TubeNail Wordpress plugin. Replaces any Youtube URL with its corresponding thumbnail, avoiding embedded content.

tubenail.php

<?php

/*
 * Plugin Name:       TubeNail
 * Description:       Replaces any Youtube URL with its corresponding thumbnail, avoiding embedded content.
 * Version:           1.1
 * Author:            Emilio Rubio Rigo
 * Author URI:        https://emilioblog.com
 * License:           GPLv3
 * License URI:       https://www.gnu.org/licenses/gpl-3.0.html
 */

// 3rd party tricks: regex https://stackoverflow.com/a/78374748, CSS https://stackoverflow.com/a/37424730, SVG compression https://vecta.io/nano

function TubeNail_function($text) {
    $pattern = '/(https?:\/\/)?(((m|www)\.)?(youtube(-nocookie)?|youtube.googleapis)\.com.*(v\/|v=|vi=|vi\/|e\/|embed\/|shorts\/|user\/.*\/u\/\d+\/)|youtu\.be\/)([_0-9a-z-]+)/im';
    $replacement = <<<'EOD'
    <style>
        .tn-container {
            text-align: center;
            margin-bottom: 1.6em;
        }
        .tn-video {
            position: relative;
            display: inline-block;
        }
        .tn-video:before {
            content: "";
            position: absolute;
            width: 100%;
            height: 100%;
            z-index: 10;
            background: transparent url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 135.467 135.467' height='512' width='512' %3E%3Ccircle r='67.733' cy='67.733' cx='67.733' fill='%230170b9' fill-rule='evenodd'/%3E%3Cpath d='M111.531 67.733L78.715 86.68l-32.816 18.946V67.733 29.841l32.816 18.946z' fill='%23fff' stroke='%23fff' stroke-width='7.408' stroke-linejoin='round'/%3E%3C/svg%3E") center center no-repeat;
            background-size: 25%;
        }
    </style>
    <div class='tn-container'>
        <a class='tn-video' href='https://youtube.com/watch?v=${1}' target='_blank'><img src='https://img.youtube.com/vi/${1}/hqdefault.jpg'></a>
    </div>
EOD;

    $text = preg_replace($pattern, $replacement, $text);
    return $text;
}

add_filter('the_content', 'TubeNail_function');