--- a/dom/media/mediasource/SourceBuffer.cpp
+++ b/dom/media/mediasource/SourceBuffer.cpp
@@ -422,17 +422,17 @@ SourceBuffer::AbortUpdating()
   QueueAsyncSimpleEvent("updateend");
 }
 
 void
 SourceBuffer::CheckEndTime()
 {
   MOZ_ASSERT(NS_IsMainThread());
   // Check if we need to update mMediaSource duration
-  double endTime = GetBufferedEnd();
+  double endTime = mContentManager->GroupEndTimestamp().ToSeconds();
   double duration = mMediaSource->Duration();
   if (endTime > duration) {
     mMediaSource->SetDuration(endTime, MSRangeRemovalAction::SKIP);
   }
 }
 
 void
 SourceBuffer::AppendData(const uint8_t* aData, uint32_t aLength, ErrorResult& aRv)

--- a/dom/media/mediasource/SourceBufferContentManager.h
+++ b/dom/media/mediasource/SourceBufferContentManager.h
@@ -95,16 +95,17 @@ public:
 
   virtual AppendState GetAppendState()
   {
     return AppendState::WAITING_FOR_SEGMENT;
   }
 
   virtual void SetGroupStartTimestamp(const TimeUnit& aGroupStartTimestamp) {}
   virtual void RestartGroupStartTimestamp() {}
+  virtual TimeUnit GroupEndTimestamp() = 0;
 
 #if defined(DEBUG)
   virtual void Dump(const char* aPath) { }
 #endif
 
 protected:
   virtual ~SourceBufferContentManager() { }
 };

--- a/dom/media/mediasource/TrackBuffer.h
+++ b/dom/media/mediasource/TrackBuffer.h
@@ -63,16 +63,22 @@ public:
 
   void Ended() override
   {
     EndCurrentDecoder();
   }
 
   void Detach() override;
 
+  TimeUnit GroupEndTimestamp() override
+  {
+    return Buffered().GetEnd();
+  }
+
+
   // Mark the current decoder's resource as ended, clear mCurrentDecoder and
   // reset mLast{Start,End}Timestamp.  Main thread only.
   void DiscardCurrentDecoder();
   // Mark the current decoder's resource as ended.
   void EndCurrentDecoder();
 
   // Returns true if an init segment has been appended.
   bool HasInitSegment();

--- a/dom/media/mediasource/TrackBuffersManager.cpp
+++ b/dom/media/mediasource/TrackBuffersManager.cpp
@@ -1223,16 +1223,18 @@ TrackBuffersManager::CompleteCodedFrameP
     if (HasAudio()) {
       MSE_DEBUG("audio new buffered range = %s",
                 DumpTimeRanges(mAudioBufferedRanges).get());
     }
     if (HasVideo()) {
       MSE_DEBUG("video new buffered range = %s",
                 DumpTimeRanges(mVideoBufferedRanges).get());
     }
+
+    mOfficialGroupEndTimestamp = mGroupEndTimestamp;
   }
 
   // Update our reported total size.
   mSizeSourceBuffer = mVideoTracks.mSizeBuffer + mAudioTracks.mSizeBuffer;
 
   // Return to step 6.4 of Segment Parser Loop algorithm
   // 4. If this SourceBuffer is full and cannot accept more media data, then set the buffer full flag to true.
   if (mSizeSourceBuffer >= mEvictionThreshold) {
@@ -1668,16 +1670,23 @@ TrackBuffersManager::RestartGroupStartTi
       NS_NewRunnableMethod(this, &TrackBuffersManager::RestartGroupStartTimestamp);
     GetTaskQueue()->Dispatch(task.forget());
     return;
   }
   MOZ_ASSERT(OnTaskQueue());
   mGroupStartTimestamp = Some(mGroupEndTimestamp);
 }
 
+TimeUnit
+TrackBuffersManager::GroupEndTimestamp()
+{
+  MonitorAutoLock mon(mMonitor);
+  return mOfficialGroupEndTimestamp;
+}
+
 MediaInfo
 TrackBuffersManager::GetMetadata()
 {
   MonitorAutoLock mon(mMonitor);
   return mInfo;
 }
 
 const TimeIntervals&

--- a/dom/media/mediasource/TrackBuffersManager.h
+++ b/dom/media/mediasource/TrackBuffersManager.h
@@ -66,16 +66,17 @@ public:
 
   AppendState GetAppendState() override
   {
     return mAppendState;
   }
 
   void SetGroupStartTimestamp(const TimeUnit& aGroupStartTimestamp) override;
   void RestartGroupStartTimestamp() override;
+  TimeUnit GroupEndTimestamp() override;
 
   // Interface for MediaSourceDemuxer
   MediaInfo GetMetadata();
   const TrackBuffer& GetTrackBuffer(TrackInfo::TrackType aTrack);
   const TimeIntervals& Buffered(TrackInfo::TrackType);
   bool IsEnded() const
   {
     return mEnded;
@@ -313,14 +314,15 @@ private:
   uint32_t mEvictionThreshold;
   Atomic<bool> mEvictionOccurred;
 
   // Monitor to protect following objects accessed across multipple threads.
   mutable Monitor mMonitor;
   // Stable audio and video track time ranges.
   TimeIntervals mVideoBufferedRanges;
   TimeIntervals mAudioBufferedRanges;
+  TimeUnit mOfficialGroupEndTimestamp;
   // MediaInfo of the first init segment read.
   MediaInfo mInfo;
 };
 
 } // namespace mozilla
 #endif /* MOZILLA_TRACKBUFFERSMANAGER_H_ */