Bug 1707584 - part6 : defer pausing video element during the style refresh. r=emilio

alastor0325 · alastor0325 · commit b418243a4446 · 2026-02-06T22:58:59.000Z
During the style refresh, it is prohibited to change the element state. Therefore, we should defer pausing the video element, which could change the element state, until the refresh has settled. Differential Revision: https://phabricator.services.mozilla.com/D282114
diff --git a/dom/media/mediaelement/HTMLMediaElement.h b/dom/media/mediaelement/HTMLMediaElement.h
@@ -1842,6 +1842,8 @@ class HTMLMediaElement : public nsGenericHTMLElement,
   // https://html.spec.whatwg.org/multipage/media.html#pending-text-track-change-notification-flag
   bool mPendingTextTrackChanged = false;
 
+  Visibility mVisibilityState = Visibility::Untracked;
+
  public:
   // This function will be called whenever a text track that is in a media
   // element's list of text tracks has its text track mode change value
@@ -1898,8 +1900,6 @@ class HTMLMediaElement : public nsGenericHTMLElement,
   // https://html.spec.whatwg.org/multipage/media.html#is-currently-stalled
   bool mIsCurrentlyStalled = false;
 
-  Visibility mVisibilityState = Visibility::Untracked;
-
   UniquePtr<ErrorSink> mErrorSink;
 
   // This wrapper will handle all audio channel related stuffs, eg. the
diff --git a/dom/media/mediaelement/HTMLVideoElement.cpp b/dom/media/mediaelement/HTMLVideoElement.cpp
@@ -768,9 +768,19 @@ void HTMLVideoElement::OnVisibilityChange(Visibility aNewVisibility) {
   if ((aNewVisibility == Visibility::ApproximatelyNonVisible &&
        !IsCloningElementVisually()) &&
       mCanAutoplayFlag) {
-    LOG("pause non-audible autoplay video when it's invisible");
-    PauseInternal();
-    mCanAutoplayFlag = true;
+    // Defer pausing the element to avoid changing the element state during the
+    // style refresh.
+    NS_DispatchToMainThread(NS_NewRunnableFunction(
+        __func__, [self = RefPtr<HTMLMediaElement>(this), this] {
+          // https://html.spec.whatwg.org/multipage/media.html#ready-states:intersect-the-viewport-3
+          if (mVisibilityState != Visibility::ApproximatelyNonVisible ||
+              !mCanAutoplayFlag) {
+            return;
+          }
+          LOG("pause non-audible autoplay video when it's invisible");
+          PauseInternal();
+          mCanAutoplayFlag = true;
+        }));
     return;
   }
 }
