http://www.html5rocks.com/en/tutorials/getusermedia/intro/

mdiaSupportDetection

function hasGetUserMedia() {
  return !!(navigator.getUserMedia || navigator.webkitGetUserMedia ||
            navigator.mozGetUserMedia || navigator.msGetUserMedia);
}

if (hasGetUserMedia()) {
  alert('getUserMedia() IS supported in your browser');
} else {
  alert('getUserMedia() is not supported in your browser');
}

OR

if (Modernizr.getusermedia){
var gUM = Modernizr.prefixed('getUserMedia', navigator);
gUM({video: true}, function( //...
//...
}