New USB Type-C to HDMI spec lets you ditch the dongle

HDMI Alt Mode allows HDMI video to pass along a USB-C cable dongle-free.

Mark Walton – Sep 5, 2016 4:00 pm | 89

Credit: Andrew Cunningham

HDMI Licensing, the outfit that decides what is or what isn’t HDMI compatible, is releasing HDMI Alternate Mode (Alt Mode) for USB Type-C devices.

The new spec will finally allow HDMI video signals to pass along a USB Type-C cable without the need to use a pricey dongle or dock to convert the DisplayPort signals that are natively output via the Type-C standard.

Future smartphones, tablets, cameras, and laptops—which will hopefully include Apple’s Macbook with its solitary Type-C port—will only need a cheap dumb convertor or simple USB Type-C to HDMI cable in order to work with a HDMI display.

Aside from ridding the world of pricey dongles for laptop users, HDMI Alt Mode could also cut down on the plethora of HDMI connectors used on other devices. While it’s unlikely that HDMI Type A—the familiar full size connector used on the vast majority of televisions and other A/V equipment—will disappear, the less common HDMI Type C (Mini HDMI) and HDMI Type D (Micro HDMI) ports found on some smartphones and cameras could be replaced by Type-C.

But there are some odd restrictions attached to HDMI Alt Mode. For starters, it’s not backwards compatible with existing devices or upgradeable via software, so those currently using dongles will have to hang onto them. Secondly, HDMI Alt Mode only supports the older HDMI 1.4b standard, rather than HDMI 2.0b. That means 4K (UHD) video will work, but only at 30FPS, making it essentially useless for gamers or productivity users. High Dynamic Range (HDR) content, the current hotness in TV tech, isn’t supported either.

The HDMI 1.4b restriction is particularly puzzling given USB Type-C already supports DisplayPort 1.3 via DisplayPort Alt Mode. This supports 4K displays at 120Hz, 5K displays (5120×2880) at 60Hz, and even 8K displays (7680×4320) at 30Hz. However, Audio Return Channel (ARC), 3D, HDMI Ethernet Channel (HEC), Consumer Electronic Control (CEC), Deep Color, x.v.Color, and HDCP 2.2 are all supported via HDMI Alt Mode.

HDMI Alt Mode joins the likes of DisplayPort, Mobile High-Definition Link (MHL), and Thunderbolt 3, all of which are already supported over USB Type-C. Indeed, Thunderbolt 3 is quickly becoming the standard connection on laptops, acting as a “superset” host for USB 3.1 (at full 10Gbps speed), DisplayPort 1.3, PCI Express Gen 3 (enabling external graphics card docks like the Razer Core) and the Thunderbolt standard.