Use Web Audio for browser voice meter

lib/screens/mapflow_shell.dart

@@ -11,6 +11,7 @@ import 'package:record/record.dart';
 import '../api/mapflow_api.dart';
 import '../auth/telegram_login_button.dart';
 import '../auth/telegram_session.dart' as telegram_session;
+import '../audio/browser_voice_meter.dart';
 import '../models/place_models.dart';
 import '../state/place_controller.dart';
 
@@ -724,6 +725,7 @@ class _AddExperienceFlowState extends ConsumerState<AddExperienceFlow> {
 
   final _api = MapflowApi();
   final _recorder = AudioRecorder();
+  final _browserVoiceMeter = BrowserVoiceMeter();
   final _waveSamples = List<double>.filled(160, 0.0);
   final _visualRandom = math.Random();
 
@@ -738,6 +740,7 @@ class _AddExperienceFlowState extends ConsumerState<AddExperienceFlow> {
   var _recording = false;
   var _submitting = false;
   var _micAllowed = true;
+  var _usingBrowserVoiceMeter = false;
   var _ambientLevel = 0.008;
   var _voiceCeiling = 0.045;
   var _noiseDb = -72.0;
@@ -758,6 +761,7 @@ class _AddExperienceFlowState extends ConsumerState<AddExperienceFlow> {
     _visualTimer?.cancel();
     _amplitudeTimer?.cancel();
     _audioStreamSub?.cancel();
+    _browserVoiceMeter.dispose();
     _recorder.dispose();
     super.dispose();
   }
@@ -784,6 +788,22 @@ class _AddExperienceFlowState extends ConsumerState<AddExperienceFlow> {
   }
 
   Future<void> _startRecording() async {
+    if (_browserVoiceMeter.isSupported) {
+      await _browserVoiceMeter.start(_handleBrowserVoiceFrame);
+      _lastAudioChunkAt = DateTime.now();
+      _lastInformationAt = _lastAudioChunkAt;
+      _startIdleWave();
+      _startDurationTimer();
+      setState(() {
+        _micAllowed = true;
+        _recording = true;
+        _usingBrowserVoiceMeter = true;
+        _liveLevel = 0;
+        _informationUnits = 0;
+      });
+      return;
+    }
+
     final hasPermission = await _recorder.hasPermission();
     if (!hasPermission) {
       setState(() => _micAllowed = false);
@@ -805,19 +825,12 @@ class _AddExperienceFlowState extends ConsumerState<AddExperienceFlow> {
     _lastInformationAt = _lastAudioChunkAt;
     _startIdleWave();
     _startAmplitudePolling();
-    _timer = Timer.periodic(const Duration(seconds: 1), (_) {
-      if (!mounted) {
-        return;
-      }
-      setState(() => _seconds += 1);
-      ref
-          .read(placeControllerProvider.notifier)
-          .setReviewDuration(Duration(seconds: _seconds));
-    });
+    _startDurationTimer();
 
     setState(() {
       _micAllowed = true;
       _recording = true;
+      _usingBrowserVoiceMeter = false;
       _liveLevel = 0;
       _informationUnits = 0;
     });
@@ -827,9 +840,13 @@ class _AddExperienceFlowState extends ConsumerState<AddExperienceFlow> {
     _timer?.cancel();
     _visualTimer?.cancel();
     _amplitudeTimer?.cancel();
-    await _audioStreamSub?.cancel();
-    _audioStreamSub = null;
-    await _recorder.stop();
+    if (_usingBrowserVoiceMeter) {
+      await _browserVoiceMeter.stop();
+    } else {
+      await _audioStreamSub?.cancel();
+      _audioStreamSub = null;
+      await _recorder.stop();
+    }
     _lastAudioChunkAt = null;
     _lastInformationAt = null;
     if (!mounted) {
@@ -837,10 +854,24 @@ class _AddExperienceFlowState extends ConsumerState<AddExperienceFlow> {
     }
     setState(() {
       _recording = false;
+      _usingBrowserVoiceMeter = false;
       _liveLevel = 0;
     });
   }
 
+  void _startDurationTimer() {
+    _timer?.cancel();
+    _timer = Timer.periodic(const Duration(seconds: 1), (_) {
+      if (!mounted) {
+        return;
+      }
+      setState(() => _seconds += 1);
+      ref
+          .read(placeControllerProvider.notifier)
+          .setReviewDuration(Duration(seconds: _seconds));
+    });
+  }
+
   void _startIdleWave() {
     _visualTimer?.cancel();
     _visualTimer = Timer.periodic(const Duration(milliseconds: 70), (_) {
@@ -910,6 +941,28 @@ class _AddExperienceFlowState extends ConsumerState<AddExperienceFlow> {
     });
   }
 
+  void _handleBrowserVoiceFrame(VoiceMeterFrame frame) {
+    if (!mounted || !_recording) {
+      return;
+    }
+
+    final now = DateTime.now();
+    final informationDelta = _consumeInformationDelta(frame.level, now);
+    _lastAudioChunkAt = now;
+    setState(() {
+      if (frame.samples.isNotEmpty) {
+        _waveSamples
+          ..removeRange(0, frame.samples.length)
+          ..addAll(frame.samples);
+      }
+      _liveLevel = _smoothLevel(_liveLevel, frame.level);
+      _informationUnits = math.min(
+        _minimumInformationUnits,
+        _informationUnits + informationDelta,
+      );
+    });
+  }
+
   double _normalizeDbLevel(double currentDb) {
     final db = currentDb.clamp(-160.0, 0.0);
     if (db < _noiseDb) {