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Comment by crote | Hacker News Reader

HDMI Alt Mode was basically dead on arrival.

The computer world pretty much standardized on DisplayPort already, so USB-C devices would already have to support DisplayPort Alt Mode anyways. Why add support for yet another Alt Mode when DP-to-HDMI converter chips are dirt cheap, and pretty much all USB-C-to-HDMI cables will be using those anyways due to the aforementioned DP ubiquity.

One thing which really bothers me is that all those Alt Mode specifications are proprietary. USB-C itself is a completely open spec and anyone can download the PDFs from their website - but the Alt Modes require you to join the VESA / HDMI consortium, with an associated member fee and NDA.

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> The computer world pretty much standardized on DisplayPort already

Do you know why that is? I live in the Apple world do I didn’t follow the changes.

Last time I had a PC it was VGA and DVI, which gives you a sense of the timeline. Then it seems to have been HDMI for a while (?) and now seems to be moving to DisplayPort.

Is there a reason DisplayPort over Thunderbolt didn’t catch on? Maybe something about how common add-in GPUs are making implementing TB harder?

DisplayPort is royalty-free while HDMI charges licensing per unit. Additionally, Intel strongly supported DP so many boards came with support even if there was nothing to connect it to, and Intel ensured support in USB specs. Eventually enough display manufacturers added support* and DP became common enough, this generated demand and we ended with a self-reinforcing system. There's still a lot of HDMI, so I wouldn't say the computer world is standardized. In my experience, people just use whatever port is available...

* Display turnaround time is significant. Displays can survive a decade comfortably. A few people brag about their 10000K display with 10000Hz refresh rates, but many people just keep their display until it drops or until they buy a new system. So DP took a long time to be universally supported and that hampered adoption for a long time.

> Then it seems to have been HDMI for a while (?)

Not really. HDMI is basically DVI++ but it's first and foremost a TV and video interface.

Once DVI started to be limiting, both PCs and high-end monitors adopted DP. HDMI came to PCs and monitors later, sometimes with limitations, for instance my Dell U2711 couldn't run at its native resolution over HDMI. A few years later UHD 4:4:4 was literally impossible from a PC GPU before HDMI 2.0, while not a problem even on older DP 1.2.

Also DP can do cool things like carrying the signals for multiple monitors (daisy chaining)... I have one usb type c cable that does power display and usb for my 2 dell monitors... it is awesome... sadly Apple never implemented DP daisy chaining this and when you try it with their hardware you only get a mirrored output.

Yes, it’s a pity they never implemented that.

Presumably some deal with Intel to push Thunderbolt :/ It’s an open spec now, but at the time Apple was pushing Thunderbolt hard, only Intel was building the chips for it, both for computers and peripherals (ie monitors, docks etc.)

HDMI was designed by the entertainment industry to connect HD televisions. Its initial version was electronically basically half of a DVI connector, with some audio data thrown into the video stream. Plenty for a 1080p 60Hz stream, but not much beyond that.

DisplayPort was developed by VESA for computer use. It supported a higher bandwidth than HDMI and rapidly gained support for features like variable refresh rates, compression, and feeding multiple monitors through a single cable.

Nowadays it doesn't really matter that much, and they both essentially have the same capabilities. It's now HDMI for televisions and DP for computers because History.

It's not the real deal, but https://www.quantumdata.com/assets/essentials_displayport_us... looks to be quite useful for understanding DP Alt Mode. I've used their DP regular protocol PDFs, though because this is a transcript of an animated webinar, there are images covering text which you'll need to remove in a PDF editor or LibreOffice Draw (which can import PDFs).

Also, there is MHL alt mode which sends the signal over one pair like DP.mi don’t know if this gets used but at least it makes sense unlike HDMI mode.

The reason why HDMI alt mode is awful is that it uses most the wires for HDMI. That doesn’t leave any wires for other uses like USB3. It may even use USB2 wires. The UsB-C docks would be impossible. The only use is for passive adapters.

