Two computers, one monitor, zero fiddling (2025)

https://alexplescan.com/posts/2025/08/16/kvm/

by ankitg12 • 2 months ago

273 144 2 months ago

alexplescan.com

abstractspoon• 2 months ago

Zero fiddling, but substantial financial outlay

swiftcoder3• 2 months ago

Any somewhat-modern monitor with multiple outputs should be able to do this. DDC support has been around for a while

bartvk• 2 months ago

Yeah but this monitor also switches its internal USB hub to USB-C. Is that really standard behavior?

connectsnk• 2 months ago

Isn’t the answer buy a kvm switch? If yes this could have been really short

Vvector• 2 months ago

He bought a $900 monitor that has a KVM built in

csomar• 2 months ago

Yeah, I read the whole article looking for any meat in there and there is none. I played with different setups as I, too, use both macos and linux. I remember doing a two screen setup where if you move the mouse to the edge of the linux screen, it appears on the macos one.

I guess everything old is new again?

topspin2• 2 months ago

~$900, and it takes ~3 seconds to switch...

I'll pursue this when "they" decide to get real and make this not suck. Until then, I have sufficient alternatives.

I appreciate the writeup. It convinces me that integrated KVM stuff ~~ except for fewer wires ~~ isn't much better than the mess that's prevailed for years now, and I'm not missing much.

applfanboysbgon2• 2 months ago

Conclusion
And there you have it. A KVM solution that doesn’t require an external KVM device to pass inputs through, and a switch that can be triggered using a keyboard alone.

swiftcoder3• 2 months ago

Depends on what class of monitor you want to run it with. A KVM that can handle 4K 144hz VRR is... not cheap, if available at all.

duskwuff• 2 months ago

"8K" KVMs are available on Amazon for under $100; they'll handle 4K@144 no problem.

giobox• 2 months ago

A KVM that can handle 4K 144hz VRR is... not cheap, if available at all

It's supported by the relatively old HDMI 2.1/DisplayPort 1.4 standards - it shouldn't be that hard to find a KVM that can do this.

rcoveson• 2 months ago

No, the worst part of a KVM switch is the video signal switching. You want as few switches in the video signal path as possible and the higher bandwidth you need them to be the more expensive they're going to be. You're already paying for the one in your monitor, so taking advantage of that is the right solution.

IME even high-end KVM switches experience occasional signal interruption or, more often, failure to synchronize at all on output switch.

Do what OP did.

dfxm12• 2 months ago

Depends on your threshold for "fiddling". The author's is quite inclusive.

nickdothutton• 2 months ago

I have a couple of Eizo EV3285, which have enough separate physical inputs for the 3 machines I use to drive them. Only real PITA is having to press the input selector on both. Must admit I wasn't even aware of DDC!

space_ghost• 2 months ago

I did something similar last year with a monitor without built-in KVM but with good DCC support (Ultrasharp U3417W) and Synergy [0].

I use Synergy as part of my desk setup already, but needed a way to view the UI of a normally headless machine. The solution I built was a small shell script that terminated the active Synergy session and started a new one with a different config file (so keyboard/mouse input would map to the normally-headless machine), and fired off a DCC command to the monitor to change its input. The same script ran with a different argument would switch back to the normal display/control configuration. This solution worked pretty well until I was able to retire the headless machine early this year.

[0] https://symless.com/synergy

empiricus2• 2 months ago

does synergy works better now? 3 years ago, every week I would get into a situations where one machine was not connecting to the other, and I had to randomly restart synergy so maybe it connects. fun to do that 5 min before the meetings.

forsalebypwner• 2 months ago

It's definitely very dependent on the stability of both machine's network.

I also recommend checking out the open source fork of Synergy, which is also compatible with Synergy clients https://github.com/deskflow/deskflow

mbauman• 2 months ago

I loved synergy back in 2005 when it was _actually_ open source! It was probably my first open source contribution! But then it was enshittified and made impossible to build from source in order to support the commercial dreams.

criddell• 2 months ago

The bottom tier is a one-time $15 purchase, the top tier is only $29. That doesn't seem all that evil...

culopatin3• 2 months ago

I had one of the versions of this monitor and I miss the PIP and two displays half and half, the KVM, it was truly nice.I never had to move any wires. I wish there was one just like it but 120hz and higher brightness that’s not $1.5k

ryandrake• 2 months ago

This is great. The Holy Grail of work/personal computing setups IMO. Too bad it’s so expensive.

