AA Suite

Screen mirroring, a web browser and YouTube's TV interface on your car's Android Auto display.

🇮🇹 Leggi in italiano

Android Auto gives you maps, music and messages. AA Suite adds the three things it deliberately leaves out: your phone's screen, a real web browser, and YouTube in TV mode, which a passenger can drive from their own phone with the ordinary cast button.

It works by registering as a navigation car app — the only category granted ACCESS_SURFACE — and then drawing whatever it likes on the car's surface.

Important

Personal use. This app cannot be published on the Play Store: mirroring a phone screen and showing web content on the car display are both outside what Play's Android Auto policies allow for public distribution. It is installed through Play Console's internal testing track. See Distribution.

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Contents

• The car menu
• The three modes
• Sharing a link from a second phone
• Settings
• Architecture
• Requirements
• Building
• One-time phone setup
• Running without a car
• Distribution
• Testing
• Known limitations
• License

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The car menu

Grid (default)	List

The layout is a preference, switched from the Settings screen behind the ⚙ action in the top right.

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The three modes

Screen mirroring

Puts the phone's screen on the car display.

• MediaProjection feeds a VirtualDisplay that writes straight onto the car's surface, with nothing in between
• Taps and swipes made on the car display are mapped back into phone coordinates and replayed as real gestures through an accessibility service
• Action bar: menu · play/pause · back · home
• Two renderings: aspect-fit (whole screen, black bars) or fill screen (center-crop, edges trimmed)
• The phone's brightness can drop to its minimum while mirroring — the car display is unaffected, the battery is not

Web browser

A genuine browser rendered on the car display.

• A WebView lives on a private VirtualDisplay shown through a Presentation, backed by the car surface
• Car taps become MotionEvents dispatched into the view hierarchy
• Bookmarks are edited on the phone and browsed from the car
• Google search or a direct URL from the car's search screen
• A page can also be pushed from the phone to the car display with one tap

YouTube Cast

The phone connected to the car behaves like a YouTube smart TV.

• Loads youtube.com/tv behind a smart-TV user agent, which serves the leanback interface
• The car display is narrower than a TV, so the WebView zooms out until the page has a 1280px viewport to lay itself out in, instead of being squeezed
• Pair once: on the car, Settings → Link with TV code; on the passenger's phone, YouTube → Watch on TV → enter the code. It goes over the internet, so no shared network is needed, and it survives restarts in the WebView's cookies
• From then on the passenger's cast button sends videos to the car
• Audio comes out of the car speakers through Android Auto itself

Note

Out of reach: acting as a receiver for Netflix, Disney+ or Prime Video. Those apps only talk to certified Chromecast receivers with hardware DRM — no third-party app can stand in for one.

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Sharing a link from a second phone

A passenger can send any link to the car display through Android's ordinary share sheet.

sequenceDiagram
    participant P as Passenger's phone (AA Share)
    participant C as Car phone (ShareServer :8977)
    participant D as Car display
    P->>C: POST /open — shared text
    Note over C: first URL extracted
    C->>D: open in the car browser
    C-->>P: 200 OK / 400 no URL found

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• AA Share (the companion/ module) is a minimal app that appears in the share sheet and posts the text to the car phone
• The destination is the network's DHCP gateway — the intended setup is the car phone's hotspot
• On the car side ShareServer is a bare-sockets HTTP server, alive for as long as the Android Auto session, which pulls the first URL out of the text and opens it in the car browser

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Settings

Behind the ⚙ action on the main menu:

Setting	What it does
Menu layout	Grid or list
Landscape rotation lock	Forces the phone into landscape through an invisible overlay window — useful while mirroring
Fill screen	Center-crops the mirrored screen; in the web modes it crops the video to cover the whole display

Layout and fill-screen persist across restarts. The rotation lock is volatile by nature: it reflects whether the overlay is currently up.

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Architecture

graph TD
    Host["Android Auto host (car display)"] -->|surface + input| Router[SurfaceRouter]
    Router --> Mirror[MirrorScreen]
    Router --> Web["WebSink (browser, YouTube)"]
    Mirror --> Service["MirrorService — MediaProjection"]
    Mirror --> A11y["Accessibility service — taps and swipes"]
    Web --> Display["WebDisplay — VirtualDisplay + Presentation + WebView"]
    Share["ShareServer :8977"] --> Display
    Companion["AA Share (second phone)"] -->|POST /open| Share

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Exactly one SurfaceCallback is registered per session: SurfaceRouter owns it and swaps the active mode underneath, because the host does not re-deliver onSurfaceAvailable when the callback changes.

