opendisplay

Product Introduction

1. Definition: OpenDisplay is a free, open-source software solution that transforms an iPhone, iPad, or secondary Mac into a fully functional, low-latency extended display for a primary Mac computer. It operates as a client-server application, utilizing a "Sender" app on the host Mac and a "Receiver" app on the display device.
2. Core Value Proposition: It exists to provide a cost-free, privacy-focused, and hardware-agnostic alternative to proprietary solutions like Apple Sidecar, Duet Display, and Luna Display. It solves the problem of workspace extension without requiring subscriptions, specific Apple ID matching, or proprietary hardware dongles.

Main Features

1. True Extended Display over USB & WiFi: OpenDisplay creates a virtual display on the host Mac using the CGVirtualDisplay API (similar to tools like BetterDisplay), captures it via ScreenCaptureKit, and hardware-encodes the video stream using Apple's VideoToolbox in H.264 real-time mode. This stream is sent over a direct TCP connection, either through a USB cable via usbmux for the lowest latency or over a local WiFi network using Bonjour for zero-configuration discovery.
2. Multi-Device Support & Retina Sharpness: The software supports using multiple iOS devices (e.g., an iPhone and an iPad) simultaneously as separate extended displays, which can be arranged in macOS System Settings like physical monitors. It delivers a pixel-perfect HiDPI (@2x) Retina resolution, ensuring text and UI elements are rendered with native sharpness on the external device's screen.
3. Cross-Platform Input & Privacy-Centric Design: The receiver app sends touch and multi-touch gestures (tap, drag, two-finger scroll) back to the host Mac, where they are injected as system-level mouse and trackpad events. The entire system is designed for privacy, establishing a direct peer-to-peer connection with no intermediary servers, user accounts, or telemetry data collection.

Problems Solved

1. Pain Point: The high cost and restrictive compatibility of existing second-screen solutions. Apple Sidecar is free but limited to specific Mac/iPad hardware pairs and requires both devices to share the same Apple ID. Alternatives like Duet Display require a subscription, and Luna Display necessitates a physical hardware dongle purchase.
2. Target Audience: Budget-conscious professionals (developers, designers, students), users with mixed Apple ID ecosystems (e.g., using a partner's iPad), individuals with older "spare" Macs or iOS devices, and privacy advocates who prefer open-source, auditable software.
3. Use Cases: Extending a MacBook's desktop for coding with an IDE on the main screen and documentation/terminal on an iPad; using an old iPhone in portrait mode as a dedicated monitor for a chat or messaging app; repurposing an aging MacBook as a secondary Retina display for a desktop Mac over a Thunderbolt cable.

Unique Advantages

1. Differentiation: Unlike Apple Sidecar, OpenDisplay works across different Apple IDs and supports iPhones. Unlike Duet Display, it is completely free with no subscription. Unlike Luna Display, it requires no additional hardware purchase. It is the only solution in this category that is fully open-source (GPL-3.0 licensed), allowing for public code audit and community contributions.
2. Key Innovation: Its streamlined, direct-connection architecture that leverages core Apple frameworks (CGVirtualDisplay, ScreenCaptureKit, VideoToolbox, usbmux) to achieve low-latency performance without a complex commercial backend. The ability to also use a secondary Mac as a receiver app, turning it into a high-quality wired or wireless display, is a unique and powerful feature not commonly found in other software.

Frequently Asked Questions (FAQ)

1. Is OpenDisplay really free, and how does it compare to Apple Sidecar? Yes, OpenDisplay is completely free and open-source. Compared to Apple Sidecar, OpenDisplay works across different Apple IDs, supports iPhones and older Macs as displays, and offers a wired USB mode for lower latency, but it displays the purple screen-recording indicator as it uses standard macOS capture APIs.
2. How do I use my iPad as a second monitor with OpenDisplay? To use your iPad as a second monitor, download and install the OpenDisplay Sender app on your primary Mac (macOS 14+) and the OpenDisplay Receiver app from the App Store on your iPad (iPadOS 16+). Connect the devices via USB or ensure they are on the same WiFi, then select your iPad from the dropdown in the Mac Sender app to establish the extended display.
3. Can I use an Android phone as a second monitor for my Mac with OpenDisplay? The official OpenDisplay project does not provide an Android app. However, because the protocol is open-source, third-party developers have created compatible Android receiver clients. You can find links to these community projects (like gprot42/android-opendisplay) on the OpenDisplay website, but they are unofficial and not supported by the main developer.
4. Why is there a purple screen-recording indicator when using OpenDisplay? The purple indicator is a macOS privacy feature that appears for any application using the ScreenCaptureKit API to capture the screen. This includes all third-party display mirroring apps like Duet Display, OBS, and Zoom. Only built-in system features like Apple Sidecar are exempt from this indicator.
5. What are the system requirements for OpenDisplay? The Sender app requires macOS 14 Sonoma or later on the primary Mac. The iOS/iPadOS Receiver requires iOS/iPadOS 16 or later. To use an older Mac as a display via the Mac Receiver app, it needs macOS 12 Monterey or later. A USB-C/Lightning cable is recommended for the best performance.