# Native codecs (libvpx, Opus, Speex)

The app loads `libandroidcast_codecs.so` for availability probes and future software encode/decode paths.

## Current status

| Component | Java | Native | Notes |
|-----------|------|--------|-------|
| FEC 3/4 + RS | Yes | — | v2 **per-shard** on wire (`FecShardWire`); v1 monolithic decode still accepted |
| NACK + retransmit cache | Yes | — | UDP `MSG_NACK`, combined with FEC when enabled |
| libvpx VP8/VP9 | Native | Encode + decode | Screen cast via ImageReader; receiver libvpx (decoder uses `VPX_CODEC_USE_ERROR_CONCEALMENT` when supported) or MediaCodec fallback |
| Opus / Speex | Probe + static link when `lib*.a` built | Encode/decode JNI sinks | `scripts/build-native-codecs.sh` → CMake autolink |

## Enable native codecs (developer)

1. Initialize all third-party submodules:

   ```bash
   bash scripts/init-third-party-submodules.sh
   ```

2. Build static libs per ABI (NDK auto-detected via `scripts/android-ndk.sh`):

   ```bash
   ./scripts/build-native-codecs.sh arm64-v8a
   ./scripts/build-native-codecs.sh armeabi-v7a   # if shipped in APK
   ```

   If the repo path has **spaces**, the script stages under `/tmp/androidcast-libvpx-$USER`.

3. Gradle / CMake link `build/native/<abi>/lib*.a` when present and set `ANDROIDCAST_HAVE_LIBVPX`, `ANDROIDCAST_HAVE_OPUS`, `ANDROIDCAST_HAVE_SPEEX` accordingly.

4. `./gradlew assembleDebug`

Optional override: `ANDROIDCAST_LIBVPX_LIB` only applies when its path contains the current ABI name (e.g. `.../arm64-v8a/libvpx.a`).

ABIs without matching `.a` files still build; missing codecs are disabled on those architectures.

## Stream protection defaults

- Default: **None** (no FEC/NACK)
- Enable in **Global settings → Stream protection (UDP)**
- After handshake, sender and receiver negotiate the effective mode (no protocol version bump)
- Until negotiation completes, UDP protection stays **off**; peers without FEC support **ignore** protected frames

Full checklist: [docs/ROADMAP.md](../docs/ROADMAP.md)