Modules

Module	Contents
app/	The main app, installed on the phone that plugs into the car
companion/	AA Share, for the passenger's phone

Packages

Package	Responsibility
core/	Pure, testable logic: aspect fit/fill maths, touch mapping, scroll gesture path, web viewport, URL resolution, mirror state reducer
mirror/	Foreground service, MediaProjection, the FrameSource abstraction, fill rendering
car/	Car App Library screens and the surface arbiter
browser/	WebDisplay: a WebView on a virtual display, with touch, scrolling and back
input/	Accessibility (tap, swipe, back, home), media keys, rotation lock, brightness saver
share/	The share HTTP server and parsing of the received text
setup/	Phone-side setup activity, bookmarks, preferences

Three things worth knowing

Scrolling is a finger, not a scrollBy. The host reports scrolling as a stream of small distances. Replaying each one through WebView.scrollBy() moves only the root document, which a modern page never scrolls — its content sits in containers with their own overflow. AA Suite folds them into one real drag instead: ACTION_DOWN at the centre, a trail of ACTION_MOVE, and the finger lifts 140 ms after the last event. That scrolls whatever container is under it.

The virtual display cannot outgrow the surface. The host paints the buffer pixel for pixel, so a VirtualDisplay larger than the surface produces a magnified crop, not more room. To give a TV page the wide viewport it expects you change the WebView's zoom, not the display's resolution.

A TV's back button is not the browser history. YouTube's TV interface routes navigation itself and leaves the WebView history empty, so goBack() has nowhere to go. Back reaches it as a keydown carrying the remote back-key codes (Escape, webOS, Tizen), injected through JavaScript — a native key event would need the WebView to hold the focus, which it never does inside a Presentation.

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Requirements

• Android 8+ phone (minSdk 26), 10+ recommended
• The Android Auto app installed on the phone
• A car or head unit with Android Auto over USB — developed and tested against a Nissan Qashqai J12 and the Desktop Head Unit

Building

./gradlew installDebug             # main app, phone in USB debugging
./gradlew :companion:installDebug  # AA Share, on the passenger's phone
./gradlew test                     # unit tests
./gradlew bundleRelease            # signed AAB for Play Console

Release signing reads keystore/keystore.properties and its keystore, both kept out of version control; without them the signing config is simply skipped and debug builds still work.

One-time phone setup

1. Android Auto app → Settings → tap Version ten times to unlock developer mode
2. ⋮ → Developer settings → enable Unknown sources (required for builds installed over adb)
3. Settings → Customise launcher → enable AA Suite
4. Open AA Suite on the phone and grant: screen capture, the accessibility service, and "Display over other apps"

Running without a car

# Android Studio → SDK Manager → SDK Tools → Android Auto Desktop Head Unit
# On the phone: Android Auto → Developer settings → Start head unit server
adb forward tcp:5277 tcp:5277
"$LOCALAPPDATA/Android/Sdk/extras/google/auto/desktop-head-unit.exe"

Order matters: the phone's server must already be listening when the DHU starts, or it sits on Waiting for phone. A ~/.android/headunit.ini pins the emulated display's resolution, which is worth setting before taking screenshots.

Distribution

Template-based Android Auto apps do not appear on real cars unless they were installed from the Play Store, even with unknown sources enabled. Testing in an actual car therefore means uploading the AAB to Play Console's internal testing track and installing from there.

Testing

Unit tests cover the pure logic in core/, with no Android dependencies: fit and fill geometry, car-to-phone touch mapping, the scroll gesture path, web viewport zoom, the mirror state reducer, shared-URL parsing, bookmark encoding, and the share server's HTTP handling.

./gradlew test

Known limitations

• YouTube Cast, back button: it takes two presses to leave a video — the cause has not been isolated yet
• 16:9 video on a 2:1 display: side bars remain unless fill screen is on, which crops the picture in exchange
• Receiving casts from Netflix, Disney+, Prime Video: impossible by licensing and DRM, not a bug waiting to be fixed

License

MIT © 2026 iAlias