Web Platform Tests for HTML video and audio element lazy loading via the loading attribute by scottjehl · Pull Request #57051 · web-platform-tests/wpt

scottjehl · 2026-01-07T21:36:52Z

These tests support the proposal for the addition of a loading attribute
on the video and audio elements, designed to enable lazy-loading of resources related to those elements.

Related HTML Standard Proposal: whatwg/html#11980
Related issue: whatwg/html#10376

These are designed to pass in a browser that supports the proposed feature (verified in a locally patched browser).

Co-authored-by: Zach Lysobey zlysobey@squarespace.com
Co-authored-by: Brad Frost bfrost@squarespace.com
Co-authored-by: Credo Duarte cduarte@squarespace.com

…g attribute These tests support the proposal for the addition of a loading attribute on the video element, designed to enable lazy-loading for video and poster data. HTML Standard PR here whatwg/html#11980 Co-authored-by: Zach Lysobey <zlysobey@squarespace.com> Co-authored-by: Brad Frost <bfrost@squarespace.com> Co-authored-by: Credo Duarte <cduarte@squarespace.com>

…d with a proposed HTML feature

rename files to use a .tentative.html convention since they correspond with a proposed HTML feature

scottjehl · 2026-01-08T15:44:10Z

Renamed the files to be .tentative.html since they correspond with a proposed HTML feature. Thanks for the tip @keithamus

html/semantics/embedded-content/the-video-element/video-loading-attr-default.tentative.html

.../semantics/embedded-content/the-video-element/video-loading-autoplay-deferred.tentative.html

html/semantics/embedded-content/the-video-element/video-loading-eager.tentative.html

.../semantics/embedded-content/the-video-element/video-loading-autoplay-deferred.tentative.html

html/semantics/embedded-content/the-video-element/video-loading-lazy-in-viewport.tentative.html

...ics/embedded-content/the-video-element/video-loading-lazy-poster-when-visible.tentative.html

...semantics/embedded-content/the-video-element/video-loading-lazy-window-onload.tentative.html

…plementations

… event and added a fallback if event never fires.

…t event comes after window load

… scscroll, as the poster image will impact its rendered size and be useful as a proxy for poster lazy loading

…ms to be more reliable

scottjehl · 2026-01-15T01:06:41Z

Thanks for the review.
After latest revisions:

Re-verified these tests fail in existing stable browsers (aside from visibility-deferred autoplay tests in browsers that support that already).
Re-verified these are all passing in our local patched webkit and firefox (for whatever that's worth).

html/dom/elements-embedded.js

…ure is tentative. note with comments

…the document will not load

…d not load data

…o, only audio. removed.

scottjehl · 2026-02-10T18:15:29Z

I just added some tests to round out the suite a bit (disconnected node, missing controls attribute, non-rendered elements), and the reflection tests are tentative again so they can be considered for merge before the spec

https://github.com/web-platform-tests/wpt/pull/57051/changes/2283368b8484740e0f2925fd1b034067fc9bcd80..9f8574c45a83547ecef49ff478a62a36fb01bd09

hjanuschka · 2026-02-12T15:16:55Z

is there a ETA when this PR can land? on chromium side we are almost done with review (and potentially landing it behind a flag), but would be great to have tests landed first, rn i have them commited into my chromium cl (to see if they turn green), landing it would most likely send a WPT bot and might mess it up.

keithamus

Given these are all tentative, and there's no obvious issues (racey conditions). In addition the major feedback from @zcorpan has been addressed, I think we should merge this in.

Stale

keithamus · 2026-02-12T15:58:51Z

@scottjehl for next steps, please raise a PR which renames these from tentative to not (so .tentative.html becomes .html), please also uncomment the changesi n elements-embedded. Raise this as a PR and attach it to the HTML spec PR, that way we can make these tests official as the spec PR lands.

