HDMI 2.1 & 2.1a Compliance Certification – Utter Confusion!
I have never hidden my disdain for BOTH HDMI and HDCP but now I have good reason to truly despise the entire set of standards.
At CES 2022 yet another version of HDMI was introduced, 2.1a. The point here is that just because a device is labelled HDMI 2.(x) doesn’t now mean that it supports all or even any of the features that the level defines….yes really, that’s according to the latest HDMI certification process! So what is going on now and what does 2.1a bring to us?
HDMI was unleashed upon us in 2002 as version V1.0 with a very basic range of functionality. The idea was to simplify connectivity between AV and home theater devices and support encryption in order to stop pristine copies of the digital signal being made. Since that day more and more features have been added in order to support the ever growing needs of the connected hardware and media.
Image Credit HDMI.ORG.
As can be seen from the above table the feature set has truly grown over the years. The current version 2.1 supports uncompressed data rates of up to 48Gbps, 4K/120Hz, 8K/60Hz and resolutions up to 10K. In the early days, and even recently, the 2.1 data rate was capped at about 40Gbps due to HDMI silicon chip restrictions, plus we all needed those new certified HDMI cables even for relatively short runs. Other important features in HDMI 2.1 included; VRR (Variable Refresh Rate), ALLM (Auto Low Latency Mode), QFT (Quick Frame Transport) and QMS (Quick Media Switching) mostly to satisfy gaming demands, plus the enabling of eARC (Enhanced Audio Return Channel).
The problem now is that manufacturers are NO LONGER required by the HDMI Certification process to include all (or even any) of the feature set that a port labelled as HDMI 2.1 compliant can support. It would appear that as compliance testing for version 2.0 has been discontinued, that 2.0 is now considered a sub set of 2.1 and that as many of the features are optional anyway, all equipment submitted for certification will be treated as if it is HDMI 2.1. So it appears that there are only two requirements that need to be met by the manufacturer in order to use the 2.1 certification:
- The device must support at least one 2.1 feature
- The devices specifications must state what features each HDMI 2.1 port supports
This effectively lets a 2.0 or even 1.4 device look like a 2.1 device. So much for conformity and uniformity. Apparently we now all have are own HDMI standards!!
All of the above isn’t exactly new. A recent example would be the 4KP120 and 8KP60 debacle with Denon, Marantz and Yamaha. Now things are just getting more complicated for the public who are put in the position of having to research what HDMI functions they require and determine if all the equipment they are purchasing has those required functions. Based upon my experience many HT store sales assistants barely know anything about this topic let alone the average member of the public.
HDMI Version 2.1a
So what has HDMI 2.1a brought us? Source-Based Tone Mapping, or SBTM. I immediately see many readers saying what is this, do I need it or is it a solution looking for a problem?
Mapping the brightness levels to video levels for the original standard dynamic range (SDR) of 100 nits caused few display problems. However, high dynamic range (HDR) 4K signals typically use brightness levels of 600-2,000 nits or even as high as 10,000 nits. These higher peak white highlights of 4,000-10,000 nits well exceed the capabilities of many displays and if not correctly processed cause clipping, white crush and loss of white level definition. Tone mapping is the process whereby the display electronics reduces those highlight levels in some gradual way ‘mapping’ them to the ‘nits’ capability of the display. A side effect of this mapping process is that some displays and in particular projectors can end up creating a rather ‘dim’ image in a vain attempt to give enough ‘headroom’ for those rarely used highlight peaks.
Unfortunately there is no industry standard way of doing this mapping and it is left to each of the manufacturers of each display type to process the HDR signal in a suitable way for their display(s). This new SBTM HDMI standard splits the tone mapping between the signal source like DVD players, set-top boxes, streaming sources and game consoles and the display device, be it a TV or projector. It is claimed that this process will provide better handling and display of, in particular, mixed video signals that contain both HDR and SDR material, like menus and thumbnails. To be honest I have never seen any problems with such material, so to me it looks like a solution looking for a problem. Even ‘dim’ HDR images can be somewhat mitigated with good ISF calibration, automatic processing and/or selection of an appropriate EOTF curve. Your experience may of course vary. On top of that, multiple pieces of hardware are now subject to yet more firmware upgrades and compatibility issues. This problem again is not totally new, as some TV’s, notably older Sony 4K displays, needed the player (source) to process Dolby Vision HDR, a process called source-led rather than display-led, and was selected in the players setup menu.
This new SBTM feature handles all forms of HDR, but both the source and display must support the new HDMI 2.1a version. Sorry, but good luck with that, as I believe no manufacturers (as of Jan 2022) support this feature. Meaning that either you need all new devices if you want it or ALL your sources and displays will need firmware upgrades IF they can even support the feature. Again it’s in the manufacturers hands.
As I said at the opening to this post, DO NOT assume that just because a device is labelled HDMI 2.1 or 2.1a that it supports all the features listed above as it often will NOT. More importantly the number of features supported by EACH HDMI port maybe different even though they may all carry the same HDMI 2.1 labelling. It is up to the manufacturer to list those features that THEIR version of the HDMI standard supports on each port in their advertising literature and YOUR responsibility to see if they are all what YOU need to make your HT system work correctly!
Read more about SBTM at HDMI.org.
Read more about HDMI2.1 at HDMI.org.
See my earlier posts on HDMI versions:
