Mac Studio HDMI 2.1 through TB4 Port with Adapter Not Supported?

So here's what I've found out and consider this to be an answer to my original question. Talking with Apple, they recently updated these links with information on the Mac Studio:

Identify the ports on your Mac

https://support.apple.com/en-us/HT210980

Play HDR video on Mac

https://support.apple.com/en-us/HT207806

About the Apple USB-C Digital AV Multiport Adapter

https://support.apple.com/en-us/HT207806

Of interest to me for the Mac Studio Ultra:

• Up to 5 displays on the HDMI port and any 4 of the 6 USB-C (TB4) ports.
• HDMI port is HDMI 2.0. No indication that it supplies power.
• The Apple A2119 TB3 to HDMI adapter supports HDMI 2.0, is HDCP compliant, supports HDR10 and Dolby Vision, 1080p/60, 3840/2160/30, 3840/2160/60, over 1 billion colors (10 bit color depth). This implies the USB-C port supports these functions such that they can be converted to HDMI.
• Apple Pro Display XDR support Dolby Vision, HDR10, and HLG. Dolby Vision and HLG
• The USB-C ports on the Mac Studio support charging (i.e. power delivery).
• Apple says the M1 USB-C ports are limited to 1 display per port.

Dolby says that MacOS supports Dolby Vision and Dolby ATMOS on Catalina (and above I would assume) with Dolby Digital+/JOC:

OS and Device Support

https://developer.dolby.com/platforms/apple/macos/os-support/

HDMI 2.0 (standard) is limited to 18 Gb/s and can support:

https://www.rtings.com/images/reviews/tv/articles/misc/misc-formatdataratetable-large.jpg

4K/60 YCrCb 4:2:0, 4:2:2. 4:4:4 8/10/12 bit color

4K/60 RGB 4:4:4 8 bit color

And AFAIK, that includes static or dynamic metadata for HDR, HDR10, Dolby Vision, HLG, Dolby ATMOS, DTS-X

Getting above these on HDMI requires HDMI 2.1 48Gb/s interfaces. Apple's Mac Studio Display is 5K/60 and the Apple XDR display is 6K/60. These attach with TB4 interfaces and they presumably are using DP 1.4 Alt Mode tunneling (and not HDMI so the 18 Gb/s HDMI 2.0 limit does not apply).

Also, Blu Ray Ultra Disks are 4K 4:2:0 and can have deep color and HDR dynamic metadata and multi-channel immersive audio so HDMI 2.0 is sufficient. And amusingly, you don't need a HDMI "Ultra" (8K) cable for a BluRay 4K UltraHD disk.

My plan:

My LG C1 needs to be attached to my Mac Studio at about 30' cable length, it has HDMI 2.1 ports, and it supports 4K/120 4:4:4 10 bit HDR10/Dolby Vision/ATMOS.

I'll use:

• Monoprice SlimRun AV 8K Certified Ultra High Speed Active HDMI Cable, HDMI 2.1, AOC, 10m, 32ft. This needs power from the connected ports. HDMI 2.1 complaint ports supply power.
• Hyper: HyperDrive USB-C to 8K 60Hz / 4K 144Hz HDMI Adapter

Hyper confirmed that the 8K adapter will pass power from the USB-C to the HDMI port so the active cable should work. The active cable is needed to go the 30' distance at 8K (15 ft seems to be about the practical limit for a passive HDMI certified cable) so the HDMI 2.1 power delivery solves that problem. The adapter is also good to 8K which supports my TV's full capabilities and it should work with a 4K/120 source if I had one (or an 8K/60 Source and TV if I had both of those) so I'm somewhat future proofed. They also have a 4K/60 HDMI 2.0 adapter that is slightly cheaper than the 8K ($40 vs $50)

I'll mention that Hyper also says they have adapters and hubs that gets around the Apple limit of one display per USB-C port on M1s that is working on Mac Mini and MacBook Pro M1 systems. . Since the M1 Ultra has 6 USB-C ports, its cheaper for me to buy two of the HDMI 2.1 8K adapters than one dual-4K port HDMI 2.0 adapter, so I'll probably not need this - but its a possible solution for M1s that have fewer ports than you need. Some of their hubs also looked interesting if you need other ports, but an 8K/60 HDMI port pretty much uses up the available USB-C 40GB/s bandwidth so I didn't go there.

