Openx is the open source ad management system tool. By which we can implement ad banners, video ads to be played before actual videos. Administrator can manage all the banners & video ads from the openx admin panel without distrubing the site that using the ad management. It is very much user friendly and save our time for development. We can get the solution for any problem while using this open source tool from openx forums: forum.openx.org.
And the Openx website is: www.openx.org