DdcSwitch

Switch your monitor's input source from Windows or macOS – with a hotkey,
or automatically right before the computer shuts down.

English · 简体中文 · 繁體中文 · 日本語 · 한국어 · Español · Français · Deutsch · Português · Русский

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One monitor, two computers – say a Windows PC on HDMI and a MacBook on USB‑C. Changing inputs means fumbling with the monitor's buttons, and after you shut Windows down the monitor keeps staring at a dead HDMI port.

DdcSwitch talks to the monitor over DDC/CI, the same channel the on-screen menu uses. Press a hotkey to switch, and when you shut Windows down it hands the screen over to the other computer for you.

Features

• Hotkeys – up to three global shortcuts, each switching to its own input (for example Ctrl+Alt+Win+→ for the Mac).
• Switch before shutdown – flips the input once shutdown is certain. Restarts, sign-outs and installers closing the app are recognised and skipped.
• Optional switch before sleep.
• Tray menu – switch inputs, toggle the shutdown switch and start-up, open settings and the log.
• Knows your monitor – reads the current input and the inputs the monitor reports, so you don't have to guess codes.
• Small and native – one ~600 KB executable, no runtime, no admin rights, no external tools. It calls the Windows Monitor Configuration API (dxva2.dll) directly.
• 10 languages – English, 简体中文, 繁體中文, 日本語, 한국어, Español, Français, Deutsch, Português (Brasil), Русский. Follows the Windows display language by default.
• Transparent – every shutdown decision is written to a log you can open from the tray.

Requirements

• Windows 10 or 11 (x64).
• A monitor with DDC/CI enabled in its on-screen menu. Most external monitors support it over HDMI, DisplayPort and USB‑C. Laptop panels don't, and some docks, adapters and KVM switches don't pass DDC/CI through.

Installation

Download DdcSwitch-<version>-windows-x64.zip from the latest release, extract it to a permanent folder (for example %LOCALAPPDATA%\Programs\DdcSwitch) and run DdcSwitch.exe. The exe isn't code-signed, so SmartScreen may warn you the first time: choose More info → Run anyway.

To build it yourself you need Rust (MSVC toolchain):

git clone https://github.com/pokoblin/DdcSwitch.git
cd DdcSwitch
.\install.ps1

install.ps1 builds a release binary, copies it to %LOCALAPPDATA%\Programs\DdcSwitch\ and starts it. On first launch DdcSwitch adds itself to Start with Windows, because the shutdown switch only works while it runs. You can turn that off in the tray menu.

If the Windows SDK (rc.exe) is installed, the icon and version information are embedded in the exe. Without it the build still works.

Uninstall

& "$env:LOCALAPPDATA\Programs\DdcSwitch\uninstall.ps1" -RemoveSettings

Quick start

1. Find the input code of the other computer. Open Settings from the tray icon. The status line shows the current input and the inputs your monitor reports, for example Monitor reports: 25 (0x19), 15 - DP-1, 17 - HDMI-1. Codes are defined by the VESA MCCS standard (15 DP‑1, 16 DP‑2, 17 HDMI‑1, 18 HDMI‑2, 27 USB‑C), but vendors deviate: a Dell U2725QE uses 25 for USB‑C. When in doubt, try one with DdcSwitch.exe --set <code>.
2. Set up a hotkey. Give the row a name, pick the target input, click the hotkey box and press the keys. The Win key can't be recorded there, so tick + Win if you want it.
3. Set the shutdown input. Under Shutdown / sleep, choose the input to switch to before Windows powers off.

How the shutdown switch works

1. DdcSwitch keeps a hidden top-level window and registers as one of the last applications to be notified of a shutdown (SetProcessShutdownParameters).
2. It only acts on WM_ENDSESSION(TRUE) – when the shutdown is definite. If another app blocks the shutdown, the "These apps are preventing shutdown" screen stays on Windows' input where you can see it, and a cancelled shutdown changes nothing.
3. Restart or power off? Windows doesn't say. Every user-initiated shutdown (Start menu, shutdown.exe, Windows Update) writes event 1074 to the System log before applications are notified, and its data says power off or restart. DdcSwitch reads that event. If the type can't be determined, it switches anyway.
4. Sign-outs and Restart Manager requests (installers updating the app) are ignored.
5. Each step is logged, so after the next boot Open log shows what happened.

Configuration

Settings live in %APPDATA%\DdcSwitch\config.ini. The settings window writes it, but you can edit it by hand too (restart DdcSwitch afterwards).

Key	Default	Meaning
language	auto	auto, en, zh-Hans, zh-Hant, ja, ko, es, fr, de, pt-BR, ru
monitor	1	Monitor number, as listed by --list
monitor_name		Preferred over monitor when a monitor with this name is connected
hotkeyN		N = 1–3, e.g. Ctrl+Alt+Win+Right
hotkeyN_enabled		true / false
hotkeyN_name		Label shown in the menu
hotkeyN_input		Input code (25, 0x19, or an alias such as hdmi1, dp1, usbc)
shutdown_switch	true	Switch before shutdown
shutdown_input	25	Input to switch to before shutdown or sleep
skip_on_restart	true	Don't switch when Windows restarts
sleep_switch	false	Also switch before sleep
notify_success	false	Show a notification after every switch, not only on failure

The log is %APPDATA%\DdcSwitch\DdcSwitch.log.