Apple is also claiming a Mac Studio Ultra can have up to 18 8K/60 video streams active. One might hope that one day they would upgrade MacOS so that it didn't limit their ports to HDMI 2.0.

Disclaimer: I have no relationships with Apple or Hyper other than as a potential consumer. Hyper had the best 8K spec'ed adapter I have found so far at an affordable price. I have attempted to accurately summarize any information I found above, but I have not verified any of the claims made at this point since I don't have the Mac Studio to try it on yet.

So Grant Bennet-Alder, as I said, I have an HDMI certified 8K cable (Hologram verified by HDMI App).

I have an LG 55c1 that has HDMI 2.1 ports that I'm hearing work running 4K/120 HDR 4:4:4 with other gear (xBox Series X).

The Sabrent on Amazon has Q/A that says it doesn't support 4K/120 with MacOS.

https://www.amazon.com/Sabrent-Function-Resolution-Thunderbolt-Compatible/dp/B08Y246V8X

The limitation appears to be on the Apple end.

I was hoping someone would pop up and say they have something working with an LG C1 and could say what they are getting.

I found this:

https://tongfamily.com/2021/12/11/lg-c9-and-macbook-pro-2021-ultracolor-hdr-chroma-444-and-4k120hz/

----extract-----------

MacBook Pro 2012 HDMI 2.0 limit to 4K@60 4:2:2

Well, if you plug in a cable (I actually had a bad one) that is HDMI

2.1 certified so it can handle the full 48Gbps, you are going to be

unhappy because Apple in their infinite wisdom supplied an HDMI 2.0 port. This matters because HDMI 2.0 is only 18Gbps.

What that means practically is that with a standard HDMI cable

connected to the LG, the most you should be able to see is 3840 x 2160

at 60 Hertz and Chroma sampling of 4:2:2. And in fact, if you plug a

MacBook Pro in, you should see the panel light up. Go to System

Preferences > Displays and then right-click on the icon which is the

LG and you should see Refresh Rate of 60Hz and then if you have done

this right there should be a checkbox for High Dynamic Range.

Click that and you get 4K@60 4:2:2 and you can verify it at the

diagnostic menu. YOu should also the letters HDR popup for a second at

the upper right of the screen

Kind of disappointing when the display can handle 4K@120 4:4:4

-----------------

So based on this I'd say this about Mac Book Pro (I assume Mac Studio at least as capable as Mac Book Pro):

1) The HDMI 2.0 port must be at least HDCP 2.1 or the LG wouldn't talk 4K to it.

2) The HDMI 2.0 port can handle 4k/60 4:2:2 HDR.

Again, numerous other places point to MacOS as the limit, like here:

https://forums.macrumors.com/threads/mac-mini-4k-120hz.2267035/page-10?post=30690647#post-30690647

This post shows some displays working 4K/120 but can't tell if any that work are HDMI attached or whether HDR and what Chroma. The LG Cx ones all say they don't work with 4K/120 - in one place says "MacOS only supports HDMI 2.0". The LG UltraGear 27GP950-B that is said to work 4K/144 has both HDMI and Display Port inputs.

https://tonsky.me/blog/monitors-mac/

So - my speculation so far:

