Because of obsolete code, the media player that I'd been using for websites stopped playing MP3 files. After looking around and trying several, I didn't find any HTML5 MP3 players that I liked. So what then? Fortunately, all the browsers support playing MP3 files without a player. The catch is they can only do one song at a time and the screen goes black. So it's really a question of how important it is for you, the webmaster, what kind of a user experience you want to offer. For a full blown music site, I'd say some kind of media player would be a requirement, but for a lot of sites, they may have only a few MP3s peppered about and their visitors may only get around to averaging a few plays. In that case, I'd argue that a media player is optional.