I'm on a MacBook as well and had a tuff time getting it to work. While viewing the video casting screen where the chat is on the left hand side and the video stuff is on the right, open up the Camera Options payne and click on the bottom left icon, it will open up your Permissions window. Make sure you give the site permission by clicking the box to the left of the green check. Then click on the camera icon all the way to the bottom right. This will allow you to select which camera you want the site to use. You want to select the camera name with USB in the title. Then Save. Once you have done that, look to the bottom right hand corner of the video chat interface, where it has a blank silhouette with the side profile of a man on it. To the left of that generic image, you will see a row of vertical buttons. Click on the one on top, this will start the videocast.