• Display Port works 4K/144 (if you don't go through HDMI to get to your TV's Display Port)
• HDMI does not work 4K/120 because of MacOS limitation.
• The numerous places indicating "a MacOS limitation" would lead me to speculate that the HDMI/TB3 ports could support HDMI 2.1. - but that's just a guess based on no evidence.
• I would guess all the Mac Studio HDMI support is at HDMI 2.0b level (Dolby Vision/HDR10/HLG/4K60 4.2.2 10 bit color) or you would be hearing a lot more chatter from the video content folks.
• The folks that care about 4K/120 HDR the most are gamers. AFAIK. They probably will not like no 4K/120 and will have to make a call between whether they like Mac Studio price/performance more than the care about better graphics performance and 4K/120. That is a point in time statement. Possibly will need 8K screen monitors for video post at some point and if they are mostly HDMI based, it will drive more of a need for HDMI 2.1.
• Either this is a lot of work for Apple (macOS) and it's priority has not risen to the point that they are interested in implementing, or there are some other hardware reasons they chose to not address this in the machines they are currently releasing. The AVR/AV Pre vendors went through a pretty serious upheaval with a chip bug in one vendors chip set that set HDMI 2.1 4K/120 into a tail spin until just recently. Coincidence? More likely, getting Mac Pro M1 Dual-Ultra out taking all their bandwidth.

I still would really like to hear from others who could confirm on Mac Studio 4K/60 HDR - Dolby Vision/ATMOS/10 bit color works on HDMI port and on TB4 converted to HDMI .

Well, If you know one that works let me know. I was looking for one and found this....

Cable Matters 48Gbps USB C to HDMI Adapter Supporting 4K 120Hz and 8K HDR -

Thunderbolt 3 and Thunderbolt 4 Port Compatible - Maximum Supported

Resolution on Any MacBook via This Adapter is 4K@60Hz

https://www.amazon.com/Cable-Matters-48Gbps-Adapter-Supporting/dp/B08MSWMXT4/ref=sr_1_5?crid=387TLDXJOTQOJ&keywords=8k+tb4+to+hdmi+adapter&qid=1648148905&sprefix=8k+tb4+to+hdmi+adappte%2Caps%2C107&sr=8-5

Perhaps I should add, I've got a 32 ft 8K HDMI Certified Optical Cable from Monoprice that I believe needs power from the port.

Monoprice SlimRun AV 8K Certified Ultra High Speed Active HDMI Cable, HDMI 2.1, AOC, 10m, 32ft

https://www.monoprice.com/product?p_id=43329

The Mac Studio is ordered. The adapter has not been bought yet.

AFAIK, you are correct. HDMI 2.1 has a 48 Gb/s link data rate. TB4 is 40 Gb/s link data rate. The HDMI 2.1 link effective data rate will not exceed the effect data rate of the TB4 ports. DSC is a wild card here because compression would increase the effective data rate without increasing the link data rates.

I can't say I've seen a clear reference that explains which video formats can be handled by 40 Gb/s with or without DSC. The one I referenced has (resolution, frame, rate, chroma, bit depth, and RBG or not - but generally is missing HDR type or Audio type - which I hope comes along for free). It shows HDMI 2.1 getting up to 10K/120 4:2:0 or 10K/60 4:2:2 with DSC on 48 Gb/s links. That's the equivalent of 120.29 Gb/s uncompressed - so 3x the bandwidth with DSC.

From the bandwidth chart I referenced in my last post, I believe 40 GBs uncompressed should cover.

4K/120 YCrCb 12bit, 4:2:2 (32.08 Gb/s)

4K/120 RGB 8 bit 4:4:4 (32.08 Gb/s)

8K/30 4:2:2 12 bit (32.08 GB/s)

The adapter I referenced says "8K 60Hz or 4K 144Hz requires sourcing with DP 1.4 DSC 1.1/1.21"

That is running through the same USB-C connector.

It also says "8K video requires a desktop computer with an Nvidia RTX 2060/2070/2080 or an AMD Radeon RX 6000 Series GPU. Laptops with 11th generation Intel Tiger Lake CPUs and Intel Iris Xe graphics, such as the Intel Evo certified laptops also support 8K". So there are folks doing this today through a USB-C.

Whether the hardware in the Mac Studio supports DSC is unanswered AFAIK. It appears that MacOS at least is limiting it to 4K/60 today. I'm not holding by breath, but given there is competition, I wouldn't be dumbfounded if there was a software upgrade that turned it on.

I continue to be frustrated with vendors advertising specs with:

4K or 8K and no Hz

4K/60, 4K/120, 8K/30, 8K/60 and no chroma or color depth.

4K/60, 4K/120, 8K/30, 8K/60 chroma and both depth, but no mention of HDR video and audio modes.

No mention of standards compliance.

And with the lack of a bandwidth calculator that includes all the options of resolution, frame rate, chroma, color depth, SDR or HDR type, HDMI standard, USB standard, DCP standard, Display Port Standard, etc.

For example the Mac Studio "tech spec" says they have an "HDMI port".

Very frustrating and wasting a lot of some folks time.

So expanding around what you said based on info from wikipedia ....

DP 1.4 running over USB4 - 4 lanes at 8.1 Gb/s = 32.4 Gb/s link data rate.

8/10 encoding gives 32.4 * 8/10 = 25.95 Gb/s effective data rate.

HDMI 2.0 running over 3 data lines at 6 Gb/s = 18 Gb/s link data rate

8/10 encoding gives 18 * 8/10 14.4 Gb/s effective data rate

HDMI 2.1 running over 4 lanes at 12 Gb/s = 48 Gb/s link data rate

16/18 encoding gives 48 * 16/18 = 42.66 effective data rate.

4K (3820x2160) = 8.29 MPix / frame

6K (6016 x 3384) = 20.36 MPix / frame (Apple XDR display)

8K (7680 x 4320) = 33.17 MPix/ frame

4:4:4 10 bit is 30 bits/pix

4:2:2 10 bit is 20 bits/pix (avg)

4.2:0 10 bit is 15 bits/pix (avg)

The maximum audio bandwdith on HMDI 2.0 or 2.1 (192K samples/channels X 32 channels x 24 bit samples) is about 147 Mb/s which is noise compared to video bandwidth. HDR formats have some additional metadata which I believe is noise compared to the audio bandwidth - so Ignore HDR and audio overhead other than it needs at least 10 bit color in the video.

There is a CVT spec that adds overhead for blanking between lines and between frames. The numbers below reflect CVT-V2 which I think is the current thing.

4K/60 10 bit 4:2:2 = 8.29 pix/rfame * 20 bit/pix * 60 frames/sec = 11.94 Gb/s -> 12.54 Gb/s with CTV < HDMI 2.0 @ 14.4

4K/60 10 bit 4:4:4 - 8.29 * 30 * 60 = 14.93 Gb/s -> 15.68 Gb/s with CVT < HDMI 2.1 @ 42.66 or DP 1.4 @ 25.9

Should not need DSC on HDMI 2.1 or DIsplay port 1.4. HDMI 2.0 would need to drop to 4:2:2.

4K/120 10 bit 4:2:2 = 2x 4K/60 10 bit 4:2:2 = 25.08 with CTV < HDMI 2.1 @ 42.66 or DP 1.4 @ 25.9

Should not need DSC on HDMI 2.1 or DIsplay port 1.4

8K/30 10 bit 4:2:2 = 33.17 * 20 * 30 = 19.90 Gb/s -> 20.40 with CTV < HDMI 2.1 @ 42.66 or DP 1.4 @ 25.9

Should not need DSC on HDMI 2.1 or DIsplay port 1.4

8K/60 10 bit 4:2:2 = 33.17 * 20 * 60 = 399.80Gb/s -> 40.80 with CTV < HDMI 2.1 @ 42.66 but > DP 1.4 @ 25.9

Should not need DSC on HDMI 2.1 but would need DSC on DIsplay port 1.4

If I assume the apple display is 6K/60 10 bit, the video data depending on chroma subsampling needs at least:

4:2:0 20.36 x 15 x 60 = 18.3 Gb/s

4:2:2 20.36 x 20 x 60 = 24.43 Gb/s

4:4:4 20.36 x 30 x 60 = 36.64 Gb/s.

