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

• USB AOA accessory mode detection and connection
• TLS 1.2 mutual authentication (phone as server)
• Version negotiation (protocol v1.7)
• Service discovery (request/response)
• Channel open on target channels (video, audio, input, sensor)
• Ping/pong keepalive (bidirectional)
• Audio focus request/response handling
• Navigation focus request/response handling
• Voice session request handling
• Graceful shutdown handling
• Priority write queue (control messages over video)
• Wait for audio focus grant before sending audio (500ms timeout per HUIG)
• Bluetooth pairing exchange (BluetoothPairingRequest/Response)
• Handle multiple USB reconnections without AOAP re-init

Video Projection

• H.264 encoding via MediaCodec (800x480 @ 30fps, Baseline profile)
• MediaProjection screen capture (with user permission dialog)
• Video channel setup (SETUP → CONFIG → FOCUS → START flow)
• Zero-based timestamps in microseconds
• SPS/PPS prepended to keyframes (Annex B format)
• Flow control (max_unacked tracking, backpressure)
• Frame pacing (consistent 33ms intervals)
• Stable long-running video (30+ minutes confirmed)
• Resolution negotiation from head unit's service discovery
• Adaptive bitrate based on connection quality

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

• Sensor channel open
• Sensor start request/response handling
• Night mode data parsing and sending
• Driving status data parsing and sending
• GPS location forwarding
• Compass heading
• Car speed
• RPM
• Odometer (total + trip mileage)
• Fuel level and range
• Parking brake state
• Gear position (P/R/N/D/1-10)
• OBD-II diagnostics
• Environment (temperature, pressure, rain)
• HVAC (target/current temperature)
• Dead reckoning
• Passenger presence
• Door state (hood, boot, individual doors)
• Light state (headlights, indicators, hazards)
• Tire pressure
• Accelerometer (3-axis)
• Gyroscope (3-axis)
• GPS satellite data
• Respond to head unit sensor requests proactively

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

• Bluetooth pairing coordination (A2DP, HFP)
• Navigation turn-by-turn to instrument cluster
• Navigation state (maneuvers, lanes, distances, current position)
• Media status (now playing info)
• Media playback metadata (track, artist, album)
• Media browser (browse phone media library from head unit)
• Phone status (call state notifications)
• Generic notifications (subscribe/unsubscribe system)
• Vendor extensions
• Wireless Android Auto (WiFi + Bluetooth handoff)
• Channel close notification
• Car connected devices request/response
• User switch request/response
• Battery status notification
• Call availability status
• Service discovery update (dynamic channel changes)
• Input feedback (haptic/visual feedback to head unit)
• Microphone request/response (voice input from head unit)
• Audio underflow notification
• Radio service (AM/FM/HD/DAB tuning, presets, RDS)

⚠️ 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 — Connection drops after extended streaming due to head unit USB buffer overflow. FIXED (2026-05-30): Root cause was sending AUTH_COMPLETE back to the HU, which triggered an internal error state. Connection now stable for 30+ minutes with video. See bugfix.md for details.
• 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: