I see that in the video section, there is a lot of different video format and a couple of user ask how come they cannot see the videos they are downloading. Here is the answer to solve almost any video problems.
This is a superb pack of Codec that looks to be real safe, stable and it works great.
It's called the K-Lite Mega Codec Pack ( Mb) and you can find it
There is an alternative codec for QuickTime and RealMedia so you don't have to install these media player as they will play in a basic media player without any adds and all other stuff that loads in your lauch bar.
If you have QuickTime and RealMedia, you can uninstall these and you will get a clean setup to play these media after installing the codec pack.
You'll get DVD decoder, encoding / decoding latest DivX, XdiV, MPEG1/2, OGG Vorbis and a big bunch of other
This is one of the best pack of codec I have ever found. Woks like a charm on my system.