The easiest way is to play WebM files through a third-party player such as VLC player and KMPlayer, etc. VLC player is a free acclaimed player that is installed on a wide range of users' PCs. If you don't have it, you can download it from the official website. It is very easy to play WebM file directly.
Now I have told you a lot of ways to solve the problem that WebM files can't be played in Windows Media Player. You can choose the way you like to play them. If the article is useful to you, please share it with others.