You can use the oEmbed in Comments plugin. This is the code the author, Evan Solomon, uses in this plugin, I used it on a site a while back just copy it in your themes functions file or even better, download his plugin 🙂
class ES_oEmbed_Comments {
function __construct() {
add_action( 'init', array( $this, 'init' ) );
}
function init() {
if ( is_admin() )
return;
$this->add_filter();
}
/**
* Setup filter with correct priority to do oEmbed in comments
*/
function add_filter() {
// make_clickable breaks oEmbed regex, make sure we go earlier
$clickable = has_filter( 'get_comment_text', 'make_clickable' );
$priority = ( $clickable ) ? $clickable - 1 : 10;
add_filter( 'get_comment_text', array( $this, 'oembed_filter' ), $priority );
}
/**
* Safely add oEmbed media to a comment
*/
function oembed_filter( $comment_text ) {
global $wp_embed;
// Automatic discovery would be a security risk, safety first
add_filter( 'embed_oembed_discover', '__return_false', 999 );
$comment_text = $wp_embed->autoembed( $comment_text );
// ...but don't break your posts if you use it
remove_filter( 'embed_oembed_discover', '__return_false', 999 );
return $comment_text;
}
}
new ES_oEmbed_Comments;