scottjehl · 2026-02-12T18:32:47Z

Thanks @keithamus !
That PR is up: #57754

…ttribute https://bugs.webkit.org/show_bug.cgi?id=303995 Reviewed by NOBODY (OOPS!). Implement proposed loading attribute for video and audio elements. This patch implements a proposed loading attribute for video and audio elements, enabling lazy loading of media sources and video poster images, and deferring autoplay. This change is proposed to be added to the HTML spec in the following PR: whatwg/html#11980 This patch is passing video and audio WPT tests from the following PR: web-platform-tests/wpt#57051 * Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml: * Source/WebCore/Sources.txt: * Source/WebCore/WebCore.xcodeproj/project.pbxproj: * Source/WebCore/dom/Document.cpp: (WebCore::Document::lazyLoadMediaObserver): * Source/WebCore/dom/Document.h: * Source/WebCore/html/HTMLMediaElement.cpp: (WebCore::HTMLMediaElement::didMoveToNewDocument): (WebCore::HTMLMediaElement::attributeChanged): (WebCore::HTMLMediaElement::didFinishInsertingNode): (WebCore::HTMLMediaElement::removedFromAncestor): (WebCore::HTMLMediaElement::hasLazyLoadableAttributeValue): (WebCore::HTMLMediaElement::isLazyLoadable const): (WebCore::HTMLMediaElement::loadDeferredMedia): (WebCore::HTMLMediaElement::resumeLazyLoadingIfNeeded): (WebCore::HTMLMediaElement::loading const): (WebCore::HTMLMediaElement::setLoading): (WebCore::HTMLMediaElement::play): (WebCore::HTMLMediaElement::sourceWasAdded): (WebCore::HTMLMediaElement::setShouldDelayLoadEvent): * Source/WebCore/html/HTMLMediaElement.h: * Source/WebCore/html/HTMLMediaElement.idl: * Source/WebCore/html/HTMLVideoElement.cpp: (WebCore::HTMLVideoElement::rendererIsNeeded): (WebCore::HTMLVideoElement::supportsFullscreen const): (WebCore::HTMLVideoElement::hasAvailableVideoFrame const): (WebCore::HTMLVideoElement::webkitEnterFullscreen): (WebCore::HTMLVideoElement::loadDeferredMedia): * Source/WebCore/html/HTMLVideoElement.h: * Source/WebCore/html/LazyLoadMediaObserver.cpp: Added. (WebCore::LazyLoadMediaObserver::observe): (WebCore::LazyLoadMediaObserver::unobserve): (WebCore::LazyLoadMediaObserver::intersectionObserver): (WebCore::LazyLoadMediaObserver::isObserved const): * Source/WebCore/html/LazyLoadMediaObserver.h: Added. * Source/WebCore/html/parser/HTMLParserOptions.cpp: * Source/WebCore/html/parser/HTMLPreloadScanner.cpp: (WebCore::TokenPreloadScanner::StartTagScanner::processAttribute): * Source/WebCore/html/shadow/DataListButtonElement.cpp: * Source/WebCore/html/shadow/SpinButtonElement.cpp: * Source/WebCore/loader/ImageLoader.cpp: (WebCore::ImageLoader::updateFromElement): (WebCore::ImageLoader::didUpdateCachedImage): (WebCore::ImageLoader::notifyFinished): (WebCore::ImageLoader::updatedHasPendingEvent): (WebCore::ImageLoader::decode):

arai-a · 2026-02-17T06:39:46Z

html/dom/elements-embedded.js

    controls: "boolean",
    controlsList: {type: "tokenlist", domAttrName: "controlsList"},
-    defaultMuted: {type: "boolean", domAttrName: "muted"},
+    defaultMuted: {type: "boolean", domAttrName: "muted"}/*,


This is a syntax error.
It needs a comma between this property and the next property.

…ttribute https://bugs.webkit.org/show_bug.cgi?id=303995 Reviewed by NOBODY (OOPS!). Implement proposed loading attribute for video and audio elements. This patch implements a proposed loading attribute for video and audio elements, enabling lazy loading of media sources and video poster images, and deferring autoplay. This change is proposed to be added to the HTML spec in the following PR: whatwg/html#11980 This patch is passing video and audio WPT tests from the following PR: web-platform-tests/wpt#57051 * Source/WTF/Scripts/Preferences/UnifiedWebPreferences.yaml: * Source/WebCore/Sources.txt: * Source/WebCore/WebCore.xcodeproj/project.pbxproj: * Source/WebCore/dom/Document.cpp: (WebCore::Document::lazyLoadMediaObserver): * Source/WebCore/dom/Document.h: * Source/WebCore/html/HTMLMediaElement.cpp: (WebCore::HTMLMediaElement::didMoveToNewDocument): (WebCore::HTMLMediaElement::attributeChanged): (WebCore::HTMLMediaElement::didFinishInsertingNode): (WebCore::HTMLMediaElement::removedFromAncestor): (WebCore::HTMLMediaElement::hasLazyLoadableAttributeValue): (WebCore::HTMLMediaElement::isLazyLoadable const): (WebCore::HTMLMediaElement::loadDeferredMedia): (WebCore::HTMLMediaElement::resumeLazyLoadingIfNeeded): (WebCore::HTMLMediaElement::loading const): (WebCore::HTMLMediaElement::setLoading): (WebCore::HTMLMediaElement::play): (WebCore::HTMLMediaElement::sourceWasAdded): (WebCore::HTMLMediaElement::setShouldDelayLoadEvent): * Source/WebCore/html/HTMLMediaElement.h: * Source/WebCore/html/HTMLMediaElement.idl: * Source/WebCore/html/HTMLVideoElement.cpp: (WebCore::HTMLVideoElement::rendererIsNeeded): (WebCore::HTMLVideoElement::supportsFullscreen const): (WebCore::HTMLVideoElement::hasAvailableVideoFrame const): (WebCore::HTMLVideoElement::webkitEnterFullscreen): (WebCore::HTMLVideoElement::loadDeferredMedia): * Source/WebCore/html/HTMLVideoElement.h: * Source/WebCore/html/LazyLoadMediaObserver.cpp: Added. (WebCore::LazyLoadMediaObserver::observe): (WebCore::LazyLoadMediaObserver::unobserve): (WebCore::LazyLoadMediaObserver::intersectionObserver): (WebCore::LazyLoadMediaObserver::isObserved const): * Source/WebCore/html/LazyLoadMediaObserver.h: Added. * Source/WebCore/html/parser/HTMLParserOptions.cpp: * Source/WebCore/html/parser/HTMLPreloadScanner.cpp: (WebCore::TokenPreloadScanner::StartTagScanner::processAttribute): * Source/WebCore/html/shadow/DataListButtonElement.cpp: * Source/WebCore/html/shadow/SpinButtonElement.cpp: * Source/WebCore/loader/ImageLoader.cpp: (WebCore::ImageLoader::updateFromElement): (WebCore::ImageLoader::didUpdateCachedImage): (WebCore::ImageLoader::notifyFinished): (WebCore::ImageLoader::updatedHasPendingEvent): (WebCore::ImageLoader::decode):

