Like the original Apple TV 4K, the second-generation Apple TV 4K supports 4K HDR content for brighter, more realistic colors and greater detail than is available with the 1080p Apple TV HD.
Both HDR10 and Dolby Vision are supported, and new to the second-generation version is support for high frame rate HDR, which brings more fluid, crisp video. The second-generation Apple TV 4K offers twice the frame rate for high dynamic range video thanks to the HDMI 2.1 port, maxing out at 60 frames per second.
Apple says fast-action sports look smoother, nature documentaries come alive, and YouTube videos "jump off the screen."
The Apple TV 4K requires a compatible 4K television to display content at a 4K resolution, and features like Dolby Vision require a TV that supports Dolby Vision. The Apple TV 4K connects to a television set using HDMI, and an HDMI cable is not included.
To stream content in 4K from iTunes, Netflix, or another source, Apple recommends that customers have a minimum connection speed of 25Mb/s. If an internet connection isn't fast enough for transferring 4K content, Apple downscales the video quality.
Apple does not allow users to download 4K content from iTunes, with 4K content limited to streaming.
Supported Photo, Video, and Audio Formats
The Apple TV 4K supports H.264, HEVC (H.265), HEVC Dolby Vision, and MPEG-4. As for photos, it can display images in the following formats: HEIF, JPEG, GIF, and TIFF.
Supported audio formats include HE-AAC (V1), AAC (up to 320 Kbps), protected AAC (from iTunes Store), MP3 (up to 320 Kbps), MP3 VBR, Apple Lossless, FLAC, AIFF, and WAV; AC-3 (Dolby Digital 5.1), E-AC-3 (Dolby Digital Plus 7.1 surround sound), and Dolby Atmos
The Apple TV supports Spatial Audio with Dolby Atmos and standard lossless audio, ranging from 16-bit at 44.1 kHz to 24-bit at 48 kHz. Apple says that the Apple TV 4K "currently doesn't support Hi-Res Lossless," leaving the door open to the possibility of a future software update with Hi-Res Lossless support for the device in the future.
Alongside the 2021 Apple TV 4K, Apple added a new Color Balance feature that uses an iPhone with a Face ID camera to calibrate the colors on the Apple TV.
In the video section of the Apple TV settings, there's a Color Balance option to initiate the feature. You can hold your iPhone up to the TV screen, with the iPhone detecting the color and comparing it to industry standards for adjustment purposes. This feature is not available when Dolby Vision is enabled on a compatible TV set.
Source : https://www.macrumors.com/roundup/apple-tv/603