If you only have one or two things you're selling, and somebody has already downloaded and watched them, you're out of luck. But if you're bundling with other content serving diverse interests, offering the promise of new content down the road, and giving your audience something for paying that they can't get for pirating, you can set a better hook. Suddenly, when content from you or your partners is pirated, it becomes a loss-leader advertisement for your venture, and the cost of that (and benefit from it) is shared across your group. There's a site that just got featured on Reddit not too long ago, http://www.swearnet.com, that really captured my interest in this regard, if you want to see an example of how this type of thing could work in action.
Piracy always struck me as something only the biggest interests could gain anything from worrying about; an efficiency problem where so much product is being moved that getting 1-2% more of it paid for could make more sense than trying to reach 1-2% more audience, perhaps because they've already saturated their target market.