wireless camera app for Android

Stream a phone's camera to a tablet over WiFi/hotspot.
WebSocket transport with native YUV-to-JPEG encoding,
UDP auto-discovery, remote control (zoom, flash, camera switch,
rotate, mirror) from the viewer.

android/app/build.gradle.kts

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+plugins {
+    id("com.android.application")
+    id("kotlin-android")
+    // The Flutter Gradle Plugin must be applied after the Android and Kotlin Gradle plugins.
+    id("dev.flutter.flutter-gradle-plugin")
+}
+
+android {
+    namespace = "com.kschappell.external_cam"
+    compileSdk = flutter.compileSdkVersion
+    ndkVersion = flutter.ndkVersion
+
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_17
+        targetCompatibility = JavaVersion.VERSION_17
+    }
+
+    kotlinOptions {
+        jvmTarget = JavaVersion.VERSION_17.toString()
+    }
+
+    defaultConfig {
+        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
+        applicationId = "com.kschappell.external_cam"
+        // You can update the following values to match your application needs.
+        // For more information, see: https://flutter.dev/to/review-gradle-config.
+        minSdk = flutter.minSdkVersion
+        targetSdk = flutter.targetSdkVersion
+        versionCode = flutter.versionCode
+        versionName = flutter.versionName
+    }
+
+    buildTypes {
+        release {
+            // TODO: Add your own signing config for the release build.
+            // Signing with the debug keys for now, so `flutter run --release` works.
+            signingConfig = signingConfigs.getByName("debug")
+        }
+    }
+}
+
+flutter {
+    source = "../.."
+}

android/app/src/debug/AndroidManifest.xml

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+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- The INTERNET permission is required for development. Specifically,
+         the Flutter tool needs it to communicate with the running application
+         to allow setting breakpoints, to provide hot reload, etc.
+    -->
+    <uses-permission android:name="android.permission.INTERNET"/>
+</manifest>

android/app/src/main/AndroidManifest.xml

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+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <uses-permission android:name="android.permission.CAMERA" />
+    <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
+    <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
+    <uses-permission android:name="android.permission.CHANGE_WIFI_MULTICAST_STATE" />
+
+    <application
+        android:label="External Cam"
+        android:name="${applicationName}"
+        android:icon="@mipmap/ic_launcher"
+        android:usesCleartextTraffic="true">
+        <activity
+            android:name=".MainActivity"
+            android:exported="true"
+            android:launchMode="singleTop"
+            android:taskAffinity=""
+            android:theme="@style/LaunchTheme"
+            android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
+            android:hardwareAccelerated="true"
+            android:windowSoftInputMode="adjustResize">
+            <meta-data
+              android:name="io.flutter.embedding.android.NormalTheme"
+              android:resource="@style/NormalTheme"
+              />
+            <intent-filter>
+                <action android:name="android.intent.action.MAIN"/>
+                <category android:name="android.intent.category.LAUNCHER"/>
+            </intent-filter>
+        </activity>
+        <meta-data
+            android:name="flutterEmbedding"
+            android:value="2" />
+    </application>
+    <queries>
+        <intent>
+            <action android:name="android.intent.action.PROCESS_TEXT"/>
+            <data android:mimeType="text/plain"/>
+        </intent>
+    </queries>
+</manifest>

