Initial reviews of the new Apple TV 4K highlighted that Apple will add support for Quick Media Switching Variable Refresh Rate (QMS VRR) via a software update to tvOS.
QMS VRR prevents momentary blackouts that occur when switching between content playing in different frame rates. As TechCrunch highlights, users who already have the "Match Content" setting for frame rates turned on may already be familiar with this, "since it happens almost any time you start streaming an actual show or movie from most apps." From The Verge's Apple TV 4K review:
The third-gen Apple TV 4K has another bit of future proofing up its sleeve: later this year, a software update will add support for what's known as QMS VRR. This enables compatible TVs to switch between different frame rates without any black screens or noticeable picture interruptions. How many TVs work with QMS VRR, you ask? Well, zero at the moment. But you'll start seeing them hit the market next year; stay tuned for more news about this feature at CES. I've never been that bothered by the short flicker when changing frame rates, but I won't miss it, either.
It is worth noting that QMS VRR does not prevent blackouts when switching between color spaces or HDR content. The new video quality feature is set to be added via a software update to tvOS.
According to YouTuber Andru Edwards, the feature will not come to the second-generation Apple TV 4K, even though that device introduced support for high-framerate HDR content up to 60 fps and HDMI 2.1 last year.
