Miracast is not a standalone app you need to download; it is a built-in feature of Windows 8.1. If your hardware supports it, you can use it for free without installing additional software. How to Use Miracast on Windows 8.1
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Golden Rule: Never download a "Miracast installer." If a website asks you to pay for a "Miracast download," it is a scam. Microsoft provides this feature for free inside Windows 8.1. Miracast is not a standalone app you need
If you do not see the "Add a wireless display" option, your system may not meet the hardware or driver requirements: miracast download for windows 8.1 free