All modern browsers will play video (Theora and WebM) and audio (Vorbis and MP3) files from Wikipedia, no modifications needed.
On iOS, iPadOS, and older macOS devices, software decoding will be used. This might be a bit slow compared to what you are used to on such devices. Internet Explorer is NOT supported.
Playing the files
You can try your player using the Wikimedia Commons Sound and Video files.
Creating media files
To learn how to create video or audio files for Wikipedia and its sister projects, check Wikipedia:Creation and usage of media files.