AirPlay Display — iPad as a Mac secondary display

Turns a jailbroken iPad Air 2 (iOS 15.8.8, palera1n rootful) into a wireless secondary display for a Mac, using macOS's built-in AirPlay Screen Mirroring — including "Use as Separate Display" (true extended desktop). No software on the Mac side.

It's a from-scratch AirPlay video mirroring receiver that runs on the iPad. It reuses UxPlay's C protocol/FairPlay core (libairplay.a) and adds an iOS front-end that decodes the H.264/H.265 stream with VideoToolbox and renders it full-screen via AVSampleBufferDisplayLayer.

Status: WORKING ✅

Mirror and separate-display confirmed end-to-end on real hardware.

Layout

docs/c-architecture.md      full design + milestones
src/app/                    iOS app (Obj-C): main, AppDelegate, DisplayView, Receiver
src/c-build-libairplay.sh   cross-compile UxPlay lib/ -> build/ios/libairplay.a
src/c-build-app.sh          compile+link+sign the app  -> build/ios/AirPlayDisplay.app
src/c-deploy.sh             build + push + install + relaunch on the iPad (fast iterate)
src/c-package-deb.sh        package -> build/deb/*.deb
src/c-build-repo.sh         assemble Sileo repo -> build/repo/
vendor/UxPlay/              upstream source (protocol/FairPlay core we fork)
vendor/theos/               iOS cross-compile toolchain + iPhoneOS16.5 SDK
vendor/ios-deps/            libcrypto + libplist (headers+dylibs) pulled from the iPad

Build from scratch

./src/c-build-libairplay.sh   # core static lib
./src/c-build-app.sh          # the .app
./src/c-package-deb.sh        # the .deb
./src/c-build-repo.sh         # the Sileo repo

Install on the iPad

Via the Sileo repo (while the Mac is serving it on the LAN):

1. Sileo → Sources → ＋ → http://<mac-ip>:8088/
2. Install AirPlay Display.

Or directly: dpkg -i com.wawtor.airplaydisplay_0.1_iphoneos-arm.deb

Use

1. Launch AirPlay Display on the iPad (it shows "Waiting for a Mac…").
2. On the Mac: Control Center → Screen Mirroring → "… (Display)".
3. Open Screen Mirroring again → Use as Separate Display for extended desktop.

Key implementation notes / gotchas

• raop_init2 keyfile must be "", never NULL (strlen crash in ed25519 keygen).
• raop_start_httpd returns 1 on success (negative = error), not 0.
• All 33 raop_callbacks_s fields must be non-NULL or the handshake calls a NULL pointer and crashes; report_client_request must set *admit = true.
• Video arrives as Annex-B NALs (SPS/PPS prepended to the first frame) → converted to AVCC CMSampleBuffer → AVSampleBufferDisplayLayer.
• Binaries need a platform-application entitlement (ldid -Sents.plist) or AMFI kills them (Killed: 9). A Mac-side ldid signature with entitlements is honored on-device.
• "Use as Separate Display" is offered even with the default model=AppleTV3,2 — no model spoof needed (matches UxPlay issue #58).