Speed Volume

Speed Volume is an Android app that adjusts STREAM_MUSIC volume from the device's current speed. It is designed for driving and supports a walking or running fallback when GPS temporarily has no fresh fix.

The app runs as a location foreground service. It is not a replacement for a vehicle's safety systems, and it cannot make GPS work indoors, inside tunnels, or when the phone manufacturer stops background execution.

What it does

• Maps filtered speed to media volume with a responsive square-root curve.
• Uses GPS as the authoritative source for vehicle speed.
• Falls back to step cadence and a calibrated stride for walking/running when GPS has been stale for more than five seconds.
• Smooths noisy GPS using a standstill deadband, acceleration rejection, displacement cross-checking, median filtering, and adaptive EMA smoothing.
• Moves volume toward its target every 50 ms and detects OEMs that silently refuse volume changes.
• Provides an ongoing notification, a Quick Settings tile, and a live status screen.
• Recovers location requests after screen lock or Doze when callbacks become stale, subject to device and OEM policy.

How the engine works

GPS fixes (500 ms) ──┐
                     ├─ source-aware filter ── speed ── curve ── target volume
step detector ───────┘                              └─ exponential volume ramp

1. SpeedVolumeService promotes itself to a location foreground service and requests GPS_PROVIDER updates every 500 ms.
2. SpeedFilter treats speeds below 3 km/h as stationary, rejects samples implying more than 12 m/s² acceleration, cross-checks weak fixes against displacement speed, then applies median-of-3 and adaptive EMA smoothing.
3. If the last GPS fix is older than five seconds, SensorMotion estimates walking/running speed from recent step cadence. The estimate is capped at 18 km/h and is not intended to replace GPS for driving.
4. GPS-verified walking or running calibrates stride length gradually. The filter history is reset whenever the source changes, so stale GPS speed does not bleed into a motion estimate.
5. Speed is mapped between the configured standstill volume and full volume. The default full-volume threshold is 80 km/h; the default standstill level is approximately 15% of the media stream's maximum.
6. VolumeRamp approaches the target exponentially and reports the actual stream level back to the activity, tile, and notification.

Reliable setup for a locked screen

Android and phone manufacturers restrict background work. Complete all of the following on the test device:

1. Open Speed Volume and grant precise location.
2. Grant Allow all the time location access. This app requires it for its Quick Settings and locked-screen workflow.
3. Grant notifications on Android 13 and newer. The ongoing notification is how Android recognizes and exposes the foreground service.
4. Set the app's battery usage to Unrestricted or disable battery optimization for it.
5. Enable the manufacturer's Auto-start, Allow background activity, or equivalent setting. Common battery killers include ColorOS, MIUI, EMUI, One UI power saving, and aggressive third-party task managers.
6. Start tracking once while the app is visibly open. Confirm that the ongoing Speed Volume active notification appears before locking the phone.
7. Lock the phone and test in an open-sky location. GPS speed needs a usable satellite fix; the step fallback is for pedestrians, not vehicles.

Android's foreground-service and background-location rules change across API levels. See the official guidance for foreground-service background starts and background location.

If the service still stops only on one phone model, that is usually an OEM power-management policy. The app can re-register its location request, but it cannot override a manufacturer force-stop or task-killer policy.

Permissions and device access

Permission or setting	Purpose
Fine location	GPS speed and displacement
Background location	Locked-screen and Quick Settings operation
Notifications	Visible foreground-service notification on Android 13+
Modify audio settings	Adjusts the STREAM_MUSIC volume
Battery optimization exemption	Prevents OEM/Doze termination where supported
Step detector hardware	Optional walking/running fallback; no permission is required

Quick Settings tile

Add Speed Volume from the notification shade's tile editor. Alternatively, on a connected development device:

adb shell cmd statusbar add-tile \
  com.example.speedvolume/com.example.speedvolume.SpeedVolumeTile

The tile starts and stops the service. If required permissions are missing, it tells you to open the app and complete setup. Long-pressing the tile opens the app.

Build, test, and install

The app has no runtime AndroidX, Material, or third-party dependencies. JUnit is used for local engine tests. The project uses AGP 9.0.1, Gradle 9.2.1, compile SDK 36, and Java 17 source compatibility.

./gradlew testDebugUnitTest   # filter and motion-engine tests
./gradlew lintDebug           # Android static analysis
./gradlew assembleDebug       # app/build/outputs/apk/debug/app-debug.apk
./gradlew installDebug        # install on a connected device

Use a physical device for functional testing. An emulator generally does not provide realistic GPS speed, sensor cadence, Bluetooth audio, or OEM power management.

In-app controls

• Full volume above speed: speed at which the media stream reaches maximum.
• Standstill volume level: minimum volume used at 0–3 km/h.
• Status pill: whether the service is running.
• Source row: GPS fix, motion sensors, or looking for a fix.
• Warnings: GPS disabled, volume changes blocked, or service start failure.
• Stop: stops the foreground service and prevents a sticky restart.

Troubleshooting

It works only while the app is open

Check Allow all the time, notifications, unrestricted battery usage, and the manufacturer's auto-start/background setting. Start the service while the app is visible and verify the persistent notification before locking.

It stops when the phone locks

The service may have been killed by Doze or an OEM task killer. Re-enable unrestricted battery usage and auto-start. Do not force-stop the app; Android does not reliably restart force-stopped applications.

Speed stays at -- or zero

Move outdoors and wait for a GPS fix. For walking/running, confirm that the phone has a step-detector sensor and that recent steps are being detected. A vehicle still requires GPS; motion fallback is intentionally limited to pedestrian speeds.

Volume does not change

The app adjusts the same media stream used by Bluetooth car audio. If the warning appears, the ROM may be blocking programmatic media-volume changes. Check device-admin, car-mode, audio-policy, or OEM restrictions.

The tile does nothing

Open the app, grant background location, and try starting from the app once. If the tile starts and then immediately becomes inactive, inspect the ongoing notification and the device's background-execution settings.

Project layout

app/src/main/java/com/example/speedvolume/
├── MainActivity.kt          # setup UI, permissions, and controls
├── SpeedVolumeService.kt    # foreground service, GPS, sensors, recovery
├── SpeedFilter.kt           # GPS/displacement filtering
├── VolumeRamp.kt            # exponential volume approach and block detection
├── SensorMotion.kt          # cadence and stride calibration
├── SpeedVolumeTile.kt       # Quick Settings integration
└── ServiceState.kt          # activity/tile/service state bridge

app/src/test/java/com/example/speedvolume/
├── SpeedFilterTest.kt       # filter edge cases
└── SensorMotionTest.kt      # cadence and stale-sensor behavior

Versioning and license

Release history is recorded in CHANGELOG.md. Inspect tags with:

git tag
git log --oneline --decorate

The project is licensed under the MIT License.