# 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 | — | `ProtectionEnvelope`, handshake-safe scopes |
| NACK + retransmit cache | Yes | — | UDP `MSG_NACK`, combined with FEC when enabled |
| libvpx VP8/VP9 | Stub | Probe only | HW passthrough until `ANDROIDCAST_LIBVPX_LIB` is linked |
| Opus / Speex | Stub | Probe only | Submodules under `third-party/` |

## Enable libvpx (developer)

1. `git submodule update --init third-party/libvpx`
2. Build `libvpx.a` for your ABI (script stub: `scripts/build-native-codecs.sh`)
3. Rebuild the APK with the static library path:

```bash
export ANDROIDCAST_LIBVPX_LIB=/path/to/libvpx.a
./gradlew assembleDebug
```

CMake defines `ANDROIDCAST_HAVE_LIBVPX=1` and links the archive when the variable is set.

## Stream protection defaults

- Default: **None** (no FEC/NACK)
- Enable in **Global settings → Stream protection (UDP)**
- After handshake, sender and receiver negotiate the effective mode