HDMI standards are a huge mess and HDMI 2.1 in particular is frustrating. Enjoying 120Hz gaming on a PS5 or Xbox Series X, for example, can be a particularly harrowing experience.
Now the HDMI Forum has announced its latest revision of the HDMI spec stack, HDMI 2.1a, which adds a major new feature, Source Based Tone Mapping or SBTM (Source Based Tone Mapping).
SBTM is a new HDR function that download part of HDR tone mapping to content source (such as PC or decoder) along with the tone mapping that the TV or monitor does.
SBTM is not a new HDR standard and therefore it is not a replacement for HDR10 or Dolby VisionRather, it is intended to help existing HDR configurations work better.
Allows the content source to better optimize the content that passes to the screen, eliminating the need for the user to manually calibrate their monitors for HDR. The source device is responsible for configuring the content for the specific screen.
The HDMI Forum notes that manufacturers of set top boxes, games and televisions can add support for HDMI 2.1a through firmware updates “Depending on your project.”
However, given the usual trajectory of TV updates, it seems almost certain that, in most cases, users won’t get the new features until they purchase a new HDMI 2.1a compatible TV.
Like all the other features unique to HDMI 2.1 like variable refresh rates, low latency automatic connections and the bandwidth needed to deliver things like 10K resolution or 120Hz refresh rates, SBTM will be an optional feature that manufacturers will be able to support, but not something they are required to provide.
This is because Now that the HDMI 2.1 standard exists, the HDMI 2.0 standard no longer exists: All new HDMI 2.0 ports must be grouped under the HDMI 2.1 branding, despite not using any of the new features included in the “new” 2.1 standard.
HDMI 2.1a will work in a similar way: once the standard is released, per the rules of the HDMI license manager, all new ports will theoretically be labeled HDMI 2.1aBut they won’t have to offer the new SBTM or any of the HDMI 2.1 features.
The HDMI Forum’s argument is that its standards have always worked that way and that optional features allow manufacturers flexibility in terms of the functionality they offer (basic equipment, for example, probably doesn’t need ports that support 8K 120Hz gaming VRR ).
Companies are required to list the features their hardware supports to make it clear to customers what their hardware is capable of.
On the other hand, most manufacturers are not following the recommendations for port labeling. They continue to label HDMI 2.0 ports as “HDMI 2.0” and reserve HDMI 2.1 labeling for ports that actually support the new features as this is more useful to customers.
However, there is a chance that less scrupulous companies will start marketing HDMI 2.1 ports that don’t offer any 2.1 or 2.1a functionality.