While the Apple TV 4K can play 4K videos from sources like iTunes and Netflix, that support is conspicuously missing from one of the most popular tvOS apps, YouTube.
YouTube videos are limited to 1080p, according to early reviewers such as The Verge. The issue appears to be Apple's decision not to support Google's VP9 codec, despite it being open and free to use. The same problem prevents 4K YouTube videos from playing in the Mac and iOS versions of Safari.
Apple reportedly has no timeframe for when — or if — it will add VP9. The Apple TV relies on H.264/HEVC, the company's preferred video format across all its devices.
The lack of 4K YouTube video could be problematic for Apple, since that service has a growing library of 4K content, and rival devices like the Roku Ultra, Chromecast Ultra, and Amazon Fire TV do offer the higher resolution.
The new Apple TV is also missing support for Dolby Atmos surround sound, despite simultaneously pioneering Dolby's Vision HDR format. In that case however, Apple has promised a software update.
The Apple TV 4K ships this Friday, starting at $179 for a 32-gigabyte model.