Formats that are generally played back by a competent Media player include DVD, CDDA, MPEG video, DivX, MP3, Karaoke (*.Kar), Ogg-variants and FLAC. Generally speaking, the more formats it can play, the better it is. Hard-to-get-at formats like QuickTime using the Sorenson codec are less common in media players.
A good media player will also look up titles and song names from an online database such as CDDB or FreeDB and playback both files stored on the users hard disk and media streams provided through the Internet and is therefore often seen as a companion of the web browser.
There also exist hardware media players, such as MP3 players.