +33,7 @@ import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Random;
 import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
+import org.checkerframework.checker.nullness.qual.RequiresNonNull;
 
 /**
  * Default {@link PlaybackSessionManager} which instantiates a new session for each window in the
@@ -184,7 +185,7 @@ public final class DefaultPlaybackSessionManager implements PlaybackSessionManag
         }
       }
     }
-    updateSessionsWithDiscontinuity(eventTime, Player.DISCONTINUITY_REASON_INTERNAL);
+    updateCurrentSession(eventTime);
   }
 
   @Override
@@ -208,6 +209,31 @@ public final class DefaultPlaybackSessionManager implements PlaybackSessionManag
         }
       }
     }
+    updateCurrentSession(eventTime);
+  }
+
+  @Override
+  @Nullable
+  public synchronized String getActiveSessionId() {
+    return currentSessionId;
+  }
+
+  @Override
+  public synchronized void finishAllSessions(EventTime eventTime) {
+    currentSessionId = null;
+    Iterator<SessionDescriptor> iterator = sessions.values().iterator();
+    while (iterator.hasNext()) {
+      SessionDescriptor session = iterator.next();
+      iterator.remove();
+      if (session.isCreated && listener != null) {
+        listener.onSessionFinished(
+            eventTime, session.sessionId, /* automaticTransitionToNextPlayback= */ false);
+      }
+    }
+  }
+
+  @RequiresNonNull("listener")
+  private void updateCurrentSession(EventTime eventTime) {
     @Nullable SessionDescriptor previousSessionDescriptor = sessions.get(currentSessionId);
     SessionDescriptor currentSessionDescriptor =
         getOrAddSession(eventTime.windowIndex, eventTime.mediaPeriodId);
@@ -234,20 +260,6 @@ public final class DefaultPlaybackSessionManager implements PlaybackSessionManag
     }
   }
 
-  @Override
-  public void finishAllSessions(EventTime eventTime) {
-    currentSessionId = null;
-    Iterator<SessionDescriptor> iterator = sessions.values().iterator();
-    while (iterator.hasNext()) {
-      SessionDescriptor session = iterator.next();
-      iterator.remove();
-      if (session.isCreated && listener != null) {
-        listener.onSessionFinished(
-            eventTime, session.sessionId, /* automaticTransitionToNextPlayback= */ false);
-      }
-    }
-  }
-
   private SessionDescriptor getOrAddSession(
       int windowIndex, @Nullable MediaPeriodId mediaPeriodId) {
     // There should only be one matching session if mediaPeriodId is non-null. If mediaPeriodId is

library/core/src/main/java/com/google/android/exoplayer2/analytics/PlaybackSessionManager.java

@@ -15,6 +15,7 @@
  */
 package com.google.android.exoplayer2.analytics;
 
+import androidx.annotation.Nullable;
 import com.google.android.exoplayer2.Player.DiscontinuityReason;
 import com.google.android.exoplayer2.Timeline;
 import com.google.android.exoplayer2.analytics.AnalyticsListener.EventTime;
@@ -129,6 +130,13 @@ public interface PlaybackSessionManager {
   void updateSessionsWithDiscontinuity(EventTime eventTime, @DiscontinuityReason int reason);
 
   /**
+   * Returns the session identifier of the session that is currently actively playing, or {@code
+   * null} if there no such session.
+   */
+  @Nullable
+  String getActiveSessionId();
+
+  /**
    * Finishes all existing sessions and calls their respective {@link
    * Listener#onSessionFinished(EventTime, String, boolean)} callback.
    *

library/core/src/main/java/com/google/android/exoplayer2/util/EventLogger.java

@@ -188,11 +188,6 @@ public class EventLogger implements AnalyticsListener {
   }
 
   @Override
-  public void onSeekStarted(EventTime eventTime) {
-    logd(eventTime, "seekStarted");
-  }
-
-  @Override
   public void onPlaybackParametersChanged(
       EventTime eventTime, PlaybackParameters playbackParameters) {
     logd(eventTime, "playbackParameters", playbackParameters.toString());