As surprising as it sounds, YouTube lacked the ability to play videos in 4K on the Apple TV, until now. Apple TV can now play YouTube videos in 4K but still without HDR support or 60fps. Meh.
According to the website Flatpanels HD, Apple is using Google’s proprietary VP9 video codec for YouTube 4K playback. We are not sure why it’s not using the new AV1 codec that was developed as a partnership between Apple, Google, Netflix, and others.
YouTube and Apple have a history related to not supporting codecs. We hope Apple will use the new AV1 codec in the future and bring support for 4K HDR and 60 fps as well.