RealPlayer was announced to be compatible with Windows 10 in 2005. Since then the software received multiple updates to enhance support, compatibility and various issues.
If you have the possibility, visit the following link and download the latest version. It's also advised to remove the currently installed one and clean the registry items. You can use a tool like CCleaner to safely clean and delete obsolete registry files. Afterward, download the software and install it.
Since RealPlayer is just like any other multimedia player, it still uses its own or 3rd party codecs. This means you can install a 3rd party set of codecs developed by someone and RealPlayer will use them to decode the files that you want to play.
Access the application's page at Software Informer for CCCP codecs to download a version and then install it. I believe this will vastly improve the quality of played files into the RealPlayer application.