diff --git a/dom/media/DecoderTraits.cpp b/dom/media/DecoderTraits.cpp
index dfb66d69f14c..472d52e49921 100644
--- a/dom/media/DecoderTraits.cpp
+++ b/dom/media/DecoderTraits.cpp
@@ -339,7 +339,7 @@ DecoderTraits::CreateDecoder(MediaDecoderInit& aInit,
 /* static */
 MediaDecoderReader*
 DecoderTraits::CreateReader(const MediaContainerType& aType,
-                            const MediaDecoderReaderInit& aInit)
+                            MediaDecoderReaderInit& aInit)
 {
   MOZ_ASSERT(NS_IsMainThread());
   MediaDecoderReader* decoderReader = nullptr;
diff --git a/dom/media/DecoderTraits.h b/dom/media/DecoderTraits.h
index f29e73066168..7458d8a10927 100644
--- a/dom/media/DecoderTraits.h
+++ b/dom/media/DecoderTraits.h
@@ -52,7 +52,7 @@ public:
   // Create a reader for thew given MIME type aType. Returns null
   // if we were unable to create the reader.
   static MediaDecoderReader* CreateReader(const MediaContainerType& aType,
-                                          const MediaDecoderReaderInit& aInit);
+                                          MediaDecoderReaderInit& aInit);
 
   // Returns true if MIME type aType is supported in video documents,
   // or false otherwise. Not all platforms support all MIME types, and
diff --git a/dom/media/MediaDecoder.cpp b/dom/media/MediaDecoder.cpp
index 6bce928bdef5..7500a43d2075 100644
--- a/dom/media/MediaDecoder.cpp
+++ b/dom/media/MediaDecoder.cpp
@@ -1058,19 +1058,23 @@ MediaDecoder::DurationChanged()
   }
 }
 
+already_AddRefed<KnowsCompositor>
+MediaDecoder::GetCompositor()
+{
+  MediaDecoderOwner* owner = GetOwner();
+  nsIDocument* ownerDoc = owner ? owner->GetDocument() : nullptr;
+  RefPtr<LayerManager> layerManager =
+    ownerDoc ? nsContentUtils::LayerManagerForDocument(ownerDoc) : nullptr;
+  RefPtr<KnowsCompositor> knows =
+    layerManager ? layerManager->AsShadowForwarder() : nullptr;
+  return knows.forget();
+}
+
 void
 MediaDecoder::NotifyCompositor()
 {
-  MediaDecoderOwner* owner = GetOwner();
-  NS_ENSURE_TRUE_VOID(owner);
-
-  nsIDocument* ownerDoc = owner->GetDocument();
-  NS_ENSURE_TRUE_VOID(ownerDoc);
-
-  RefPtr<LayerManager> layerManager =
-    nsContentUtils::LayerManagerForDocument(ownerDoc);
-  if (layerManager) {
-    RefPtr<KnowsCompositor> knowsCompositor = layerManager->AsShadowForwarder();
+  RefPtr<KnowsCompositor> knowsCompositor = GetCompositor();
+  if (knowsCompositor) {
     mCompositorUpdatedEvent.Notify(knowsCompositor);
   }
 }
diff --git a/dom/media/MediaDecoder.h b/dom/media/MediaDecoder.h
index 930ce5fcb831..33fbfeceb399 100644
--- a/dom/media/MediaDecoder.h
+++ b/dom/media/MediaDecoder.h
@@ -512,6 +512,8 @@ protected:
     return mCurrentPosition.Ref();
   }
 
+  already_AddRefed<layers::KnowsCompositor> GetCompositor();
+
   // Official duration of the media resource as observed by script.
   double mDuration;
 
diff --git a/dom/media/MediaDecoderReader.cpp b/dom/media/MediaDecoderReader.cpp
index 77be0d875124..452f57ccdf0f 100644
--- a/dom/media/MediaDecoderReader.cpp
+++ b/dom/media/MediaDecoderReader.cpp
@@ -68,7 +68,7 @@ public:
   size_t mSize;
 };
 
-MediaDecoderReader::MediaDecoderReader(const MediaDecoderReaderInit& aInit)
+MediaDecoderReader::MediaDecoderReader(MediaDecoderReaderInit& aInit)
   : mAudioCompactor(mAudioQueue)
   , mDecoder(aInit.mDecoder)
   , mTaskQueue(new TaskQueue(
diff --git a/dom/media/MediaDecoderReader.h b/dom/media/MediaDecoderReader.h
index 99f02a21d2a0..2470baf01cb8 100644
--- a/dom/media/MediaDecoderReader.h
+++ b/dom/media/MediaDecoderReader.h
@@ -67,6 +67,7 @@ struct MOZ_STACK_CLASS MediaDecoderReaderInit
   AbstractMediaDecoder* const mDecoder;
   MediaResource* mResource = nullptr;
   VideoFrameContainer* mVideoFrameContainer = nullptr;
+  already_AddRefed<layers::KnowsCompositor> mKnowsCompositor;
 
   explicit MediaDecoderReaderInit(AbstractMediaDecoder* aDecoder)
     : mDecoder(aDecoder)
@@ -110,7 +111,7 @@ public:
 
