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.
