feat(poc/audio): add Android mobile audio spike
Closes the mobile half of the PoC plan §2 audio exit criterion
left open by poc/audio-capture-playback-spike. The desktop and
mobile halves together fully retire the audio PoC.
Stack:
Kotlin (MainActivity) → JNI → Rust cdylib
→ cpal 0.16 → Oboe (AAudio / OpenSL ES) → Android audio HAL
Layout:
rust crate (src/lib.rs) — JNI_OnLoad, initContext,
playSine440, record1sToFile;
panic-catching at JNI boundary;
android_logger → logcat
android/ (Gradle 8.7, — minSdk 24, compileSdk 34, AGP 8.5.2.
AGP 8.5.2, Kotlin 1.9.24) cargoBuildRust task wraps cargo-ndk
-P 26 -t <abi> for all four ABIs;
wired into preBuild so AGP picks up
the produced .so files.
Verified on 2026-05-13 on a physical Motorola Moto G Stylus 5G
(2023), Android 14 SDK 34 arm64-v8a:
- Playback: 500 ms 440 Hz mono sine, 22,050 frames emitted at
44.1 kHz through cpal/Oboe/AAudio/device speaker.
- Capture: 1 s from default input, 42,624 frames written to
/data/data/app.chanora.poc.audio/files/chanora_poc_capture.wav.
File pulled via 'adb exec-out run-as ... cat' and confirmed
by file(1) as 'RIFF (little-endian) data, WAVE audio,
Microsoft PCM, 16 bit, mono 44100 Hz'. Header bytes
cross-checked against the reported frame count.
Notes:
- cpal links libaaudio (introduced API 26), so cargo-ndk targets
API 26 via -P 26 while the Android module's minSdk stays at 24
(DEC-004). API 24/25 devices would fall back to OpenSL ES at
runtime; not exercised here.
- JNI panic safety: every JNI entry point wraps its body in
std::panic::catch_unwind and a tracing panic hook routes
panic messages to logcat under tag 'ChanoraAudioPoC'. Without
this, cpal panicking inside an extern "system" function would
abort the process.
- The emulator AVD chanora-poc-api34 and its system image were
installed during Phase 0 but emulator verification was skipped
once the physical-device run succeeded. Real-device evidence
is stronger.
Surfaced finding: DEC-011.1 mobile half promoted from Deferred to
Accepted for Android in the same docs commit; iOS remains
explicitly Deferred (requires macOS + Xcode hardware).
Authority: PoC plan §2, DEC-011, DEC-011.1.
Not product code; not promoted into chanora_audio.
This commit is contained in:
EdisonJwa
@@ -0,0 +1,124 @@
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plugins {
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id("com.android.application")
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id("org.jetbrains.kotlin.android")
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}
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android {
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namespace = "app.chanora.poc.audio"
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compileSdk = 34
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defaultConfig {
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applicationId = "app.chanora.poc.audio"
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minSdk = 24 // matches DEC-004
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targetSdk = 34
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versionCode = 1
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versionName = "0.1.0-poc"
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ndk {
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// Keep all four common ABIs so the same APK works on both
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// the x86_64 emulator and a physical arm64 device.
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abiFilters += listOf("x86_64", "arm64-v8a", "armeabi-v7a", "x86")
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}
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}
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sourceSets {
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getByName("main") {
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// cargo-ndk drops .so files here.
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jniLibs.srcDirs("src/main/jniLibs")
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}
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}
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buildTypes {
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getByName("debug") {
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isMinifyEnabled = false
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}
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getByName("release") {
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isMinifyEnabled = false
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}
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}
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compileOptions {
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sourceCompatibility = JavaVersion.VERSION_17
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targetCompatibility = JavaVersion.VERSION_17
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}
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kotlinOptions {
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jvmTarget = "17"
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}
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packaging {
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// Avoid duplicate-resource conflicts from native libs if any
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// future deps bring them in.
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resources.excludes += setOf("META-INF/AL2.0", "META-INF/LGPL2.1")
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}
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}
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dependencies {
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implementation("androidx.core:core-ktx:1.13.1")
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implementation("androidx.appcompat:appcompat:1.7.0")
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}
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// ---------------------------------------------------------------------
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// Rust cdylib build via cargo-ndk.
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//
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// Each ABI maps to a Rust target triple; cargo-ndk handles linker
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// selection. The task copies the produced .so into the per-ABI
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// jniLibs directory expected by Android Gradle Plugin.
