Following news that Apple is only streaming 4K movies, not offering downloads, the Cupertino company has now detailed 4K streaming requirements in a recent support document.

“Apple recommends a minimum speed of 25 Mbps for 4K streaming,” reads the document.  You’ll want to take this into account when watching 4K movies on an Apple TV 4K connected to a 4K-compatible television.

This doesn’t come as a surprise. The higher the quality of the video you’re streaming, the faster your Internet connection has to be. If your Internet connection is slower than 25 Mbps or the transfer speed drops, your device will automatically switch the video quality to a lower quality version.

“When you buy or rent a movie or TV show from iTunes Store, the device that you’re using might warn you that it can’t play 1080p (HD) or 4K video content,” Apple explains. “Instead, your device automatically plays the highest-quality version of that video that it can.”

Your other Apple devices will play the higher-quality version if they’re compatible.

Before the support document appeared on Apple’s website, automated hardware troubleshooting responses discovered in the tvOS code suggested that uninterrupted 4K streaming would require a minimum 15Mbps broadband connection.

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You can stream movies from iTunes Store using the iTunes Store or TV app on iOS, iTunes for Mac or Windows and the iTunes Movies or TV app on your fourth-geneartion Apple TV or later.

As mentioned, Apple has cautioned that you can download a local copy of an HD movie to an iPhone, iPad, iPod touch, Mac or PC, and might be able to download HDR and Dolby Vision versions of an HD movie to your iOS devices, but you cannot download a 4K version locally.