How to make an If Else on Excerpt Filter

Question

Im trying to do an if/else on a custom excerpt filter in functions.php file but not having any luck. Heres what I have. What I am trying to do is customize one of the excerpts being generated. I need to have 'Watch Video' instead of the read more for one post. I tried wrapping that in an if (is_single('my page')) but it doesn't have any affect. Any help anyone could provide would be greatly appreciated!

thanks!

function custom_excerpt($text) { 

  $excerpt = '' . strip_tags($text) . '<span class="readmore"><a href="'.get_the_permalink().'" rel="nofollow">Read More &raquo;</a></span>';

   return $excerpt;
}
add_filter('the_excerpt', 'custom_excerpt');

Answer 1

Here is the solution that seemed to work. Thanks Tom

function new_excerpt_more($more) {
    global $post;
    $thePostID = $post->ID;
    if($thePostID == 1128) {
    return '...<a class="readmore" href="'. get_permalink($post->ID) .  '">Watch Video &raquo;</a>';
    } else {
    return '...<a class="readmore" href="'. get_permalink($post->ID) . '">Read more &raquo;</a>';
    }
}
add_filter('excerpt_more', 'new_excerpt_more');