Haado way, use Aegisub.
Easy way for MKV's: Use The KMPlayer to play those vids, it's areally good player. In default it uses your custom font, which can be changed (inlarged, oulined ect.), when you go into the preferences menu, you can easily activate fansubbers typesets, which can't really be altered, only retimed.
Try it, it's worth your time. I like it more then WMPclassic due to the features and it playing everything with the help of CCCP and RealAlternative and the high customizability.
In before KEKEKE ZERG RUSH KOREAN BLOATWEAR.