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Add native loading=lazy support for video elements #2450

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Add native loading=lazy support for video elements #2450

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39f797e
Add native loading=lazy support for video elements
adamsilverstein Apr 9, 2026
668f515
Merge branch 'trunk' into add-native-video-support
adamsilverstein Apr 23, 2026
771be4f
Apply suggestions from code review
adamsilverstein May 11, 2026
e871d03
Short-circuit lazy video IntersectionObserver when native lazy-loadin…
adamsilverstein May 11, 2026
d8e6794
Update test snapshots to reflect renamed const in lazy-load-video.js
adamsilverstein May 11, 2026
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5 changes: 5 additions & 0 deletions plugins/image-prioritizer/class-image-prioritizer-video-tag-visitor.php
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Original file line number Diff line number Diff line change
Expand Up @@ -216,14 +216,19 @@ private function lazy_load_videos( ?string $poster, OD_Tag_Visitor_Context $cont
if ( 'auto' !== $initial_preload ) {
$processor->set_attribute( 'preload', 'auto' );
}
$processor->remove_attribute( 'loading' );
return;
}

// If the element is visible in any viewport, do not lazy-load it.
if ( $max_intersection_ratio > 0 ) {
$processor->remove_attribute( 'loading' );
return;
}

// Add native lazy loading for browsers that support it.
$processor->set_attribute( 'loading', 'lazy' );

if ( 'none' !== $initial_preload ) {
$processor->set_attribute( 'data-original-preload', null !== $initial_preload ? $initial_preload : 'default' );
$processor->set_attribute( 'preload', 'none' );
Expand Down
72 changes: 42 additions & 30 deletions plugins/image-prioritizer/lazy-load-video.js
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Original file line number Diff line number Diff line change
@@ -1,38 +1,50 @@
const lazyVideoObserver = new IntersectionObserver(
( entries ) => {
for ( const entry of entries ) {
if ( entry.isIntersecting ) {
const video = /** @type {HTMLVideoElement} */ entry.target;
const restoreVideo = ( /** @type {HTMLVideoElement} */ video ) => {
const poster = video.getAttribute( 'data-original-poster' );
if ( poster ) {
video.setAttribute( 'poster', poster );
}

const poster = video.getAttribute( 'data-original-poster' );
if ( poster ) {
video.setAttribute( 'poster', poster );
}
if ( video.hasAttribute( 'data-original-autoplay' ) ) {
video.setAttribute( 'autoplay', 'autoplay' );
}

if ( video.hasAttribute( 'data-original-autoplay' ) ) {
video.setAttribute( 'autoplay', 'autoplay' );
}
const preload = video.getAttribute( 'data-original-preload' );
if ( preload ) {
if ( 'default' === preload ) {
video.removeAttribute( 'preload' );
} else {
video.setAttribute( 'preload', preload );
}
}
};

const preload = video.getAttribute( 'data-original-preload' );
if ( preload ) {
if ( 'default' === preload ) {
video.removeAttribute( 'preload' );
} else {
video.setAttribute( 'preload', preload );
}
}
const videos = document.querySelectorAll( 'video.od-lazy-video' );

lazyVideoObserver.unobserve( video );
// When the browser natively supports lazy-loading on video, restore the original
// attributes immediately and rely on loading="lazy" to defer the video load.
if ( 'loading' in HTMLMediaElement.prototype ) {
for ( const video of videos ) {
restoreVideo( /** @type {HTMLVideoElement} */ ( video ) );
}
} else {
const lazyVideoObserver = new IntersectionObserver(
( entries ) => {
for ( const entry of entries ) {
if ( entry.isIntersecting ) {
restoreVideo(
/** @type {HTMLVideoElement} */ ( entry.target )
);
lazyVideoObserver.unobserve( entry.target );
}
}
},
{
rootMargin: '100% 0% 100% 0%',
threshold: 0,
}
},
{
rootMargin: '100% 0% 100% 0%',
threshold: 0,
}
);
);

const videos = document.querySelectorAll( 'video.od-lazy-video' );
for ( const video of videos ) {
lazyVideoObserver.observe( video );
for ( const video of videos ) {
lazyVideoObserver.observe( video );
}
}
8 changes: 4 additions & 4 deletions plugins/image-prioritizer/tests/test-cases/multiple-videos-on-all-breakpoints/expected.html
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13 changes: 13 additions & 0 deletions plugins/image-prioritizer/tests/test-cases/video-hidden-on-all-breakpoints/buffer.html
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
<html lang="en">
<head>
<meta charset="utf-8">
<title>...</title>
<meta name="generator" content="optimization-detective 0.0.0">
<meta name="generator" content="image-prioritizer 0.0.0">
</head>
<body>
<div id="page">
<video class="desktop" width="1200" height="500" src="https://example.com/header.mp4" preload="auto" autoplay></video>
</div>
</body>
</html>
16 changes: 16 additions & 0 deletions plugins/image-prioritizer/tests/test-cases/video-hidden-on-all-breakpoints/expected.html
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30 changes: 30 additions & 0 deletions plugins/image-prioritizer/tests/test-cases/video-hidden-on-all-breakpoints/set-up.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
<?php
return static function ( Test_Image_Prioritizer_Helper $test_case ): void {
$breakpoint_max_widths = array( 480, 600, 782 );