I wish a KVM switch was a standard component of normal priced monitors these days. Especially one that also routed through all your peripherals, speakers, and everything.

clan3• 2 months ago

Most people are unaware that the should buy a monitor with USB and DP-Alt mode. The same people are also unaware that they should ensure the same for the laptop they are buying.

Lower prices are always nice. But such things can be found at reasonable prices. I think awareness is a larger problem.

I am happy enough with the built-in speakers. But I do agree that line level aux out on the back would be nice.

Leftium• 2 months ago

I found a monitor supporting KVM for only $132. It's an MSI, but not sure if the model is available outside of Korea: MSI MD272XPW[1]

The monitor with the specs I wanted was $201[2]

[1] https://prod.danawa.com/info/?pcode=29877128

[2] https://prod.danawa.com/info/?pcode=74545976

timeinput• 2 months ago

I have a few boxes that I switch between, but for some software it's nicer that my "main machine" be on DVI, and everything else HDMI. I may have to look at some scripting option where if the keyboard / mouse disappear (KVM switched away) change the display to use the HDMI input.

I do worry that would just add more trouble / race conditions / issues around this stuff. I feel like nvidia + linux + monitors doing anything other than staying on + attached all the time causes some headaches.

sethammons• 2 months ago

It never occurred to me that you can send commands across DDC to your monitor. Binding that to a key on the keyboard in different OSs to trigger the monitor's built in KVM is a nice touch. I only change between my computers a couple times a day else I'd be setting this up this evening

mdswanson• 2 months ago

FYI that if you have the right kind of Dell monitor, you can download their Display Manager software to do the same thing (and more): https://www.dell.com/en-us/lp/ddpm

Selkirk• 2 months ago

I bought the "right kind of Dell," for this purpose but ddpm is unusable for me as it slams CPU periodically.

timonoko2• 2 months ago

If you turn one computer display off as in "xrandr --output DVI-D-0 --off", the monitor automatically selects some other computer to display.

Thus I have 2 computers and 3 displays, and I can do sentences like "displays 13", which uses only displays 1 and 3 and sends ssh-command "displays 2" to the other computer.

timonoko2• 2 months ago

How do you change display-modes with ssh?

  os.system(f'ssh -Y {compu2} "DISPLAY=:0; display.py {modes};"')

clan3• 2 months ago

What a great idea. It should be obvious and easy but DDC commands are hard to find and should be documented better.

I have a Dell U4323QE in the office and look forward to trying this out. I wondered if it was the same DDC commands so I googled a little and found this gist (concerning DDM):

https://gist.github.com/nebriv/cb934a3b702346c5988f2aba5ee39...

Which has the very useful comment:

https://gist.github.com/nebriv/cb934a3b702346c5988f2aba5ee39...

Which states:

#define LUMINANCE 0x10 #define CONTRAST 0x12 #define VOLUME 0x62 #define MUTE 0x8D #define PBP 0xE9 #define SWAP_USB 0xE7 #define SWAP_INPUT 0xE5 #define INPUT 0x60 #define SUB_INPUT 0xE8 #define INPUT_ALT 0xF4 // alternate address, used for LG exclusively? #define STANDBY 0xD6

I much prefer simple DDC commands over using something like Synergy or Barrier. I think it is a much cleaner solution.

culopatin3• 2 months ago

There is a myriad of apps that handle all the DDC commands for you, it’s a non issue unless you want to write something custom.

vardalab• 2 months ago

Yeah, this all sounds good in theory, but there's a lot of edge cases. For example, for me switching between Mac and Linux what often happens is that Linux just for some reason the it turns off the monitor port and it's black until I reboot and there was no easy way to get it back. This is while using fancy Dell monitors built-in KVM. Ultimately, I have settled on remote desktops as a more viable and quicker option.

sciencesama• 2 months ago

now we need the same for two macs !

pixelatedindex• 2 months ago

What’s stopping you from running the same command on both Macs? Maybe I missed something.

smw• 2 months ago

It's mentioned elsewhere, but check out DeskFlow (oss) https://github.com/deskflow/deskflow

mikestew• 2 months ago

BenQ claims that their monitors will handle that:

https://www.benq.com/en-us/monitor/home/ma270s.html

https://www.benq.com/en-us/knowledge-center/knowledge/one-se...

I've got one (MA270S) hooked to a MBP (recommended, if you don't want to spend the dosh on an Apple display), but I haven't yet dug out another Mac to test the KVM. Considering that it's a $900 monitor, like the one in TFA, it damned well better work as advertised.

