gistfile1.txt

add_filter( 'get_comment_text', 'add_post_oembed_comment_support', 0 );
function add_post_oembed_comment_support( $comment_text ) {
	if ( ! class_exists( 'WP_oEmbed' ) ) {
		include( ABSPATH . WPINC . '/class-oembed.php' );
	}
	$WP_oEmbed = new WP_oEmbed();
	if ( $WP_oEmbed->get_provider( $comment_text, array( 'discover' => false ) ) ) {
		return $comment_text;
	}
	return $GLOBALS['wp_embed']->autoembed( $comment_text );
}