New 21.5-inch Retina 4K models expected.
QuickTime 7.5.7 for DisplayPort Allows Standard Definition Playback
This update is recommended for owners of MacBook, MacBook Air, and MacBook Pro with Mini DisplayPort. The update addresses an issue where some standard definition purchases from the iTunes Store do not play on some external displays.Based on early testing by MacRumors reader Ampidire, this update appears to allow standard definition (SD) content to play unhindered over the mini DisplayPort.
Just last week, it was revealed that Apple's new mini DisplayPort enforces HDCP protection. This prevents the playback of HDCP flagged content over non-secure video output. In the example given, one customer was unable to play back an SD iTunes movie over a mini DisplayPort <-> VGA connector. Several readers objected to this restriction as iTunes movies downloaded to your computer are only offered in standard definition, while the HDCP protection was intended to prevent digital copying of high definition content.
This latest update appears to remove the HDCP enforcement on standard definition content, which means that current movie content purchased or rented on a Mac should playback unrestricted. While Apple does offer high definition movies for rental through Apple TV, it's not clear when Apple will begin offering this to Mac users.