Above is an example of WordPress 3.6's built in video player (MediaElement). If you hit F5 to reload the page you will see that the player styles take about a second to kick-in. The causes the player to look slightly different for a portion of the first second. I know a second isn't much but this will notice more on sites that use shared servers (slower sites).
Not exactly sure what is happening. Are there some styles being loaded first then after about a second they get overridden by the player styles? How can I have the player styles load first so the player looks exactly as it should do from the very start?