Audio driver is needed for mirroring functionality as long as you wish to cast also audio with video. If you prefer to use file or web video streaming modes, you don't need it.
Click on this image and download the audio-driver installer:
(Uninstall procedure can be found in the FAQ section; Q: How to uninstall the audio driver.)
You will be guided through the installation in 4 simple steps...
Introduction
Information about the driver install size
(Do not change location...)
Password
And actual installation...
If open, do not forget to reopen your media player after the installation.