Open Android Auto

An open-source implementation of the Android Auto phone-side app. This app runs on your phone and projects to a car's head unit over USB, replacing Google's proprietary com.google.android.projection.gearhead APK.

⚠️ WORK IN PROGRESS

This project is in early development. The protocol handshake and video projection are working with a real head unit. The phone screen is successfully displayed on the car's head unit for several seconds before disconnecting (video stability is being improved).

Features

Protocol & Connection

Video Projection

Touch Input

Input channel open and binding request
Touch event parsing (single and multi-touch)
Key event parsing (buttons, media keys)
Coordinate mapping (head unit → phone resolution)
TouchInjector with MotionEvent creation
Inject touch events into VirtualDisplay
Key event injection into Android system

Audio

Audio channel open and setup
Wait for audio focus grant before sending audio (500ms timeout per HUIG)
Send AUDIO_FOCUS RELEASE on initial connect, then GAIN when playing
Phone audio capture (MediaProjection AudioPlaybackCapture)
PCM/AAC encoding and streaming to head unit
Microphone input from head unit (voice commands)
Multiple audio channels (media, system, speech, guidance)
Audio silence streaming to keep channel active

Sensors

Video (additional)

Resolution negotiation from head unit's service discovery
Adaptive bitrate based on connection quality
Support for 720p, 1080p, 1440p, 4K resolutions
Portrait mode resolutions (720x1280, 1080x1920, etc.)
UI config updates (theme, insets)

Other

⚠️ DISCLAIMER

USE AT YOUR OWN RISK. This software is provided "as is", without warranty of any kind.

This software may cause unexpected behaviour with your car's head unit
This software may damage your phone or head unit — the authors accept no liability
DO NOT use this application while driving
DO NOT interact with this application while operating a vehicle
This application is intended for development and testing purposes only
Always pull over and stop your vehicle before interacting with any phone application
The authors are not responsible for any accidents, injuries, or damages resulting from the use of this software

Architecture

USB Plug-in → MainActivity → ProjectionService
                                    ↓
                    UsbAoaTransport (USB AOA accessory mode)
                                    ↓
                    MessageFramer (16KB frame fragmentation)
                                    ↓
                    InBandTls (TLSv1.2 via SSLEngine)
                                    ↓
                    ProtocolEngine (AAP state machine)
                                    ↓
                    ┌───────────┼───────────┐
                 Video      Input       Audio
                (H.264)   (touch/keys)  (PCM)

Known Bugs

Channel assignment assumes order — We assign the first av_channel in SERVICE_DISCOVERY_RESPONSE as video and the second as audio. This works with the car head unit (channel 1 = video) but fails with openauto (channel 4 = audio, not video). Fix: parse the stream_type field inside av_channel to distinguish VIDEO(3) from AUDIO(1).
Video stability — OPEN. The AUTH_COMPLETE fix (2026-05-30) resolved the idle disconnect, but video streaming still causes the HU to abruptly stop all communication and then physically drop USB power (VBUS) after a variable 9-240s. Disconnect is inconsistent (5 KB/s fails, 170 KB/s lasts longer), so it is not bandwidth or flow control. Full evidence, ruled-out causes and open hypotheses in docs/connection-stability.md (formerly bugfix.md).
Duplicate device listing on head unit — The head unit's smartphone page shows our app as two separate entries (one for Android Auto, one for Bluetooth) instead of a single entry with both capabilities. This is caused by Android 12+ blocking access to the real Bluetooth MAC address (returns 02:00:00:00:00:00). Workaround: write the real address to a config file via adb shell "echo $(adb shell settings get secure bluetooth_address) > /sdcard/Android/data/org.openandroidauto/files/bt_address.txt". Need a UI settings screen to let the user enter their BT MAC manually.
Voice assistant button not handled — When the driver presses the voice/assistant button on the head unit, we receive a VOICE_SESSION_REQUEST and attempt to launch a voice assistant (Dicio or system default). However, the launched assistant doesn't receive audio from the head unit's microphone yet.

Video Stability Test Results

Test pattern (color bars) at 800x480, I-frame interval 1 second:

AndroidAuto

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