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.
It provides many interesting features like the possibility to play YouTube videos, search and download subtitles or cast to external devices like smartphones and tablets.
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...