Bug 1120222 - Set AudioSink name to title of MediaElement's parent r=padenot

Differential Revision: https://phabricator.services.mozilla.com/D93462

dom/html/HTMLMediaElement.cpp

@@ -4119,6 +4119,49 @@ class HTMLMediaElement::ShutdownObserver : public nsIObserver {
 
 NS_IMPL_ISUPPORTS(HTMLMediaElement::ShutdownObserver, nsIObserver)
 
+class HTMLMediaElement::TitleChangeObserver final : public nsIObserver {
+ public:
+  NS_DECL_ISUPPORTS
+
+  explicit TitleChangeObserver(HTMLMediaElement* aElement)
+      : mElement(aElement) {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(aElement);
+  }
+
+  NS_IMETHOD Observe(nsISupports*, const char* aTopic,
+                     const char16_t*) override {
+    if (mElement) {
+      mElement->UpdateStreamName();
+    }
+
+    return NS_OK;
+  }
+
+  void Subscribe() {
+    nsCOMPtr<nsIObserverService> observerService =
+        mozilla::services::GetObserverService();
+    if (observerService) {
+      observerService->AddObserver(this, "document-title-changed", false);
+    }
+  }
+
+  void Unsubscribe() {
+    nsCOMPtr<nsIObserverService> observerService =
+        mozilla::services::GetObserverService();
+    if (observerService) {
+      observerService->RemoveObserver(this, "document-title-changed");
+    }
+  }
+
+ private:
+  ~TitleChangeObserver() = default;
+
+  WeakPtr<HTMLMediaElement> mElement;
+};
+
+NS_IMPL_ISUPPORTS(HTMLMediaElement::TitleChangeObserver, nsIObserver)
+
 HTMLMediaElement::HTMLMediaElement(
     already_AddRefed<mozilla::dom::NodeInfo>&& aNodeInfo)
     : nsGenericHTMLElement(std::move(aNodeInfo)),
@@ -4128,6 +4171,7 @@ HTMLMediaElement::HTMLMediaElement(
       mAbstractMainThread(
           OwnerDoc()->AbstractMainThreadFor(TaskCategory::Other)),
       mShutdownObserver(new ShutdownObserver),
+      mTitleChangeObserver(new TitleChangeObserver(this)),
       mEventBlocker(new EventBlocker(this)),
       mPlayed(new TimeRanges(ToSupports(OwnerDoc()))),
       mTracksCaptured(nullptr, "HTMLMediaElement::mTracksCaptured"),
@@ -4209,6 +4253,8 @@ HTMLMediaElement::~HTMLMediaElement() {
 
   mShutdownObserver->Unsubscribe();
 
+  mTitleChangeObserver->Unsubscribe();
+
   if (mVideoFrameContainer) {
     mVideoFrameContainer->ForgetElement();
   }
@@ -7134,6 +7180,13 @@ void HTMLMediaElement::SetMediaInfo(const MediaInfo& aInfo) {
   if ((aInfo.HasAudio() != oldHasAudio) && mResumeDelayedPlaybackAgent) {
     mResumeDelayedPlaybackAgent->UpdateAudibleState(this, IsAudible());
   }
+  nsILoadContext* loadContext = OwnerDoc()->GetLoadContext();
+  if (HasAudio() && loadContext && !loadContext->UsePrivateBrowsing()) {
+    mTitleChangeObserver->Subscribe();
+    UpdateStreamName();
+  } else {
+    mTitleChangeObserver->Unsubscribe();
+  }
   if (mAudioChannelWrapper) {
     mAudioChannelWrapper->AudioCaptureTrackChangeIfNeeded();
   }
@@ -7622,6 +7675,17 @@ void HTMLMediaElement::StartMediaControlKeyListenerIfNeeded() {
   mMediaControlKeyListener->Start();
 }
 
+void HTMLMediaElement::UpdateStreamName() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  nsAutoString aTitle;
+  OwnerDoc()->GetTitle(aTitle);
+
+  if (mDecoder) {
+    mDecoder->SetStreamName(aTitle);
+  }
+}
+
 void HTMLMediaElement::SetSecondaryMediaStreamRenderer(
     VideoFrameContainer* aContainer,
     FirstFrameVideoOutput* aFirstFrameOutput /* = nullptr */) {