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ndk/README.md

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+# 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