Force youtube embed to start in 720p

(This answer was updated, as the previous method using vq isn't recognized anymore.)

Specifying the height of the video will change the quality accordingly. example for html 5;

<iframe style='width:100%; height:800px;' src='https://www.youtube.com/embed/xxxxxxxx'></iframe>

If you don't want to hardcode the width and height you can add a class to the iframe for css media queries.

Tested on a working server + passes the w3.org nuhtml validator.

You can do this by adding a parameter &hd=1 to the video URL. That forces the video to start in the highest resolution available for the video. However you cannot specifically set it to 720p, because not every video has that hd ish.

http://www.youtube.com/watch?v=VIDEO_ID&hd=1

http://code.google.com/apis/youtube/player_parameters.html

UPDATE: as of 2014, hd is deprecated https://developers.google.com/youtube/player_parameters?csw=1#Deprecated_Parameters