add_filter(
'od_breakpoint_max_widths',
static function () use ( $breakpoint_max_widths ) {
return $breakpoint_max_widths;
}
);

foreach ( array_merge( $breakpoint_max_widths, array( 1000 ) ) as $viewport_width ) {
$test_case->store_url_metric(
od_get_url_metrics_slug( od_get_normalized_query_vars() ),
$test_case->get_sample_url_metric(
array(
'viewport_width' => $viewport_width,
'elements' => array(
array(
'isLCP' => false,
'xpath' => '/HTML/BODY/DIV[@id=\'page\']/*[1][self::VIDEO]',
'boundingClientRect' => $test_case->get_sample_dom_rect(),
'intersectionRatio' => 0.0,
),
),
)
)
);
}
};
13 changes: 13 additions & 0 deletions ...ioritizer/tests/test-cases/video-with-loading-lazy-already-set-and-is-visible/buffer.html
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
<html lang="en">
<head>
<meta charset="utf-8">
<title>...</title>
<meta name="generator" content="optimization-detective 0.0.0">
<meta name="generator" content="image-prioritizer 0.0.0">
</head>
<body>
<div id="page">
<video class="desktop" poster="https://example.com/poster.jpg" width="1200" height="500" src="https://example.com/header.mp4" loading="lazy"></video>
</div>
</body>
</html>
15 changes: 15 additions & 0 deletions ...ritizer/tests/test-cases/video-with-loading-lazy-already-set-and-is-visible/expected.html
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30 changes: 30 additions & 0 deletions ...rioritizer/tests/test-cases/video-with-loading-lazy-already-set-and-is-visible/set-up.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
<?php
return static function ( Test_Image_Prioritizer_Helper $test_case ): void {
$breakpoint_max_widths = array( 480, 600, 782 );

add_filter(
'od_breakpoint_max_widths',
static function () use ( $breakpoint_max_widths ) {
return $breakpoint_max_widths;
}
);

foreach ( array_merge( $breakpoint_max_widths, array( 1000 ) ) as $viewport_width ) {
$test_case->store_url_metric(
od_get_url_metrics_slug( od_get_normalized_query_vars() ),
$test_case->get_sample_url_metric(
array(
'viewport_width' => $viewport_width,
'elements' => array(
array(
'isLCP' => false,
'xpath' => '/HTML/BODY/DIV[@id=\'page\']/*[1][self::VIDEO]',
'boundingClientRect' => $test_case->get_sample_dom_rect(),
'intersectionRatio' => 0.5,
),
),
)
)
);
}
};
13 changes: 13 additions & 0 deletions ...ins/image-prioritizer/tests/test-cases/video-with-loading-lazy-on-lcp-element/buffer.html
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
<html lang="en">
<head>
<meta charset="utf-8">
<title>...</title>
<meta name="generator" content="optimization-detective 0.0.0">
<meta name="generator" content="image-prioritizer 0.0.0">
</head>
<body>
<div id="page">
<video class="desktop" poster="https://example.com/poster.jpg" width="1200" height="500" src="https://example.com/header.mp4" loading="lazy"></video>
</div>
</body>
</html>
16 changes: 16 additions & 0 deletions ...s/image-prioritizer/tests/test-cases/video-with-loading-lazy-on-lcp-element/expected.html
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30 changes: 30 additions & 0 deletions plugins/image-prioritizer/tests/test-cases/video-with-loading-lazy-on-lcp-element/set-up.php
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Original file line number Diff line number Diff line change
@@ -0,0 +1,30 @@
<?php
return static function ( Test_Image_Prioritizer_Helper $test_case ): void {
$breakpoint_max_widths = array( 480, 600, 782 );

add_filter(
'od_breakpoint_max_widths',
static function () use ( $breakpoint_max_widths ) {
return $breakpoint_max_widths;
}
);

foreach ( array_merge( $breakpoint_max_widths, array( 1000 ) ) as $viewport_width ) {
$test_case->store_url_metric(
od_get_url_metrics_slug( od_get_normalized_query_vars() ),
$test_case->get_sample_url_metric(
array(
'viewport_width' => $viewport_width,
'elements' => array(
array(
'isLCP' => true,
'xpath' => '/HTML/BODY/DIV[@id=\'page\']/*[1][self::VIDEO]',
'boundingClientRect' => $test_case->get_sample_dom_rect(),
'intersectionRatio' => 1.0,
),
),
)
)
);
}
};
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