IshKebab2• 2 months ago

You can do this with even less fiddling just by getting a KVM that supports video. There are reasonably priced ones that can even do 4K 60Hz. This also means you don't have to deal with monitors that don't implement input switching via DDC/CI (thanks LG).

clan3• 2 months ago

I did that at home. But I needed to try several KVMs until I found one which was stable. And I hate all the cables.

I agree that the industry hates its consumers and likes to mess things up. CEC never always quite the same. Not supported on many GPUs etc.

I do not want to appear to condone LG. But actually (sorry!) some supoort[0] it using DDC side channels (0x50 rather that 0x51). But I agree it is painful. Yet I prefer it over my cable spaghetti.

[0] https://github.com/rockowitz/ddcutil/wiki/Switching-input-so...

threetonesun• 2 months ago

it's much more reasonable and trivial on lower quality monitors but if one of the two PCs is for gaming you're going to want 4k at at least 120Hz which, last I checked, didn't exist (or was very expensive). You also might have a hard time finding one that takes DisplayPort in, which is preferable for Linux.

Personally I just run the USB devices into a $5 USB A/B switch and manually change the inputs on the monitor.

IshKebab2• 2 months ago

You definitely don't need more than 60Hz for gaming. That's a super nice luxury.

elric• 2 months ago

Last time I looked (which was some years ago), I couldn't find any that support display over Thunderbolt without resorting to DisplayLink.

VimEscapeArtist• 2 months ago

I use 2 computers without a KVM. My keyboard, mouse, and soundbar all support Bluetooth. All wired to the PC by default. When I switch to the Mac, I just flip each device to Bluetooth mode.

ZeWaka• 2 months ago

Yep, similar - I just use a wired USB hub that can toggle between two outputs.

I just have the monitors auto-switch on (lack of) input when I put one machine to sleep. The single click buttons on the monitor also switch.

spacedoutman• 2 months ago

Personally i prefer two computers, two monitors, one mouse/keyboard.

Deskhop has been a lifesaver https://github.com/hrvach/deskhop

the_sleaze_• 2 months ago

I do the same but with a usb-c dongle. For whatever reason my brain needs a hard reset when switching between tasks otherwise my productivity nose dives.

pavel_lishin• 2 months ago

For macs, if you're signed into the same Apple account on both, you can "share" the same keyboard and mouse across them.

It does tend to be finicky - sometimes it just refuses to connect, and won't tell me why, and sometimes it'll forget the arrangement. And it requires you to be signed into one account on two machines, which some people may not want to do on corporate laptops.

ndr42• 2 months ago

Yes and then sometimes your mouse is gone (just to be found on some iPad display) :-/

montag• 2 months ago

Unfortunately, finicky isn’t acceptable when it comes to keyboard and mouse.

seemaze2• 2 months ago

I use two computers displayed side-by-side with the picture-in-picture feature of a single ultra-wide monitor.

Input leap[0] is a great open source KVM software version of the deskhop which allows me to control both computers on the same monitor with the sam peripherals.

[0]https://github.com/input-leap/input-leap

fluidcruft• 2 months ago

That's too bad that it requires software installed. I love deskhop because it needs absolutely nothing installed on the machines.

taneq• 2 months ago

I had a setup like this back in 2000 using VNC, it always used to spin people out when they realised one of my monitors was a SPARCstation and the other was a WinME box. :D

mckn1ght2• 2 months ago

I gave up on a hardware solution to this and currently just use Screen Sharing to "remote" into my personal machine from my work machine, which I guess only works because they're both macs, although VNC probably solves this in a cross platform way. I have an Apple studio monitor so built-in KVM isn't possible, although maybe there's a jailbreak for it since it has its own processor and firmware? I still just vastly prefer the quality of Apple displays so I optimize for that first.

Also, OT but I have the same keyboard as OP and love it :) I want to hack a TouchID key from the Magic Keyboard I bought into the chassis. But it can't traverse the Screen Sharing hack, so I do still think about this from time to time.

dllu• 2 months ago

Does screen sharing actually have reasonable resolution and latency befitting of the Apple Studio Monitor?

Doohickey-d• 2 months ago

On LAN (no internet, wired), it's quite decent. With e.g. Parsec, it's quite high image quality, low single digit latency, so quite usable.

mckn1ght2• 2 months ago

Not really, unfortunately, even on wired LAN latency is noticeable, but I'm just editing code so it's at least doable. Resolution isn't bad. I wouldn't recommend it for graphic work or gaming. The only benefit that isn't degraded is the nanotexture on the studio montor, haha.

albert_e• 2 months ago

I am just using RDP from one PC into another presently -- to solve this in a low complexity way. Tried a lot of approaches in the past -- none were reliable for me.

