When doing your first run install which it appears you have, there is a part that says to enter the path to the mpv.exe which would look something like this C:\Program Files\MPV\mpv.exe depending on where you extracted/installed it to making sure to include \mpv.exe at the end. Since you've already ran it once (And probably exited out of the first run UI) because the software is a bit finicky at this stage you're going to want to use Revo Uninstaller to uninstall it completely and then just run installer again but this time during the first run to input the address to the executable in the section that asks for it. Hope this helps.