The options how the Home Multimedia Library will show and use files can be set by using this window.
To open options window click on the User Files Filtering button located at main software window ribbon bar in Software\Options\File Handling menu.
Here you may specify which of media files you want use with Media Player software.
By default all supported media files are set to use.
If a file is checked then software will use it, if a file is not checked the software will redirect a call to the Windows system or will not use it at all.
If you are not interested in processing or playing of all of supported files, here you may exclude some of them.