Fix issue with updating the last rebuffer time

The last rebuffer time was being updated erroneously, even in the absence of rebuffering events, resulting in incorrect `bs` (buffer starvation) key in CMCD.

Issue: #1124
PiperOrigin-RevId: 629731796

RELEASENOTES.md

@@ -13,6 +13,9 @@
     *   Add `ExoPlayer.setPriority` (and `Builder.setPriority`) to define the
         priority value used in `PriorityTaskManager` and for MediaCodec
         importance from API 35.
+    *   Fix issue with updating the last rebuffer time which resulted in
+        incorrect `bs` (buffer starvation) key in CMCD
+        ([#1124](https://github.com/androidx/media/issues/1124)).
 *   Transformer:
     *   Work around a decoder bug where the number of audio channels was capped
         at stereo when handling PCM input.

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/ExoPlayerImplInternal.java

@@ -3019,7 +3019,7 @@ private static boolean isUsingPlaceholderPeriod(
   private void updateRebufferingState(boolean isRebuffering, boolean resetLastRebufferRealtimeMs) {
     this.isRebuffering = isRebuffering;
     this.lastRebufferRealtimeMs =
-        resetLastRebufferRealtimeMs ? C.TIME_UNSET : clock.elapsedRealtime();
+        isRebuffering && !resetLastRebufferRealtimeMs ? clock.elapsedRealtime() : C.TIME_UNSET;
   }
 
   /**