Plex not playing some files on my media server

[villianizz]

So I have my media server setup to play throughout my local network in my house with out internet but some of the media I try and play gives me the infamous codec not found or failed conversion error I’m just wondering if there is a place to download the codecs for plex it’s a couple different file types some are avi some are Mkv I’ve tried downloading the klite codes for my computer that didn’t work all the movies play fine on my pc but not through plex on the same pc can someone please help me out with this issue