android_cast/ndk

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	Stub	Probe only	Submodules under third-party/

Enable libvpx (developer)

1. git submodule update --init third-party/libvpx

2. Build libvpx.a per ABI (NDK is auto-detected; see scripts/android-ndk.sh):

   ./scripts/build-native-codecs.sh arm64-v8a

   (If the repo path has spaces, the script uses /tmp/androidcast-libvpx-$USER automatically.)

3. Build each ABI you ship (Gradle links build/native/<abi>/libvpx.a automatically):

./scripts/build-native-codecs.sh arm64-v8a
./scripts/build-native-codecs.sh armeabi-v7a   # if armeabi-v7a is in your APK
./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 a matching libvpx.a still build; software VPx is 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