--- a/dom/media/mediasource/TrackBuffersManager.cpp
+++ b/dom/media/mediasource/TrackBuffersManager.cpp
@@ -99,17 +99,16 @@ TrackBuffersManager::TrackBuffersManager
   , mTaskQueue(aParentDecoder->GetDemuxer()->GetTaskQueue())
   , mSourceBufferAttributes(aAttributes)
   , mParentDecoder(new nsMainThreadPtrHolder<MediaSourceDecoder>(aParentDecoder, false /* strict */))
   , mEvictionThreshold(Preferences::GetUint("media.mediasource.eviction_threshold",
                                             100 * (1 << 20)))
   , mEvictionOccurred(false)
   , mMonitor("TrackBuffersManager")
   , mAppendRunning(false)
-  , mSegmentParserLoopRunning(false)
 {
   MOZ_ASSERT(NS_IsMainThread(), "Must be instanciated on the main thread");
 }
 
 TrackBuffersManager::~TrackBuffersManager()
 {
   ShutdownDemuxers();
 }
@@ -296,17 +295,17 @@ TrackBuffersManager::Detach()
   MOZ_ASSERT(NS_IsMainThread());
   MSE_DEBUG("");
 }
 
 void
 TrackBuffersManager::CompleteResetParserState()
 {
   MOZ_ASSERT(OnTaskQueue());
-  MOZ_DIAGNOSTIC_ASSERT(!mSegmentParserLoopRunning);
+  MOZ_DIAGNOSTIC_ASSERT(!mAppendRunning, "Append is running");
   MSE_DEBUG("");
 
   for (auto& track : GetTracksList()) {
     // 2. Unset the last decode timestamp on all track buffers.
     // 3. Unset the last frame duration on all track buffers.
     // 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();
@@ -424,25 +423,25 @@ TrackBuffersManager::DoEvictData(const T
                    TimeUnit::FromInfinity()));
   }
 }
 
 RefPtr<TrackBuffersManager::RangeRemovalPromise>
 TrackBuffersManager::CodedFrameRemovalWithPromise(TimeInterval aInterval)
 {
   MOZ_ASSERT(OnTaskQueue());
+  MOZ_DIAGNOSTIC_ASSERT(!mAppendRunning, "Logic error: Append in progress");
   bool rv = CodedFrameRemoval(aInterval);
   return RangeRemovalPromise::CreateAndResolve(rv, __func__);
 }
 
 bool
 TrackBuffersManager::CodedFrameRemoval(TimeInterval aInterval)
 {
   MOZ_ASSERT(OnTaskQueue());
-  MOZ_ASSERT(!mSegmentParserLoopRunning, "Logic error: Append in progress");
   MSE_DEBUG("From %.2fs to %.2f",
             aInterval.mStart.ToSeconds(), aInterval.mEnd.ToSeconds());
 
 #if DEBUG
   if (HasVideo()) {
     MSE_DEBUG("before video ranges=%s",
               DumpTimeRanges(mVideoTracks.mBufferedRanges).get());
   }
@@ -571,18 +570,16 @@ TrackBuffersManager::AppendIncomingBuffe
                  TimeUnit::FromSeconds(mSourceBufferAttributes->GetAppendWindowEnd()));
 }
 
 void
 TrackBuffersManager::SegmentParserLoop()
 {
   MOZ_ASSERT(OnTaskQueue());
 
-  mSegmentParserLoopRunning = true;
-
   while (true) {
     // 1. If the input buffer is empty, then jump to the need more data step below.
     if (!mInputBuffer || mInputBuffer->IsEmpty()) {
       NeedMoreData();
       return;
     }
     // 2. If the input buffer contains bytes that violate the SourceBuffer
     // byte stream format specification, then run the append error algorithm with
@@ -697,31 +694,29 @@ TrackBuffersManager::SegmentParserLoop()
 }
 
 void
 TrackBuffersManager::NeedMoreData()
 {
   MSE_DEBUG("");
   RestoreCachedVariables();
   mAppendRunning = false;
-  mSegmentParserLoopRunning = false;
   {
     // Wake-up any pending Abort()
     MonitorAutoLock mon(mMonitor);
     mon.NotifyAll();
   }
   mAppendPromise.ResolveIfExists(mActiveTrack, __func__);
 }
 
 void
 TrackBuffersManager::RejectAppend(nsresult aRejectValue, const char* aName)
 {
   MSE_DEBUG("rv=%d", aRejectValue);
   mAppendRunning = false;
-  mSegmentParserLoopRunning = false;
   {
     // Wake-up any pending Abort()
     MonitorAutoLock mon(mMonitor);
     mon.NotifyAll();
   }
   mAppendPromise.RejectIfExists(aRejectValue, aName);
 }
 

--- a/dom/media/mediasource/TrackBuffersManager.h
+++ b/dom/media/mediasource/TrackBuffersManager.h
@@ -345,21 +345,18 @@ private:
   // Global size of this source buffer content.
   Atomic<int64_t> mSizeSourceBuffer;
   uint32_t mEvictionThreshold;
   Atomic<bool> mEvictionOccurred;
 
   // Monitor to protect following objects accessed across multipple threads.
   // mMonitor is also notified if the value of mAppendRunning becomes false.
   mutable Monitor mMonitor;
-  // Set to true while SegmentParserLoop is running.
+  // Set to true while a BufferAppend is running or is pending.
   Atomic<bool> mAppendRunning;
-  // Set to true while SegmentParserLoop is running.
-  // This is for diagnostic only. Only accessed on the task queue.
-  bool mSegmentParserLoopRunning;
   // Stable audio and video track time ranges.
   media::TimeIntervals mVideoBufferedRanges;
   media::TimeIntervals mAudioBufferedRanges;
   media::TimeUnit mOfficialGroupEndTimestamp;
   // MediaInfo of the first init segment read.
   MediaInfo mInfo;
 };