Tab Display

Use an Android tablet as a wired, low-latency second display for your Mac, with pen and touch.

_{Download the Mac app (DMG) and tablet app (APK) · Getting started}

Tab Display is a Sidecar-style extended display for Android tablets. A menu bar app on the Mac creates a virtual display, streams it over a USB cable with hardware HEVC encoding, and the tablet decodes it in hardware and shows it pixel-for-pixel. Stylus and touch input go back over the same cable.

Features

• Extended desktop over USB. No Wi‑Fi and no developer mode. Plug in, and the tablet becomes a second display.
• Retina sharp. HiDPI at the tablet's native resolution (Sharpest is exact 2×, or choose More/Most space). Text is sharpened when the screen goes idle.
• Stylus with pressure and tilt. Hover moves the pointer, and the side button right-clicks. It works in pressure-aware apps.
• Touch. One- and two-finger scrolling with momentum, tap to click, two-finger tap to right-click.
• Any orientation. Rotate the tablet and the Mac's display reshapes in place. Split-screen works too.
• Hardware all the way. ScreenCaptureKit → VideoToolbox HEVC → USB → MediaCodec, with no CPU pixel copies. About 26 ms average from the Mac compositing a frame to it reaching the tablet's screen (details).
• Installs its own tablet app. The Mac app bundles the Android app and can install or update it over USB.
• Not tied to one tablet. The tablet reports its resolution, size, refresh rate and decoders, and the Mac adapts. Tested on a Galaxy Tab S9 and a Galaxy Tab S6 Lite.

The Mac menu: status, live latency, display size, quality

The tablet explains what to do when it isn't connected

Getting started

Requirements: a Mac with Apple silicon on macOS 14 or later; an Android 14+ tablet with a hardware HEVC or H.264 decoder; a USB‑C cable that carries data.

1. Download TabDisplay-<version>.dmg from the latest release and drag Tab Display to Applications. The first time, macOS blocks it because the build isn't notarized yet: open System Settings › Privacy & Security and click Open Anyway.
2. Grant Screen Recording and Accessibility when asked, then quit and reopen Tab Display.
3. Install the tablet app, either:
   • from the Mac: turn on USB debugging on the tablet, plug it in, open the Tab Display menu and click Install; or
   • by sideloading TabDisplay-<version>.apk from the same release onto the tablet.
4. Plug the tablet in, then click Connect next to it in the menu. On the tablet, tick "Always open Tab Display" and tap OK. From then on it connects automatically whenever you plug it in.

On the tablet, a three-finger tap toggles a latency HUD. The Mac menu's Advanced section has the refresh rate, idle text sharpening and a live latency chart with CSV export.

macOS shows its purple screen-recording indicator while the tablet is connected, because Tab Display captures its virtual display with ScreenCaptureKit.

How it works

Mac                                                      Tablet
CGVirtualDisplay → ScreenCaptureKit (NV12, GPU) ──┐
                   VideoToolbox HEVC (hardware) ──┤  USB (Android Open Accessory, ~80 MB/s)
                                                  └──────────────► MediaCodec (hardware) → SurfaceView
CGEvent tablet/mouse/scroll injection ◄──────────────────────────── stylus & touch (unbuffered)

• Virtual display: the private CGVirtualDisplay API (as used by DeskPad), in HiDPI modes derived from the tablet's panel.
• Transport: Android Open Accessory over USB bulk endpoints, through a small framed protocol (protocol/spec.md). It reconnects on replug, sleep/wake and app restarts.
• Latency: the stream never queues. While the encoder is busy, only the newest frame is kept, and the tablet presents each frame the moment it's decoded. Every stage is timestamped on a shared clock (shown in the HUD and the latency window).

Measurements on an M3 MacBook Air with a Galaxy Tab S9, design decisions and experiments are in docs/RESULTS.md.

Building

cd mac && ./build.sh --install     # builds and bundles the Android app, then installs Tab Display.app

Needs the Xcode Command Line Tools, the Android SDK (platform 36, NDK 26.1) and JDK 17. See docs/DEVELOPMENT.md for the full build, signing and notarization, Play publishing, and the test and measurement tools.

Privacy

No accounts, no analytics, no internet access: everything stays on the USB cable between your Mac and your tablet. See PRIVACY.md.

Acknowledgements

• libusb (LGPL-2.1), bundled as a replaceable dynamic library.
• DeskPad (MIT) for documenting the CGVirtualDisplay API.
• The AOSP adb protocol and Android Open Accessory documentation.