find shortcode inside content of post

Question

I've a post with a video, contained inside the content. So, the content of my post is like:

"Lorem ipsum dolor sit amet, consectetur adipiscing elit. Curabitur aliquam quam sed imperdiet viverra. In ornare semper nisl, ac sodales metus facilisis ac. Morbi quis erat id magna dapibus consequat. Vestibulum sollicitudin hendrerit nisl sit amet lacinia. Mauris sed sodales quam. Mauris semper, ante quis imperdiet iaculis, neque eros pulvinar eros, id aliquet magna mauris at sapien. Sed sodales, diam venenatis aliquam ornare, nisl lorem accumsan eros, vitae suscipit dolor purus quis odio. Integer quis hendrerit sapien, at pretium neque. Nullam convallis auctor enim et malesuada. Suspendisse id fermentum risus..

[video width="100%" height="360" url="http://www.youtube.com/watch?v=sd1273xA"]"

Where the shortcode is displayed like text... I need to display the video...to use do_shortcode.

I'm trying without luck:

function your_prefix_detect_shortcode()
{
    global $post;

    $pattern = get_shortcode_regex();

    if (   preg_match_all( '/'. $pattern .'/s', $post->post_content, $matches )
            && array_key_exists( 2, $matches )
            && in_array( 'video', $matches[2] ) )
    {
       echo do_shortcode("[$matches[0][0]]");
    }

}
add_action( 'wp', 'your_prefix_detect_shortcode' );

EDIT: The content is called from single.php like:

<p class="titulillos">Descripción: <br><span><?php echo nl2br($post->post_content); ?></span></p>

EDIT2: I'm having problems with encoding...because when processing the shortcode, for example, height isn't 360px, it's "360" And the result is a fatal error doing calcs