My codec is break

I don't know how to install codeds. I think I've tried, but am not sure I did anything useful. My ad-hoc solution is to "swap" between Media Player and DivX.

My question: Is there some easy way to identify the codecs needed for a certain file and then install them?

So please, Computer Geek Squad - help me!

Thanks. But what's VLC? Is it this: http://www.videolan.org/vlc/streaming.html