Gspot Help.

Helllo
I am unable to play an Mkv. file in media player, so i used gspot to detect what codecs were needed its says i have all the codecs installed and i was able to play it in the little gspot player, but when i clsoe gspot and try to open it with media player it still does not work..
my question is, is there a way to configure the file so it works with media player