Or, you could use Longtail Video (ad service from the people who make the JW Player). It's free and they provide you with the ability to add pre, mid, and post roll ads to your site without having to create XML files (simply add the code they provide and add you ads to your back office. The JW player has built in support for it).

Visit http://www.longtailvideo.com/referral.a ... lqekkkdbmt