EvanAnderson2• 2 months ago

RDP works unreasonably well, given the price.

a-dub2• 2 months ago

back in the '00s i used a hardware kvm that could be controlled by the keyboard with some weird key combo (~ ~ (1|2)? maybe?). these days i strongly prefer deskflow (oss version of synergy) for this sort of thing or just ordinary remote desktop for the secondary. (depends on the task, if you're just building for the secondary or reading email it doesn't really matter- but if you're developing interactive applications or you need to reboot a bunch or something, then having the physical hardware with a local head can help).

sam_lowry_• 2 months ago

I still use hardware KVMs. Tesmart is OKish, but fails within a couple years, usualy. AV Access is on par with it.

Level1Techs are the best but also cost double or triple.

tosti• 2 months ago

Where I worked in the 00s, they had rack mountable kvm. The clients were just a small box with utp and the peripherals. A double press on ctrl opened a menu and you could choose a server. Neat.

Brendinooo• 2 months ago

I didn't know that DDC was a thing! Super cool.

bni2• 2 months ago

This is great, I have a monitor with built in KVM (CORSAIR XENEON 27QHD240 OLED)

m1ddc works fine on my Mac, but why isn't there a single multiplatform cli tool that can be ran on Mac/Linux/Windows?

I need a Windows one for this to be useful for me.

fiddyschmitt5• 2 months ago

For Windows:

https://github.com/fiddyschmitt/SimpleKVM

If you only have two computers, you just need one instance of SimpleKVM to switch between the computers.

chatmasta• 2 months ago

Just dropping a note to say I’ve had the same monitor for a year and I absolutely love it. I don’t care about this seamless switching — I just use HDMI1 for Xbox, HDMI2 for my computer, and then swap hobby/work when needed. It’s also good motivation to turn off the work laptop when I’m done with the day.

The monitor is fantastic though. I’ve had no issues yet, knock on wood.

opan• 2 months ago

I do something similar with my ThinkPad and Steam Deck connected to different ports, and I change inputs and plug in a controller when I want to play a game then.

marceldegraaf• 2 months ago

I have my Windows gaming rig in a rack at home, and run Apollo [1] on it. Using that, I can game on any Apple TV (with an Xbox controller) or the MacBook (connected to a display/keyboard/mouse) anywhere in my home. With wired networking 60fps at 4K is no problem at all.

This would be easy to set up the other way around, too: having a gaming rig on your desk with Moonlight, and running Linux on another machine somewhere in the network with Apollo to host the development setup.

No KVM (or KVM-equipped monitor) or other special hardware needed.

1: https://github.com/ClassicOldSong/Apollo

amiga386• 2 months ago

With Windows and AutoHotkey and https://www.nirsoft.net/utils/control_my_monitor.html

You can add this .ahk script to run at startup:

    ^F4::
      Run C:\Users\YourNameHere\Documents\AutoHotkey\ControlMyMonitor /SwitchValue Primary 60 17 3
      Return

Where the file path is where you've put ControlMyMonitor.exe, "Primary" means the main Windows display, the "60" means input select, and the "17" and "3" are the values you observe in ControlMyMonitor when each display you want to switch between is enabled.

You can now press Ctrl+F4 to toggle inputs.

iaresee• 2 months ago

Oh nice! I've been doing this on the Mac side with BetterDisplay, but on the Windows side I couldn't find an equivalent and have had the awful Dell software installed to do it there. This'll let me dump the Dell software! Thanks!

fiddyschmitt5• 2 months ago

For Windows, I wrote SimpleKVM. I'm proud of the little monitor diagram it shows. Keen to hear your thoughts if you get to try it.

https://github.com/fiddyschmitt/SimpleKVM

bni2• 2 months ago

Thank you precisely what I was looking for on the Windows side

jmuguy• 2 months ago

Its amazing to me how annoying these problems can be and there's no real one size fits all solution. I have a desktop PC and macbook, and two monitors. I use a KVM and also switch inputs on the monitors themselves.

I tried very unsuccessfully to do something with DDC/CI when the KVM would switch between systems. The idea being when the OS detect the presence of the keyboard/mouse because the KVM had switched to them they'd send a change source command but DDC/CI is such a disaster in terms of support.

We need someone like Framework to make a "monitor for hackers" that actually has robust, well documented, DDC/CI support and I'd be all over it.

jijijijij• 2 months ago

We need someone like Framework to make a "monitor for hackers" that actually has robust, well documented, DDC/CI support and I'd be all over it.

