I\'ve looked around, and as far as I can see it\'s not possible, but say you\'re embedding a YouTube iframe, is it possible to round those corners using CSS?
The way to go is wrapping the iframe in a circular div as other users suggested. The only difference being that you have to add an additional style position:relative to the wrapper for it to work in Chrome browser.
So the code would go like this:
.circle {
width: 320px;
height: 320px;
-moz-border-radius: 50%;
-webkit-border-radius: 50%;
border-radius: 50%;
overflow:hidden;
position:relative;
}