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// ---------------------------------------------------------------------
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val rustCrateDir = rootProject.projectDir.parentFile // ../ -> the spike root
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val rustTargetDir = file("$rustCrateDir/target")
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val jniLibsDir = file("$projectDir/src/main/jniLibs")
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val cargoBuildRust = tasks.register("cargoBuildRust") {
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group = "build"
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description = "Builds the Rust cdylib for all enabled Android ABIs via cargo ndk."
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val abis = listOf(
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Triple("x86_64", "x86_64-linux-android", "x86_64"),
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Triple("arm64-v8a", "aarch64-linux-android", "arm64-v8a"),
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Triple("armeabi-v7a", "armv7-linux-androideabi", "armeabi-v7a"),
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Triple("x86", "i686-linux-android", "x86")
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)
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doLast {
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// Resolve cargo: try CARGO_HOME/bin first, then PATH, then the
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// rustup shim location.
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val cargoBinDir = System.getenv("CARGO_HOME")?.let { "$it/bin" }
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?: "${System.getProperty("user.home")}/.cargo/bin"
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val cargo = listOf("$cargoBinDir/cargo", "/usr/local/bin/cargo", "/usr/bin/cargo")
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.firstOrNull { file(it).exists() }
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?: error("cargo not found; install via rustup")
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val cargoNdkBin = listOf("$cargoBinDir/cargo-ndk", "/usr/local/bin/cargo-ndk")
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.firstOrNull { file(it).exists() }
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check(cargoNdkBin != null) { "cargo-ndk not installed (cargo install cargo-ndk)" }
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val ndkHome = System.getenv("ANDROID_NDK_HOME")
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?: System.getenv("NDK_HOME")
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?: "/opt/android-sdk/ndk/26.3.11579264"
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check(file(ndkHome).exists()) { "NDK not found at $ndkHome" }
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// cargo-ndk is a cargo subcommand; invoke via `cargo ndk ...`.
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// We must ensure cargo's PATH lookup can find cargo-ndk too.
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// `-p 26` selects API 26 for the NDK toolchain so cpal can
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// link against libaaudio (introduced in API 26). minSdk in
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// the Android module stays at 24 — the device just won't
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// execute the AAudio code path below API 26; cpal/Oboe falls
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// back to OpenSL ES there.
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val abiArgs = abis.flatMap { listOf("-t", it.first) }
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val cargoCmd = listOf(cargo, "ndk", "-P", "26") + abiArgs +
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listOf("-o", jniLibsDir.absolutePath, "build", "--release",
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"--manifest-path", "$rustCrateDir/Cargo.toml")
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println("[cargoBuildRust] running: ${cargoCmd.joinToString(" ")}")
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exec {
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commandLine(cargoCmd)
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environment("ANDROID_NDK_HOME", ndkHome)
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environment("PATH", "$cargoBinDir:${System.getenv("PATH")}")
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}
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}
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}
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// Make Android's preBuild depend on the Rust build so AGP picks up the .so files.
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tasks.matching { it.name == "preBuild" }.configureEach {
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dependsOn(cargoBuildRust)
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}
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@@ -0,0 +1,21 @@
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<?xml version="1.0" encoding="utf-8"?>
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<manifest xmlns:android="http://schemas.android.com/apk/res/android">
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<!-- Required for capture. Cpal's Oboe input stream needs this. -->
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<uses-permission android:name="android.permission.RECORD_AUDIO" />
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<application
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android:label="Chanora Audio PoC"
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android:allowBackup="false"
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android:supportsRtl="true"
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android:theme="@android:style/Theme.Material.Light">
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<activity
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android:name=".MainActivity"
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android:exported="true">
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<intent-filter>
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<action android:name="android.intent.action.MAIN" />
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<category android:name="android.intent.category.LAUNCHER" />
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</intent-filter>
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</activity>
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</application>
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</manifest>
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+134
@@ -0,0 +1,134 @@
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package app.chanora.poc.audio
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import android.Manifest
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import android.app.Activity
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import android.content.pm.PackageManager
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import android.os.Bundle
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import android.util.Log
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import android.view.View
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import android.widget.Button
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import android.widget.LinearLayout
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import android.widget.TextView
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import androidx.core.app.ActivityCompat
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import androidx.core.content.ContextCompat
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import java.io.File
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import kotlin.concurrent.thread
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/**
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* Chanora PoC — Android mobile audio spike.