wpt-pr-bot added the html label Jan 7, 2026

wpt-pr-bot assigned annevk Jan 7, 2026

wpt-pr-bot requested review from annevk, foolip, jdm and jgraham January 7, 2026 21:37

scottjehl mentioned this pull request Jan 7, 2026

Add support for video and audio element lazy-loading via the loading attribute whatwg/html#11980

Open

5 tasks

scottjehl and others added 2 commits January 8, 2026 10:24

rename files to use a .tentative.html convention since they correspon…

0b1b671

…d with a proposed HTML feature

Merge pull request #2 from Squarespace/scottjehl/tentative-rename

bb70f86

rename files to use a .tentative.html convention since they correspond with a proposed HTML feature

zcorpan requested changes Jan 14, 2026

View reviewed changes

scottjehl added 14 commits January 14, 2026 14:21

normalize the https links to squarespace and titles

958e09b

omit rel help links to tentative urls

12e5e03

one more https link:

2c8ab51

increase distance for below-viewport to 1000vh to tolerate varying im…

93197db

…plementations

loadstart firing should fail this test as well

75414dc

add 2s trickle to video request and compare loadeddata to onload in test

b463e44

changed test to rely less on timing and more on events. used the play…

c285504

… event and added a fallback if event never fires.

let test harness timeout on its own if event never fires

53a9a24

modified this test to check that an in-viewport lazy video's loadstar…

772ebf5

…t event comes after window load

adjust test to compare the size of the video element before and after…

95fdaae

… scscroll, as the poster image will impact its rendered size and be useful as a proxy for poster lazy loading

add trickle 2s to reduce flaky

136a26b

simplify test to compare onload to video load completeness

a302230

t.step unnecessary here

e2e728c

fix lint errors

aafc795

scottjehl requested a review from zcorpan January 14, 2026 23:45

scottjehl added 2 commits January 14, 2026 19:30

changed this test to use the width and height proxy instead as it see…

8460c52

…ms to be more reliable

simplify this test to look for eager to load data regardless of location

3b761e0

scottjehl requested a review from zcorpan February 5, 2026 12:26

keithamus reviewed Feb 5, 2026

View reviewed changes

html/dom/elements-embedded.js Outdated Show resolved Hide resolved

scottjehl added 5 commits February 6, 2026 13:23

media lazy loading: bring back html-based reflection tests while feat…

2283368

…ure is tentative. note with comments

add a test to verify lazy audio and video that is never connected to …

e59714f

…the document will not load

video and audio lazy loading: tests within a scrolling element

9af3407

add tests for lazy video and audio elements that are hidden and shoul…

4c0bf76

…d not load data

video lazy loading: test for no controls attr was not related to vide…

9f8574c

…o, only audio. removed.

credod mentioned this pull request Feb 6, 2026

Implement HTML video and audio element lazy-loading via the loading attribute Squarespace/WebKit#29

Closed

credod mentioned this pull request Feb 9, 2026

Implement HTML video and audio element lazy-loading via the loading attribute WebKit/WebKit#58208

Closed

credod mentioned this pull request Feb 9, 2026

Implement HTML video and audio element lazy-loading via the loading attribute WebKit/WebKit#58220

Open

keithamus approved these changes Feb 12, 2026

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keithamus merged commit cb58273 into web-platform-tests:master Feb 12, 2026
26 checks passed

arai-a reviewed Feb 17, 2026

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arai-a mentioned this pull request Feb 17, 2026

Fix syntax error in html/dom/elements-embedded.js #57824

Merged

scottjehl mentioned this pull request Feb 20, 2026

Document HTMLMediaElement (Video & Audio) Lazy Loading (Experimental) mdn/mdn#809

Open

scottjehl mentioned this pull request Feb 25, 2026

Add support for video and audio element lazy-loading via the loading attribute WebKit/standards-positions#586

Open

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