WP Sample function convert Youtube URL (ACF) to post content (for using existing Embeds feature in WordPress)

functions.php

<?php

// For example, logged in to your WordPress and hit http://sample.com/?action=update_videos once

add_action('wp', function() {
	if ( !is_user_logged_in() ) return;

	if ( empty( $_GET['action'] ) ) return;

	if ($_GET['action'] !== 'update_videos') return;

	$post_args = [
		'post_type' => 'video',
		'post_status' => 'publish',
		'posts_per_page' => -1,
		'fields' => 'ids',
		'meta_key' => 'youtube_url'
	];

	$posts = get_posts($post_args);

	foreach ($posts as $post_id) {
		$youtube_url = get_field('youtube_url', $post_id);

		if ( !empty($youtube_url ) ) {
			wp_update_post([
				'ID' => $post_id,
				'post_content' => $youtube_url
			]);

			delete_field('youtube_url', $post_id);
		}
	}
});