MacBook Air M4 to 8K - did anyone succeed ?

Succeeded. This was complicated enough, I will write it up for others to be able to succeed. The focus of this writeup firstly is to fill in where manufacturers' documentation wasn't sufficient to succeed. If there is demand, this writeup could be adjusted further.

CableMatters cable part 201392-BLK-6 was used between a MacBook Air M4 and a Samsung QN900B 8K TV. Several adjustments were necessary.

From CableMatters website, a download of a tool for firmware flashing was needed. Followed instructions to choose firmware for Mac. Succeeded running the firmware flashing tool in Parallels in Windows 11 on that MacBook. Was important to install .NET 6 SDK in Windows. Did not work with only .NET 8. Did not work with only .NET 6 runtime. Had to be .NET 6 SDK. Probably also succeeded at firmware flashing on an actual Windows Intel laptop, when using .NET 6 SDK. Also important to run as Administrator. Also important if using Parallels, to let Parallels access device VMM7100. Then when done, disconnecting the cable on both ends to restart it for the new firmware in that cable to become active.

Notably, but safe to ignore, in case you pay close attention, that tool apparently installed a firmware from a file named Spyder_fw_USBC_CM_MBP4k120, and then says it installed version 7.02.123. You probably can ignore that. You possibly know you succeeded if Settings Displays starts showing the external monitor with optionally 144 Hertz instead of 60 Hertz, either way max 4K, but I do not swear to that.

That cable then still worked on a Linux Intel and/or a Windows Intel with 8K, but I cannot say it stayed that way.

Grabbed myself an EDID from this cable while it was plugged into a Linux box, and this cable and monitor had 7680x4320 in the list, but 7680x4320 still didn't show as an option in the Mac's Settings Displays.

Read up about resolutions, EDID, DSC, HDMI, Thunderbolt speeds. Notably, the MacBook Air M4 has Thunderbolt 4, hence 40 Gbps only. This is not yet like the newest MacBook Pro having Thunderbolt 5 at twice that speed. That could mean a limit to 8K 30Hz, not 60Hz. Apparently, as implemented in macOS at this time (15.4), Settings Displays wasn't willing to offer that.

Used the open source command line tool displayplacer. Thank you, Jake Hilborn. Wanted something simple that doesn't really install itself, no closed source code, etc.. Used its list command. Made sure I had HDR off. Then used it to set for my carefully picked correct (!) id for the external monitor something like

displayplacer "id:1234567890 res:7680x4320 hz:30 color_depth:8"

It worked! 8K on the TV.

To be accurate in reporting I must mention, I actually used a mode number from the list. But I do not want to make that example command line easy to copy verbatim, because it might have bad effects on someone else's machine.

Here is why for now I will not use it this way for now: Every few minutes it flickered to black for a couple of seconds.

The QN900B is from 2022. It seems to have a hard time with at least some kind of 8K loads. Supposedly has to do with chroma translations, YCbCr 4:4:4, 4:2:2, 4:2:0. I do not remember from a few months ago whether it does better at 25 Hz or 24 Hz, instead of 30 Hz. Every few minutes it flickered to black for a couple of seconds. Presumably the QN900C and QN900D from one year later each have better processors and can better handle those kind of signals. This may work better for you with a newer model of that series TV. I also only guess it is the TV's problem, while it could be the cable's processing problem — I don't have evidence that I can clearly tie to either suspect. Maybe I remember the TV apparently was hitting limits in the past in the warm season under that kind of load, not certain.

The Mac's Activity Monitor was showing unremarkable GPU load, hence I am not suspecting the Mac, for now at least.

Now you know it is possible. And you know it is pushing limits, apparently 30 Hz only, or better even less. It may lose signal for a couple of seconds every few minutes, and hence you may not want to use it as a regular 8K work environment.

If anyone gets better results, please mention your setup in a reply in this discussion. Thank you.

Also remember if testing with those QN900B (maybe also with newer QN900 like C and D), if switching computers, or maybe if not using a connection for a while, the TV annoyingly has a habit of forgetting in Settings / All Settings / Connection / External Device Manager / Input Signal Plus if you had it switched on for any one of the four HDMI inputs. Keep checking that while experimenting. If it is off then one presumably cannot do this kind of 8K input, no 8K EDID, or some kind of problem like that. It is only a problem while switching around devices and experimenting. It is not or much less a problem once you settle on one computer and run it like that every day, as far as I remember from using it.

Update: Got 8K 50Hz working apparently reliably, at least for half an hour of using it, before going on to other tasks.

Did same thing with displayplacer as described earlier, this time for the equivalent of

displayplacer "id:1234567890 res:7680x4320 hz:50 color_depth:8"

although again as a shortcut I used a mode number from running displayplacer list on this specific Mac for this specific external display model.

This presumably proves DSC (Display Stream Compression) is in use. Thank you Apple. There was no need for my earlier comparison to Windows, because this now works here too. I cannot delete my earlier comparison to Windows, sorry. At least the discussion kept me going to find this better solution.

