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Comment by atoav | Hacker News Reader

HDMI Switching like that takes long because there is a EDID negotiation going on between the minitor and the input devices.

If you want to switch fast and often your best bet is getting an HDMI switcher that is basically always connected to the monitor and both sources and then toggles between the two. Beware of the supported resolutions and framerates.

A cheap hack would also be to connect your second source to the first using a HDMI Grabber (basically a HDMI-source-to-USB-webcam-converter) and open a fullscreen window displaying that. Then you could e.g. switch by switching virtual desktops.

Another post recommended rhe Blackmagic Atem, this should also work.

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Note that an expensive HDMI switcher is different from a cheap dongle goblin from Amazon. Try the cheap one first but if you really need instant switching you’re looking at a professional AV device.

http://decimator.com/ Has some really good shit including (accidental) hdmi copy protection removal.

I am a media technician myself and the odd thing is that I have found no real corellation between price and capabilities when it comes to HDMI switchers, splitters and grabbers.

Sometimes the 400 Euro grabber works sometimes the 30 Euro one works. The expensive ones are surely more rugged tho.

I suspect all most manufacturers do is build a decice around some existing HDMI IC and if your stuff is supported by that IC and they didn't cut a ton of corners it works. Maybe you need the 4000 Euro price class to run it all, I never tried.

That’s what I’ve seen. Some super expensive gear works often but having various devices with various chipsets seems the way to go.

Even with one of the fancy KVM switches that were recommended here my switching isn’t instant. It did go down from 10-20 seconds of flickering to +/- 2 seconds though.

May not be worth it if you are already at 4s though.

What model do you use that gave you 2 seconds switching time? One of the mentioned Rextron or something else?

My "NEWCARE HDMI 2.0b Switch 3 in 1 Out" switcher is that fast.

Thanks just ordered one!

Can I inquire how you switch inputs (mouse, keyboard) along with the hdmi?

I've found the simplest way is to just use a mouse and keyboard that support bluetooth and RF and just keep the RF dongle on one PC and the bluetooth paired to the other PC. If you're running Windows, Mouse Without Borders is a handy utility and I'm sure there's an equivalent for Linux. I often find myself just using Moonlight streaming as a remote desktop since my tower is a lot more powerful than my laptop.

On linux you can use Barrier / Input Leap. No Wayland support though, still work in progress for unforeseeable future. Can't find any KVM app that works on Wayland yet. RKVM used to work on Wayland but not anymore.

No Wayland support though, still work in progress for unforeseeable future

Linux isn't my daily driver so this might be a dumb question, but what's up with Wayland? I feel like I've been hearing for a solid decade that X is dead yet whenever someone recommends me a piece of software it never works on Wayland. Wayland is fourteen damn years old at this point.

Wayland itself is actually pretty solid right now as long as you're not using nvidia card. In the past, applications that need to interact with other applications (e.g. remote desktop, screen recording, keystroke injection, etc) can't be ported to wayland due the lack of api. Those api now already exist in wayland, but completely different which requires huge effort by application developers to rewrite their app. So right now we're just mostly waiting until those apps finally run on wayland, and nvidia finally stop being buggy on wayland.

Most app developers are dragging their feet when it comes to supporting wayland, but with big distros now shipping wayland by default, the pressure to make sure their apps work in wayland is really high in the past two years. For example, just last week vscode finally fix rendering issues that plagued wayland + nvidia users for years (had to use insiders version with some extra args but at least I can use vscode in wayland now). I think the rate of developers finally adding wayland support in their apps is finally accelerating.

I have the https://www.amazon.co.jp/-/en/gp/aw/d/B078LY741V?psc=1&ref=p...

Please note that I’m having issues with their smart keyboard port, but that may be related to the interaction between the two.

I have some knockoff brand off of Amazon, but it has full HDMI EDID emulation so stuff doesn't move around when switching screens. The input switching is about 2.5 seconds or so. The listing [0] looks scammy, and I thought so too when I bought it, but it works -much- better than the previous unit I had from Tesmart, which had generally good reviews but didn't work at all for my purposes, and it was like 40% of the price. I took the plunge on this one as the Tesmart didn't behave nicely with my thunderbolt docks hanging off my various mac laptops, which was extremely, maddeningly frustrating to not have it work all the time.

[0] https://www.amazon.com/gp/product/B088WGKFZH

Workstation GPUs (Nvidia Quadro[1][2] / AMD Radeon Pro[3]) can emulate/force an EDID in the driver settings and the OS will "think" a display is attached. At least in theory that should get around the handshake.

[1] https://www.nvidia.com/content/Control-Panel-Help/vLatest/en...

[2] https://nvidia.custhelp.com/app/answers/detail/a_id/3569/~/m...

[3] https://portal.7thsense.one/user-guides/MC264-display-config...

> HDMI Switching like that takes long because there is a EDID negotiation going on between the minitor and the input devices.

Why does the negotiation take so long, though? There doesn't intuitively seem to be a lot of information.

> A cheap hack would also be to connect your second source to the first using a HDMI Grabber (basically a HDMI-source-to-USB-webcam-converter) and open a fullscreen window displaying that. Then you could e.g. switch by switching virtual desktops.

Is this something you've tried before and could go into more detail about? I've got an HDMI grabber for using a DSLR as a webcam, but never thought to output the display of one of my computers to another. This would solve a lot of issues regarding switching between work and personal laptops.

But why is this at input selection? Have manufacturers cheapened out and only 1 port (with DP-AUX, HDMI-I2C ...) is active at the CPU?

Interesting tangent: I wanted to know what ATEM stood for - nothing: https://forum.blackmagicdesign.com/viewtopic.php?f=4&t=11160...

What if you modify the cables to remove the DDC wire?

Can no EDID negotiation be faster?

EDID is important because it is the only way for the host to know which resolution, color depth, frame rate the monitor supports.

Even if you remove the DDC wires, the OS will still try to communicate, and it might delay this even more because of the retries and delays in code.

You might get a headstart if you hardcode the EDID in the OS itself. There are ways to do this on Linux [1], Intel macOS [2] and Windows [3].

[1] http://billauer.co.il/blog/2020/08/linux-override-fake-edid/

[2] https://github.com/mbruggmann/osx-edid-overrides

[3] https://learn.microsoft.com/en-us/windows-hardware/drivers/d...

But why is EDID negotiation slow?

See my answer here: https://news.ycombinator.com/item?id=34050157

TLDR: because it is done over a slow protocol (I²C) and because of artificial delays in code to account for slower devices

Why wait until the user switches input sources to do the negotiation? Why not do it earlier so that the new input is ready to go?

The monitor is not the active device in this situation, the host (Mac/PC/SBC) is.

The negotiation is done when the host initiates it, usually when the cable is connected to a port or when coming back from deeper sleep/standby.

If the host remains active after the negotiation, the monitor doesn't go through the process again, I explained how that worked for me here: https://news.ycombinator.com/item?id=34051428

The problem that OP has is when the host being switched to is in standby. In that mode, most devices deactivate the video ports completely, disconnecting the monitors and removing them from the hardware device tree.

Switching to the inactive input without waking up the host device will usually show a "No signal" message on the monitor. Waking the device before switching to the input could improve the waiting time, but that is an implementation detail depending on both the monitor and the OS and can't be guaranteed.

> Can no EDID negotiation be faster?

No, at this point removing EDID will simply get the display not detected at all. It used to be optional in the times of VGA, where you could just drive out 640x480 "blind", but there's too much stuff in there these days.

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