I suggest to install Ubuntu Restricted Extras through Ubuntu Software Center. It will install all media codecs plus java and flash plugins.
Well I think you need to enable multiverse on Software and Updates (if you use Ubuntu 12.04, you can access software properties or something like that from Ubuntu Software Center > Edit menu)
Then close the Software Center and open Software Updater (Update Manager on 12.04) to update the package lists. Alternatively you can run
sudo apt-get update from Terminal.
After update got completed, open Software Center again and look for Ubuntu restricted extras to install.
If you still can’t find the package, try
sudo apt-get install ubuntu-restricted-extras from a Terminal and see if it results in an error.