If you’re using a USB-C port to connect a computer to a display, you’re most likely using DisplayPort Alternate Mode (Alt Mode), and due to non-existent adoption, we can pretty much guarantee you’re not using HDMI Alt Mode. According to the HDMI Licensing Administrator (HDMI LA), you never will because the feature is dead.
HDMI Alt Mode allows HDMI video signals to travel from a USB-C port to an HDMI host, like a TV. It’s similar to DisplayPort Alt Mode, which lets you connect DisplayPort displays to USB-C ports. NotebookCheck spoke with HDMI LA, which is responsible for licensing the HDMI Forum’s HDMI specs, at CES 2023 in Las Vegas last week and learned that there won’t be any certified adapters supporting HDMI Alt Mode over USB.
“According to HDMI LA, there are simply no more uses for Alt Mode,” the publication reported on Wednesday. “One of the reasons is that companies like Apple have begun putting HDMI ports on their products again. HDMI Alt Mode also no longer offers any advantages. As a result, the specification will not receive any further updates.”
A losing battle
The HDMI announcement comes as USB-C relentlessly dominates various consumer gadgets. Makers of thin-and-light laptops like the Dell XPS 13 and more experimental designs like foldable PCs are increasingly running out of room for anything but slim, space-saving USB-C. There are plenty of products, from laptops to smartphones, that solely rely on USB-C (and wireless tech) for all accessories and even for receiving power.
That means there are plenty of people finding themselves connecting displays via USB… they’re just using DisplayPort’s Alt Mode to do it instead.
Released in 2014, DisplayPort Alt Mode already had a head start on HDMI Alt Mode, which the HDMI Forum announced in 2016. The technology can even support HDMI 2.0.
HDMI Alt Mode feels out of date, since it maxes out at HDMI 1.4b. The HDMI LA’s page about HDMI Alt Mode addresses the lack of HDMI 2.0 support, pointing out that the HDMI Forum is responsible for HDMI specs and hasn’t made any public statements about HDMI Alt Mode supporting HDMI 2.0b. It makes no mention of newer HDMI specs.
HDMI over Alt Mode supported HDMI features like Audio Return Channel, HDMI Ethernet Channel, Consumer Electronic Control, Deep Color, and x.v.Color. The HDMI Forum saw it being used to connect PCs, tablets, and phones to displays like TVs, monitors, and projectors. But it ultimately couldn’t compete with DisplayPort’s Alt Mode, which can support HDMI displays with higher refresh rates (4K at 60 fps uncompressed versus 30 fps, for example). The latest version of DisplayPort Alt Mode can also support 24-bit color, while HDMI’s take is limited to 8-bit. The latest USB standard, USB4, doesn’t even support HDMI Alt Mode.
These higher specs help explain why so many products, from USB-C ports on laptops to countless HDMI-to-USB-C adapters and cables, have opted for DisplayPort Alt Mode.
In fact, the HDMI LA admitted to NotebookCheck that it doesn’t know of any HDMI to USB-C adapter that uses HDMI Alt Mode. NotebookCheck also spoke with people “familiar with the certification process” at the USB Implementers Forum, who said that they also don’t know of any HDMI Alt Mode adapters.
In a way, this makes things easier. As noted by NotebookCheck, the death of HDMI Alt Mode means you can be sure that an HDMI adapter will work with your system, so long as it has a USB-C port supporting DisplayPort Alt Mode.
Currently, there is a certification program for HDMI to USB-C cables, and one is in the works for USB-C to HDMI adapters to help people buy the correct adapter for their HDMI ports. DisplayPort-based HDMI to USB adapters get “base certification,” but this isn’t obvious to consumers, NotebookCheck noted.
https://arstechnica.com/?p=1909479