function video_shortcode($atts) {
    // Attribute extrahieren
    $atts = shortcode_atts(
        array(
            'src' => '', // Video-URL
            'width' => '600', // Standardbreite
            'height' => '400' // Standardhöhe
        ),
        $atts,
        'video'
    );

    // Video-Tag erstellen
    $output = '<video width="' . esc_attr($atts['width']) . '" height="' . esc_attr($atts['height']) . '" controls>';
    $output .= '<source src="' . esc_url($atts['src']) . '" type="video/mp4">'; // type nach Bedarf anpassen
    $output .= 'Dein Browser unterstützt das Video-Tag nicht.';
    $output .= '</video>';
    
    return $output;
}

add_shortcode('video', 'video_shortcode');

After you enter this code into the functions.php you can use the shortcode [video] in your posts, pages or widgets, and with the attributes src, width and height For example:

[video src="URL_DES_VIDEOS" width="800" height="450"]

Do not forget, URL_OF_VIDEO with the actual URL of your video.

Please make sure you use a child theme or create a custom plugin to add the code so that your changes are not lost when you update the theme.