DisplayPort is packet-based and can be multiplexed with other USB-C traffic through a hub
HDMI is not packet-based and so when it uses USB-C it takes over the entire cable (alt-mode)
HDMI is not packet-based and so when it uses USB-C it takes over the entire cable (alt-mode)
AFAIK, when HDMI is used over USB-C, it's actually DisplayPort over USB-C; while a HDMI alt mode was specified, nobody actually implemented it, everyone instead implemented the DisplayPort alt mode and then used a DP-to-HDMI converter chip whenever an HDMI output was required.
> DisplayPort is packet-based and can be multiplexed with other USB-C traffic through a hub
That's the case only for USB4 (and AFAIK earlier Thunderbolt 3). Other USB-C ports with DisplayPort alt mode simply use some of the USB 3.x pairs for raw DisplayPort, and whenever the use of all four USB 3.x pairs is required for DisplayPort due to the target resolution, then only USB 2.x can be available (USB 2.x has its own dedicated pair in the cable).
Back in the Thunderbolt 3 era, it was up to each motherboard manufacturer to decide how many pairs they routed to USB alt-mode, so it's not necessarily a safe bet to depend on it working.
So, in one specific example, 4k60 over USB alt-mode DisplayPort is not supported on Apple's $4999 iMac Pro, as USB alt-mode is only assigned two pairs; however, 4k60 over Thunderbolt DisplayPort is supported, as Thunderbolt is assigned four pairs. The only way to get 4k60 out of that device is to use a Thunderbolt-only DisplayPort adapter, that has no USB mode at all.
This was resolved by USB 4 and Thunderbolt 4 both incorporating a more modern DSC (display stream compression), among other things as described above, but your mileage will vary much more wildly with USB 3.
This is part of why DP is $$$ compared to HDMI. I would love to see DP start eating HDMI's lunch after this and the absolute shit show that was the HDMI 2.0 roll out but cheaper to implement is almost certainly going to be the driving factor when it comes to consumer grade TV / Displays and no console or other set top box maker is going to bother putting display port on their device if nobody's got a TV that can use it.
Why is that more expensive?
In terms of complexity, implementing DP vs HDMI 2.1 is not materially different. They both have fixed rate links, packets, Reed-Solomon forward error correction, DSC, etc.
But IIRC DP is royalty free, and HDMI is not.
You can check that there in this presentation (https://www.vesa.org/wp-content/uploads/2011/01/ICCE-Present...), page 32 and 33.
The majority of DP traffic is still brute force video data, interspersed with heavily packetized secondary data.
Over the years, I've spent many hours wading through DisplayPort data debug traces, and I've always wondered what people were smoking when they called it 'packetized like Ethernet'. It's just not true. (And FWIW: even old HDMI can transport secondary data packets just the way you can with DP. It's how audio-over-HDMI is done...)
"ARC" seems to be "Audio over HDMI using CEC for discovery and control", which (if you've bothered to run CEC over the DisplayPort AUX channel) you get the rest automatically with DisplayPort.
However, because both CEC and ARC are HDMI standards, you bet your biscuits that the HDMI Consortium will bar anyone who wants to use HDMI ports on their devices from shipping official firm/software that does the braindead-simple thing of running CEC over DP AUX, and having ARC-compatible firm/software.
As is nearly always the case (and when it's not, it's not for long) DisplayPort is totally capable of everything HDMI is, but the HDMI Consortium stands in the way of having commercially-distributed DisplayPort "home theater" products that are compatible with the nice-to-have HDMI features.
Like you point out, there's no technical reason DisplayPort cannot provide similar features. The issue is the lack of any standards for them built into the DisplayPort specification. Some of these features, like CEC, are 20 years old and could easily be improved upon in an ecosystem that doesn't have to worry about backwards compatibility.
Ah, okay.
Well, DisplayPort handles EDID, DDC/CI, E-DDC & friends... that's the CEC-equivalents handled. VESA does have standards for remote control of displays... it turns out that that's a thing that people want to be able to do.
> The issue is the lack of any standards for them built into the DisplayPort specification.
Nah. DisplayPort already supports everything (or just about everything) CEC can do.
The reason you don't see this stuff often making its way into TVs is because the HDMI Consortium gets in the way of folks who want to add DP ports to their TVs. The reason you don't see explicit support for HDMI Consortium protocols such as CEC in VESA standards is -again- because the HDMI Consortium gets in the way of folks who want to add DP ports to their TVs... so why bother? (Especially when actually supporting the protocol is trivial... squirt exactly what you'd send over the HDMI cable over the DP AUX channel, instead.)
If it was actually politically possible to have DP ports on TVs, then you'd see some of the more esoteric aspects of CEC (like manipulating a TV tuner) be quickly standardized into the VESA equivalents... assuming that VESA didn't just say "Oh yeah, y'all just go talk CEC to these new DP-equipped TVs. You already know how.".
[1] While the physical TOSLINK cable is able to support higher channel counts via ADAT[2], I'm not aware of any TVs with ADAT support.
Similarly, while 192 kHz / 24-bit TOSLINK support is common in pro audio and audiophile gear, the standard only requires 48 kHz / 20-bit. I imagine most TVs output 48 kHz / 20-bit, if only for the sake of configuration simplicity: TOSLINK is strictly unidirectional, so automatically negotiating format support beyond mandatory minima is impossible.
Great news! DisplayPort supports:
> 1–8 channels, 16 or 24-bit linear PCM; 32–192 kHz sampling rate; maximum bitrate 36,864 kbit/s (4,608 kB/s)
eARC lets your TV pass those along to your compatible receiver even if the TV itself can't make heads or tails of the format.
No, I think you're wrong about that.
> DisplayPort v1.2 also adds new audio enhancements including the following: — Audio Copy Protection and category codes — High definition audio formats such as Dolby MAT, DTS HD, all Blu-Ray formats, and the DRA standard from China — Synchronization assist between audio and video, multiple audio channels, and multiple audio sink devices using Global Time Code (GTC)
MAT claims to require an Atmos-capable decoder, so that sure seems like Atmos to me. I dunno what DTS HD, but that sounds like a souped-up DTS. Also take note of the "High definition audio formats such as" statement... that list of formats is incomplete.
The quote comes from: <https://vesa.org/press/vesa%C2%AE-introduces-displayporttm-v...>
DisplayPort Multi Stream Transport (MST) serves that role. Given that you'd only be passing along the audio data, rather than the video data, you could save money by putting the slowest available hardware (only BRR-capable) into the receiver.
Or, the TV could "just" pass along the audio stream to any plugged-in receiver. You don't gotta have a standard for that... just a standardized way to ask the TV to do it (assuming that you want to control the behavior and not have the conditional be "Is there a receiver plugged in? Pass along the audio and don't send it to the TV speakers.").
I think the biggest difference in DP vs HDMI cost is simply scale - there's probably orders of magnitude more HDMI chips sold than DP.
What does this exactly mean? I have an USB-C 4x1 Hub with HDMI that works at the same time as using 2 x USB-A 3.0, 1 x USB-C. Thanks!
Pretty much noone used HDMI Alt Mode on USB-C and is now deprecated IIRC.