as what I know QuickTime Alternative mainly is a browser plugin more than being a QuickTime codec in computer (but it has Move Splitter, so it will help play some files too).
Well, actually no, QuickTime Alternative (QTA) is
both a browser plugin and a codec that's used by Media Player Classic (MPC) for standalone playing of QuickTime files. (QuickTime Alternative Lite aka QT Lite is usually the same thing as QTA, but distributed without MPC.) Since you don't need or actually use QTA, Omid, it's understandable you could be misinformed about that.
Similary, Real Alternative (RA) is both a browser plugin and a codec that's required by MPC for standalone playing of Real media files. I use a MPC fork, Media Player Classic Home Cinema (MPC-HT), as my default media player because it has more features than MPC and is still in very active development.
http://www.free-codecs.com/download/real_alternative.htmhttp://mpc-hc.sourceforge.net/but I prefer to don't use it, I use Win7Codeck Pack in my computer so I can play every kind of media files in my computer using Windows Media Player or media player classic or my other favorite media players. so instead of install QuickTime alternative, I download media files in my computer and then play them using my own player instead of watch or listen inside browser. also it's safer too! (to have fewer plugins inside player).
At times I use VLC media player because it has some features that MPC-HT doesn't. As explained by others elsewhere, VLC has all the codecs it needs built right in. It even supports most QuickTime and Real files. VLC also provides browser plugins, but I use QTA and RA for that.
http://www.videolan.org/vlc/