Bug 1653390 - part6 : add audible check back in media element. r=bryce

In D73335, we remove those check which causes a regression where inaudible media is also able to be controlled by media control keys.

In order not to control those inaudible media, we should add the check back. If the media is inaudible, then we should not start the listener that would connect media element to the media control.

In addition, I also found that starting the listener for inaudible media would make the media controller's playback state incorrect, because the playback state is calculated by all controlled media. If an inaudible media is playing, the playback state should not consider that media.

Differential Revision: https://phabricator.services.mozilla.com/D84115

dom/html/HTMLMediaElement.cpp

@@ -401,19 +401,22 @@ class HTMLMediaElement::MediaControlKeyListener final
     MOZ_ASSERT(aElement);
   }
 
-  // Return false if the listener can't be started. Otherwise, return true.
-  bool Start() {
+  /**
+   * Start listening to the media control keys which would make media being able
+   * to be controlled via pressing media control keys.
+   */
+  void Start() {
     MOZ_ASSERT(NS_IsMainThread());
     if (IsStarted()) {
       // We have already been started, do not notify start twice.
-      return true;
+      return;
     }
 
     // Fail to init media agent, we are not able to notify the media controller
     // any update and also are not able to receive media control key events.
     if (!InitMediaAgent()) {
-      MEDIACONTROL_LOG("Fail to init content media agent!");
-      return false;
+      MEDIACONTROL_LOG("Failed to start due to not able to init media agent!");
+      return;
     }
 
     NotifyPlaybackStateChanged(MediaPlaybackState::eStarted);
@@ -423,7 +426,6 @@ class HTMLMediaElement::MediaControlKeyListener final
     if (!Owner()->Paused()) {
       NotifyMediaStartedPlaying();
     }
-    return true;
   }
 
   /**
@@ -545,7 +547,7 @@ class HTMLMediaElement::MediaControlKeyListener final
     // we would also notify `ePlayed`.
     bool wasInPlayingState = mState == MediaPlaybackState::ePlayed;
     StopIfNeeded();
-    Unused << Start();
+    Start();
     if (wasInPlayingState) {
       NotifyMediaStartedPlaying();
     }
@@ -5535,8 +5537,6 @@ void HTMLMediaElement::MetadataLoaded(const MediaInfo* aInfo,
     mDefaultPlaybackStartPosition = 0.0;
   }
 
-  StartListeningMediaControlKeyIfNeeded();
-
   mWatchManager.ManualNotify(&HTMLMediaElement::UpdateReadyStateInternal);
 }
 
@@ -6555,7 +6555,7 @@ void HTMLMediaElement::SuspendOrResumeElement(bool aSuspendElement) {
         !AutoplayPolicy::IsAllowedToPlay(*this)) {
       MaybeNotifyAutoplayBlocked();
     }
-    StartListeningMediaControlKeyIfNeeded();
+    StartMediaControlKeyListenerIfNeeded();
   }
   if (StaticPrefs::media_testing_only_events()) {
     auto dispatcher = MakeRefPtr<AsyncEventDispatcher>(
@@ -7402,7 +7402,12 @@ void HTMLMediaElement::NotifyAudioPlaybackChanged(
   if (mAudioChannelWrapper) {
     mAudioChannelWrapper->NotifyAudioPlaybackChanged(aReason);
   }
-  mMediaControlKeyListener->UpdateMediaAudibleState(IsAudible());
+  // We would start the listener after media becomes audible.
+  const bool isAudible = IsAudible();
+  if (isAudible && !mMediaControlKeyListener->IsStarted()) {
+    StartMediaControlKeyListenerIfNeeded();
+  }
+  mMediaControlKeyListener->UpdateMediaAudibleState(isAudible);
   // only request wake lock for audible media.
   UpdateWakeLock();
 }
@@ -7863,7 +7868,7 @@ void HTMLMediaElement::NotifyMediaControlPlaybackStateChanged() {
   }
 }
 
-void HTMLMediaElement::StartListeningMediaControlKeyIfNeeded() {
+bool HTMLMediaElement::ShouldStartMediaControlKeyListener() const {
   // In order to filter out notification-ish sound, we use this pref to set the
   // eligible media duration to prevent showing media control for those short
   // sound.
@@ -7871,13 +7876,27 @@ void HTMLMediaElement::StartListeningMediaControlKeyIfNeeded() {
       StaticPrefs::media_mediacontrol_eligible_media_duration_s()) {
     MEDIACONTROL_LOG("Not listening because media's duration %f is too short.",
                      Duration());
-    return;
+    return false;
   }
 
-  if (mMediaControlKeyListener->IsStarted() ||
-      !mMediaControlKeyListener->Start()) {
+  // This includes cases such like `video is muted`, `video has zero volume`,
+  // `video's audio track is still inaudible` and `tab is muted by audio channel
+  // (tab sound indicator)`, all these cases would make media inaudible.
+  // `ComputedVolume()` would return the final volume applied the affection made
+  // by audio channel, which is used to detect if the tab is muted by audio
+  // channel.
+  if (!IsAudible() || ComputedVolume() == 0.0f) {
+    MEDIACONTROL_LOG("Not listening because media is inaudible");
+    return false;
+  }
+  return true;
+}
+
+void HTMLMediaElement::StartMediaControlKeyListenerIfNeeded() {
+  if (!ShouldStartMediaControlKeyListener()) {
     return;
   }
+  mMediaControlKeyListener->Start();
 }
 
 void HTMLMediaElement::UpdateMediaControlAfterPictureInPictureModeChanged() {