MPlayer is a powerful multimedia player and more - It plays almost anything from CD/DVD and the like, to container formats, such as avi, mp4 or ogg, it also plays many different audio and video formats, it has supports for subtitles and can play streaming formats, and many others. It has a useful and powerful companion for video encoding called mencoder.
Debian also ships mpv, which is a more recent fork of MPlayer (actually a fork of MPlayer2 which was in turn a fork of MPlayer).
MPlayer has many independently developed GUIs:
Binary codecs (optional)
MPlayer can use binary codecs to extend support for file formats, see MultimediaCodecs.
Render video as ASCII art: mplayer -vo caca MyFile.mpg or mplayer -vo aa MyFile.mpg
https://people.debian.org/~mjr/mplayer.html - The Debian and mplayer FAQ
Upstream specific information