Quick Media Switching, part of the HDMI 2.1 standard that allows a television to adjust its refresh rate without delay or screen blackout, does not always work flawlessly with all HDMI devices. This seems to be due to different implementations.
The German Heise in the form of c’t magazine message on this issue confirmed by Jeff Park of HDMI Licensing. The bottom line is that qms has been part of the HDMI 2.1 standard for many years and no change has been made to the specification, but the organization behind the HDMI standard has included a clarification of qms in version 2.1a. The authority does this because the specification in 2.1 would leave too much room for interpretation for manufacturers.
Now, according to c’t magazine, it appears that manufacturers have approached the implementation of QMS differently. This may result in a situation where the media player and screen have different implementations, which means that no handshake occurs and the black screen still appears again.
Technically, this is because certain manufacturers do not use Variable Refresh Rate as a basis for QMS. Vrr ensures that the frame rate of the screen is adjusted to the input and this technology should also have been the basis for qms in accordance with the HDMI 2.1 specification. In practice, this appears not to have always been applied. Partly because of this, it is now often referred to as ‘qms-vrr’.
Park acknowledges that there is no clarity about devices such as receivers that are still equipped with QMS in accordance with the 2.1 standard. There is no official test that reliably shows whether the implementation meets the most recent specification. There is a good chance that many receivers with HDMI 2.1 have not received the QMS-VRR implementation, so that the combination of such a receiver with, for example, a 2023 LG TV with QMS-VRR support will not lead to the desired result.