diff --git a/dom/media/MediaDecoderReader.h b/dom/media/MediaDecoderReader.h
index 6c4356e79c60..d224abb502d1 100644
--- a/dom/media/MediaDecoderReader.h
+++ b/dom/media/MediaDecoderReader.h
@@ -243,6 +243,18 @@ public:
     return mOnMediaNotSeekable;
   }
 
+  // Notified if the reader can't decode a sample due to a missing decryption
+  // key.
+  MediaEventSource<TrackInfo::TrackType>& OnTrackWaitingForKey()
+  {
+    return mOnTrackWaitingForKey;
+  }
+
+  MediaEventProducer<TrackInfo::TrackType>& OnTrackWaitingForKeyProducer()
+  {
+    return mOnTrackWaitingForKey;
+  }
+
   // Switch the video decoder to BlankDecoderModule. It might takes effective
   // since a few samples later depends on how much demuxed samples are already
   // queued in the original video decoder.
@@ -306,6 +318,9 @@ protected:
   // Notify if this media is not seekable.
   MediaEventProducer<void> mOnMediaNotSeekable;
 
+  // Notify if we are waiting for a decryption key.
+  MediaEventProducer<TrackInfo::TrackType> mOnTrackWaitingForKey;
+
 private:
   virtual nsresult InitInternal() { return NS_OK; }
 
diff --git a/dom/media/MediaFormatReader.cpp b/dom/media/MediaFormatReader.cpp
index ad0b2a5d5430..6528406bf41f 100644
--- a/dom/media/MediaFormatReader.cpp
+++ b/dom/media/MediaFormatReader.cpp
@@ -389,7 +389,9 @@ MediaFormatReader::DecoderFactory::DoCreateDecoder(TrackType aTrack)
         ownerData.mTaskQueue,
         mOwner->mCrashHelper,
         ownerData.mIsBlankDecode,
-        &result
+        &result,
+        aTrack,
+        &mOwner->OnTrackWaitingForKeyProducer()
       });
       break;
     }
@@ -406,7 +408,9 @@ MediaFormatReader::DecoderFactory::DoCreateDecoder(TrackType aTrack)
         mOwner->GetImageContainer(),
         mOwner->mCrashHelper,
         ownerData.mIsBlankDecode,
-        &result
+        &result,
+        aTrack,
+        &mOwner->OnTrackWaitingForKeyProducer()
       });
       break;
     }
@@ -847,6 +851,8 @@ MediaFormatReader::MediaFormatReader(AbstractMediaDecoder* aDecoder,
       aDecoder->CompositorUpdatedEvent()->Connect(
         mTaskQueue, this, &MediaFormatReader::NotifyCompositorUpdated);
   }
+  mOnTrackWaitingForKeyListener = OnTrackWaitingForKey().Connect(
+    mTaskQueue, this, &MediaFormatReader::NotifyWaitingForKey);
 }
 
 MediaFormatReader::~MediaFormatReader()
@@ -895,6 +901,7 @@ MediaFormatReader::Shutdown()
   mDemuxer = nullptr;
 
   mCompositorUpdatedListener.DisconnectIfExists();
+  mOnTrackWaitingForKeyListener.Disconnect();
 
   RefPtr<ShutdownPromise> p = mShutdownPromise.Ensure(__func__);
   ShutdownPromise::All(OwnerThread(), promises)
@@ -1523,6 +1530,21 @@ MediaFormatReader::NotifyWaitingForData(TrackType aTrack)
   ScheduleUpdate(aTrack);
 }
 
+void
+MediaFormatReader::NotifyWaitingForKey(TrackType aTrack)
+{
+  MOZ_ASSERT(OnTaskQueue());
+  auto& decoder = GetDecoderData(aTrack);
+  if (mDecoder) {
+    mDecoder->NotifyWaitingForKey();
+  }
+  if (!decoder.mDecodeRequest.Exists()) {
+    LOGV("WaitingForKey received while no pending decode. Ignoring");
+  }
+  decoder.mWaitingForKey = true;
+  ScheduleUpdate(aTrack);
+}
+
 void
 MediaFormatReader::NotifyEndOfStream(TrackType aTrack)
 {
@@ -2013,6 +2035,10 @@ MediaFormatReader::Update(TrackType aTrack)
       // EOS state. We can immediately reject the data promise.
       LOG("Rejecting %s promise: EOS", TrackTypeToStr(aTrack));
       decoder.RejectPromise(NS_ERROR_DOM_MEDIA_END_OF_STREAM, __func__);
+    } else if (decoder.mWaitingForKey) {
+      LOG("Rejecting %s promise: WAITING_FOR_DATA due to waiting for key",
+          TrackTypeToStr(aTrack));
+      decoder.RejectPromise(NS_ERROR_DOM_MEDIA_WAITING_FOR_DATA, __func__);
     }
   }
 
@@ -2054,13 +2080,23 @@ MediaFormatReader::Update(TrackType aTrack)
        decoder.mWaitingForData, decoder.HasPromise(),
        decoder.mLastStreamSourceID);
 
-  if ((decoder.mWaitingForData &&
-       (!decoder.mTimeThreshold || decoder.mTimeThreshold.ref().mWaiting))) {
+  if ((decoder.mWaitingForData
+       && (!decoder.mTimeThreshold || decoder.mTimeThreshold.ref().mWaiting))
+      || (decoder.mWaitingForKey && decoder.mDecodeRequest.Exists())) {
     // Nothing more we can do at present.
     LOGV("Still waiting for data or key.");
     return;
   }
 
+  if (decoder.mWaitingForKey) {
+    decoder.mWaitingForKey = false;
+    if (decoder.HasWaitingPromise() && !decoder.IsWaiting()) {
+      LOGV("No longer waiting for key. Resolving waiting promise");
+      decoder.mWaitingPromise.Resolve(decoder.mType, __func__);
+      return;
+    }
+  }
+
   if (!needInput) {
     LOGV("No need for additional input (pending:%u)",
          uint32_t(decoder.mOutput.Length()));
diff --git a/dom/media/MediaFormatReader.h b/dom/media/MediaFormatReader.h
index c85af13da692..b217edebb0ed 100644
--- a/dom/media/MediaFormatReader.h
+++ b/dom/media/MediaFormatReader.h
@@ -141,6 +141,7 @@ private:
   void NotifyDrainComplete(TrackType aTrack);
   void NotifyError(TrackType aTrack, const MediaResult& aError);
   void NotifyWaitingForData(TrackType aTrack);
+  void NotifyWaitingForKey(TrackType aTrack);
   void NotifyEndOfStream(TrackType aTrack);
 
   void ExtractCryptoInitData(nsTArray<uint8_t>& aInitData);
@@ -170,6 +171,7 @@ private:
       , mUpdateScheduled(false)
       , mDemuxEOS(false)
       , mWaitingForData(false)
+      , mWaitingForKey(false)
       , mReceivedNewData(false)
       , mNeedDraining(false)
       , mDraining(false)
@@ -226,6 +228,7 @@ private:
     bool mUpdateScheduled;
     bool mDemuxEOS;
     bool mWaitingForData;
+    bool mWaitingForKey;
     bool mReceivedNewData;
 
     // Pending seek.
@@ -245,7 +248,7 @@ private:
     bool IsWaiting() const
     {
       MOZ_ASSERT(mOwner->OnTaskQueue());
-      return mWaitingForData;
+      return mWaitingForData || mWaitingForKey;
     }
 
     // MediaDataDecoder handler's variables.
@@ -373,6 +376,7 @@ private:
       MOZ_ASSERT(mOwner->OnTaskQueue());
       mDemuxEOS = false;
       mWaitingForData = false;
+      mWaitingForKey = false;
       mQueuedSamples.Clear();
       mNeedDraining = false;
       mDecodeRequest.DisconnectIfExists();
@@ -560,6 +564,7 @@ private:
   UniquePtr<DecoderFactory> mDecoderFactory;
 
   MediaEventListener mCompositorUpdatedListener;
+  MediaEventListener mOnTrackWaitingForKeyListener;
 
   void OnFirstDemuxCompleted(TrackInfo::TrackType aType,
                              RefPtr<MediaTrackDemuxer::SamplesHolder> aSamples);
diff --git a/dom/media/platforms/PlatformDecoderModule.h b/dom/media/platforms/PlatformDecoderModule.h
index e01e55088d81..ad5b5a1cb530 100644
--- a/dom/media/platforms/PlatformDecoderModule.h
+++ b/dom/media/platforms/PlatformDecoderModule.h
@@ -81,6 +81,8 @@ struct MOZ_STACK_CLASS CreateDecoderParams final
   RefPtr<layers::KnowsCompositor> mKnowsCompositor;
   RefPtr<GMPCrashHelper> mCrashHelper;
   bool mUseBlankDecoder = false;
+  TrackInfo::TrackType mType = TrackInfo::kUndefinedTrack;
+  MediaEventProducer<TrackInfo::TrackType>* mOnWaitingForKeyEvent = nullptr;
 
 private:
   void Set(TaskQueue* aTaskQueue) { mTaskQueue = aTaskQueue; }
@@ -99,6 +101,14 @@ private:
   {
     mKnowsCompositor = aKnowsCompositor;
   }
+  void Set(TrackInfo::TrackType aType)
+  {
+    mType = aType;
+  }
+  void Set(MediaEventProducer<TrackInfo::TrackType>* aOnWaitingForKey)
+  {
+    mOnWaitingForKeyEvent = aOnWaitingForKey;
+  }
   template <typename T1, typename T2, typename... Ts>
   void Set(T1&& a1, T2&& a2, Ts&&... args)
   {
diff --git a/dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp b/dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp
index 8fdb16685e95..36f0cf352eaa 100644
--- a/dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp
+++ b/dom/media/platforms/agnostic/eme/EMEDecoderModule.cpp
@@ -27,13 +27,14 @@ extern already_AddRefed<PlatformDecoderModule> CreateBlankDecoderModule();
 class EMEDecryptor : public MediaDataDecoder
 {
 public:
-  EMEDecryptor(MediaDataDecoder* aDecoder,
-               CDMProxy* aProxy,
-               TaskQueue* aDecodeTaskQueue)
+  EMEDecryptor(MediaDataDecoder* aDecoder, CDMProxy* aProxy,
+               TaskQueue* aDecodeTaskQueue, TrackInfo::TrackType aType,
+               MediaEventProducer<TrackInfo::TrackType>* aOnWaitingForKey)
     : mDecoder(aDecoder)
     , mTaskQueue(aDecodeTaskQueue)
     , mProxy(aProxy)
-    , mSamplesWaitingForKey(new SamplesWaitingForKey(mProxy))
+    , mSamplesWaitingForKey(
+        new SamplesWaitingForKey(mProxy, aType, aOnWaitingForKey))
     , mIsShutdown(false)
   {
   }
@@ -204,12 +205,15 @@ private:
 class EMEMediaDataDecoderProxy : public MediaDataDecoderProxy
 {
 public:
-  EMEMediaDataDecoderProxy(already_AddRefed<AbstractThread> aProxyThread,
-                           CDMProxy* aProxy)
-   : MediaDataDecoderProxy(Move(aProxyThread))
-   , mTaskQueue(AbstractThread::GetCurrent()->AsTaskQueue())
-   , mSamplesWaitingForKey(new SamplesWaitingForKey(aProxy))
-   , mProxy(aProxy)
+  EMEMediaDataDecoderProxy(
+    already_AddRefed<AbstractThread> aProxyThread, CDMProxy* aProxy,
+    TrackInfo::TrackType aType,
+    MediaEventProducer<TrackInfo::TrackType>* aOnWaitingForKey)
+    : MediaDataDecoderProxy(Move(aProxyThread))
+    , mTaskQueue(AbstractThread::GetCurrent()->AsTaskQueue())
+    , mSamplesWaitingForKey(
+        new SamplesWaitingForKey(aProxy, aType, aOnWaitingForKey))
+    , mProxy(aProxy)
   {
   }
 
@@ -289,7 +293,7 @@ EMEDecoderModule::~EMEDecoderModule()
 }
 
 static already_AddRefed<MediaDataDecoderProxy>
-CreateDecoderWrapper(CDMProxy* aProxy)
+CreateDecoderWrapper(CDMProxy* aProxy, const CreateDecoderParams& aParams)
 {
   RefPtr<gmp::GeckoMediaPluginService> s(gmp::GeckoMediaPluginService::GetGeckoMediaPluginService());
   if (!s) {
@@ -299,8 +303,8 @@ CreateDecoderWrapper(CDMProxy* aProxy)
   if (!thread) {
     return nullptr;
   }
-  RefPtr<MediaDataDecoderProxy> decoder(
-    new EMEMediaDataDecoderProxy(thread.forget(), aProxy));
+  RefPtr<MediaDataDecoderProxy> decoder(new EMEMediaDataDecoderProxy(
+    thread.forget(), aProxy, aParams.mType, aParams.mOnWaitingForKeyEvent));
   return decoder.forget();
 }
 
@@ -317,7 +321,8 @@ EMEDecoderModule::CreateVideoDecoder(const CreateDecoderParams& aParams)
 
   if (SupportsMimeType(aParams.mConfig.mMimeType, nullptr)) {
     // GMP decodes. Assume that means it can decrypt too.
-    RefPtr<MediaDataDecoderProxy> wrapper = CreateDecoderWrapper(mProxy);
+    RefPtr<MediaDataDecoderProxy> wrapper =
+      CreateDecoderWrapper(mProxy, aParams);
     auto params = GMPVideoDecoderParams(aParams);
     wrapper->SetProxyTarget(new EMEVideoDecoder(mProxy, params));
     return wrapper.forget();
@@ -330,7 +335,8 @@ EMEDecoderModule::CreateVideoDecoder(const CreateDecoderParams& aParams)
   }
 
   RefPtr<MediaDataDecoder> emeDecoder(new EMEDecryptor(
-    decoder, mProxy, AbstractThread::GetCurrent()->AsTaskQueue()));
+    decoder, mProxy, AbstractThread::GetCurrent()->AsTaskQueue(),
+    aParams.mType, aParams.mOnWaitingForKeyEvent));
   return emeDecoder.forget();
 }
 
@@ -355,7 +361,8 @@ EMEDecoderModule::CreateAudioDecoder(const CreateDecoderParams& aParams)
   }
 
   RefPtr<MediaDataDecoder> emeDecoder(new EMEDecryptor(
-    decoder, mProxy, AbstractThread::GetCurrent()->AsTaskQueue()));
+    decoder, mProxy, AbstractThread::GetCurrent()->AsTaskQueue(),
+    aParams.mType, aParams.mOnWaitingForKeyEvent));
   return emeDecoder.forget();
 }
 
diff --git a/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.cpp b/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.cpp
index c0fa9af954a4..e9dee73ea704 100644
--- a/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.cpp
+++ b/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.cpp
@@ -8,13 +8,18 @@
 #include "mozilla/CDMCaps.h"
 #include "mozilla/TaskQueue.h"
 #include "MediaData.h"
+#include "MediaEventSource.h"
 #include "SamplesWaitingForKey.h"
 
 namespace mozilla {
 
-SamplesWaitingForKey::SamplesWaitingForKey(CDMProxy* aProxy)
+SamplesWaitingForKey::SamplesWaitingForKey(
+  CDMProxy* aProxy, TrackInfo::TrackType aType,
+  MediaEventProducer<TrackInfo::TrackType>* aOnWaitingForKey)
   : mMutex("SamplesWaitingForKey")
   , mProxy(aProxy)
+  , mType(aType)
+  , mOnWaitingForKeyEvent(aOnWaitingForKey)
 {
 }
 
