Netflix has a new competitor, and it's a behemoth: Walmart. The world's biggest retailer added Vudu, a movie streaming service it bought 18 months ago, to its site yesterday. Walmart now offers 20,000 titles to rent for $1 to $5.99, or to buy for $4.99 and up; new titles will be available the same day they come out on DVD. The service arrives just two weeks after Netflix hiked its prices; more than 2 million customers are expected to cancel their Netflix subscriptions. The AP notes that Walmart does not offer subscriptions, however, making its service more akin to Apple's iTunes. (More Walmart stories.)