android/app/src/main/kotlin/com/kschappell/external_cam/MainActivity.kt

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+package com.kschappell.external_cam
+
+import android.content.Context
+import android.graphics.ImageFormat
+import android.graphics.Rect
+import android.graphics.YuvImage
+import android.net.wifi.WifiManager
+import io.flutter.embedding.android.FlutterActivity
+import io.flutter.embedding.engine.FlutterEngine
+import io.flutter.plugin.common.MethodChannel
+import java.io.ByteArrayOutputStream
+
+class MainActivity : FlutterActivity() {
+    private var multicastLock: WifiManager.MulticastLock? = null
+
+    override fun configureFlutterEngine(flutterEngine: FlutterEngine) {
+        super.configureFlutterEngine(flutterEngine)
+        acquireMulticastLock()
+
+        MethodChannel(flutterEngine.dartExecutor.binaryMessenger, "com.kschappell.external_cam/jpeg")
+            .setMethodCallHandler { call, result ->
+                if (call.method == "encodeJpeg") {
+                    result.success(
+                        encodeYuvToJpeg(
+                            width = call.argument("width")!!,
+                            height = call.argument("height")!!,
+                            yBuffer = call.argument("y")!!,
+                            uBuffer = call.argument("u")!!,
+                            vBuffer = call.argument("v")!!,
+                            yRowStride = call.argument("yRowStride")!!,
+                            uvRowStride = call.argument("uvRowStride")!!,
+                            uvPixelStride = call.argument("uvPixelStride")!!,
+                            quality = call.argument("quality") ?: 70,
+                        )
+                    )
+                } else {
+                    result.notImplemented()
+                }
+            }
+    }
+
+    private fun acquireMulticastLock() {
+        val wifi = applicationContext.getSystemService(Context.WIFI_SERVICE) as WifiManager
+        multicastLock = wifi.createMulticastLock("external_cam").apply {
+            setReferenceCounted(true)
+            acquire()
+        }
+    }
+
+    override fun onDestroy() {
+        multicastLock?.release()
+        super.onDestroy()
+    }
+
+    private fun encodeYuvToJpeg(
+        width: Int,
+        height: Int,
+        yBuffer: ByteArray,
+        uBuffer: ByteArray,
+        vBuffer: ByteArray,
+        yRowStride: Int,
+        uvRowStride: Int,
+        uvPixelStride: Int,
+        quality: Int,
+    ): ByteArray {
+        val nv21 = ByteArray(width * height * 3 / 2)
+        var pos = 0
+
+        if (yRowStride == width) {
+            System.arraycopy(yBuffer, 0, nv21, 0, width * height)
+            pos = width * height
+        } else {
+            for (row in 0 until height) {
+                System.arraycopy(yBuffer, row * yRowStride, nv21, pos, width)
+                pos += width
+            }
+        }
+
+        val uvHeight = height / 2
+        val uvWidth = width / 2
+        val uvSize = uvWidth * uvHeight * 2
+        if (uvPixelStride == 2 && uvRowStride == width && vBuffer.size >= uvSize) {
+            System.arraycopy(vBuffer, 0, nv21, pos, uvSize)
+        } else {
+            for (row in 0 until uvHeight) {
+                val offset = row * uvRowStride
+                for (col in 0 until uvWidth) {
+                    val uvOffset = offset + col * uvPixelStride
+                    nv21[pos++] = vBuffer[uvOffset]
+                    nv21[pos++] = uBuffer[uvOffset]
+                }
+            }
+        }
+
+        val yuvImage = YuvImage(nv21, ImageFormat.NV21, width, height, null)
+        val stream = ByteArrayOutputStream(width * height / 4)
+        yuvImage.compressToJpeg(Rect(0, 0, width, height), quality, stream)
+        return stream.toByteArray()
+    }
+}

android/app/src/main/res/drawable-v21/launch_background.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="?android:colorBackground" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>

android/app/src/main/res/drawable/launch_background.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<!-- Modify this file to customize your launch splash screen -->
+<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
+    <item android:drawable="@android:color/white" />
+
+    <!-- You can insert your own image assets here -->
+    <!-- <item>
+        <bitmap
+            android:gravity="center"
+            android:src="@mipmap/launch_image" />
+    </item> -->
+</layer-list>

android/app/src/main/res/values-night/styles.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is on -->
+    <style name="LaunchTheme" parent="@android:style/Theme.Black.NoTitleBar">
+        <!-- Show a splash screen on the activity. Automatically removed when
+             the Flutter engine draws its first frame -->
+        <item name="android:windowBackground">@drawable/launch_background</item>
+    </style>
+    <!-- Theme applied to the Android Window as soon as the process has started.
+         This theme determines the color of the Android Window while your
+         Flutter UI initializes, as well as behind your Flutter UI while its
+         running.
+
+         This Theme is only used starting with V2 of Flutter's Android embedding. -->
+    <style name="NormalTheme" parent="@android:style/Theme.Black.NoTitleBar">
+        <item name="android:windowBackground">?android:colorBackground</item>
+    </style>
+</resources>

android/app/src/main/res/values/styles.xml

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+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <!-- Theme applied to the Android Window while the process is starting when the OS's Dark Mode setting is off -->
+    <style name="LaunchTheme" parent="@android:style/Theme.Light.NoTitleBar">
+        <!-- Show a splash screen on the activity. Automatically removed when
+             the Flutter engine draws its first frame -->
+        <item name="android:windowBackground">@drawable/launch_background</item>
+    </style>
+    <!-- Theme applied to the Android Window as soon as the process has started.
+         This theme determines the color of the Android Window while your
+         Flutter UI initializes, as well as behind your Flutter UI while its
+         running.
+
+         This Theme is only used starting with V2 of Flutter's Android embedding. -->
+    <style name="NormalTheme" parent="@android:style/Theme.Light.NoTitleBar">
+        <item name="android:windowBackground">?android:colorBackground</item>
+    </style>
+</resources>

android/app/src/profile/AndroidManifest.xml

@@ -0,0 +1,7 @@
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- The INTERNET permission is required for development. Specifically,
+         the Flutter tool needs it to communicate with the running application
+         to allow setting breakpoints, to provide hot reload, etc.
+    -->
+    <uses-permission android:name="android.permission.INTERNET"/>
+</manifest>