which is your video player? Does it play videos without codecs? Does it play cd/dvd images? Does it play 'unknown formats' ( a common term with downloaded videos ) ? My video player plays all these kinds ! VLC Media Player
VideoLan (aka VLC) is the best one you can find. I've never found I video which I could not play there, and I haven't got to deal with all those codec packs installation or whatever. It just works!
Well, I am using VLC and Quick Time Player but my suggestion to VLC is the best to other player.......
vlc is good, but i like subedit, it's free and has more options than vlc. if you close a movie, the next time you open it, it'll start from where you left it. and you can increase/decrease the size of the subtitles, which i don't believe you can do with vlc.