here's some choice cuts from this article:
the entire tvOS interface has been reworked to run in 4K HDR, but it also won’t let the device switch modes on your TV: from 4K to 1080p, from HDR to SDR, or from a 24Hz refresh rate (for movies) to a 60Hz rate (for games and interface animations). That means that, out of the box, any non-4K content you watch will be upscaled and processed into 4K HDR, running at the highest refresh rate your TV supports, which is usually 60Hz.
Looks like SDR content is upscaled to HDR...
The Apple TV also automatically preferences refresh rate over any other setting: if your TV supports 60Hz HDR10 but only 30Hz Dolby Vision (like 2016 LG OLEDs), the Apple TV will pick HDR10, even though HDR10 looks worse than Dolby Vision. Apple told me that’s because it wants the interface and games to run as smoothly as possible; it’s found that the interface judders at 30Hz. So you’ll get worse HDR but a smoother interface, all because the Apple TV won’t switch modes.
does this mean that 2016 OLEDs will not be able to use Dolby Vision?
If you have a previous Apple TV, this lack of mode switching is familiar, but remapping SDR content into HDR is a whole new ballgame, and unfortunately, Apple’s HDR video processing is hit or miss. It was great when I watched HD content from iTunes, but it fell down in other apps. I watched The Dark Knight in HD on HBO Go with our video team, and the Apple TV 4K HDR processing blew out all the contrast in the image, sharpened everything to hell, and turned the film grain into noise. The same movie looked fine on iTunes, but it just looked bad from HBO Go. I checked on my older 1080p Apple TV, and HBO Go looked fine. So there’s definitely work to be done here.
The good news is Apple told me it’s continuing to refine the processing it’s doing with the goal of making HD SDR content look normal
this is not good news. Good news would be to have mode switching. But why wouldn't they have mode switching? Why are they heck bent on upconverting all content? Why do they destroy most calibration settings? Why can't 2016 OLEDs get Dolby Vision?
All of this adds up to a real devil’s bargain that wouldn’t exist if the Apple TV would simply switch modes on your TV. I asked about it, and Apple told me it thinks mode switching is “inelegant,” because TVs often flicker and display built-in interface elements when they do it. (There’s some classic Apple-ness here.)
Ahhh. A 1 second screen flicker.
So from the jump, the Apple TV forces you to run your nice new 4K HDR TV at a suboptimal setting at some point during the course of using it. The specifics of this problem might only be of interest to A/V nerds, but the way it looks in the end will affect every single Apple TV 4K owner. I suspect Apple will eventually add an advanced setting to allow for mode switching, but out of the box right now, this is what you get.
Non-starter. I need to wait for a software upgrade. Or wait until the Xbox One X disappoints me with similar BS... I've waited for this to be my HDR device since my terrible Xbox One S, Shield, and Roku Ultra experiences... The Xbox One S may have fixed their issues (for me it was a Dolby Atmos issue at the time).