Thanks for the reply Alex!
I'm using the mirror mode at this moment when I stream via my macbook air or imac. My macbook pro is from 2010 and didn't have the airplay mode so I installed Air Parrot which works great on the Pro aswell!
The mirrormode is doing the job at this moment but a complete stream would be better. Like you see in this picture, you can choose to stream through/Play on Chromecast