HDMI 2.1 chip bug also causes problems for Quick Media Switching

Mike Wheatley

The faulty HDMI 2.1 chip bug that caused numerous problems for AV receivers sold by the likes of Denon, Marantz and Yamaha has reared its ugly head again with the first implementations of Quick Media Switching (QMS), it has been revealed.


Denon, Marantz and Yamaha launched their first HDMI 2.1 receivers in 2020, enabling users to pass-through the PS5 and Xbox Series X’s highest-quality video signals, such as 4K@120Hz, 8K@60Hz or 120Hz VRR. However, early adopters quickly came across a bug that was caused by the internal HDMI 2.1 chip made by a company called Nuvoton. All three brands scrambled to find a solution, but it wasn’t easy, and led to product recalls and a replacement HDMI board to amend the situation.

However, the new board did not fully fix the issue, and the bug is now causing issues with the new QMS feature that is being rolled out on LG Electronics’ 2023 OLED TVs and the 2022 Apple TV 4K.

QMS is an HDMI 2.1a feature that is supposed to eliminate AV blackouts when the frame rate is changed, but not when there's a switch in resolution or dynamic range formats.

According to Heise.de, which first discovered the original HDMI 2.1 bug, there are problems caused by changes in QMS from when it was first announced as part of HDMI 2.1, and now present in HDMI 2.1a, mean that early iterations of QMS are not compatible with the above devices.

So, the correct and certified HDMI 2.1a QMS implementation found in the Apple TV 4K (2022) and LG’s 2023 OLED TVs will not work when it’s passed through Denon’s, Marantz’s and Yamaha’s HDMI 2.1 receivers.

Heise.de first spotted the bug, and it was later confirmed by HDMI Licensing CTO Jeff Park. Apparently, the issue stems from the fact that QMS was not clearly defined in the original HDMI 2.1 specification. As a result, Nuvoton, the company that builds HDMI 2.1 chips for most AV receivers, is stuck with an incomplete QMS implementation that was never certified.

Heise.de said that it looks like there won’t be any solution to the problem, unlike the original issues where a fix was developed. “According to our current knowledge, the QMS implementation of the current chips cannot be "bent" to fit with a firmware update. According to c't information, Nuvoton's roadmap also does not envisage the next revision of the HDMI chip until 2026. Until then, no processor with QMS according to HDMI 2.1a will come from the manufacturer," the magazine wrote.

The problem for Denon, Marantz and Yamaha is that all three brands have marketed their AV receivers as supporting QMS, but it seems likely the feature will never actually work on their earliest models.

To enjoy QMS support, it will be necessary to connect the Apple TV 4K (2022) or a future media player that supports the feature directly to a 2023 LG OLED or future TV model, then pass back the audio to the receiver via the TVs’ eARC port. Whether or not you'll want to do so is another matter, for the QMS feature itself is also proving to be a little clunky, as this video shows: