Forcing WP to embedd a video when using a shortcode

There may be a more graceful way to do this, but it works:

function shortcode_youtube($atts) {  
    extract(shortcode_atts(array(  
        "id"    => '', 
        "align" => 'aligncenter'  
    ), $atts));

    global $wp_embed;
    $content="http://www.youtube.com/watch?v=" . $id . '';
    $embed = $wp_embed->run_shortcode( $content );

    return '<div class="'.$align.'">' . $embed . '</div>';  
}  
add_shortcode("youtube", "shortcode_youtube");