No, no, no. They need to modify their laptops so I can use the laptop's monitor and keyboard with e.g. a RPi without networking. Using the laptop IO for headless computers flipping a switch, or better ad-hoc streaming into some virtual environment would be such a win!

heatmiser• 2 months ago

I solved the multi-computer-to-multi-monitor problem with a Level1Techs KVM[1]. The price (~$500 for the variant I purchased) initially gave me pause, but the longer I've had it, the happier I am with my decision.

It handles all the switching at the hardware level and thus has no perceptible lag for video or anything else. I'm able to connect a single set of peripherals, in my case, two monitors, a keyboard, a trackball, and a USB audio interface, to both my Linux desktop and a CalDigit Thunderbolt dock connected to my laptop. The L1T KVM has hotkeys[2] that let me switch between systems, with only a 1–2 second delay.

The benefit, for me, of this extra box now mounted under my desk is that when I upgrade my monitor, I only care about how good a display it is, not whether there's some perfect confluence of KVM, refresh rate, aspect ratio, display technology, etc. I find the monitor I want and let a separate IO routing layer.

[1] https://www.store.level1techs.com/products/p/14-kvm-switch-d...

[2] https://forum.level1techs.com/t/official-l1techs-kvm-faq-ult...

nickzelei• 2 months ago

I’m looking for a setup like this. I currently have a simple usb-c splitter that I use to switch my keyboard between the two. I bought a similar one for display ports but it doesn’t work super well, so I ditched it and just manually move the display port from my desktop to my caldigit.

They were both $20. The keyboard one works fine. I’d love to have a kvm like this but the price certainly gets gives me pause when I got halfway there for basically $20-$40.

Muromec• 2 months ago

There is an actual KVM that does both (display and usb) for 25 eurobucks sold on the communist ecommerce website.

seany2• 2 months ago

I really wish some one made one of these as a DP 1.4 _matrix_ instead of a true KVM. 8in 8 out would be amazing

tim--3• 2 months ago

These exist, but are exceptionally niche, and very, extremely expensive.

sharts2• 2 months ago

I wasted money on their KVM and it sucked for vfio stuff. Never again.

TimeBearingDown• 2 months ago

any details? considering this.

m4632• 2 months ago

kvm usb switching is always broken, sometimes subtly, sometimes obvious

I use mechanical USB switches to individually switch USB lines like this:

https://www.amazon.com/dp/B01I0Y3GEE

one for keyboard, one for mouse

Problems it avoids

- cable speed usb

- no extra latency

- using boot-up hold-key-down sequences on macos works fine

- keyboard doesn't get hung in weird states

- no hotkey conflicts

- no mouse gets in weird state on one system that persists to another

etc etc etc

vogelke• 2 months ago

I have a Dell 2208 monitor with 4 USB-2 ports. If I bought three of these switches, would I be able to share keyboard/mouse/monitor between two machines? My monitor does not have HDMI, just VGA.

gblargg2• 2 months ago

There are electronic versions of 2-1 switches that also just connect the data lines through, no hub, but use electronic switches rather than multi-pole mechanical switches (they naturally work bidirectionally, so you can switch a computer between two devices as well as one device between two computers).

dietr1ch• 2 months ago

I found KVMs to be annoying and settled on a USB switch and letting my monitor auto-switch inputs.

My mouse felt laggy under the KVM because of the high polling rate it wanted to use. Some key combinations also got added delay because of the way the KVM listened to shortcuts.

Instead of the $200 KVM a $20 alternative with a dedicated switching button did what I wanted in a much better way. Maybe if you need to switch back and forth more often a KVM would be alright? But at that point I guess dedicated monitors with the USB switch would still be better.

tim--3• 2 months ago

I went down a similar rabbit hole a while back and ended up building something that attacks the same problem from the opposite direction: instead of just a hardware box that switches everything (video + USB), I wrote Fence[1], a software layer that automates switching USB input devices when you glide the mouse to the edge of the screen.

The idea is basically "Synergy's convenience, but with real hardware switching." You run a tiny client on each machine. When your cursor hits the left edge of your desktop, Fence tells a USB and HDMI Switch to physically redirect your keyboard and mouse to the next PC.

The switching happens in hardware and you can design your layout per-direction and per-device.

Where the L1T KVM is the "one box handles video and IO beautifully" approach, Fence is more of an "IO routing layer" that lets you keep your existing monitors and their auto-input-switching (or a separate video path).

I built it specifically to be cross-platform. You don't pass clicks/keystrokes over the network, just a "switch to pc2 PC, left edge" message.

