--- a/dom/media/platforms/agnostic/gmp/GMPAudioDecoder.cpp
+++ b/dom/media/platforms/agnostic/gmp/GMPAudioDecoder.cpp
@@ -121,16 +121,31 @@ AudioCallbackAdapter::Error(GMPErr aErr)
 
 void
 AudioCallbackAdapter::Terminated()
 {
   NS_WARNING("AAC GMP decoder terminated.");
   mCallback->Error(MediaDataDecoderError::FATAL_ERROR);
 }
 
+GMPAudioDecoder::GMPAudioDecoder(const AudioInfo& aConfig,
+                                 TaskQueue* aTaskQueue,
+                                 MediaDataDecoderCallbackProxy* aCallback,
+                                 AudioCallbackAdapter* aAdapter)
+  : mConfig(aConfig)
+  , mCallback(aCallback)
+  , mGMP(nullptr)
+  , mAdapter(aAdapter)
+{
+  MOZ_ASSERT(!aAdapter || aCallback == aAdapter->Callback());
+  if (!aAdapter) {
+    mAdapter = new AudioCallbackAdapter(aCallback);
+  }
+}
+
 void
 GMPAudioDecoder::InitTags(nsTArray<nsCString>& aTags)
 {
   aTags.AppendElement(NS_LITERAL_CSTRING("aac"));
   const Maybe<nsCString> gmp(
     GMPDecoderModule::PreferredGMP(NS_LITERAL_CSTRING("audio/mp4a-latm")));
   if (gmp.isSome()) {
     aTags.AppendElement(gmp.value());

--- a/dom/media/platforms/agnostic/gmp/GMPAudioDecoder.h
+++ b/dom/media/platforms/agnostic/gmp/GMPAudioDecoder.h
@@ -20,16 +20,18 @@ public:
   explicit AudioCallbackAdapter(MediaDataDecoderCallbackProxy* aCallback)
    : mCallback(aCallback)
    , mLastStreamOffset(0)
    , mAudioFrameSum(0)
    , mAudioFrameOffset(0)
    , mMustRecaptureAudioPosition(true)
   {}
 
+  MediaDataDecoderCallbackProxy* Callback() const { return mCallback; }
+
   // GMPAudioDecoderCallbackProxy
   void Decoded(const nsTArray<int16_t>& aPCM, uint64_t aTimeStamp, uint32_t aChannels, uint32_t aRate) override;
   void InputDataExhausted() override;
   void DrainComplete() override;
   void ResetComplete() override;
   void Error(GMPErr aErr) override;
   void Terminated() override;
 
@@ -42,38 +44,21 @@ private:
   int64_t mLastStreamOffset;
 
   int64_t mAudioFrameSum;
   int64_t mAudioFrameOffset;
   bool mMustRecaptureAudioPosition;
 };
 
 class GMPAudioDecoder : public MediaDataDecoder {
-protected:
+public:
   GMPAudioDecoder(const AudioInfo& aConfig,
                   TaskQueue* aTaskQueue,
                   MediaDataDecoderCallbackProxy* aCallback,
-                  AudioCallbackAdapter* aAdapter)
-   : mConfig(aConfig)
-   , mCallback(aCallback)
-   , mGMP(nullptr)
-   , mAdapter(aAdapter)
-  {
-  }
-
-public:
-  GMPAudioDecoder(const AudioInfo& aConfig,
-                  TaskQueue* aTaskQueue,
-                  MediaDataDecoderCallbackProxy* aCallback)
-   : mConfig(aConfig)
-   , mCallback(aCallback)
-   , mGMP(nullptr)
-   , mAdapter(new AudioCallbackAdapter(aCallback))
-  {
-  }
+                  AudioCallbackAdapter* aAdapter);
 
   RefPtr<InitPromise> Init() override;
   nsresult Input(MediaRawData* aSample) override;
   nsresult Flush() override;
   nsresult Drain() override;
   nsresult Shutdown() override;
   const char* GetDescriptionName() const override
   {

--- a/dom/media/platforms/agnostic/gmp/GMPDecoderModule.cpp
+++ b/dom/media/platforms/agnostic/gmp/GMPDecoderModule.cpp
@@ -59,17 +59,18 @@ GMPDecoderModule::CreateVideoDecoder(con
     }
   }
 
   RefPtr<MediaDataDecoderProxy> wrapper = CreateDecoderWrapper(aParams.mCallback);
   wrapper->SetProxyTarget(new GMPVideoDecoder(aParams.VideoConfig(),
                                               aParams.mLayersBackend,
                                               aParams.mImageContainer,
                                               aParams.mTaskQueue,
-                                              wrapper->Callback()));
+                                              wrapper->Callback(),
+                                              nullptr));
   return wrapper.forget();
 }
 
 already_AddRefed<MediaDataDecoder>
 GMPDecoderModule::CreateAudioDecoder(const CreateDecoderParams& aParams)
 {
   if (!aParams.mConfig.mMimeType.EqualsLiteral("audio/mp4a-latm")) {
     return nullptr;
@@ -80,17 +81,18 @@ GMPDecoderModule::CreateAudioDecoder(con
     if (preferredGMP.isSome()) {
       aParams.mDiagnostics->SetGMP(preferredGMP.value());
     }
   }
 
