The easiest way to send an online video to your Chromecast is to use the Google Chrome browser. Download and install it from here if you haven’t already, and then read on to know what to do next. These steps work the same way on an Mac or Windows PC.
How to Mirror Your Computer to Your TV With Chromecast
Make sure your computer is connected to the same Wi-Fi network your Chromecast was set up to use.
Launch Google Chrome on your Mac or Windows PC.
Click on the menu button on the top right (three vertical lines or dots).
Click on Cast. A popup box will appear.
Click on OK, Got it to enable casting from services such as Hangout, and then click on the name of your Chromecast to start mirroring your browser tab.