If Safari prompts you to install Silverlight on your Mac computer running OS X 10.10 Yosemite, your computer may not have the capability to use the HTML5 player. Follow the steps below to ensure your Mac computer can use the HTML5 player.
Click on the Apple logo in the upper left corner of your screen.
Select About This Mac.
Leave the window open and check to make sure your computer has the following:
Early 2011 model or newer Mac
OS X 10.10 Yosemite or newer OS
Certain late Intel Sandy Bridge or any Intel Ivy Bridge/Haswell processor