I would guess they have blanking so these numbers would be slightly higher.

If they don't support DSC, I would assume they don't support 4:4:4.

The 4:2:2 would be on the edge of exceeding the 25.9 Display Port limit.

If they support 4:2:2, I think it's still a question of whether they need DSC or not to get there.

And possibly still a question of whether firmware/software changes could enable DSC on the hardware at some point.

Not much point in spending time on what might happen either way.

Well, you might want to re-read what I said. "DSC" is Display Stream Compression and that is what HDMI 2.1 and Display Port use for compression. You might also consider 4:2:0 and 4:2:2 or lower frame rates as a way to reduce bandwidth with perhaps a noticeable difference in the video.

I'm not contending that the protocols have a problem with higher resolutions. Yes, DIsplay Port 1.4 can get to about 3x 25.9 Gb/s effective bandwidth with DSC and HDMI 2.1 can get to about 3x 42.6 Gb/s with DSC which is way more than enough to support 8K/120 4:4:4. HDMI 2.1 support tops out at 10K/120. And Display Port 2.0 is more up around 80 Gb/s uncompressed which gets you up into 16K resolution. DSC is not lossless, but it is considered 'visually lossless' (i.e. you can't see a difference).

The question I'm trying to resolve is what a Mac Studio might support through a TB4 port given I"m converting to HDMI 2.1 with an adapter. It appear to be the case that Mac Studio/MacOS is limited to 4K/60 on its HDMI port and on a TB4 port converted to HDMI 2.1 (at least for the present). And I don't think they've qualified what chroma sub-sampling they support at 4K/60 on either port. The HDMI 2.0 port would be limited to 4:2:2. The TB4 port, I don't know, but it should be more than able to do 4K/60 4:4:4.

I've tried to bound what might be possible based on the scant documentation that Apple provides. The Hyper adapter says you need DIsplay Port 1.4 with DSC 1.1 or 1.2 (which is compression) to get to 8K/60 or 4K/144 (chroma sub-sampling not specified but I'm guessing 4:4:4). Based on what I've said in my last post - I can see why - the HDMI and Display port protocols wouldn't get yet you there without DSC. What I think is still in the gray zone is 4K/60 4:4:4, 4K/120 4:2:2, and 8K/30 4:2:2. The HDMI port on Mac studio is HDMI 2.0 so none of these would be supported. On the TB4 port, I don't know whether 4K/60 4:4:4 is allowed, but it could be based on the Display port 1.4 bandwidth without DSC. I would say 4K/120 4:2:2 and 8K/30 4:2:2 could be supported as well on Display Port 1.4 without DSC based on Display port 1.4 bandwidth and it is only the MacStudio (or lack of a source) that is preventing it. Since the Mac Studio TB4 port probably doesn't know or care what's plugged into it, it would probably run up to the Display 1.4 limit without DSC and allow 4K/60 4:4:4, since it is already exceeding the needed bandwidth with the 6K XDR . I haven't spent much time seeing what the video post folks are saying about what they can get out the box on an HDMI port. Their displays usually have more port options and HDMI might not be what they typically use.

By looking into what I've found on the Apple XDR display, I think it's still a question whether the Mac Studio TB4 port supports or could support DSC, but I don't think the XDR display implies that it does. Whether the existing hardware could support DSC with a software/firmware upgrade is purely speculation.

The reason I'm curious about this is that I expected their HDMI port to support HDMI 2.1, but it doesn't. And then that just begs the question about what the TB4 port is capable of when it's coverted to HDMI 2.1 (by an adapter that has DisplayPort 1.4 on the input side). I was looking for an easy answer from the forum, but ended up trying to answer as best I could myself with what I could find out. It was probably just as well that I got more on board with the interface protocol capabilities - there are lots of complexities there that probably most folks would rather not have to concerned with - and I'm trusting that Wikipedia's stuff is accurate. Thanks for all the info you have all provided!