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*
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* Two buttons:
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* 1) Play 500 ms 440 Hz sine wave through the default output device.
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* 2) Record 1 s from the default input device to app-private storage.
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*
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* Both call into the Rust cdylib via JNI. Status is logged to logcat
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* under the tag "ChanoraAudioPoC" (Rust) and "ChanoraPoCActivity"
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* (Kotlin). The UI also displays the result string.
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*/
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class MainActivity : Activity() {
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private companion object {
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const val TAG = "ChanoraPoCActivity"
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const val REQ_RECORD = 1001
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}
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private lateinit var status: TextView
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private lateinit var recordBtn: Button
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override fun onCreate(savedInstanceState: Bundle?) {
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super.onCreate(savedInstanceState)
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// Hand the Application Context to the Rust side BEFORE any
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// audio call, so cpal's Oboe backend can find Android audio
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// services via ndk_context.
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NativeAudio.initContext(applicationContext)
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val root = LinearLayout(this).apply {
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orientation = LinearLayout.VERTICAL
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setPadding(48, 48, 48, 48)
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}
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val title = TextView(this).apply {
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text = "Chanora Audio PoC (Android)"
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textSize = 20f
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}
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status = TextView(this).apply {
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text = "ready"
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textSize = 14f
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setPadding(0, 24, 0, 24)
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}
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val playBtn = Button(this).apply {
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text = "Play 500 ms sine"
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setOnClickListener { onPlay() }
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}
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recordBtn = Button(this).apply {
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text = "Record 1 s to file"
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setOnClickListener { onRecord() }
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}
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root.addView(title)
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root.addView(status)
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root.addView(playBtn)
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root.addView(recordBtn)
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setContentView(root)
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}
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private fun setStatus(s: String) {
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Log.i(TAG, s)
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runOnUiThread { status.text = s }
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}
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private fun onPlay() {
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setStatus("playing…")
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thread(name = "chanora-poc-play") {
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val frames = NativeAudio.playSine440(500L)
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if (frames < 0) {
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setStatus("PLAY ERROR (see logcat)")
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} else {
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setStatus("PLAY OK frames=$frames")
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}
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}
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}
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private fun onRecord() {
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if (ContextCompat.checkSelfPermission(this, Manifest.permission.RECORD_AUDIO)
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!= PackageManager.PERMISSION_GRANTED) {
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ActivityCompat.requestPermissions(this, arrayOf(Manifest.permission.RECORD_AUDIO), REQ_RECORD)
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setStatus("requesting RECORD_AUDIO…")
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return
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}
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doRecord()
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}
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private fun doRecord() {
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setStatus("recording 1 s…")
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thread(name = "chanora-poc-record") {
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val path = File(filesDir, "chanora_poc_capture.wav").absolutePath
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val frames = NativeAudio.record1sToFile(path, 1000L)
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if (frames < 0) {
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setStatus("RECORD ERROR (see logcat)")
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} else {
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val sz = File(path).length()
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setStatus("RECORD OK frames=$frames bytes=$sz path=$path")
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}
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}
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}
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override fun onRequestPermissionsResult(
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requestCode: Int,
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permissions: Array<out String>,
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grantResults: IntArray
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) {
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super.onRequestPermissionsResult(requestCode, permissions, grantResults)
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if (requestCode == REQ_RECORD) {
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if (grantResults.firstOrNull() == PackageManager.PERMISSION_GRANTED) {
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doRecord()
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} else {
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setStatus("RECORD_AUDIO permission denied")
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}
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}
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}
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}
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+22
@@ -0,0 +1,22 @@
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package app.chanora.poc.audio
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import android.content.Context
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object NativeAudio {
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init {
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System.loadLibrary("audio_capture_playback_android_spike")
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}
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/**
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* Must be called once after `System.loadLibrary` with the
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* application Context. Initialises the Rust-side `ndk_context`
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* that cpal/Oboe relies on to locate Android audio services.
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*/
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external fun initContext(context: Context)
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/** Returns the number of frames emitted, or -1 on error. */
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external fun playSine440(durationMs: Long): Long
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/** Returns the number of frames captured, or -1 on error. */
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external fun record1sToFile(path: String, durationMs: Long): Long
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}
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