Apple has released a new QuickTime update, which will be of particular interest to owners of MacBook and MacBook Pro unibody computers because it fixes a widely publicized issue where some users were unable to play legally purchased movie files from iTunes on external displays.
You see, Apple's new mini DisplayPort enforces HDCP protection. But while the scheme is intended to prevent digital copying of high definition content, several users were complaining last week about being unable to playback standard definition iTunes movies over a mini DisplayPort to VGA connector. According to notes provided with the update, QuickTime 7.5.7 addresses this issue, meaning that current SD movie content purchased or rented on a Mac should playback unrestricted.
You can download this update via Software Update (Apple menu > Software Update) or by visiting the Apple support website.