eGPU with 4K 60 4:4:4 10b-HDR HDMI

[sanichor]

Hello,
I'm looking into eGPU and I would like to know if there is a way to get a 4K 60 4:4:4 10b-HDR signal from a MacBook Pro intel. I've read that this signal has a bitrate of 22.28Gbps which is inferior to limit of Thunderbolt 3 (32Gbps). I've also read that it needs HDMI 2.1 and I don't know if MacOS Sonoma or Windows 10 BootCamp supports it. The other way would be to use the DisplayPort 1.4 with DSC from the eGPU but I don't know either if this is compatible.

 

[Bigwaff]

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[joevt]

4K60 HDMI is 594MHz.
4:4:4 10bpc is 30bpp.
594MHz is 594 x 30bpp = 17.82 Gbps. This translates to 22.275 Gbps if you consider that DisplayPort uses 8b/10b encoding.

Thunderbolt does not use the 8b/10b encoding when tunnelling DisplayPort from the host Mac to the DisplayPort of a Thunderbolt device because Thunderbolt uses 64b/66b encoding.

Thunderbolt 3 transmits bits on the wire at 41.25 Gbps which is 40 Gbps before 64b/66b encoding.

I prefer to list bandwidth before encoding instead of the bandwidth of the bits on the wire.

32Gbps is PCIe 3.0 x4. PCIe uses 128b130b encoding so this is 31.5 Gbps of data but Thunderbolt is usually limited to ≈22 Gbps for data. PCIe is not used for transmitting DisplayPort from the host Mac to a Thunderbolt device.

The host Mac can send over Thunderbolt two DisplayPort signals of 17.28 Gbps each or one at 25.92 Gbps and another at 8.64 Gbps. For Macs with GPUs that don't support DSC, the Apple Pro Display XDR uses a special mode mode where it receives two DisplayPort signals at 25.92 Gbps each but only 19.4 Gbps is actually sent in each signal since Thunderbolt does not send the DisplayPort stuffing symbols that are used to fill the bandwidth of a DisplayPort connection.

For eGPU, it doesn't matter if it's connected with Thunderbolt 40 Gbps, 20 Gbps, or 10 Gbps or even PCI 133 MB/s (1 Gbps). The video signal comes from the GPU in the eGPU, not from the Mac. The data pathway might have an affect on game refresh rate but does not affect resolution or display refresh rate.

Back to your original question.
Apple can send 4K60 10bpc HDR from some DisplayPort 1.2 (HBR2 17.28 Gbps) ports if it's using CVT-RB timing (533 MHz) instead of HDMi timing (594 MHz).

You'll want a DisplayPort 1.4 GPU to be sure (HBR3 25.92 Gbps). Radeon RX 580 or later. If the display only supports HDMI, then you'll need a DisplayPort 1.4 to HDMI 2.1 adapter to go with it. I don't think DSC is required unless you want to go to 120Hz.

I don't know which GPUs/adapters can do 4K60 4:4:4 10bpc HDR. For DisplayPort (no adapters), I have no problem getting HDR at 533 MHz (Radeon Pro W5700, and Intel iGPU of Mac mini 2018).
I don't have a HDMI 2.1 display to test.

For modern GPUs used by Intel Macs, AllRez will list all modes and their pixel/color format.