Codec2 Player 🎙️

A pure-native Android app that plays and creates Codec 2 — the world's smallest open-source voice codec — in about ~300 KB installed.

No third-party libraries (no AndroidX, no Kotlin, no Material) — just core android.* plus a single small JNI .so. Single ABI (armeabi-v7a). The whole app installs in roughly the size of a couple of screenshots.

The app ships with English and Turkish, switchable in Settings → Language (independent of the device locale). This README is in English.

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What is Codec 2?

Codec 2 (by David Rowe, LGPL) compresses human speech to 450 – 3200 bits per second. How small is that? In this app, a 3-minute song shrinks to ~14 KB in the 450 mode. It's built for radio/satellite/low-bandwidth voice and tiny voice archives.

✨ Features

Playback

• Multi-file playlist; tap to play, auto-advance
• One glowing play/pause button (pulse + circular progress ring)
• Touch-and-drag waveform scrubber, elapsed / total time
• ⏮ ⏭ prev/next; long-press to seek ±10 s; "prev" restarts the track after 3 s
• Shuffle; 3-state repeat (off / all / one)
• Playback speed 0.75×–2×
• Audio gain (dB) — unlimited, can go negative, free-form value
• Sleep timer (15/30/60 min)
• Resume where you left off (track + position persisted)
• Mode is auto-detected from the file header (3200…450); colour-coded badges
• Plays normal audio too — mp3 / ogg / m4a / aac / wav / flac via the device's own MediaPlayer (true streaming, any length); .c2 files use the built-in codec2 decoder. Routed by file header, so a huge song never gets force-decoded into RAM. Handy to A/B a track against its codec2 version.

Background & notification

• Foreground Service + MediaSession (lock screen / headset buttons)
• Notification prev/play-pause/next; notification hides when app is foregrounded
• Battery: wakelock only while playing; auto-pause when headphones are unplugged

Files & conversion

• Add files / multiple files via SAF; recursively scan a folder (no permission needed)
• Open .c2 files from outside (single & multiple intent-filters) → added to the list and played
• Convert any audio to .c2 (mp3/aac/m4a/opus/ogg/wav/flac…) using the device's own codecs (MediaCodec) — no external library. Pick a size↔quality mode; the output is written next to the original (auto-numbered on collision)
• Share as WAV: decodes .c2 back to a normal WAV and shares it (tiny built-in ContentProvider)
• Reorder the list + long-press menu (no delete); Info dialog shows file size
• Live Log / Console screen (prints conversion steps)

Design — animated gradient background, glowing/pulsing controls, smooth blue↔pink colour shift, accent stripe on the playing row, marquee for long names, press-scale animation, mode-coloured labels — all library-free, pure canvas/animator.

📦 Why is it so small?

Part	Size
libcodec2player.so (armeabi-v7a, encode+decode)	~263 KB
classes.dex (the whole app)	~10 KB
res + manifest + signature	~3 KB
Total ≈ installed size	~300 KB

• Only the Codec 2 voice core is compiled; the FreeDV radio modems (OFDM/COHPSK/FSK/FDMDV) and the LDPC tables (H_*.c, megabytes) are left out. Encode is essentially free on top of decode (decode-only .so 268,544 B → encode+decode 268,800 B).
• extractNativeLibs=false → the .so is mmap'd from the APK, not copied on install.
• android:debuggable="true" → run-from-apk; the system skips dex2oat/oat, so installed size ≈ APK size. (Personal-use trick; not recommended for store distribution.)
• Single ABI, R8 + shrinkResources, v1-only EC signature.

🔨 Building

It's a standard Android project (AGP 8.0.2, compileSdk 33, minSdk 21):

./gradlew assembleRelease

It was developed with a portable, offline toolchain (bundled JDK + SDK + Gradle) driven by a Derle.ps1 script that also runs zipalign -p + apksigner (v1-only, EC) and applies the minimal-installed-size settings above.

How the native .so is built

libcodec2player.so is the voice-only subset of Codec 2 1.0.x plus the JNI bridge in src/main/cpp/Codec2JNI.c, compiled with NDK clang (single ABI, -O2, --gc-sections) and stripped. Codebook .c files are generated from .txt (native/gen_cb.py). The steps live in native/build_jni.ps1. (The Codec 2 source itself comes from upstream; this repo ships the prebuilt .so.)

🌍 Translations

The UI is fully localised and the language can be switched in-app (Settings → Language: System / English / Türkçe), independent of the device locale. Strings live in res/values/strings.xml (English, default) and res/values-tr/strings.xml (Turkish). To add a language, copy strings.xml into res/values-<lang>/, translate the values, and add it to the picker in SettingsActivity. PRs welcome.

📜 License

• Application source (the original code in this repo): MIT — see LICENSE.
• The bundled libcodec2player.so is derived from Codec 2 and is licensed under LGPL-2.1, © David Rowe and contributors — https://github.com/drowe67/codec2.

🙏 Credits

• David Rowe and the Codec 2 team — the codec itself.
• The .c2 file header (C0 DE C2 …) and the JNI approach were referenced from the Codec2Recorder project.