Command line

Without arguments DdcSwitch runs in the tray; starting it again opens the settings of the running instance. For diagnostics:

DdcSwitch.exe --list            List DDC/CI monitors
DdcSwitch.exe --get             Read the current input
DdcSwitch.exe --set 25          Switch input
DdcSwitch.exe --caps            Read the capabilities string and supported inputs
DdcSwitch.exe --detect          Show how the last shutdown/restart is classified
DdcSwitch.exe --quit            Ask the running tray app to exit
Options: --monitor N, --config <path>

Troubleshooting

• A hotkey does nothing. Another program owns that combination (an AutoHotkey script, for example). DdcSwitch shows a notification when it can't register a hotkey. Choose another combination or free it in the other program.
• "Could not read the current input". Check that DDC/CI is enabled in the monitor menu. Many monitors only answer DDC/CI on the input that is currently shown, and some docks or KVM switches block it.
• The wrong monitor is switched. Pick the monitor in Settings and press OK; its name is saved so the right one is found even if the numbering changes.
• Did the shutdown switch run? Open the log from the tray menu after the next start. It records the shutdown type that was detected and the result of the switch.
• Connected over Remote Desktop? An RDP session has no access to the physical monitors, so DDC/CI (hotkeys, the status line in Settings and the shutdown switch) only works while you are signed in at the PC itself.

macOS

DdcSwitch also runs on the Mac, as a menu bar app with the same features: up to three keyboard shortcuts, switching before shutdown and optionally before sleep, and the same 10 languages. It is written in Swift and SwiftUI and lives in macos/; the Windows version is not affected by it.

Requirements: macOS 13 Ventura or later. A Mac with Apple silicon is required: DdcSwitch talks DDC/CI through its display controller (tested on an M4 Pro over USB‑C and DisplayPort). Intel Macs are not supported. The built-in HDMI port of M1 Macs doesn't pass DDC/CI – use USB‑C or DisplayPort there.

Installation: download DdcSwitch-<version>-macos.zip from the latest release, unzip it, move DdcSwitch.app to Applications and open it. The app isn't notarized, so macOS blocks the first start: open System Settings › Privacy & Security and click Open Anyway. On the first start the settings window opens; turn on Launch at login there, because the shutdown switch only works while DdcSwitch runs.

To build it yourself you need Xcode or the Command Line Tools (Swift 5.9 or later):

git clone https://github.com/pokoblin/DdcSwitch.git
cd DdcSwitch/macos
./install.sh

install.sh builds the app, copies it to /Applications and starts it. ./build.sh only builds dist/DdcSwitch.app and the release zip; swift test runs the tests.

What's different on the Mac

• Shortcuts use ⌃ ⌥ ⇧ ⌘. Click the shortcut field and press the keys; Esc cancels, Delete clears. They are registered like any app's global shortcuts, so no Accessibility permission is needed.
• Settings apply immediately, as usual on macOS – there is no OK button. Problems are shown next to the setting.
• Shutdown switch: when you shut down, restart or log out, macOS asks every app to quit and tells it why. DdcSwitch switches on shutdown, skips restarts (unless Not when restarting is off) and never switches when you log out. sudo shutdown in Terminal doesn't ask apps to quit, so it doesn't switch. If another app cancels the shutdown after DdcSwitch has quit, the input has already been switched.
• Sleep switch: macOS waits until the input is switched before it goes to sleep.
• Files: settings in ~/Library/Application Support/DdcSwitch/config.ini (the same keys as on Windows plus appearance = auto/light/dark; hotkeys are written like Ctrl+Opt+Cmd+Left, and Alt/Win are read as Option/Command), log in ~/Library/Logs/DdcSwitch/DdcSwitch.log.
• Command line: the same options except --detect, for example /Applications/DdcSwitch.app/Contents/MacOS/DdcSwitch --list.
• Translations of the Mac app are in macos/Sources/DdcSwitch/I18n.swift; swift test checks the placeholders.

Uninstall on macOS

Turn off Launch at login in the settings first, then:

/Applications/DdcSwitch.app/Contents/MacOS/DdcSwitch --quit
rm -rf /Applications/DdcSwitch.app ~/Library/Application\ Support/DdcSwitch ~/Library/Logs/DdcSwitch

Contributing

Issues and pull requests are welcome.

• Translations: UI strings are in src/i18n.rs. Copy the EN block, translate it and add it to LANGUAGES. The compiler makes sure no string is missing, and cargo test checks the placeholders. README translations are in docs/i18n.

• Build and test:

  cargo build --release
  cargo test --release

Path	Contents
src/main.rs	Tray icon, hotkeys, shutdown and sleep handling
src/ddc.rs	DDC/CI via the Monitor Configuration API
src/shutdown.rs	Restart vs. power-off detection (event 1074)
src/settings.rs	Settings window
src/i18n.rs	Translations
src/config.rs	config.ini, hotkey and input parsing
build.rs	Draws the icon and embeds icon, manifest and version info

License

MIT