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Web Platform Tests for HTML video and audio element lazy loading via the loading attribute #57051

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Web Platform Tests for HTML video and audio element lazy loading via the loading attribute #57051

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@scottjehl scottjehl commented Jan 7, 2026 •
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Loading

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
@scottjehl @zachlysobey
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Web Platform Tests for HTML video element lazy loading via the loadin…
6119c88 
…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>
@wpt-pr-bot wpt-pr-bot added the html label Jan 7, 2026
@scottjehl scottjehl mentioned this pull request Jan 7, 2026
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scottjehl and others added 2 commits January 8, 2026 10:24
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rename files to use a .tentative.html convention since they correspon…
0b1b671 
…d with a proposed HTML feature
@scottjehl
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
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scottjehl commented Jan 8, 2026

Renamed the files to be .tentative.html since they correspond with a proposed HTML feature. Thanks for the tip @keithamus
zcorpan
zcorpan requested changes Jan 14, 2026
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@scottjehl
normalize the https links to squarespace and titles
958e09b
@scottjehl
omit rel help links to tentative urls
12e5e03
@scottjehl
one more https link:
2c8ab51
@scottjehl
increase distance for below-viewport to 1000vh to tolerate varying im…
93197db 
…plementations
@scottjehl
loadstart firing should fail this test as well
75414dc
@scottjehl
add 2s trickle to video request and compare loadeddata to onload in test
b463e44
@scottjehl
changed test to rely less on timing and more on events. used the play…
c285504 
… event and added a fallback if event never fires.
@scottjehl
let test harness timeout on its own if event never fires
53a9a24
@scottjehl
modified this test to check that an in-viewport lazy video's loadstar…
772ebf5 
…t event comes after window load
@scottjehl
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
@scottjehl
add trickle 2s to reduce flaky
136a26b
@scottjehl
simplify test to compare onload to video load completeness
a302230
@scottjehl
t.step unnecessary here
e2e728c
@scottjehl
fix lint errors
aafc795
@scottjehl scottjehl requested a review from zcorpan January 14, 2026 23:45
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scottjehl commented Jan 15, 2026

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).
zcorpan
zcorpan requested changes Jan 16, 2026
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scottjehl commented Jan 22, 2026

@zcorpan thanks for the change notes above. I'll be addressing these today.
@scottjehl scottjehl changed the title Web Platform Tests for HTML video element lazy loading via the loading attribute Jan 22, 2026
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scottjehl commented Jan 22, 2026

As a followup, we're now working on a pass of revisions here to broaden these tests to include audio element support.
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scottjehl commented Jan 26, 2026

Hi all. We've pushed revisions that address @zcorpan's latest round of suggestions as well as add tests for audio element support, closely following the same patterns where relevant.
@scottjehl scottjehl requested a review from zcorpan January 26, 2026 19:45
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scottjehl commented Jan 28, 2026

I made a followup video test revision today after some feedback from the folks working on a Chromium implementation: avoid media loading events for poster as UAs aren't consistent on firing them for that.
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change to margin instead of absolute positioning as something about a…
0fd0018 
…bs positioning makes tests flaky in chromium's content_shell, and these are simpler and equivalent anyhow
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