No, HDMI 2.1a will not bring longer cables, but just more confusion in labeling

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Foreign media is filled with headlines about the improved HDMI 2.1a interface, which “solves the problem of short cables”. First, HDMI’s have always been above standard in length (compared to competing DisplayPort). And secondly, the HDMI 2.1 version has already solved this problem.

The fact that hardware journalists rely on is the implementation of Cable Power technology. It allows for active cables that carry current (300 mA at 5 V) to amplify the signal over long distances (up to tens of meters). Active cables had been there before, but they still had external power, usually via USB. However, HDMI Cable Power directly envisages transmission through a single cable, and the power is supplied by a source device (computer, console, Blu-ray player, etc.), which of course Cable Power must support.

Such an HDMI has the same ending, you just have to keep in mind that the sides are not interchangeable. The cable determines in advance where the source is connected and where the output in the form of TV, monitor, projector, capture card…

The HDMI Forum, which administers the standard of the same name, states that Cable Power is part of HDMI 2.1a, Appendix 1. However, the organization announced the news last January as part of HDMI 2.1. And when it introduced HDMI 2.1a in February this year, it only mentions Source-Base Tone Mapping (SBTM) technology, which makes sure that HDR mapping is the responsibility of the source device, not the display. This shortens the processing latency and at the same time simplifies the rendering of especially computer surfaces, where the image in HDR runs in one window, but the rest works as SDR.

By the way, both SBTM and Cable Power are optional features, so just because a device or cable is HDMI 2.1a doesn’t mean it will support all features. It can easily support the capabilities of the old HDMI 2.0, which is no longer certified, so the HDMI Forum calls anything two-one. This only creates confusion, and this year’s A-scale revision did nothing to help.



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