   // The caller must ensure that Shutdown() is called before aDecoder is
   // destroyed.
-  explicit MediaDecoderReader(const MediaDecoderReaderInit& aInit);
+  explicit MediaDecoderReader(MediaDecoderReaderInit& aInit);
 
   // Initializes the reader, returns NS_OK on success, or NS_ERROR_FAILURE
   // on failure.
diff --git a/dom/media/MediaFormatReader.cpp b/dom/media/MediaFormatReader.cpp
index 26deae626ec6..d7d0ab7d76ba 100644
--- a/dom/media/MediaFormatReader.cpp
+++ b/dom/media/MediaFormatReader.cpp
@@ -9,6 +9,7 @@
 #include "AutoTaskQueue.h"
 #include "Layers.h"
 #include "MediaData.h"
+#include "MediaDecoderOwner.h"
 #include "MediaInfo.h"
 #include "MediaResource.h"
 #include "VideoFrameContainer.h"
@@ -22,8 +23,6 @@
 #include "mozilla/SyncRunnable.h"
 #include "mozilla/Telemetry.h"
 #include "mozilla/Unused.h"
-#include "mozilla/dom/HTMLMediaElement.h"
-#include "mozilla/layers/ShadowLayers.h"
 #include "nsContentUtils.h"
 #include "nsPrintfCString.h"
 #include "nsSize.h"
@@ -1094,7 +1093,7 @@ MediaFormatReader::DemuxerProxy::NotifyDataArrived()
   });
 }
 
-MediaFormatReader::MediaFormatReader(const MediaDecoderReaderInit& aInit,
+MediaFormatReader::MediaFormatReader(MediaDecoderReaderInit& aInit,
                                      MediaDataDemuxer* aDemuxer)
   : MediaDecoderReader(aInit)
   , mAudio(this, MediaData::AUDIO_DATA,
@@ -1106,6 +1105,7 @@ MediaFormatReader::MediaFormatReader(const MediaDecoderReaderInit& aInit,
   , mPendingNotifyDataArrived(false)
   , mLastReportedNumDecodedFrames(0)
   , mPreviousDecodedKeyframeTime_us(sNoPreviousDecodedKeyframe)
+  , mKnowsCompositor(aInit.mKnowsCompositor)
   , mInitDone(false)
   , mTrackDemuxersMayBlock(false)
   , mSeekScheduled(false)
@@ -1214,38 +1214,11 @@ MediaFormatReader::TearDownDecoders()
   return MediaDecoderReader::Shutdown();
 }
 
-void
-MediaFormatReader::InitLayersBackendType()
-{
-  // Extract the layer manager backend type so that platform decoders
-  // can determine whether it's worthwhile using hardware accelerated
-  // video decoding.
-  if (!mDecoder) {
-    return;
-  }
-  MediaDecoderOwner* owner = mDecoder->GetOwner();
-  if (!owner) {
-    NS_WARNING("MediaFormatReader without a decoder owner, can't get HWAccel");
-    return;
-  }
-
-  dom::HTMLMediaElement* element = owner->GetMediaElement();
-  NS_ENSURE_TRUE_VOID(element);
-
-  RefPtr<LayerManager> layerManager =
-    nsContentUtils::LayerManagerForDocument(element->OwnerDoc());
-  NS_ENSURE_TRUE_VOID(layerManager);
-
-  mKnowsCompositor = layerManager->AsShadowForwarder();
-}
-
 nsresult
 MediaFormatReader::InitInternal()
 {
   MOZ_ASSERT(NS_IsMainThread(), "Must be on main thread.");
 
-  InitLayersBackendType();
-
   mAudio.mTaskQueue = new TaskQueue(
     GetMediaThreadPool(MediaThreadType::PLATFORM_DECODER),
     "MFR::mAudio::mTaskQueue");
diff --git a/dom/media/MediaFormatReader.h b/dom/media/MediaFormatReader.h
index fafe9f79a85f..354ea4b46c42 100644
--- a/dom/media/MediaFormatReader.h
+++ b/dom/media/MediaFormatReader.h
@@ -29,7 +29,7 @@ class MediaFormatReader final : public MediaDecoderReader
   typedef MozPromise<bool, MediaResult, /* IsExclusive = */ true> NotifyDataArrivedPromise;
 
 public:
-  MediaFormatReader(const MediaDecoderReaderInit& aInit, MediaDataDemuxer* aDemuxer);
+  MediaFormatReader(MediaDecoderReaderInit& aInit, MediaDataDemuxer* aDemuxer);
 
   virtual ~MediaFormatReader();
 
diff --git a/dom/media/android/AndroidMediaReader.cpp b/dom/media/android/AndroidMediaReader.cpp
index 23d8f1ed467f..7011f4f3c233 100644
--- a/dom/media/android/AndroidMediaReader.cpp
+++ b/dom/media/android/AndroidMediaReader.cpp
@@ -26,7 +26,7 @@ typedef mozilla::layers::Image Image;
 typedef mozilla::layers::PlanarYCbCrImage PlanarYCbCrImage;
 
 AndroidMediaReader::AndroidMediaReader(const MediaContainerType& aContainerType,
-                                       const MediaDecoderReaderInit& aInit) :
+                                       MediaDecoderReaderInit& aInit) :
   MediaDecoderReader(aInit),
   mType(aContainerType),
   mPlugin(nullptr),
diff --git a/dom/media/android/AndroidMediaReader.h b/dom/media/android/AndroidMediaReader.h
index c03fa3c744c9..7705ef792aad 100644
--- a/dom/media/android/AndroidMediaReader.h
+++ b/dom/media/android/AndroidMediaReader.h
@@ -38,7 +38,7 @@ class AndroidMediaReader : public MediaDecoderReader
   MozPromiseRequestHolder<MediaDecoderReader::VideoDataPromise> mSeekRequest;
 public:
   AndroidMediaReader(const MediaContainerType& aContainerType,
-                     const MediaDecoderReaderInit& aInit);
+                     MediaDecoderReaderInit& aInit);
 
   nsresult ResetDecode(TrackSet aTracks = TrackSet(TrackInfo::kAudioTrack,
                                                    TrackInfo::kVideoTrack)) override;
diff --git a/dom/media/fmp4/MP4Decoder.cpp b/dom/media/fmp4/MP4Decoder.cpp
index aae012e38710..5871a2f07c56 100644
--- a/dom/media/fmp4/MP4Decoder.cpp
+++ b/dom/media/fmp4/MP4Decoder.cpp
@@ -34,6 +34,7 @@ MediaDecoderStateMachine* MP4Decoder::CreateStateMachine()
 {
   MediaDecoderReaderInit init(this);
   init.mVideoFrameContainer = GetVideoFrameContainer();
+  init.mKnowsCompositor = GetCompositor();
   mReader = new MediaFormatReader(init, new MP4Demuxer(mResource));
   return new MediaDecoderStateMachine(this, mReader);
 }
diff --git a/dom/media/hls/HLSDecoder.cpp b/dom/media/hls/HLSDecoder.cpp
index 6b15b88603a3..5f5b0948fa42 100644
--- a/dom/media/hls/HLSDecoder.cpp
+++ b/dom/media/hls/HLSDecoder.cpp
@@ -30,6 +30,7 @@ HLSDecoder::CreateStateMachine()
   MOZ_ASSERT(resourceWrapper);
   MediaDecoderReaderInit init(this);
   init.mVideoFrameContainer = GetVideoFrameContainer();
+  init.mKnowsCompositor = GetCompositor();
   mReader =
     new MediaFormatReader(init, new HLSDemuxer(resourceWrapper->GetPlayerId()));
 
diff --git a/dom/media/mediasource/MediaSourceDecoder.cpp b/dom/media/mediasource/MediaSourceDecoder.cpp
index e8eea91bce7e..95e64d391515 100644
--- a/dom/media/mediasource/MediaSourceDecoder.cpp
+++ b/dom/media/mediasource/MediaSourceDecoder.cpp
@@ -41,6 +41,7 @@ MediaSourceDecoder::CreateStateMachine()
   mDemuxer = new MediaSourceDemuxer(AbstractMainThread());
   MediaDecoderReaderInit init(this);
   init.mVideoFrameContainer = GetVideoFrameContainer();
+  init.mKnowsCompositor = GetCompositor();
   mReader = new MediaFormatReader(init, mDemuxer);
   return new MediaDecoderStateMachine(this, mReader);
 }
diff --git a/dom/media/ogg/OggDecoder.cpp b/dom/media/ogg/OggDecoder.cpp
index cb3e175b340c..3edbaa8fa4ff 100644
--- a/dom/media/ogg/OggDecoder.cpp
+++ b/dom/media/ogg/OggDecoder.cpp
@@ -18,6 +18,7 @@ MediaDecoderStateMachine* OggDecoder::CreateStateMachine()
   RefPtr<OggDemuxer> demuxer = new OggDemuxer(mResource);
   MediaDecoderReaderInit init(this);
   init.mVideoFrameContainer = GetVideoFrameContainer();
+  init.mKnowsCompositor = GetCompositor();
   mReader = new MediaFormatReader(init, demuxer);
   demuxer->SetChainingEvents(&mReader->TimedMetadataProducer(),
                              &mReader->MediaNotSeekableProducer());
diff --git a/dom/media/webm/WebMDecoder.cpp b/dom/media/webm/WebMDecoder.cpp
index cd782a5aa7d7..6123b825bf63 100644
--- a/dom/media/webm/WebMDecoder.cpp
+++ b/dom/media/webm/WebMDecoder.cpp
@@ -20,6 +20,7 @@ MediaDecoderStateMachine* WebMDecoder::CreateStateMachine()
 {
   MediaDecoderReaderInit init(this);
   init.mVideoFrameContainer = GetVideoFrameContainer();
+  init.mKnowsCompositor = GetCompositor();
   mReader = new MediaFormatReader(init, new WebMDemuxer(mResource));
   return new MediaDecoderStateMachine(this, mReader);
 }