Sd card issues on my galaxy tab 2, 7.0?

Hi, I've got a Samsung Galaxy Tab 2, 7.0 running 4.1.1 jelly bean, I have a 32GB SD card I'm using on it, but the thing is I want to watch hd movies on my tab but doesn't seem to be possible, I convert the movies to the Tablet's format and codec and copy them to the SD card, all other movies I've converted, work except the movies, I've downloaded almost all the players in the play store, it just keeps telling me its in "unsupported format" or "this video can't be played". Please help!