The latest versions of all major browsers are able to play sound files and videos without any additional codecs or software.
If you are not using one of the above web browsers, you only need to download and install one of the following players.
VLC media player
Go to this website and choose one of the links listed under macOS version (13 MB; 7,3 MB). Once you have downloaded the disc-image, open it and it will appear as a virtual disc on your Desktop. From the disc copy VLC.app to your Applications folder. Now you can play the sound and video files from Commons.
Do you have questions, or do you encounter problems? Please ask here.