   RefPtr<MediaDataDecoderProxy> wrapper = CreateDecoderWrapper(aParams.mCallback);
   wrapper->SetProxyTarget(new GMPAudioDecoder(aParams.AudioConfig(),
                                               aParams.mTaskQueue,
-                                              wrapper->Callback()));
+                                              wrapper->Callback(),
+                                              nullptr));
   return wrapper.forget();
 }
 
 PlatformDecoderModule::ConversionRequired
 GMPDecoderModule::DecoderNeedsConversion(const TrackInfo& aConfig) const
 {
   // GMPVideoCodecType::kGMPVideoCodecH264 specifies that encoded frames must be in AVCC format.
   if (aConfig.IsVideo()) {

--- a/dom/media/platforms/agnostic/gmp/GMPVideoDecoder.cpp
+++ b/dom/media/platforms/agnostic/gmp/GMPVideoDecoder.cpp
@@ -99,16 +99,38 @@ VideoCallbackAdapter::Error(GMPErr aErr)
 void
 VideoCallbackAdapter::Terminated()
 {
   // Note that this *may* be called from the proxy thread also.
   NS_WARNING("H.264 GMP decoder terminated.");
   mCallback->Error(MediaDataDecoderError::FATAL_ERROR);
 }
 
+GMPVideoDecoder::GMPVideoDecoder(const VideoInfo& aConfig,
+                                 layers::LayersBackend aLayersBackend,
+                                 layers::ImageContainer* aImageContainer,
+                                 TaskQueue* aTaskQueue,
+                                 MediaDataDecoderCallbackProxy* aCallback,
+                                 VideoCallbackAdapter* aAdapter)
+  : mConfig(aConfig)
+  , mCallback(aCallback)
+  , mGMP(nullptr)
+  , mHost(nullptr)
+  , mAdapter(aAdapter)
+  , mConvertNALUnitLengths(false)
+{
+  MOZ_ASSERT(!aAdapter || mCallback == aAdapter->Callback());
+  if (!aAdapter) {
+    mAdapter = new VideoCallbackAdapter(aCallback,
+                                        VideoInfo(aConfig.mDisplay.width,
+                                                  aConfig.mDisplay.height),
+                                        aImageContainer);
+  }
+}
+
 void
 GMPVideoDecoder::InitTags(nsTArray<nsCString>& aTags)
 {
   aTags.AppendElement(NS_LITERAL_CSTRING("h264"));
   const Maybe<nsCString> gmp(
     GMPDecoderModule::PreferredGMP(NS_LITERAL_CSTRING("video/avc")));
   if (gmp.isSome()) {
     aTags.AppendElement(gmp.value());

--- a/dom/media/platforms/agnostic/gmp/GMPVideoDecoder.h
+++ b/dom/media/platforms/agnostic/gmp/GMPVideoDecoder.h
@@ -22,16 +22,18 @@ public:
                        VideoInfo aVideoInfo,
                        layers::ImageContainer* aImageContainer)
    : mCallback(aCallback)
    , mLastStreamOffset(0)
    , mVideoInfo(aVideoInfo)
    , mImageContainer(aImageContainer)
   {}
 
+  MediaDataDecoderCallbackProxy* Callback() const { return mCallback; }
+
   // GMPVideoDecoderCallbackProxy
   void Decoded(GMPVideoi420Frame* aDecodedFrame) override;
   void ReceivedDecodedReferenceFrame(const uint64_t aPictureId) override;
   void ReceivedDecodedFrame(const uint64_t aPictureId) override;
   void InputDataExhausted() override;
   void DrainComplete() override;
   void ResetComplete() override;
   void Error(GMPErr aErr) override;
@@ -51,43 +53,17 @@ private:
 
 class GMPVideoDecoder : public MediaDataDecoder {
 protected:
   GMPVideoDecoder(const VideoInfo& aConfig,
                   layers::LayersBackend aLayersBackend,
                   layers::ImageContainer* aImageContainer,
                   TaskQueue* aTaskQueue,
                   MediaDataDecoderCallbackProxy* aCallback,
-                  VideoCallbackAdapter* aAdapter)
-   : mConfig(aConfig)
-   , mCallback(aCallback)
-   , mGMP(nullptr)
-   , mHost(nullptr)
-   , mAdapter(aAdapter)
-   , mConvertNALUnitLengths(false)
-  {
-  }
-
-public:
-  GMPVideoDecoder(const VideoInfo& aConfig,
-                  layers::LayersBackend aLayersBackend,
-                  layers::ImageContainer* aImageContainer,
-                  TaskQueue* aTaskQueue,
-                  MediaDataDecoderCallbackProxy* aCallback)
-   : mConfig(aConfig)
-   , mCallback(aCallback)
-   , mGMP(nullptr)
-   , mHost(nullptr)
-   , mAdapter(new VideoCallbackAdapter(aCallback,
-                                       VideoInfo(aConfig.mDisplay.width,
-                                                 aConfig.mDisplay.height),
-                                       aImageContainer))
-   , mConvertNALUnitLengths(false)
-  {
-  }
+                  VideoCallbackAdapter* aAdapter);
 
   RefPtr<InitPromise> Init() override;
   nsresult Input(MediaRawData* aSample) override;
   nsresult Flush() override;
   nsresult Drain() override;
   nsresult Shutdown() override;
   const char* GetDescriptionName() const override
   {