perf: reduce APK size - switch to audio-only FFmpeg, enable ProGuard, split APK by ABI

android/app/build.gradle.kts

@@ -29,13 +29,34 @@ android {
         versionCode = flutter.versionCode
         versionName = flutter.versionName
         multiDexEnabled = true
+        
+        // Only include arm64-v8a for smaller APK (most modern devices)
+        // Remove this line if you need to support older 32-bit devices
+        ndk {
+            abiFilters += listOf("arm64-v8a", "armeabi-v7a")
+        }
     }
 
     buildTypes {
         release {
             signingConfig = signingConfigs.getByName("debug")
-            isMinifyEnabled = false
-            isShrinkResources = false
+            // Enable code shrinking and resource shrinking
+            isMinifyEnabled = true
+            isShrinkResources = true
+            proguardFiles(
+                getDefaultProguardFile("proguard-android-optimize.txt"),
+                "proguard-rules.pro"
+            )
+        }
+    }
+    
+    // Split APKs by ABI for smaller individual downloads
+    splits {
+        abi {
+            isEnable = true
+            reset()
+            include("arm64-v8a", "armeabi-v7a")
+            isUniversalApk = true // Also generate universal APK
         }
     }
 }

android/app/proguard-rules.pro

@@ -0,0 +1,33 @@
+# Flutter specific rules
+-keep class io.flutter.app.** { *; }
+-keep class io.flutter.plugin.** { *; }
+-keep class io.flutter.util.** { *; }
+-keep class io.flutter.view.** { *; }
+-keep class io.flutter.** { *; }
+-keep class io.flutter.plugins.** { *; }
+
+# Go backend (gobackend.aar)
+-keep class gobackend.** { *; }
+-keep class go.** { *; }
+
+# FFmpeg Kit
+-keep class com.arthenica.ffmpegkit.** { *; }
+-keep class com.arthenica.smartexception.** { *; }
+
+# Keep native methods
+-keepclasseswithmembernames class * {
+    native <methods>;
+}
+
+# Kotlin coroutines
+-keepnames class kotlinx.coroutines.internal.MainDispatcherFactory {}
+-keepnames class kotlinx.coroutines.CoroutineExceptionHandler {}
+-keepclassmembers class kotlinx.coroutines.** {
+    volatile <fields>;
+}
+
+# Prevent R8 from removing metadata
+-keepattributes *Annotation*
+-keepattributes SourceFile,LineNumberTable
+-keepattributes Signature
+-keepattributes Exceptions