--- a/dom/media/MediaFormatReader.cpp
+++ b/dom/media/MediaFormatReader.cpp
@@ -1323,17 +1323,17 @@ MediaFormatReader::AsyncReadMetadata()
     ->Then(OwnerThread(), __func__, this,
            &MediaFormatReader::OnDemuxerInitDone,
            &MediaFormatReader::OnDemuxerInitFailed)
     ->Track(mDemuxerInitRequest);
   return p;
 }
 
 void
-MediaFormatReader::OnDemuxerInitDone(nsresult)
+MediaFormatReader::OnDemuxerInitDone(const MediaResult& aResult)
 {
   MOZ_ASSERT(OnTaskQueue());
   mDemuxerInitRequest.Complete();
 
   mDemuxerInitDone = true;
 
   UniquePtr<MetadataTags> tags(MakeUnique<MetadataTags>());
 
@@ -1448,16 +1448,26 @@ MediaFormatReader::OnDemuxerInitDone(nsr
       RequestDemuxSamples(TrackInfo::kAudioTrack);
     }
 
     if (HasVideo()) {
       RequestDemuxSamples(TrackInfo::kVideoTrack);
     }
   }
 
+  if (aResult != NS_OK && mDecoder) {
+    RefPtr<AbstractMediaDecoder> decoder = mDecoder;
+    mDecoder->AbstractMainThread()->Dispatch(NS_NewRunnableFunction(
+      [decoder, aResult] () {
+        if (decoder->GetOwner()) {
+          decoder->GetOwner()->DecodeWarning(aResult);
+        }
+      }));
+  }
+
   MaybeResolveMetadataPromise();
 }
 
 void
 MediaFormatReader::MaybeResolveMetadataPromise()
 {
   MOZ_ASSERT(OnTaskQueue());
 

--- a/dom/media/MediaFormatReader.h
+++ b/dom/media/MediaFormatReader.h
@@ -446,17 +446,17 @@ private:
   bool NeedInput(DecoderData& aDecoder);
 
   DecoderData& GetDecoderData(TrackType aTrack);
 
   // Demuxer objects.
   class DemuxerProxy;
   UniquePtr<DemuxerProxy> mDemuxer;
   bool mDemuxerInitDone;
-  void OnDemuxerInitDone(nsresult);
+  void OnDemuxerInitDone(const MediaResult& aResult);
   void OnDemuxerInitFailed(const MediaResult& aError);
   MozPromiseRequestHolder<MediaDataDemuxer::InitPromise> mDemuxerInitRequest;
   MozPromiseRequestHolder<NotifyDataArrivedPromise> mNotifyDataArrivedPromise;
   bool mPendingNotifyDataArrived;
   void OnDemuxFailed(TrackType aTrack, const MediaResult &aError);
 
   void DoDemuxVideo();
   void OnVideoDemuxCompleted(RefPtr<MediaTrackDemuxer::SamplesHolder> aSamples);