@@ -41,6 +46,9 @@ SamplesWaitingForKey::WaitIfKeyNotUsable(MediaRawData* aSample)
     MutexAutoLock lock(mMutex);
     mSamples.AppendElement(Move(entry));
   }
+  if (mOnWaitingForKeyEvent) {
+    mOnWaitingForKeyEvent->Notify(mType);
+  }
   caps.NotifyWhenKeyIdUsable(aSample->mCrypto.mKeyId, this);
   return p;
 }
diff --git a/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.h b/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.h
index cc4a546b4b3d..accf7cf3d540 100644
--- a/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.h
+++ b/dom/media/platforms/agnostic/eme/SamplesWaitingForKey.h
@@ -10,12 +10,14 @@
 #include "mozilla/MozPromise.h"
 #include "mozilla/Mutex.h"
 #include "mozilla/RefPtr.h"
+#include "MediaInfo.h"
 
 namespace mozilla {
 
 typedef nsTArray<uint8_t> CencKeyId;
 
 class CDMProxy;
+template <typename... Es> class MediaEventProducer;
 class MediaRawData;
 
 // Encapsulates the task of waiting for the CDMProxy to have the necessary
@@ -28,7 +30,8 @@ public:
   typedef MozPromise<RefPtr<MediaRawData>, bool, /* IsExclusive = */ true>
     WaitForKeyPromise;
 
-  explicit SamplesWaitingForKey(CDMProxy* aProxy);
+  SamplesWaitingForKey(CDMProxy* aProxy, TrackInfo::TrackType aType,
+                       MediaEventProducer<TrackInfo::TrackType>* aOnWaitingForKey);
 
   // Returns a promise that will be resolved if or when a key for decoding the
   // sample becomes usable.
@@ -50,6 +53,8 @@ private:
     MozPromiseHolder<WaitForKeyPromise> mPromise;
   };
   nsTArray<SampleEntry> mSamples;
+  const TrackInfo::TrackType mType;
+  MediaEventProducer<TrackInfo::TrackType>* const mOnWaitingForKeyEvent;
 };
 
 } // namespace mozilla
diff --git a/dom/media/platforms/wrappers/H264Converter.cpp b/dom/media/platforms/wrappers/H264Converter.cpp
index 06f534704074..d7c2ef569418 100644
--- a/dom/media/platforms/wrappers/H264Converter.cpp
+++ b/dom/media/platforms/wrappers/H264Converter.cpp
@@ -28,6 +28,8 @@ H264Converter::H264Converter(PlatformDecoderModule* aPDM,
   , mNeedAVCC(aPDM->DecoderNeedsConversion(aParams.mConfig)
       == PlatformDecoderModule::ConversionRequired::kNeedAVCC)
   , mLastError(NS_OK)
+  , mType(aParams.mType)
+  , mOnWaitingForKeyEvent(aParams.mOnWaitingForKeyEvent)
 {
   CreateDecoder(aParams.mDiagnostics);
 }
@@ -194,7 +196,9 @@ H264Converter::CreateDecoder(DecoderDoctorDiagnostics* aDiagnostics)
     aDiagnostics,
     mImageContainer,
     mKnowsCompositor,
-    mGMPCrashHelper
+    mGMPCrashHelper,
+    mType,
+    mOnWaitingForKeyEvent
   });
 
   if (!mDecoder) {
diff --git a/dom/media/platforms/wrappers/H264Converter.h b/dom/media/platforms/wrappers/H264Converter.h
index 1d0a5f8f4534..2670ed046cb5 100644
--- a/dom/media/platforms/wrappers/H264Converter.h
+++ b/dom/media/platforms/wrappers/H264Converter.h
@@ -76,6 +76,8 @@ private:
   bool mNeedAVCC;
   nsresult mLastError;
   bool mNeedKeyframe = true;
+  const TrackInfo::TrackType mType;
+  MediaEventProducer<TrackInfo::TrackType>* const mOnWaitingForKeyEvent;
 };
 
 } // namespace mozilla