Modern Image Formats - wp_calculate_image_srcset => false => no SOURCE element #2191

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1. 1ucay

   added

   [Type] BugAn existing feature is brokenAn existing feature is broken

   on Sep 26, 2025
2. github-project-automation

   added this to WP Performance Ongoingon Sep 26, 2025
3. github-project-automation

   moved this to Not Started/Backlog 📆 in WP Performance Ongoingon Sep 26, 2025
4. adamsilverstein commented on Sep 26, 2025

   

   adamsilverstein

   on Sep 26, 2025

   Member

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   Hi @1ucay - thanks for the bug report.

   is this proper behavior?

   Sounds like a bug.

   What happens if you turn off the Use < picture > Element (experimental) option?
5. b1ink0 commented on Oct 8, 2025

   

   b1ink0

   on Oct 8, 2025

   Last edited by b1ink0

   Contributor

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   Hmm, I’m not able to replicate the bug, but with the wp_calculate_image_srcset filter returning false, the <img> tag only has the src attribute with the fallback JPG image, and the <source> tag is generated with only one src in the srcset. See below:

   <picture class="wp-picture-11" style="display: contents"
     ><source
       type="image/webp"
       srcset="
         http://localhost:8888/wp-content/uploads/2025/10/10000x10000-1024x1024-jpg.webp
       " />
     <img
       data-od-unknown-tag=""
       data-od-xpath="/HTML/BODY/DIV[@class='wp-site-blocks']/*[2][self::MAIN]/*[1][self::DIV]/*[2][self::DIV]/*[6][self::FIGURE]/*[1][self::PICTURE]/*[2][self::IMG]"
       data-dominant-color="4d4d4d"
       data-has-transparency="false"
       style="--dominant-color: #4d4d4d"
       fetchpriority="high"
       decoding="async"
       width="1024"
       height="1024"
       sizes="(max-width: 645px) 100vw, 645px"
       src="http://localhost:8888/wp-content/uploads/2025/10/10000x10000-1024x1024.jpg"
       alt=""
       class="wp-image-11 not-transparent"
   /></picture>

   When the Use <picture> Element (experimental) option is disabled, this is what gets generated the <img> tag has the src with the selected modern image format.

   <figure class="wp-block-image size-large">
     <img
       data-od-unknown-tag=""
       data-od-xpath="/HTML/BODY/DIV[@class='wp-site-blocks']/*[2][self::MAIN]/*[1][self::DIV]/*[2][self::DIV]/*[6][self::FIGURE]/*[1][self::IMG]"
       data-dominant-color="4d4d4d"
       data-has-transparency="false"
       style="--dominant-color: #4d4d4d"
       fetchpriority="high"
       decoding="async"
       width="1024"
       height="1024"
       sizes="(max-width: 645px) 100vw, 645px"
       src="http://localhost:8888/wp-content/uploads/2025/10/10000x10000-1024x1024-jpg.webp"
       alt=""
       class="wp-image-11 not-transparent"
     />
   </figure>

   This issue is probably handled by the following else logic:

   performance/plugins/webp-uploads/picture-element.php

   Lines 119 to 123 in 708b55d

   	// Gets the srcset and sizes from the IMG tag.
   	$sizes = $processor->get_attribute( 'sizes' );
   	$srcset = $processor->get_attribute( 'srcset' );
   	if ( null !== $srcset && null !== $sizes ) {

   When the wp_calculate_image_srcset filter returns false, the srcset is null.

   .
   .
   .

   performance/plugins/webp-uploads/picture-element.php

   Lines 153 to 164 in 708b55d

   	} else {
   	foreach ( $mime_types as $image_mime_type ) {
   	$image_srcset = webp_uploads_get_mime_type_image( $attachment_id, $src, $image_mime_type );
   	if ( is_string( $image_srcset ) ) {
   	$picture_sources .= sprintf(
   	'<source type="%s" srcset="%s">',
   	esc_attr( $image_mime_type ),
   	esc_attr( $image_srcset )
   	);
   	}
   	}
   	}

   I believe this is the correct behavior, but I want other contributors to try to replicate it, I might be missing something.

   cc: @adamsilverstein
6. 1ucay commented on Oct 30, 2025

   

   1ucay

   on Oct 30, 2025

   Last edited by westonruter

   Author

   More actions

   I have to apologize to you all, it works fine with the filter.

   add_filter( 'wp_calculate_image_srcset', '__return_false' );

   <picture class="wp-picture-698" style="display: contents"
     ><source
       type="image/avif"
       srcset="
         /content/uploads/2025/08/generated-thumb-1756510127-400x225-jpg.avif
       " />
     <img
       width="400"
       height="225"
       src="/content/uploads/2025/08/generated-thumb-1756510127-400x225.jpg"
       class="attachment-wide-sm size-wide-sm not-transparent"
       alt="Ut dolor ea nisi do"
       fetchpriority="low"
       decoding="async"
       data-has-transparency="false"
       data-dominant-color="73bbd4"
       style="--dominant-color: #73bbd4"
   /></picture>

   👍React with 👍1Reacted by Aditya Dhade
7. adamsilverstein commented on Nov 17, 2025

   

   adamsilverstein

   on Nov 17, 2025

   Member

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   Thanks @1ucay - closing as this turned out to not be a bug.
8. adamsilverstein

   closed this as completedon Nov 17, 2025
9. github-project-automation

   moved this from Not Started/Backlog 📆 to Done 😃 in WP Performance Ongoingon Nov 17, 2025