I guess you need to install something additional "gstreamer", so that they appear in "/lib64" and the "XnView" image viewer can play them: "x264, xvid, mpg"... for videos in webm/vp8-9 format, you can drag them to a Firefox browser window.
In any case, VLC(appimage) can play and handle media very well: add folders to playlists and then search for files. IT DOES IT SO WELL, that even "emby" can't do it.