Full example - autoplay youtube video in a Modal (Bootstrap + Jquery)
<html>
<head>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.4/js/bootstrap.min.js"></script>
<script>
$(function() {
$(".video").click(function () {
var theModal = $(this).data("target"),
videoSRC = $(this).attr("data-video"),
videoSRCauto = videoSRC + "?modestbranding=1&rel=0&controls=0&showinfo=0&html5=1&autoplay=1";
$(theModal + ' iframe').attr('src', videoSRCauto);
$(theModal + ' button.close').click(function () {
$(theModal + ' iframe').attr('src', videoSRC);
});
});
});
</script>
</head>
<body>
<button class="btn btn-success btn-lg video" data-video="https://www.youtube.com/embed/8L5PqL4ylIU" data-toggle="modal" data-target="#videoModal">Play Video 1</button>
<button class="btn btn-default btn-lg video" data-video="https://www.youtube.com/embed/HBdcL7YsdBY" data-toggle="modal" data-target="#videoModal">Play Video 2</button>
<div class="modal fade" id="videoModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
<div class="modal-dialog">
<div class="modal-content">
<div class="modal-body">
<button type="button" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">×</span></button>
<iframe width="100%" height="350" src="" frameborder="0" allowfullscreen></iframe>
</div>
</div>
</div>
</div>
</body>
</html>