Annex

More screens for your Mac. You already own them.
Annex turns the monitors on your Windows PC into extra displays for your Mac, wirelessly, over your own network. Free and open source.

Download for Mac and Windows  ·  Get started  ·  Why Annex

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Your PC's monitor is sitting right there, and your MacBook is squinting at one small screen. Open Annex on both, turn the monitor on, and within a second macOS sees a brand-new display. Drag windows onto it, arrange it in System Settings, use it like any other screen. Turn it off and it's unplugged.

No cable. No dongle. No subscription. No account.

Why Annex

• It behaves like a real cable. macOS sees a real display, not an app window. Your windows stay put, even if the network drops for up to 30 seconds.
• Text stays razor sharp. Sharp mode sends full 4:4:4 colour, so code, documents and UI look the same on the PC monitor as on your Mac. Fast mode keeps video and motion smooth at 60 fps. Annex picks the right one for each monitor, or you choose.
• Fast enough to forget it's wireless. Hardware HEVC on both ends. In our tests on 5 GHz Wi-Fi, an extended display runs at 60 fps with an estimated 10–13 ms from capture to screen.
• Up to three monitors. Each PC monitor becomes its own Mac display, or mirrors one of yours, and a mirror can fill the monitor without black bars.
• Private by design. Annex only talks to your own devices on your local network. No cloud, no relay, no tracking. Everything on the wire is encrypted, and only the Mac you paired with a PIN can connect.
• Set it up once. Type a 6-digit PIN the first time. After that, both sides find each other and reconnect on their own.
• Free, and yours to change. Open source under MIT or Apache-2.0.

Who it's for

• You work on a Mac but have a Windows PC with good monitors on the same desk.
• Your gaming PC's big screen sits idle while you work on your MacBook.
• You want a second (or third, or fourth) screen for your Mac without buying one.

Get started in a minute

1. Download Annex for both machines from the latest release.
2. Open it on the PC and on the Mac, and type the PIN the PC shows into the Mac. You only do this once.
3. Turn a monitor on. Your Mac has a new display.

The step-by-step guide below covers permissions, firewall prompts and the portable Windows version.

Early days: Annex is new and has only been tested on a handful of machines so far. If something doesn't work on yours, tell us: reports from new hardware make Annex better for everyone.

What you need

• Mac: Apple silicon, macOS 13 or later.
• PC: Windows 10 or 11, 64-bit, with a GPU that decodes HEVC (NVIDIA GTX 950 / AMD RX 400 / Intel 6th gen or newer). The Annex window uses the Microsoft Edge WebView2 Runtime, which Windows 11 and up-to-date Windows 10 already have; without it Annex still runs from the tray and offers the download.
• Both on the same network. Wired Ethernet on at least one side gives the lowest latency; 5 GHz Wi-Fi works.

Install and connect

1. From the latest release, download Annex-mac-arm64.dmg for the Mac and, for the PC, either Annex-windows-x64-setup.exe (installer) or Annex-windows-x64-portable.zip (no install).
   • To check a download is exactly the file the release workflow built (releases after 1.1.0), compare it with the release's SHA256SUMS.txt, or run gh attestation verify <file> --repo msadiks/annex-app with the GitHub CLI.
2. PC: run the installer, or unzip the portable folder anywhere (a USB stick works) and run Annex.exe in it. The Annex window opens, and Annex also lives in the system tray (the monitor icon).
   • Windows may show a SmartScreen warning for a new app: choose More info → Run anyway.
   • Setup installs Annex for your Windows account. When you click Install, Windows asks for permission once, so setup can add a Windows Firewall rule for Annex: private networks, plus public networks for devices on your local subnet only. The rule opens only Annex's own ports: TCP 48800, UDP 48801 and mDNS (UDP 5353).
   • The portable copy has no installer, so allow it when Windows Firewall asks. If the firewall still blocks the Mac (for example on a network Windows marks Public), the Annex window shows a banner with a button to fix it.
   • The portable copy keeps its settings and logs in a data folder next to Annex.exe and writes nothing else to the PC.
3. Mac: open the .dmg and drag Annex to Applications, then open it. Its window opens, and it stays in the menu bar when you close the window.
   • Allow Screen Recording when macOS asks (System Settings › Privacy & Security › Screen Recording), then quit and reopen Annex.
   • Allow Local Network access when asked.
4. Pair once: in the Annex window on the PC choose Pair with your Mac (or Pair with a Mac… in the tray menu). A PIN appears on the PC. Type it into the Annex window on the Mac (menu bar icon › Pair with a PC…).
5. Plug in a monitor: turn a monitor on in the Annex window on either side, the PC tray menu or the Mac menu bar popover. Within a second the Mac shows a new display. Arrange it in System Settings › Displays like any other monitor.

From then on both apps reconnect by themselves whenever they're on the same network. Turn on Start with Windows on the PC and Start at login on the Mac to make it permanent.

Everyday use

• PC window: left-click the tray icon (or open Annex again) to show it. Turn monitors on or off, pick Mode (Auto / Sharp / Fast) and Source (Extend as a new Mac display, or Mirror one of the Mac's displays), see live stats per monitor, pair or forget the Mac, and set Start with Windows and the stats overlay (also Ctrl+Shift+F12). Closing the window keeps Annex running in the tray; Quit Annex stops it. While every PC monitor shows a Mac display, the window waits in the tray and comes back when a monitor is free.
• PC tray menu: right-click the tray icon for the same monitor settings in a menu.
• Mac menu bar popover (click the menu bar icon): the PC's live bitrate, latency and loss, and a card per PC monitor with an on/off switch. Click a card for its settings and live stats.
• Mac window (menu bar icon › Open Annex…): a picture of the Mac and the PC's monitors; click a monitor for its settings and live stats (frame rate, bitrate, loss, estimated latency). Connection shows the PC and the link, and Preferences has pointer drawing and the login option.
• Mirroring without black bars: a Mac screen and a PC monitor of different shapes leave black bars on the PC. Set the monitor's Mirror shape to Match the PC on the Mac, and while it mirrors, the Mac takes the monitor's shape instead: the PC is filled, and the Mac's own screen gets the bars.
• If the network drops, the Mac keeps the display for 30 seconds so your windows don't move. After that it's unplugged until the PC is back.

Troubleshooting

• The Mac can't find the PC: both must be on the same subnet, and Windows Firewall must let Annex in. The PC's Annex window shows a yellow banner when it doesn't (no rule, a block rule, or a network Windows marks Public); use its button to allow Annex, or set the network to Private in Windows Settings. The tray menu shows Windows Firewall is blocking your Mac too.
• Black screen on the PC: the PC shows black when the Mac is gone for 2 s (no signal). Make sure the Mac app is running and Screen Recording is allowed.
• macOS asks again about screen recording every month: that's macOS's periodic re-confirmation for apps that capture the screen. Approve it. Known workarounds exist (for example the Amnesia app, or editing the replayd plist), but they are unsupported.
• Logs: PC: Open log folder in the Annex window or tray menu (%LOCALAPPDATA%\Annex\logs, or data\logs next to a portable Annex.exe). Mac: ~/Library/Logs/Annex/annex.log. Set ANNEX_LOG=debug for more detail.
• Reset: delete %APPDATA%\Annex\config.toml on the PC (data\config.toml for the portable copy) or ~/Library/Application Support/Annex/config.toml on the Mac and pair again.

Still stuck? Open a bug report with both logs attached.

How it works

The Mac creates a virtual display (or picks an existing one to mirror), captures it with ScreenCaptureKit, packs the pixels on the GPU with Metal and encodes HEVC with VideoToolbox. Frames travel over UDP with forward error correction and per-packet encryption, while a TCP control channel (Noise handshake, PIN pairing) handles discovery, stream setup and stats. The PC decodes with FFmpeg's D3D11VA decoder and draws full screen on the chosen monitor. The full design, including the rules every change must respect, is in docs/spec.md.

Path	What it is
crates/annex-proto	Wire format, FEC, encryption, control messages, discovery, pairing. Platform independent.
crates/annex-core	Resolution rules, mode negotiation, stats, config. Platform independent.
crates/annex-sender	Sender engine: sessions, streams, packetizing and pacing. Platform independent.
crates/annex-mac	Mac capture and encode: virtual displays, ScreenCaptureKit, Metal, VideoToolbox. Also annex-mac-cli for testing.
crates/annex-win	Windows receiver: Annex.exe, its tray menu and its window (WebView2, page in ui/).
crates/annex-testsrc	Test sender that plays pre-encoded HEVC, so the PC side can be checked without a Mac.
apps/annex-mac-app	Mac menu bar app (Tauri 2) around annex-mac.
tools/	FFmpeg build, icon generation, Windows installer and packaging, Mac release script.
docs/	Design spec, measurements, release process.

Building from source

Everything is Rust (edition 2024). The protocol, core logic and sender engine are platform independent and build anywhere:

cargo test -p annex-proto -p annex-core -p annex-sender

Windows receiver (crates/annex-win), cross-compiled from Linux (or built in MSYS2) with mingw-w64 against a trimmed, LGPL-only static FFmpeg:

sudo apt install mingw-w64 nasm
rustup target add x86_64-pc-windows-gnu
tools/ffmpeg/build-mingw.sh            # HEVC decoder + D3D11VA only
cargo build --release --target x86_64-pc-windows-gnu -p annex-win

The result is a single annex.exe that needs only system DLLs and the WebView2 Runtime (its loader DLL is built in). To make the installer and the portable zip in dist/:

sudo apt install nsis zip
tools/windows/package.sh

Mac sender (crates/annex-mac) and app (apps/annex-mac-app, Tauri 2), on an Apple silicon Mac:

cargo build --release -p annex-mac          # includes annex-mac-cli for testing
npm install -g @tauri-apps/cli@2
cd apps/annex-mac-app && tauri build --bundles dmg

Test sender (crates/annex-testsrc) plays generated HEVC test patterns to a receiver, so the PC side can be checked without a Mac:

cargo run --release -p annex-testsrc -- gen --size 1920x1080 --mode sharp --out media
cargo run --release -p annex-testsrc -- run --addr <pc-ip> --media media --pin <PIN> --enable 0

Maintainers: signing and publishing a release is described in docs/releasing.md.

Contributing

Bug reports, hardware test results, documentation and code are all welcome. Please read CONTRIBUTING.md before opening a pull request, and open an issue first for anything bigger than a bug fix. Everyone taking part is expected to follow the Code of Conduct.

Found a security problem? Please don't open a public issue; see SECURITY.md.

Licence

Annex is licensed under either of MIT or Apache-2.0, at your option. Unless you explicitly state otherwise, any contribution you intentionally submit for inclusion in Annex, as defined in the Apache-2.0 licence, is dual licensed as above, without any additional terms or conditions.

The Windows receiver statically links FFmpeg (tag n8.1.3, configured LGPL-only with just the HEVC decoder and D3D11VA; see tools/ffmpeg/build-mingw.sh), which is licensed under the LGPL 2.1 or later.