I found that before I could get anything inside the iframe to be found I needed to determine if the iframe was loaded. Then if the iframe gets loaded after page load or reloaded later in the process, your click function works.
jQuery('#iframe').load(function() {
jQuery('#iframe').contents().find('#play-button').click(function () {
// do your stuff
});
}
** this may or may not work cross-domain, but determining if the iframe loaded can be used as a hackish method of determining if something has happened in the iframe. If you created a "play" button on your domain on top of the iframe it could be used to load the iframe via a click function after page load and then your load function could contain your slideshow pause.