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A free, open-source second monitor for Windows.
Connect your iPad over Wi-Fi or USB, with touch and Apple Pencil support.
Download · Setup guide · Website · Roadmap · Release notes · Discord
EternalMonitor turns an iPad into a monitor for your Windows PC. It is free, open source under the MIT license, and needs no account. The PC streams at up to 120 fps, with hardware encoding on supported graphics cards and hardware decoding on the iPad, and every tap, keystroke and Pencil stroke goes back to the PC.
- Install the Windows app. Run EternalMonitor-Setup.exe on Windows 10 (version 1809 or later) or Windows 11, 64-bit, with NVIDIA, AMD or Intel graphics. If Windows SmartScreen asks, choose More info, then Run anyway. The release page lists the file's SHA-256.
- Install the iPad app. On an iPad with iPadOS 17 or later, install TestFlight from the App Store, then open the EternalMonitor TestFlight link on the iPad and tap Install.
- Connect. With both apps open on the same network, tap your PC on the iPad or scan the QR code the PC shows. For USB, on Windows 10 22H2 or Windows 11, plug in the cable and keep Apple's free Apple Devices app open on the PC.
The setup guide walks through every step with the exact button names. The download page lists the Windows and iPad versions that go together.
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- Extend or mirror. Add the iPad as a second display beside your monitor, or mirror any screen you have. The second display stays for 10 seconds after the iPad disconnects, so a quick reconnect reuses it and Windows never keeps a phantom monitor around.
- Wi-Fi or USB. Stream over your home network, or plug in a cable for a steadier picture that can also charge the iPad from a USB-C port. A cable takes over a running Wi-Fi session, and unplugging it falls back to Wi-Fi.
- Apple Pencil as a real pen. Windows receives Windows Ink pressure and tilt, and the pen lands under the tip on any monitor layout. Drawing mode ignores your palm on the canvas, and Clip Studio Paint works with its Tablet PC setting.
- Touch, keyboard and pointer. Tap to click, drag, scroll with two fingers and hold to right-click. Hardware keyboards, trackpads and mice work too, with sticky modifiers and middle-click.
- Hardware encoding. Supported NVIDIA, AMD and Intel graphics encode the stream at 30, 60, 90 or 120 fps.
- Loss repair on Wi-Fi. When a packet goes missing, the iPad asks for it again right away, so one dropped packet rarely costs a frame. The bitrate follows your network.
- PC audio. Sound plays on the iPad, and you can mute it without stopping the video.
- Fit or fill. Fit shows the whole PC picture, with bars where the shapes differ. Fill uses the iPad's entire screen and trims the edges that don't fit.
- Pairing. The first Wi-Fi connection asks for a six-digit code or a QR scan. After that the iPad remembers the PC. USB needs no code.
- Recovers and explains. The picture comes back by itself after the lock screen, a display change or a stream restart. Both apps say what happened and what to do, and Send feedback writes an email to the studio with your setup filled in.
- Updates in one click. A popup tells you when a new version is out. On Windows, Update now checks the download and installs it with one Windows prompt; on the iPad, it opens TestFlight. The Windows app runs without a console window.
This README and the website are available in 11 languages.
- Use an iPad as a second monitor for Windows: the full guide.
- Compatibility: PCs and iPads people run EternalMonitor on.
- Alternatives: how EternalMonitor compares with other ways to use an iPad as a screen.
- Roadmap: what is coming next.
Share your setup. Tell us which PC and iPad you use with the compatibility report, or post it on the Sideband Discord. With your permission, it goes on the compatibility page.
The current release is v0.3.3 for Windows, with v0.3.3 (build 364) for the iPad. It brings Second screen to more laptops with Intel and NVIDIA graphics: the iPad shows the PC's main screen right away, then switches to the second screen once Windows adds it. RELEASE_NOTES.md covers every version, and ROADMAP.md what comes next.
The v0.3.3 release checks passed on Windows, macOS and iPad simulators, and docs/hardware-verification.md records hands-on results on a real PC and iPad from v0.3.0.
Both apps share diagnostics so problems can be found and fixed: device details, app errors and stream statistics, including PC and iPad names, audio device names and network addresses. Diagnostics never include screen content, audio or pairing credentials. Turn sharing off in Settings. Automatic diagnostics and the privacy notice list exactly what is sent and how long it is kept. On iPad, open Settings > Support > Diagnostics to copy or export a report.
The Windows host is written in Rust. It captures the desktop with DXGI, encodes through FFmpeg with NVIDIA NVENC, AMD AMF or Intel Quick Sync on supported graphics hardware (H.264 by default, or HEVC), and sends each frame as numbered UDP fragments. Over USB the same messages travel through a framed tunnel that Apple's device service provides. The iPad app is native Swift. It reassembles fragments, decodes with VideoToolbox and renders with Metal. On Wi-Fi it also requests any fragments that are missing. PC audio is captured with WASAPI and sent as Opus; the iPad plays it through a jitter buffer and conceals lost audio instead of requesting it again. Input and receiver reports go back on the same session, and the host uses those reports to adapt the bitrate between 4 and 50 Mbps.
ARCHITECTURE.md describes the pipeline and protocol v2, and docs/decisions.md explains why each part works the way it does.
The workspace holds the Rust host (host/), the protocol crate eternal-wire
(proto/) and the Swift iPad app (ios/).
Windows host
Requirements: Windows 10 version 1809 or later, Rust 1.98.0 (pinned by
rust-toolchain.toml, MSVC), an FFmpeg 7.1 shared SDK and LLVM/libclang for
bindgen.
