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New Apple TV 4K (2021) has untapped HDMI 2.1 potential

Apple Tv Review 4k
Apple Tv Review 4k (Image credit: Stephen Warwick / iMore)

What you need to know

  • Apple's new Apple TV 4K (2021) features an HDMI 2.1 port.
  • One reviewer's testing has confirmed the device isn't currently making use of the feature, however.
  • Using the old delivery means the Apple TV is currently capped at 18gbps and can't support chroma 4:4:4.

A recent review of the new Apple TV 4K (2021) has revealed that Apple's most recent home entertainment offering isn't currently flexing all of its HDMI 2.1 muscles.

As noted by Apple TV aficionado Sigmund Judge at Screentimes.net, the new Apple TV 4K comes with HDMI 2.1, paving the way for a world of improved connectivity and higher bandwidths. According to Judge's tests, however, plenty of that potential remains untapped.

As Judge notes HDMI 2.1 could allow data throughput of 48gbps, which is a lot more than HDMI 2.0, and could allow for 4K HDR content at 120fps for sport, gaming content, and content filmed on iPhone to be displayed correctly. However, according to Judge the new Apple TV is currently still using an older signaling method called TMDS (Transition-Minimised Differential Signalling), rather than FRL (Fixed Rate Link). The difference is explained as follows:

HDMI 2.1 employs that additional clock channel to be repurposed for data. In the new specification these data channels have been renamed as lanes and replace the TMDS process with a fresh approach called FRL (Fixed Rate Link) featuring four lanes of 12gbps and supporting playback across a spectrum of SD up to 10K whilst maintaining a transmission of up-to 48gbps. Whilst 8K and 10K may be theoretically possible on Apple TV 4K it is important to note the name of the product being marketed.

Judge continues:

Please keep in mind as exciting as 48gbps is everything in the signal chain has to be able to support that bandwidth, and that's where the new Apple TV 4K brings us some puzzling information to ponder on. During my early tests running tvOS 14.6 I noticed that when running at 4K HDR 60 the newly released Apple TV 4K was using the TMDS signalling method instead of FRL and thus it dropped the chroma subsample from 4:4:4 to 4:2:2. This means that whilst there may physically be a HDMI 2.1 port in the new Apple TV 4K it is currently limited to the bandwidth of the TMDS signaling method described earlier. It is unknown if and when the full capabilities of the HDMI 2.1 FRL specification will be unlocked or if the system on chip is capable of driving those high numbers. Judging on the lifespan of the previous generation of Apple TV 4K I would be shocked if Apple didn't unlock the capability during the course of its lifecycle or as soon as tvOS 15.

The Apple TV is currently a 4K HDR 60fps capable device, so the TMDS signaling method is obviously all that it needs to run that resolution and frame rate, as the review points out though this means that chroma is reduced from 4:4:4 to 4:2:2.

The news confirms that Apple's new Apple TV hardware in theory is capable of much greater content delivery than it currently offers, as Judge states it could theoretically deliver 8K or 10K content, as well as 120Hz. I'd be inclined to agree with Judge that these findings confirm that there is a lot of untapped potential in the new Apple TV 4K, and I can't wait to see where Apple takes it. With WWDC and a new tvOS just a few days away, we might not have to wait long.

The new Apple TV 4K (2021) is already available at a slight discount in our round-up of the best Apple TV deals.

Stephen Warwick
Stephen Warwick

Stephen Warwick has written about Apple for five years at iMore and previously elsewhere. He covers all of iMore's latest breaking news regarding all of Apple's products and services, both hardware and software. Stephen has interviewed industry experts in a range of fields including finance, litigation, security, and more. He also specializes in curating and reviewing audio hardware and has experience beyond journalism in sound engineering, production, and design.

Before becoming a writer Stephen studied Ancient History at University and also worked at Apple for more than two years. Stephen is also a host on the iMore show, a weekly podcast recorded live that discusses the latest in breaking Apple news, as well as featuring fun trivia about all things Apple.