Prioritize loading poster image of video LCP elements

plugins/image-prioritizer/class-image-prioritizer-video-tag-visitor.php

@@ -0,0 +1,94 @@
+<?php
+/**
+ * Tag visitor that optimizes VIDEO tags:
+ * - Adds preload links for poster images if in a breakpoint group's LCP.
+ *
+ * @package image-prioritizer
+ *
+ * @since n.e.x.t
+ */
+
+// Exit if accessed directly.
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+/**
+ * Image Prioritizer: Image_Prioritizer_Video_Tag_Visitor class
+ *
+ * @since n.e.x.t
+ *
+ * @access private
+ */
+final class Image_Prioritizer_Video_Tag_Visitor extends Image_Prioritizer_Tag_Visitor {
+
+	/**
+	 * Video tag.
+	 *
+	 * @var string
+	 */
+	const VIDEO = 'VIDEO';
+
+	/**
+	 * Poster attribute.
+	 *
+	 * @var string
+	 */
+	const POSTER = 'poster';
+
+	/**
+	 * Visits a tag.
+	 *
+	 * @param OD_Tag_Visitor_Context $context Tag visitor context.
+	 *
+	 * @return bool Whether the visitor visited the tag.
+	 */
+	public function __invoke( OD_Tag_Visitor_Context $context ): bool {
+		$processor = $context->processor;
+		if ( self::VIDEO !== $processor->get_tag() ) {
+			return false;
+		}
+
+		// Skip empty poster attributes and data: URLs.
+		$poster = trim( (string) $processor->get_attribute( self::POSTER ) );
+		if ( '' === $poster || $this->is_data_url( $poster ) ) {
+			return false;
+		}
+
+		$xpath = $processor->get_xpath();
+
+		// If this element is the LCP (for a breakpoint group), add a preload link for it.
+		foreach ( $context->url_metrics_group_collection->get_groups_by_lcp_element( $xpath ) as $group ) {
+			$link_attributes = array_merge(
+				array(
+					'rel'           => 'preload',
+					'fetchpriority' => 'high',
+					'as'            => 'image',
+				),
+				array_filter(
+					array(
+						'href' => (string) $processor->get_attribute( self::POSTER ),
+					),
+					static function ( string $value ): bool {
+						return '' !== $value;
+					}
+				)
+			);
+
+			$crossorigin = $processor->get_attribute( 'crossorigin' );
+			if ( is_string( $crossorigin ) ) {
+				$link_attributes['crossorigin'] = 'use-credentials' === $crossorigin ? 'use-credentials' : 'anonymous';
+			}
+
+			$link_attributes['media'] = 'screen';
+
+			$context->link_collection->add_link(
+				$link_attributes,
+				$group->get_minimum_viewport_width(),
+				$group->get_maximum_viewport_width()
+			);
+		}
+
+		return true;
+	}
+}

plugins/image-prioritizer/helper.php

@@ -36,4 +36,7 @@ function image_prioritizer_register_tag_visitors( OD_Tag_Visitor_Registry $regis
 
 	$bg_image_visitor = new Image_Prioritizer_Background_Image_Styled_Tag_Visitor();
 	$registry->register( 'bg-image-tags', $bg_image_visitor );
+
+	$video_visitor = new Image_Prioritizer_Video_Tag_Visitor();
+	$registry->register( 'video-tags', $video_visitor );
 }

plugins/image-prioritizer/load.php

@@ -78,6 +78,7 @@ static function ( string $version ): void {
 
 		require_once __DIR__ . '/class-image-prioritizer-tag-visitor.php';
 		require_once __DIR__ . '/class-image-prioritizer-img-tag-visitor.php';
+		require_once __DIR__ . '/class-image-prioritizer-video-tag-visitor.php';
 		require_once __DIR__ . '/class-image-prioritizer-background-image-styled-tag-visitor.php';
 		require_once __DIR__ . '/helper.php';
 		require_once __DIR__ . '/hooks.php';