Interestingly the 50Hz apparently worked more reliably than the 30Hz, and one can imagine maybe, as one possibility of what could be happening, 50Hz DSC compressed used less bandwidth over the wire than 30Hz without DSC compression, or something similar, but we don't know, for now at least we don't know why.

Also I am hoping 50Hz pushes less limits than 60Hz.

For the, for my purpose of sometimes maybe needing 8K, this is good. Would I use it all the time? Probably not. Would have to spend more time fine tuning what I would want to be what size or scale. Unsurprisingly it does use the GPU more when you have a more demanding use.

Could you use it all the time? If you are comfortable with eyesight and other aspects, possibly. It would be interesting to hear if you become a happy user. Possibly, to learn how other setups are working out for people.

At Use an external display with your MacBook Air - Apple Support today it says:

Connect a display to MacBook Air

MacBook Air with M4. You can connect up to two external displays in the following configurations:

• Connect two external displays with up to 6K resolution at 60 Hz or 4K resolution at 144 Hz using the Thunderbolt ports.
• Connect one display with up to 4K resolution at 240 Hz or 8K resolution at 60 Hz.

Furthermore at How many displays can be connected to MacBook Air - Apple Support today it says:

MacBook Air with M4 chip

MacBook Air models with the M4 chip support up to two external displays simultaneously with the built-in display, based on the resolution (up to 8K) and refresh rate (up to 240Hz) of each external display. Closing the lid of your MacBook Air with M4 chip will not increase the number of external displays that can be supported. You can connect displays to the Thunderbolt 4 ports on the side of the computer.

One external display

Supports one display in the following configuration:

• One display up to a native resolution of 8K (7680 x 4320) at 60Hz or 4K (3840 x 2160) at 240Hz

Two external displays

Supports two displays in the following configuration:

• Two displays up to a native resolution of 6K (6144 x 3456) at 60Hz or 4K (3840 x 2160) at 144Hz

That is quite specific, officially from Apple, and what I have read before buying.

Servant of Cats wrote:

You are assuming that Display Stream Compression is in play.

This was a good mention, thank you! After reading you saying that, I checked by actually running 8K 50Hz, and that proves DSC is in use, and it was more stable than 8K 30Hz, at least in my half an hour of using it.

Servant of Cats wrote:

An 8K display has four times as many pixels as a 4K one – so the bandwidth required for 8K @ 30 Hz is twice that of the bandwidth required for two 4K displays running at 60 Hz.

I am sure you can see that the bandwidth required for 8K @ 30 Hz is equal that of the bandwidth required for two 4K displays running at 60 Hz.

bandwidth ( 8K @ 60Hz ) === 4 * bandwidth ( 4 @ 60hz )

bandwidth ( 8K @ 30Hz ) === 2 * bandwidth ( 4 @ 60hz )

And then, using DSC (Display Stream Compression) apparently 8K 60Hz can go over Tunderbolt 4.

For example, it could be it only works with 8K TVs that support 4:4:4 chroma (the newer QN900D and QN900C), but not 4:2:2 chroma (the older QN900B).

Again, to avoid wild goose chases:

Does it work for someone, with the equipment they have? If it also does not work for you, please upvote.

Or, if you are a developer working on this, maybe this outside user experience is helpful to know. Maybe you can let us know which attempts would be dead ends, because of something you know for a fact instead of us guessing.

Stops at the usual 4K. Those screens don't offer anything between 4K and 8K in their EDID I'd assume, they don't offer 5K or 6K. Probably not for people to discuss it who haven't succeeded nor worked on the implementation.

To resolve this, one might succeed if having somewhat inside knowledge of the implementation. Is there a bug in a protocol implementation that is fixable by coding?

An Apple dev on this specific task? A Cable Matters dev? A Samsung dev? They all want to sell their hardwares, so maybe they can talk with each other to figure who isn't sending correct info, or who isn't correctly interpreting the bytes they're getting?

This post here can serve at least for public visibility "there is a problem" and hopefully a solution coming. If there isn't a report of a problem, a dev might not get allowed time to work on a fix. Hence this post, to have a starting point.

It looks like I possibly didn't do the firmware update on the cable correctly, lacking a recommended Windows laptop to run it on. Was just using a virtual Windows, wasn't a good enough fit.

Will try on normal Windows hardware, hopefully in a day or two, just one time for the firmware update on the cable.

By the way, as I am typing this, I am running this Samsung QN900B screen (2022 model) from a Windows 11 Dell XPS 13 9310 laptop (2020 model) through that Cable Matters 201392, at 8K, 60Hz. No flickering at all. Note that little 13" notebook from 2020 has no discrete graphics chip, just an Intel 11th gen CPU, i7-1195G7. How do they do that? Apparently they're using per specification DSC (Display Stream Compression), which apparently around doubles the amount of image information that can go across the cable, allowing 8K 60Hz over Thunderbolt 4. That was released by Intel in 2020 with the 11th gen CPU integrated graphics architecture.

It is 2025 and I am trying to get this MacBook Air M4 to do the same. Hopefully equally reliably like that Window Intel laptop sitting on the same desk.