The HDMI Forum has added a new feature to the HDMI 2.1a specification called HDMI Cable Power. In a nutshell, HDMI Cable Power allows active HDMI cables to draw power directly from the source rather than requiring a separate power cable.
Distance is the biggest enemy for HDMI cables, so you start to suffer from signal degradation at longer lengths. That's why passive HDMI cables are typically short and acceptable for most mainstream use. However, in those unique scenarios where you need to connect two devices over long distances, you have no choice but to opt for an active HDMI cable. These cables come with a small onboard processor that amplifies the signal. But, of course, the processor needs power, which it draws from both ends of the cable through a USB connector. Some active HDMI cables even come with a power adapter. The latest HDMI Cable Power technology aims to eliminate all this cable clutter.
A typical HDMI cable accommodates up to 50 mA in terms of power. With HDMI Cable Power, the cable can pull up to 300 mA at 5V. The feature increases the power draw by sixfold and doesn't need external connectors.
HDMI 2.1 flaunts higher bandwidth and drives resolutions up to 10K. Where HDMI 2.0 offers a maximum transmission of 18 Gbps, HDMI 2.1 boasts an impressive transmission bit rate of 48 Gbps — that's almost three times as much bandwidth. Currently, passive HDMI 2.1 cables go up to three meters. During the UHS Cable program testing phase, HDMI Forum expected passive cables to max out at five meters. HDMI Cable Power will open the doors to longer passive cables without the need for external power.
However, there are some caveats. The HDMI cables and the source device need to support the HDMI Cable Power feature to ensure proper operation. While the connection remains the same, the cables are unidirectional. In other words, one end connects specifically to the HDMI source (transmitting) device, while the other goes to the HDMI Sink (receiving) device. If you connect the cable incorrectly, there is no harm — it just won't work.
New HDMI cables with native HDMI Cable Power support will come with a separate power connector for those source devices that don't support the feature. As we've seen before, the connectors will either take the shape of a USB Micro-B or USB Type-C port.
Pricing is one of the problems with active HDMI cables. They usually cost substantially more than their passive counterparts due to the added circuitry like chips and retimers. However, cables with HDMI Cable Power should cost less than your standard active cable in a perfect world.