Apple announced the arrival of more 4K content to iTunes when it introduced the new Apple TV 4K last week. However, those who purchase the new set-top box will be limited in how they can enjoy 4K titles. According to an Apple support document, 4K content from iTunes can only be streamed, not downloaded directly to a device.

"You can download a local copy of an HD movie, and you might be able to download HDR and Dolby Vision versions, but you can't download a 4K version," the support document states.

It appears the only guarantee customers have is downloading an HD copy of purchased movies to their devices. Apple also announced last week that it will upgrade customers' previous purchases to 4K free of charge. But, judging by this support document, you won't be able to download the 4K version of the titles you already purchased—only the HD versions.

While the support document doesn't offer an explanation for this restriction, it's likely due to local storage capacities, as 4K movies come in at around 100GB. The new Apple TV 4K comes in 32GB and 64GB storage configurations. While those capacities should be fine for downloading games, apps, and a couple of HD titles, there's little room for an entire 4K film. Apple is selling 4K content on iTunes at the same price as HD content, so it's also possible that the company made deals with movie studios that included a restriction on 4K downloads.

In addition to iTunes, the Apple TV 4K supports 4K streaming from Netflix and other streaming services. Later this year, Apple plans to include Amazon Prime Video on its set-top box, and it will support 4K content from that service as well. However, it doesn't currently support 4K video from YouTube. The Apple TV 4K only supports H.264, HEVC (H.265), and MP4 video formats for streaming and 4K videos on YouTube are streamed in the VP9 format, which isn't supported by the new device.