wcfm-allow-youtube-embed

add_filter( 'wp_kses_allowed_html', function($tags, $context) {
if ( current_user_can('administrator') && 'post' === $context ) {
$tags['iframe'] = array(
'src' => true,
'height' => true,
'width' => true,
'frameborder' => true,
'allowfullscreen' => true,
);
}
return $tags;
}, 10, 2 );