Transferring video from PC to Iphone

[S40PZ]

So I have some videos, they are animes actually. They were originally English in the first place, but you could change the language and add subtitles as well. I dont know why but wmp and other players couldnt open the video because its extension was .mkv (I think). So I downloaded vlc player and it worked ! I sent the videos Pc to my Iphone by using Dropbox, but when I opened the videos it was in English and without subtitles like it was and I can't change it. Why did this happen ? Is there a way to solve it or do you know another way to transfer videos PC to Iphone.