Quicktime, developed by Apple, is the native media player for the Macintosh. It will play both video and audio and is everywhere in the Mac world.
Other types of media - especially video content in the Windows Media Player format - can sometimes be troublesome unless you know this small trick.
If you are having problems playing video from certain websites, CNN for example, the quick fix is Flip4Mac WMV. This System Preference takes video and audio in the Windows Media Player format and plays is seamlessly on your Mac. It is an essential download for all Mac users and, once installed, plays without any intervention from you at all.
You can find out more information at the link below as well as the Flip4Mac free download itself.