Simply it's too much trouble. What you want to view/watch, is the new format and you are going to have to get used to it!
You are going to run into it more often and you can't expect people to convert movies for you.
I can convert movie files for sure, but I sure aint gonna bother wasting my time when you can simply do as recomended above.
When you install smplayer, it comes with the necessary codecs and you can play all the movie/music files you want.
Uninstall Quicktime and any other players as you will not need them anymore....... and just have one player.
There are free converters out there, so why don't you do it yourself if you can't get by with the players you already have??