The video streams directly on the Chromecast and is not a mirror of your computer screen (which is usually laggy). This is a more effective method to stream to the Chromecast than casting the screen/window.
This tutorial uses a method to force Kodi to stream videos to the Google Chrome browser and then cast the video, using Google Cast, directly to the Chromecast. You can now stream videos from Kodi on your Apple computer (Macbook Pro & Air, Mac Mini, iMac, etc.) to your TV via the Chromecast.
Learn how to stream Kodi (XBMC) from your Mac OS X computer to your Google Chromecast.