Add Flutter GUI example for VAD with a microphone. (#905)

sherpa-onnx/flutter/lib/src/sherpa_onnx_bindings.dart

@@ -345,6 +345,12 @@ typedef SherpaOnnxReadWaveNative = Pointer<SherpaOnnxWave> Function(
 
 typedef SherpaOnnxReadWave = SherpaOnnxReadWaveNative;
 
+typedef SherpaOnnxWriteWaveNative = Int32 Function(
+    Pointer<Float>, Int32, Int32, Pointer<Utf8>);
+
+typedef SherpaOnnxWriteWave = int Function(
+    Pointer<Float>, int, int, Pointer<Utf8>);
+
 typedef SherpaOnnxFreeWaveNative = Void Function(Pointer<SherpaOnnxWave>);
 
 typedef SherpaOnnxFreeWave = void Function(Pointer<SherpaOnnxWave>);
@@ -448,6 +454,8 @@ class SherpaOnnxBindings {
 
   static SherpaOnnxReadWave? readWave;
 
+  static SherpaOnnxWriteWave? writeWave;
+
   static SherpaOnnxFreeWave? freeWave;
 
   static void init(DynamicLibrary dynamicLibrary) {
@@ -686,6 +694,11 @@ class SherpaOnnxBindings {
         .lookup<NativeFunction<SherpaOnnxReadWaveNative>>('SherpaOnnxReadWave')
         .asFunction();
 
+    writeWave ??= dynamicLibrary
+        .lookup<NativeFunction<SherpaOnnxWriteWaveNative>>(
+            'SherpaOnnxWriteWave')
+        .asFunction();
+
     freeWave ??= dynamicLibrary
         .lookup<NativeFunction<SherpaOnnxFreeWaveNative>>('SherpaOnnxFreeWave')
         .asFunction();

sherpa-onnx/flutter/lib/src/vad.dart

@@ -113,7 +113,7 @@ class CircularBuffer {
 }
 
 class VoiceActivityDetector {
-  VoiceActivityDetector._({required this.ptr});
+  VoiceActivityDetector._({required this.ptr, required this.config});
 
   // The user has to invoke VoiceActivityDetector.free() to avoid memory leak.
   factory VoiceActivityDetector(
@@ -144,7 +144,7 @@ class VoiceActivityDetector {
     calloc.free(modelPtr);
     calloc.free(c);
 
-    return VoiceActivityDetector._(ptr: ptr);
+    return VoiceActivityDetector._(ptr: ptr, config: config);
   }
 
   void free() {
@@ -210,4 +210,5 @@ class VoiceActivityDetector {
   }
 
   Pointer<SherpaOnnxVoiceActivityDetector> ptr;
+  final VadModelConfig config;
 }

sherpa-onnx/flutter/lib/src/wave_writer.dart

@@ -0,0 +1,27 @@
+// Copyright (c)  2024  Xiaomi Corporation
+import 'dart:ffi';
+import 'dart:typed_data';
+import 'package:ffi/ffi.dart';
+
+import './sherpa_onnx_bindings.dart';
+
+bool writeWave(
+    {required String filename,
+    required Float32List samples,
+    required int sampleRate}) {
+  final Pointer<Utf8> filenamePtr = filename.toNativeUtf8();
+
+  final n = samples.length;
+  final Pointer<Float> p = calloc<Float>(n);
+
+  final pList = p.asTypedList(n);
+  pList.setAll(0, samples);
+
+  int ok =
+      SherpaOnnxBindings.writeWave?.call(p, n, sampleRate, filenamePtr) ?? 0;
+
+  calloc.free(p);
+  calloc.free(filenamePtr);
+
+  return ok == 1;
+}