Not a replacement for the L1T if you want one-button video+peripheral switching, but if someone likes their monitor's own input handling and just wants the "mouse to edge" workflow it's a nice middle ground.

I like the fact that moving the mouse to different edges of the screen can show exactly the source to the sink that I want.

I originally built it for live streaming with OBS, but now, I miss it when I have more than one computer I need to deal with at a time.

[1] https://github.com/timgws/kvm-switch

LiamPowell• 2 months ago

When did KVM switches get so expensive? Level1Techs doesn't appear to be much more expensive than the competition, but the margin on all of these has to be absurd. They're not a particularly niche product and the BOM cost is only going to be $20 at most (a TMUXHS4612 is $1 for reference).

I'm amazed that there's not more competition bringing the price down here.

aetch2• 2 months ago

Some KVMs emulate the display to the disconnected computer so your windows don’t get messed up on switching

sobeston• 2 months ago

Level1Techs' KVM products have always been expensive, and they're arguably the best around. There aren't many competing products.

foresto• 2 months ago

In case anyone else likes to know the panel manufacturer before buying a display, it looks like this one is made by Samsung.

https://www.displayspecifications.com/en/model/f86e3770

https://www.displayspecifications.com/en/model/49bc3e67

dominotw• 2 months ago

i have the same setup with my dell but i would love to use usbc for linux too . just one wire each to either device.

BadBadJellyBean• 2 months ago

This is awesome. I chose my monitor among others because of the built in KVM switch. I always found it annoying that I had to use the navigation nipple to switch inputs. This is now in the past.

If someone wants to know I have an MSI MPG 491C QD-OLED.

eleventen• 2 months ago

I have a Dell U3225QE with a built-in KVM and 2 macs.

One connects with Thunderbolt only. The other connects with Display Port for video and USB-C for the rest of the built-in dock.

It's OK most of the time with the nipple switch. My one piece of advice is *avoid HDMI*. I learned after getting this monitor that the HDMI protocol is a petulant unstable little shit that does not tolerate renegotiation well. Get yourself a USB-C to DisplayPort cable.

sgarland2• 2 months ago

I have had exact opposite experience WRT display technologies. I normally use USB-C <-> DP, but they are far more finicky than HDMI. I only use the former because the hub I have for my Mac doesn’t do 4K@120 Hz over HDMI.

EDIT: sorry, the reason is because the monitor has HDMI 2.0, so it can’t do 4K@120 Hz over HDMI. Otherwise, I’d use the Mac’s native HDMI port and be done with it.

nkotov• 2 months ago

I have a similar setup for my MBP + Windows Desktop. I ended up using a simple USB switcher for all the devices and just running two inputs and manually switching between screen inputs. One button press for USB switch, one source switch on monitor. If I need something from the other computer during the use, I just remote in.

fiddyschmitt5• 2 months ago

You could use SimpleKVM to detect the USB change, and trigger the monitor input change.

https://github.com/fiddyschmitt/SimpleKVM

GeorgeDewar• 2 months ago

I love this approach, but a few years ago I tried it very unsuccessfully with my Xiaomi Mi 34" ultrawide.

By very unsuccessfully, I mean that the commands to change input didn't work. I can't remember if they did nothing or crashed the monitor, but subsequent investigation led me to realise I was lucky not to brick it, as some people found certain commands cause non-recoverable issues on that monitor!

So, I suggest caution in the form of maybe checking that others have successfully used DDC commands on your particular model.

https://github.com/rockowitz/ddcutil/issues/153

BrokenCogs3• 2 months ago

Wait why not just buy a usb switch? I switch between 4 computers using the same monitor, keyboard and mouse.

adrian_b• 2 months ago

Why buy a switch when almost all monitors have multiple video inputs and they can switch them internally.

The only difficulty is that as said in TFA, the DDC commands are typically very poorly documented by the monitor manufacturers, so most computer users are not aware of them.

BrokenCogs3• 2 months ago

Most monitors don't have a keyboard and mouse input...

leosanchez• 2 months ago

I have a USB switch for 2 computers. Which switch are you using for 4 computers?

