Retro FM Android

A dedicated Android app for listening to Retro FM without going through aggregators that add ads before playback. It supports phones, Android Auto projection and Android Automotive OS (AAOS) through Media3's MediaBrowserService.

Features

• Ad-free (aggregator-free) playback of Retro FM.
• Play/pause with large, car-friendly controls.
• Shows the current song title and artist with artwork.
• Background playback with a media notification.
• Handles media buttons (headset, steering-wheel controls, car UI).
• Exposed as a media source in Android Auto and Android Automotive OS.
• Google Cast (Chromecast): cast the stream to Chromecast/Nest devices (phone app only).
• Reconnects automatically after network drops.
• Detects server-injected ads and mutes them, with a "Reklam" countdown in the UI (can be turned off with RetroFmConfig.MUTE_ADS).
• Song info comes from the stream's own ICY metadata, exactly at the song change. Since 2026-08-08 the app plays the station's own Icecast (Mad Men Media) instead of Bauer's old relay, whose metadata froze in July when Retro FM left Bauer/RadioPlay. No API is polled any more. Since 2026-09-14 the stream is Revma (RCS). History and measurements: .claude/skills/now-playing-metadata/SKILL.md.
• Sends field logs and metrics over OpenTelemetry to home-server's telemetry edge for debugging in the car (production cars have no adb) — never tokens, credentialed URLs or PII (see AGENTS.md, "Log hygiene is a wire contract", and .claude/skills/field-logs/SKILL.md).

Tech stack

• Kotlin + Jetpack Compose (Material 3)
• AndroidX Media3 (ExoPlayer + MediaSession + Cast)
• Retrofit + Kotlinx Serialization
• Coil
• MVVM + Repository

Exact versions are in the modules' build.gradle.kts — they move continuously and are not documented here.

Build

The project needs JDK 17 and the Android SDK (API 36, build-tools 36.0.0).

./gradlew :app:assembleDebug         # phone + Android Auto
./gradlew :app:assembleRelease
./gradlew :automotive:assembleDebug  # Android Automotive OS (built-in car display)
./gradlew :automotive:assembleRelease

Tests

./gradlew :core:testDebugUnitTest

Install on a device

./gradlew :app:installDebug
adb shell am start -n com.magter.retrofm/com.retrofm.android.ui.MainActivity

Android Auto / Android Automotive OS

The app registers a MediaLibraryService (Media3) so that it appears as a media source in both Android Auto and Android Automotive OS — but through two separate APKs (:app and :automotive), since one artifact cannot support both under Google's guidelines. See the :automotive entry under "Project structure" below for details.

Android Auto (the phone projected onto the car's display): works automatically when :app is installed on the phone and it is connected to any car with Android Auto support — the car's own operating system plays no part here.

Android Automotive OS (the app runs natively on the car's own display, without a phone), test in an emulator:

1. Start the Android Automotive emulator.
2. Install the car-specific APK: adb install automotive/build/outputs/apk/debug/automotive-debug.apk.
3. Open the media player in the car UI and choose "Retro FM".

Note: real cars (Volvo's AAOS units, for example) often block sideloading and developer mode in production. Sideloading works only in the emulator; a real car needs Play Store distribution through the dedicated Automotive OS track in Play Console.

Signing and release (Google Play)

Real releases go through GitHub Actions, not manual uploads: bump versionName in both app/ and automotive/build.gradle.kts, tag vX.Y.Z (the same as versionName) and push the tag. The workflow builds, signs and uploads both bundles to Play internal testing (phone → track internal, automotive → automotive:internal). versionCode is derived from the run number and is never bumped by hand. Details and traps are in AGENTS.md, section "Release".

For local release builds: :app/:automotive have a signing config that reads its values from Gradle properties — no secrets are in the repo. Without the properties the release artifact is built unsigned (useful for R8 and bundle verification). The values (the existing upload key, kept outside the repo) go in ~/.gradle/gradle.properties or are passed as -P flags:

RETROFM_UPLOAD_STORE_FILE=/absolute/path/to/upload-keystore.jks
RETROFM_UPLOAD_STORE_PASSWORD=…
RETROFM_UPLOAD_KEY_ALIAS=upload
RETROFM_UPLOAD_KEY_PASSWORD=…

Configuration

All stream URLs, API endpoints, station identity and behaviour knobs (buffers, reconnect backoff, ad mute) are in core/src/main/java/com/retrofm/android/data/config/RetroFmConfig.kt.

Project structure

The project is split into three Gradle modules:

• :core — shared code: network and data (data/, di/), playback and MediaLibraryService (playback/). No UI, no launcher activity. Used by both :app and :automotive.
• :app — the phone app. Compose UI, MainActivity, and the Android Auto markers (com.google.android.gms.car.application) in the manifest.
• :automotive — the Android Automotive OS app (runs natively on the car's own display, without a phone). The same applicationId as :app, to share one Play Store listing, but its own manifest with no launcher activity and android.hardware.type.automotive set to required="true".

Top-level packages (file-by-file lists rot — see the source tree for detail):

core/       com.retrofm.android.data      (api, config, model, repository, di)
            com.retrofm.android.playback  (player/session, ICY and ad detection,
                                           album-art ContentProvider, media tree)
            com.retrofm.android.telemetry (OpenTelemetry logs and metrics — see the field-logs skill)
app/        com.retrofm.android.ui        (Compose UI, ViewModel, theme)
automotive/ manifest + resources only     (all code comes from :core)

Notes

• Without upload values (see "Signing and release" above) the release artifact is built unsigned. With them it is signed automatically.
• The Retro FM logo and stream belong to Bauer Media. The app is intended for personal use.