# Point the build at your FFmpeg 7.1 shared SDK (the folder with bin\avcodec-*.dll)
$env:FFMPEG_DIR = "C:\ffmpeg"
cargo build --release -p eternal-host
.\target\release\eternal-host.exe # optional port argument, default 9876The host is a Windows GUI program, so it opens no console window. Started
from a terminal it prints its log there, but the prompt returns at once;
cargo run -p eternal-host waits for it. With ETERNAL_HEADLESS=1 and output
redirected (> host.log) it gets its own console, so Ctrl+C in the terminal
can't reach it: press Ctrl+C in that console's window, or use Task Manager.
scripts\win\Stop-Host.ps1 stops the hosts that remote.sh run-host started and
leaves any others running.
scripts\build-installer.ps1 builds the full Setup.exe with Inno Setup and the
same FFMPEG_DIR. scripts\package.ps1 builds a bare zip.
macOS development loop (no Windows needed)
On macOS the host swaps screen capture for a synthetic test pattern. The protocol, encoder, transport and supervisor all run for real.
brew install ffmpeg@7 pkgconf xcodegen
export PKG_CONFIG_PATH=/opt/homebrew/opt/ffmpeg@7/lib/pkgconfig
cargo test --workspace # unit, golden-vector and synthetic end-to-end tests
ETERNAL_CAPTURE=synthetic cargo run -p eternal-hostIf Xcode's command-line tools are the selected developer directory, prefix Xcode
commands with DEVELOPER_DIR=/Applications/Xcode.app/Contents/Developer.
iPad app
cd ios
xcodegen generate # project.yml is the source of truth
xcodebuild test -project EternalMonitor.xcodeproj -scheme EternalMonitor \
-destination 'platform=iOS Simulator,name=iPad Pro 11-inch (M4)'To run on a physical iPad, open the generated project in Xcode and pick your own signing team.
End-to-end tests
./scripts/e2e_ios.sh # synthetic host to the iPad simulator, H.264
EM_CODEC=hevc ./scripts/e2e_ios.sh
scripts/test_ios.sh # iPad unit and UI tests
scripts/e2e_matrix.sh # UDP, loss, burst, USB, audio, pairing, input, lifecycle
scripts/soak.sh 1800 # 30-minute frame-rate and memory checkEach row checks the decoded frame rate (at least 55 fps), drops, repairs and the
rendered pixels. e2e_matrix.sh --real runs the Windows hardware rows through the
runner in scripts/win/; read scripts/win/README.md
first. CI runs the Rust suites on Linux, macOS and Windows, the iPad tests and a
streaming system test on every pull request.
Host environment variables
| Variable | Effect |
|---|---|
ETERNAL_ENCODER |
Force an encoder (h264_nvenc, h264_amf, h264_qsv, libx264) |
ETERNAL_HEVC |
1 or 0 overrides the HEVC preference |
ETERNAL_FPS |
Override the host frame rate; the iPad's preference still caps it |
ETERNAL_INPUT |
Encoder input: yuv420 (default), auto or bgra |
ETERNAL_MAX_DGRAM |
Media datagram size, 576 to 1400 bytes |
ETERNAL_CAPTURE |
synthetic swaps DXGI for a generated test pattern |
ETERNAL_AUDIO |
synthetic selects the deterministic audio test source |
ETERNAL_HEADLESS |
1 runs without the window; Ctrl+C shuts down cleanly |
ETERNAL_ABR |
0 disables adaptive bitrate |
ETERNAL_VDD_TIMEOUT_SECS |
How long to wait for the virtual display to attach (default 30) |
ETERNAL_AMF_DIAG |
1 writes AMF bitstream diagnostics |
ETERNAL_LEGACY_PTS |
1 restores the old frame-counter timestamps |
ETERNAL_DROP, ETERNAL_REORDER, ETERNAL_JITTER_MS |
Test only: inject loss, reordering or jitter |
ETERNAL_USB_DIRECT |
Test only: a TCP endpoint in place of the USB tunnel |
| Document | What it covers |
|---|---|
| SETUP.md | Step-by-step setup for anyone, including USB and drawing |
| Known issues | Problems we know about, and what to do about each (docs/known-issues.html) |
| Privacy | What the apps send, why, how long it is kept and how to turn it off (docs/privacy.html) |
| ARCHITECTURE.md | The pipeline, protocol v2 and each component |
| docs/decisions.md | Why things are the way they are, with measurements |
| docs/pencil-drawing.md | Apple Pencil, Windows Ink and Clip Studio Paint |
| docs/pairing.md, docs/keyboard-input.md, docs/host-settings.md, docs/audio-codec.md | Feature details |
| docs/hardware-verification.md | The release test record and the hands-on checklist |
| Release testing | Shipping a build through TestFlight: signing and what to test |
| docs/design.md | The shared look of the apps and the website |
| RELEASE_NOTES.md | What changed in each version |
| ROADMAP.md | What is coming next |
Contributions of every kind are welcome: issues, ideas, fixes, docs, translations and new features. Pull requests are welcome, big or small. CONTRIBUTING.md explains how to send one and lists good first contributions, and ROADMAP.md shows the larger work ahead. Questions and ideas are welcome on the Sideband Discord.
The Sideband Discord is the place for questions, setup help and ideas. You can also email hello@sideband.studio.
Found a bug? Open an issue with both app versions and the host log, or use the feedback form on the download page, which emails the studio. Report security problems privately as described in SECURITY.md, not on Discord or in an issue.
EternalMonitor is released under the MIT License, © 2026 Sideband Studio. The Windows installer also ships third-party components under their own licenses, including the Virtual Display Driver and FFmpeg.
Built by Sideband Studio.