How can I autoplay a video using the new embed code style for Youtube?

I can't work out how to autoplay a video using the new embed code style for Youtube. I tried adding &autoplay=1 to the url, which worked with the old style, but it didn't work. For example, http://www.youtube.com/embed/JW5meKfy3fY is the embed link, but http://www.youtube.com/embed/JW5meKfy3fY&autoplay=1 doesn't work. Can anyone tell me how to do it? Thanks