SMPlayer is a free media player with built-in codecs that can play
virtually all video and audio formats. It doesn't need any external
codecs. Just install SMPlayer and you'll be able to play all formats
without the hassle to find and install codec packs.

SMPlayer is a graphical user interface (GUI) for MPlayer, which is
capable of playing almost all known video and audio formats. But apart
from providing access for the most common and useful options of MPlayer,
SMPlayer adds other interesting features like the possibility to play
Youtube videos or download subtitles.

One of the most interesting features of SMPlayer: it remembers the
settings of all files you play. So you start to watch a movie but you
have to leave... don't worry, when you open that movie again it will
be resumed at the same point you left it, and with the same settings:
audio track, subtitles, volume.

If you prefer to build SMPlayer against Qt5 rather than Qt4, install
qt5 (available from SlackBuilds.org) and run the script like that:

  USE_QT5=yes ./smplayer.SlackBuild