peteer01

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With HDMI 2.1 coming with RTX 3000 series cards, we'll have Nvidia cards where we have more bandwidth over HDMI 2.1 than we do over DP 1.4. I've hoped to find some article going into this in more depth, but it doesn't seem to be something people are focused on or talking about.

This Tom's article talks about an upcoming ASUS monitor having HDMI 2.1 and 144 Hz, but it will only "use variable refresh rates...of up to 120 Hz." Similarly, I found another article (can't post with link) stating HDMI will allow, "up to 4K 120Hz without DSC tech being required." However, the upcoming HDMI 2.1 equipped 2160p 144Hz ViewSonic monitor press release (can't link) states, "Capable of achieving 144Hz refresh rate@4K resolution through DisplayPort and HDMI."

Is HDMI 2.1 going to limit us to 120 Hz for VRR or will 144 Hz be possible?

I'm sure people who care about 4K monitors with high refresh rates already know about the three options that exist today:

1. Downconverting chroma subsampling for frame rates. With DP 1.4, this means refresh rates above 120Hz 8-bit or 98Hz 10-bit for 4K resolutions. This seems to be the case for every G-Sync Ultimate monitor I've looked at.

2. Display Stream Compression (DSC), which converts RGB to YCbCr and spreads it's compression noise across a linear pixel stream (slice) of an image. Usually better image quality than lowering chroma subsampling, but still leveraging compression based on DP 1.4 bandwidth limitations.

3. Multiple connections solve bandwidth limitations, but remove the ability to leverage VRR.

Since 4:4:4 8-bit and 10-bit 120 Hz should be 35.64 Gbps and 40.10 Gbps respectively, both fit inside of HDMI 2.1's 48 Gbps bandwidth. (Unfortunately, 4:4:4 12-bit (Dolby Vision) would be 48.12 Gbps at 120 Hz) One of the things I don't know, that I'd be interested in, is whether or not it is possible to push 144Hz over HDMI 2.1 or not. Does 144Hz need 20% more bandwidth (144 Hz is 20% more frames) or based on how the signals are sent, would bumping past 120Hz require more bandwidth than HDMI 2.1 supports?

When ViewSonic says they can support 4K at 144Hz through DisplayPort, they obviously need to use chroma subsampling or DSC to fit inside DP 1.4's bandwidth limitations. But what about HDMI 2.1 sending 4K @ 144 Hz with a single cable? What options does HDMI 2.1 offer to accomplish this? Can any one help educate me and others who are about to have a graphics card with HDMI 2.1?
 
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peteer01

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https://www.tomshardware.com/features/displayport-vs-hdmi-better-for-gaming

This Tom's article actually lined up with what I was expecting. The numbers are slightly different, but it is confirmation that HDMI 2.1 should support 10-bit 144Hz 2160p.

Not sure why initial news on the ASUS say 120 Hz for VRR, but unless someone knows more, I think it's necessary to wait to know the answers to my questions about HDMI 2.1 monitors since they aren't available yet.
 
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