Si está utilizando la nueva API asincrónica, deberá agregar el parámetro de la siguiente manera:
<!-- YOUTUBE -->
// 2. This code loads the IFrame Player API code asynchronously.
var tag = document.createElement('script');
tag.src = "http://www.youtube.com/player_api";
var firstScriptTag = document.getElementsByTagName('script')[0];
firstScriptTag.parentNode.insertBefore(tag, firstScriptTag);
// 3. This function creates an <iframe> (and YouTube player)
// after the API code downloads.
var player;
var initialVideo = 'ApkM4t9L5jE'; // YOUR YOUTUBE VIDEO ID
function onYouTubePlayerAPIReady() {
console.log("onYouTubePlayerAPIReady" + initialVideo);
player = new YT.Player('player', {
height: '381',
width: '681',
wmode: 'transparent', // SECRET SAUCE HERE
videoId: initialVideo,
playerVars: { 'autoplay': 1, 'rel': 0, 'wmode':'transparent' },
events: {
'onReady': onPlayerReady,
'onStateChange': onPlayerStateChange
}
});
}
Esto se basa en la documentación y el ejemplo de Google aquí:
http://code.google.com/apis/youtube/iframe_api_reference.html