BrokenCogs3• 2 months ago

This one: https://a.co/d/04gGroV2

mcv• 2 months ago

I'm going to have to look into this. I've got two machines using the same monitor (indeed work macbook and home linux). It's a curved 4K Samsung Oddyssey of some sort, and I can either switch through the monitor's menu, or set it to switch to the machine that gave the most recent input. The latter sounds perfect, but unfortunately both options suck. The monitor is incredibly slow to respond to anything: turning on, opening the menu, switching input, whatever. It always takes a couple of seconds, sometimes forgets to turn on at all, and often when I do something on one machine, the other suddenly wakes up, presumably by the monitor. The setup is unpredictable, and I blame the monitor.

grahamburger• 2 months ago

I have a Samsung Ultrawide monitor. It allows for two simultaneous video input displayed on the screen at once, in either 50/50 or 66/33 split. Combined with Barrier for mouse-keyboard switching and keyboard integration and I can use both devices simultaneously on the same monitor, almost as though they were a single device.

peterburkimsher• 2 months ago

I sometimes use a Raspberry Pi at work, and found the miniKVM to be a useful tool for controlling it:

https://www.crowdsupply.com/techxartisan/openterface-mini-kv...

melonamin• 2 months ago

I'm using Apple Studio Displays and have been on the lookout for a solution like this for quite a while. My grail is a Thunderbolt KVM; there are a couple on the market, but they cost a fortune and have terrible reviews. I guess the use case is so narrow that nobody is investing in it.

An alternative could be a good 5K/6K monitor with a KVM, but this is a unicorn as well...

eludwig• 2 months ago

An alternative could be a good 5K/6K monitor with a KVM, but this is a unicorn as well...

I use a Dell U3224KB (32" 6K) in this way. Thunderbolt (usbc) is connected to a Macbook Pro and DP & regular usb c is connected to Windows gaming machine. Works perfectly. And yes, the U3224KB is pretty ugly, but I've grown to love it's features.

stn8188• 2 months ago

Like many in this thread, I have a similar setup. I used to use I separate KVM, which did work but had a lot of cabling.

Eventually, I decided on just a simple USB SPDT switch that I designed [0], a USB hub, and manual input switching on the monitor. Even though it takes two actions instead of one, it's a simpler setup and has been quite reliable for years now.

[0] https://shielddigitaldesign.com/posts/2021/susb/

fiddyschmitt5• 2 months ago

Nice write-up! I wrote https://github.com/fiddyschmitt/SimpleKVM which makes the process easy on Windows.

As others have mentioned, you can use a cheap USB switch if you don't have an in-built KVM.

DDC/CI is quite interesting. Most OEMs seem to implement it just fine. But some (like LG) need special handling.

m0shen• 2 months ago

Ah I went through the same thing myself, but with Windows

https://moshen.net/posts/virtual_kvm/

culopatin3• 2 months ago

Honestly the best thing that worked for me, even if the hardware is not for everyone, is a Logitech MX Keys that supports 3 devices paired with another Logitech mouse that supports 3 devices, then flip the monitor through the inputs, super reliable. I could even have 2 devices side by side on the same screen (Dell utlrawide) and toggle between them.

Yondle• 2 months ago

Thank you! I hadn't thought of using software to handle monitor switching.. I have a very similar setup but my monitor doesn't support usb upstream so I have a dumb usb hub with a button to switch sources then still have to manually use monitor input change.

You gave me the idea to setup scripts on the windows / macos system to 'react' to hub detach events (which I click the button) and execute cli commands to change the monitor source automatically to the other machine. Too good.

onceler• 2 months ago

This is the setup I (used to) use. My monitor doesn't do usb switching, so I got a cheap ($15ish?) usb switch (one downstream port (connected to a hub), two upstream ports, and a button to switch between them), and run a script on my desktop to send ddc commands to the monitor to switch inputs when it receives usb attach/detach notifications. No keyboard shortcuts, but one button next to my keyboard switches everything.

: I've since replaced the monitor, and found that the new one doesn't support input switching via ddc, at all. But it does switch if only one input is active, and I rarely use both computers at once, so I cope.

fiddyschmitt5• 2 months ago

:) yes. For Windows, that's exactly what SimpleKVM does

https://github.com/fiddyschmitt/SimpleKVM

INTPenis• 2 months ago

I've done the same with Lenovo and BENQ monitors with built in KVM, but DDC commands were new to me. I just switched source on the monitor buttons and it would also switch all USB peripherals at the same time.

thangalin• 2 months ago

For a run-down of various hardware KVM solutions that can handle high-resolution video at high refresh rates, see:

https://hardwarerecs.stackexchange.com/q/18561/7591

The UGREEN 8K Displayport KVM Switch has been running flawlessly for four months of continuous use.

https://www.amazon.ca/gp/product/B0CFFFHFJT

yehat• 2 months ago

Tell the dude there're software KVMs - Synergy, Barrier, DeskFlow, InputLeap. I'm with Barrier for many years and it solves many use cases.

tomaskafka• 2 months ago

I am trying to do the same, and I absolutely don't understand what is happening in the 3-5 seconds while two gigahertz-level machines and a modern monitor negotiate something over tens-gigabit-per-second connection.

