Spanscreen

Use your iPhone as a second display for your Mac. Extend or mirror over Wi-Fi or a USB cable.
Built for iPhone Duo, works on every iPhone and iPad. Free and open source.

App Store · Download for Mac · Website

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Features

• Extend or mirror. Spanscreen adds a real display to macOS. Arrange it in System Settings like any monitor, or mirror your main screen.
• Retina sharp. The virtual display matches the iPhone's pixels one to one. Pick Larger, Default, More Space or Most Space.
• Wi-Fi, peer-to-peer or cable. Same network, no network at all (Apple Wireless Direct Link), or a USB cable for the lowest latency. Plug in while streaming over Wi-Fi and Spanscreen switches to the cable by itself.
• Low latency. Hardware HEVC encoding with low-latency rate control, hardware decoding and no buffering on either side. The Mac adapts the bitrate to the link and shows the measured latency.
• ProMotion. Up to 120 Hz on iPhones that support it.
• Touch and trackpad. Tap to click, hold to right-click, drag, two-finger scroll with momentum. Or switch to trackpad mode for precise pointer control. Hardware keyboards work too.
• Made for iPhone Duo. Fold or unfold and the Mac display follows: the cover screen and the large inner screen each get their own native resolution. Rotate to get a portrait display.
• Private. No account, no cloud, no tracking. The picture travels only over your local network or cable.

How it works

Mac (menu bar app)	iPhone / iPad
Creates a virtual display (CGVirtualDisplay) in the phone's resolution	Advertises itself over Bonjour (_spanscreen._tcp) and listens on TCP 47913
Captures it with ScreenCaptureKit	Decodes with AVSampleBufferDisplayLayer and shows frames immediately
Encodes HEVC with VideoToolbox (low-latency rate control, no frame reordering)	Acknowledges every frame so the Mac can measure latency and back off
Streams over TCP, or over USB through usbmuxd	Sends touch, scroll and keyboard input back
Injects input with CGEvent	Reports fold, unfold and rotation so the Mac can resize the display

The protocol lives in Packages/SpanscreenKit and is shared by both apps.

Requirements

• Mac with macOS 14 Sonoma or later (Apple silicon or Intel with a hardware HEVC encoder)
• iPhone or iPad with iOS 17 or later

Install

1. Download Spanscreen for Mac, drag it to Applications and open it. It lives in the menu bar.
2. Allow Screen Recording (to show the display on the iPhone) and Accessibility (to click with touch).
3. Install Spanscreen for iPhone and open it on the same Wi-Fi or connect the cable.
4. Choose your iPhone in the Mac menu bar, or tap your Mac on the iPhone. The first Wi-Fi connection asks for approval on the iPhone. After that, it connects by itself.

Build from source

brew install xcodegen
xcodegen generate
open Spanscreen.xcodeproj

Run the SpanscreenMac scheme on your Mac and SpanscreenIOS on your iPhone. Protocol tests:

swift test --package-path Packages/SpanscreenKit

Releases

Pushing a tag like v1.0.1 runs release.yml:

• Mac: archives with the Developer ID certificate, notarizes and staples the app and the DMG, and attaches Spanscreen.dmg to the GitHub release.
• iOS: archives with the App Store profile and uploads the build to App Store Connect.

Required repository secrets: APPLE_TEAM_ID, MAC_CERTIFICATE_P12, MAC_CERTIFICATE_PASSWORD, IOS_CERTIFICATE_P12, IOS_CERTIFICATE_PASSWORD, IOS_PROVISIONING_PROFILE, ASC_KEY_ID, ASC_ISSUER_ID, ASC_KEY_P8, KEYCHAIN_PASSWORD.

License

MIT, see LICENSE. Made by Codext.