Packages with the mplayer use flag

Global definition: Enable mplayer support for playback or encoding.

app-emacs / bongo : Buffer-oriented media player for Emacs

media-gfx / gimageview : Powerful GTK+ based image & movie viewer

media-plugins / libvisual-plugins : collection of visualization plugins for use with the libvisual framework

media-sound / gmusicbrowser : An open-source jukebox for large collections of mp3/ogg/flac files

media-sound / qmmp : Qt5-based audio player with winamp/xmms skins support

media-video / dvdrip : dvd::rip is a graphical frontend for transcode

media-video / jubler : Java subtitle editor

www-misc / xxv : WWW Admin for the VDR (Video Disk Recorder)