If Steve Jobs herded makers of all the parts into a single room, and told them they aren't leaving until this takes 10 ms, I would be immensely grateful and I bet it could be resolved in a week.

zeta0134• 2 months ago

A pox specifically on my otherwise delightful samsung OLED, which immediately upon any sort of disconnect event (say, changing the resolution, or restarting the machine) decides to spend 10-15 seconds slow-scanning every other possible input. Exactly none of which have a physical cable attached, and exactly zero of which have ever been used once.

What the devil is taking so long? I'm sure there's some technical reason that the check isn't more instant, but gosh it is frustrating every damned time.

ninalanyon• 2 months ago

The technical reason is probably that doing it faster wasn't in the specification.

sgarland2• 2 months ago

My Acer Predator can disable that option. The downside is specifically for MacOS, the Mac often gives up trying to sync before the monitor has finished its side of things, and since the Acer has a non-configurable, extremely short auto-power-off, so the two get into a death loop.

kombine• 2 months ago

This frustrates me too, switching takes even longer than 5 seconds for me. I use an external KVM switch (with a physical button) and I run a laptop via a ThinkPad docking station, so two more devices in my case.

KeplerBoy• 2 months ago

Probably link training.

The very fact that it is a tens-gigabit-per-second connection in an environment full of RF noise (we all love our high powered switching power supplies) makes it hard to get a reliable signal instantly. Still shouldn't take longer than a few hundred ms though (worst case).

gblargg2• 2 months ago

The pretty generic TV I use a a monitor apparently keeps the links up with its three inputs, at least for a while after recent use, so switching between two powered computers is quick, about half a second. I started using that rather than a KVM since the KVM caused a retrain, adding several seconds to switching.

mrheosuper• 2 months ago

Probably debouncing, when anything/any events happen, you have to ask yourself, did this event truly happens, or just some weird glitch and can safely ignore it.

mystifyingpoi• 2 months ago

For real. So many things do this. I'm particularly frustrated with Bluetooth. Why does it take multiple seconds for two devices to send a minuscule amount of rf data when connecting over known mac?

aetch2• 2 months ago

Iogear (aten) kvms let you switch without moving your hands off the keyboard. There is a hot key you can activate the. Press the input number to connect and the KVM switches.

teekert• 2 months ago

I have a Iiyama with build in hub, at first it seemed ideal, just plug everything into the monitor. But my mouse glitches when used through the hub (MX Master 3S), the internet cable is only available to the active computer (so no tasks requiring internet can run on the other computer).

All in all, I just use the USB-C to HDMI switch functionality and couple the computers to keyboard/mouse via bluetooth, plus I bought a switch for the ethernet. It's a shame it's so suboptimal.

Another minor annoyance is that when I turn off one computer and want to switch to the other, the display turns off, taking about 5-10 sec to do so. Then I manually turn it back on and it's ready in another 3 sec. So I do this thing where I hover about the turn-off button, hit it and immediately switch so the monitor won't turn off.

It's hard to make convenient tech it seems.

halfdaft• 2 months ago

For anyone that wants actually seamless switching of video and data, look to professional AV switchers and KVM. This Lindy 5x2 HDMI + USB KVM is the business [1]. I use one because I constantly switch between Mac and Linux while working on the same project and the couple of seconds of black really gets tedious pretty quickly.

https://www.lindy.eu/5-Port-Seamless-Multiview-KVM-Switch.ht...

dizhn• 2 months ago

As long as everybody is posting their favorite solutions. https://xpufx.com/posts/hundred-percent-software-kvm-switch/

alpha_trion• 2 months ago

This is pretty cool, dunno if I'd want to commit to a specific monitor brand to get this functionality though. My primary concerns with monitor selection are ports and color quality.

I have an old TrendNet KVM that I've used for years but it doesn't support Thunderbolt so it's getting a bit long in the tooth.

Hugsun• 2 months ago

Note that your monitor is a QD-OLED, not a QLED monitor.

Despite the similar names, these are two very different technologies. QD-OLED is a OLED panel that uses QD (quantum dots) to achieve a wide color gamut. QLED is a LED backlit LCD panel that uses QD in a similar way.

The difference in performance characteristics of these two panel types is dominated by the difference between OLED and LCD.

Two computers, one monitor, zero fiddling (2025)

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