Audio Out through HDMI counts towards maximum displays?

To reinforce what MartinR has already stated:

HDMI and DisplayPort and DVI before it are packetized interfaces. There are no separate lines in the interface dedicated to audio.

So to run an audio stream over HDMI, you have to crank up the entire video/audio mechanism, and populate only the Audio packets.

Video data are THE fastest data streams your Mac is designed to handle. They are so fast, they require a hardware assist to fetch the characters of display data from memory at speeds the processor could never accomplish using byte-at-a-time transfers.

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Have you considered using a USB output for your Audio, to free up that video-capable HDMI port?

Nikkiflausch wrote:

My god, stop using AI result suggestions even as inspiration for research. It guesses words that sound good, it knows nothing about content. In this case it's picking up on the the fact that "compatibility is important", that "Audio MIDI setup is the software used to set up surround sound", that an "Aggregate device" is the solution for some audio problems", and that third party software that can create virtual audio Outs is the solution for some other problems.

I'm aware of the limitations of AI-generated answers. This is why I make use of them very sparingly – and why, when I mention AI result suggestions, I make it clear that they came from an AI.

None of these individual steps have any relation to each other in the context of HDMI passthroughs except that they're all common responses to questions about audio on macOS, which HDMI passthroughs are a common question for.

If you're looking for a magic way to do HDMI passthrough without consuming a hardware display generator, I do not think you're going to find it.

There are multi-channel Thunderbolt and/or USB audio interfaces meant for professional music production, so it may be worth exploring whether there are ways of getting multi-channel output, over USB or Thunderbolt, which would work with Apple Music and a receiver and which would NOT involve using HDMI pass-through.

Nikkiflausch wrote:

I am using USB for my audio specifically because of the display limitation problem, even though none of my displays are connected through HDMI

The total number of supported displays mostly does not depend on whether you are connecting your displays using USB-C (DisplayPort), Thunderbolt, or HDMI. No matter what type of output you are using, it is going to consume the resources of at least one of the M4 Pro chip's three hardware display generators. (One of those generators is dedicated to the MacBook Pro's built-in screen, leaving two to support external displays.)

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14" MacBook Pro – M4 and M4 Pro

• Simultaneously supports full native resolution on the built-in display at 1 billion colors and:
• Up to two external displays with up to 6K resolution at 60Hz over Thunderbolt, or one external display with up to 6K resolution at 60Hz over Thunderbolt and one external display with up to 4K resolution at 144Hz over HDMI
• One external display supported at 8K resolution at 60Hz or one external display at 4K resolution at 240Hz over HDMI

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A MacBook Pro with a M4 Max chip would be able to drive up to four external displays, since that chip has five display generators, of which a M4 Max MacBook Pro's screen consumes one.

TC&C - my abbreviation of Teufel Consono & Concept. I thought it would be obvious.

HDMI is designed to carry both video and audio and the video card/chip outputs both. The HDMI signal itself is a combined video+audio signal which has to be decoded by the recipient device. That's what your Concept 8 is doing in order to extract & use the audio portion of the signal; it's just ignoring the video portion of the signal. Your MBP still thinks a display is connected because the HDMI port is in use.

Nikkiflausch wrote:

There's no image information sent through HDMI when using it just for sound, the handshake should communicate this, so macOS should know. Therefore, there would be no reason to count it towards the display limit

The HDMI out is considered the primary (default) video output and if you are conecting it to any HDMI device it will be 'seen' as a video device. Even an HDMI audio extractor, which is probably how your TC&C unit works.

While it's possible to disable HDMI audio out, I do not know of any way to disable HDMI video out.

Exactly what model TC&C unit do you have?

Nikkiflausch wrote:

I am using USB for my audio … But, again, digital passthrough isn‘t available through USB…

If you do a Google search for "dolby atmos Mac usb", Google's AI overview suggests that it is possible for one to get Dolby Atmos output over USB on a Mac.

To do this, it sounds like you would need

• A USB audio interface that supports this
• A little bit of configuration work in the Audio MIDI Setup application to create a new "Aggregate Device", or "Multi-Output Device"; and to configure the speaker layout for that device.
• A third-party helper application such as "BlackHole" or "Loopback" (I've never heard of either) "to pass the multi-channel audio signal from Apple Music to your USB audio interface."

You may need to do some research to find out whether the AI summary is onto something real or not. But maybe there is a way to get something more than stereo sound out over a USB audio interface.

On another note, are you doing full-motion Video on the Luna display ?

If you are using that display only for slow-to-change data like spreadsheets, stock quotes, or program listings, there are other solutions that might be able to give you an additional display without consuming a hardware-assisted display generator.

I started poking around to see if maybe there already was something that was an all software solution. In just a short time, I found some that might work for you.

Duet Display [commercial software but costs US$40/yr] seems to be able to do this trick.

YAM Display looks promising, but almost no manuals or documentation [but only US$8 once]

The advantage of these over Luna Display is that they create a fake display buffer in RAM, so it would free up a display generator on your Mac.

Thanks for that information.

What is the connection from the Luna display box to the actual display you are using? is it connected on to that iMac in some fashion? Is this with a cable, or with WiFi, or something else?

what model iMac is this, and does it have Thunderbolt port?

Grant Bennet-Alder wrote:

What is the connection from the Luna display box to the actual display you are using? is it connected on to that iMac in some fashion? Is this with a cable, or with WiFi, or something else?

My understanding is that there is no direct connection between the USB-C Luna Display device that consumes a DisplayPort Alt Mode signal, and the iMac. You plug the device into the Mac that needs an extra display and run Luna Display software on both Macs.

https://astropad.com/product/lunadisplay/

However, if the iMac in question is a 5K iMac, I believe users are strongly encouraged to run a USB cable between the two Macs to help carry video data.

https://help.astropad.com/article/154-usb-ethernet-connection

https://astropad.com/blog/step-by-step-guide-how-to-use-your-imac-as-a-monitor/