So, maybe I'm missing something here, but who is talking about computers? Most things that need to be connected to with HDMI, are TVs. I have 5, none of them take display port or USB-C. The all take HDMI. I have no "monitors" because... Why would I need one (I only "game" things that have to run on dosbox)?

But let's talk computers. And phones. All mine, only have USB-C. I have an old one that has micro, and I chromecast the screen from that one. I connect them all to TVs. With HDMI on the TV end.

So literally your dead on arrival example is not even present in the life of my household, while what's talked about in the article is widely used.

It's not used at all. HDMI alt-mode is several years old and nothing implements it. Even HDMI LA considers it dead now, they closed their certification program for it.

In practice, video over USB-C uses either DP alt-mode, Thunderbolt or USB4 (and the latter ones encapsulate DP over their own protocols). All USB-C to HDMI cables and adapters actually use DisplayPort and converters. HDMI alt-mode was indeed dead on arrival.

I'm not addressing the Alt-mode. Please read what was written, and reply to what was written. The comment to which I replied said you connect devices with display port, not HDMI, because all your devices are monitors. The real-world use case is USB-C to HDMI, to connect to a TV. I have no idea what my cables do, but they have USB-C on one end, and HDMI, not DP on the other, and I plug them into the TV.

The comment stated you don't need HDMI on the other end. I am not arguing for "Alt-mode" protocol, nor did I write "Alt-mode" anywhere in my comment. I am specifically replying to the wrong fact that most people use USB-C to connect to and HDMI port, not a DP port, on the other end of the cable.

From a quick google, the reason Alt mode is "dead" is because most devices natively support HDMI and you don't need alt-mode. https://www.notebookcheck.net/The-demise-of-HDMI-over-USB-C-...

You seem pretty confused.

> From a quick google, the reason Alt mode is "dead" is because most devices natively support HDMI and you don't need alt-mode.

If you do video over USB-C, you need alt-mode. Everything uses DisplayPort alt-mode and converts it to HDMI if needed. These days most devices have no other form of video connectivity than USB-C.

You link to an article that literally states "DisplayPort has won".

> The real-world use case is USB-C to HDMI, to connect to a TV.

The real world use case is to connect a PC or phone to an external display. Usually that's going to be a PC monitor, where physical DisplayPort actually is ubiquitous these days. Personally, I don't even have a TV - I'm not exactly a gamer so I don't see why would I need one.

(I actually connect my laptop to a screen using HDMI connector on the screen side, but that's only because it's about 10 years old :P)

I recently picked up a $100 external display on amazon. It's essentially a laptop screen with a magnetic cover a la surface tablet.

It's just a screen, no touch capabilities or any real processing onboard.

This screen has 3 usbc ports and a mini hdmi port. It also has an audio out jack.

In theory, it can be driven with a usbc to usbc cable from a phone or computer, but I don't have a device that can drive it this way.

The second usbc port is auxiliary power for when your phone can't power the whole screen.

The third usbc port is for daisy chaining another device.

The way I use this thing is from my (fairly old) laptop that only has display port out. I have an adapter that changes the DP port on my laptop to full side hdmi and then use the hdmi to hdmi mini cable that came with the screen.

Unfortunately, this setup does not pass sound to the audio jack. I wish my laptop had an hdmi port instead.

I have a similar portable screen with almost the same set connectors (only two USB-C ports and miniHDMI, no daisy chaining). That "(fairly old)" is the key there, as pretty much all modern laptops support DisplayPort over USB-C. I can plug that screen to my 4 year old laptop or my phone using USB-C to USB-C cable and it works, including audio.

You are missing that there is a chip in HDMI side of the cable that converts DisplayPort to HDMI. DisplayPort is what goes over the cable and what the device knows about.

> while what's talked about in the article is widely used

Except it's not, because that functionality is basically nonexistent. All the USB-C to HDMI connectors out there are actually doing the USB-C DisplayPort mode with the equivalent of a DP->HDMI hardware dongle built in.

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