Pausing YouTube iFrame API in JavaScript

Question

I have a Youtube video embedded in a slideshow that I would like to pause when the user clicks on an img thumbnail:

<li><iframe width="430" height="241" src="http://www.youtube.com/watch?v=XjUz8IT0CYg?enablejsapi=1&theme=light&showinfo=0" frameborder="0" allowfullscreen id="my-video"></iframe></li>

I've been over the Youtube API but I'm confused how to get things started.

Does the API JS load automatically when I append ?enablejsapi to the end of the YouTube video id?

Here is my JS:

var player1 = document.getElementById('my-video');

$('img').click(function () {
  player1.pauseVideo();
})

EDIT:

Here's what I did based on Matt's answer below, for anyone wondering:

<li><iframe width="430" height="241" src="http://www.youtube.com/embed/XjUz8IT0CYg?enablejsapi=1&theme=light&showinfo=0" frameborder="0" allowfullscreen id="player-1"></iframe></li>

<li><iframe width="430" height="241" src="http://www.youtube.com/embed/HVhSasnVjMQ?enablejsapi=1&theme=light&showinfo=0" frameborder="0" allowfullscreen id="player-2"></iframe></li>

And then my JS:

var tag = document.createElement('script');
tag.src = "//www.youtube.com/iframe_api";
var firstScriptTag = document.getElementsByTagName('script')[0];
firstScriptTag.parentNode.insertBefore(tag, firstScriptTag);

// Create YouTube player(s) after the API code downloads.
var player1;
var player2;

function onYouTubeIframeAPIReady() {
    player1 = new YT.Player('player-1');
    player2 = new YT.Player('player-2');
}

Then in document.ready:

$(document).ready(function () {
    $(".slideshow-1 img").click(function () {
        player1.stopVideo();
    });

    $(".slideshow-2 img").click(function () {
        player2.stopVideo();
    });
}

Answer 1

I have another solution:

<iframe id="player1" class="ytplayer" width="430" height="241" src="http://www.youtube.com/embed/HVhSasnVjMQ?enablejsapi=1&theme=light&showinfo=0" frameborder="0" allowfullscreen></iframe>
<iframe id="player2" class="ytplayer" width="430" height="241" src="http://www.youtube.com/embed/HVhSasnVjMQ?enablejsapi=1&theme=light&showinfo=0" frameborder="0" allowfullscreen></iframe>

and

$('.ytplayer').each(function(){
    //this.contentWindow.postMessage('{"event":"command","func":"' + 'stopVideo' + '","args":""}', '*');
    this.contentWindow.postMessage('{"event":"command","func":"' + 'pauseVideo' + '","args":""}', '*')
});