--- a/dom/media/mediasource/TrackBuffersManager.cpp
+++ b/dom/media/mediasource/TrackBuffersManager.cpp
@@ -371,17 +371,23 @@ TrackBuffersManager::CompleteResetParser
     // 4. Unset the highest end timestamp on all track buffers.
     // 5. Set the need random access point flag on all track buffers to true.
     track->ResetAppendState();
 
     // if we have been aborted, we may have pending frames that we are going
     // to discard now.
     track->mQueuedSamples.Clear();
   }
-  // 6. Remove all bytes from the input buffer.
+
+  // 6. If the mode attribute equals "sequence", then set the group start timestamp to the group end timestamp
+  if (mSourceBufferAttributes->GetAppendMode() == SourceBufferAppendMode::Sequence) {
+    mGroupStartTimestamp = Some(mGroupEndTimestamp);
+  }
+
+  // 7. Remove all bytes from the input buffer.
   mIncomingBuffers.Clear();
   mInputBuffer = nullptr;
   if (mCurrentInputBuffer) {
     mCurrentInputBuffer->EvictAll();
     // The demuxer will be recreated during the next run of SegmentParserLoop.
     // As such we don't need to notify it that data has been removed.
     mCurrentInputBuffer = new SourceBufferResource(mType);
   }
@@ -396,17 +402,17 @@ TrackBuffersManager::CompleteResetParser
     CreateDemuxerforMIMEType();
     // Recreate our input buffer. We can't directly assign the initData buffer
     // to mInputBuffer as it will get modified in the Segment Parser Loop.
     mInputBuffer = new MediaByteBuffer;
     mInputBuffer->AppendElements(*mInitData);
   }
   RecreateParser(true);
 
-  // 7. Set append state to WAITING_FOR_SEGMENT.
+  // 8. Set append state to WAITING_FOR_SEGMENT.
   SetAppendState(AppendState::WAITING_FOR_SEGMENT);
 
   // Reject our promise immediately.
   mAppendPromise.RejectIfExists(NS_ERROR_ABORT, __func__);
 }
 
 void
 TrackBuffersManager::DoEvictData(const TimeUnit& aPlaybackTime,