feat(android): loudness normalization for exoplayer via audiofx

close #1289

lib/mpv/player/platform/player_android.dart

@@ -12,6 +12,7 @@ class PlayerAndroid extends PlayerBase {
   int? _bufferSizeBytes;
   bool _tunnelingEnabled = true;
   String _dvConversionMode = 'auto';
+  bool _audioNormalizationEnabled = false;
 
   /// The native plugin switched from ExoPlayer to its mpv fallback for this
   /// session. Sticky for the instance lifetime, mirroring the native flag
@@ -259,6 +260,24 @@ class PlayerAndroid extends PlayerBase {
     }
   }
 
+  @override
+  Future<void> setAudioNormalization(bool enabled) async {
+    if (disposed) return;
+    _audioNormalizationEnabled = enabled;
+    final initFuture = _initFuture;
+    if (initialized) {
+      await invoke('setAudioNormalization', {'enabled': enabled});
+    } else if (initFuture != null) {
+      await initFuture;
+      if (!disposed && initialized && _audioNormalizationEnabled == enabled) {
+        await invoke('setAudioNormalization', {'enabled': enabled});
+      }
+    }
+    // Keep the mpv af property flowing through setMpvProperty so the plugin's
+    // pendingMpvProperties replay applies loudnorm if exo falls back to mpv.
+    await super.setAudioNormalization(enabled);
+  }
+
   @override
   Future<String?> getProperty(String name) async {
     if (disposed) return null;

lib/mpv/player/player.dart

@@ -209,6 +209,14 @@ abstract class Player {
   /// passed through to the audio device without decoding.
   Future<void> setAudioPassthrough(bool enabled);
 
+  /// Enable or disable loudness normalization.
+  ///
+  /// mpv backends insert/remove the `loudnorm` audio filter. Android
+  /// ExoPlayer attaches platform audio effects (DynamicsProcessing on
+  /// API 28+, LoudnessEnhancer otherwise) and forces decoded non-tunneled
+  /// PCM output while enabled so the effects can process the stream.
+  Future<void> setAudioNormalization(bool enabled);
+
   /// Show or hide the video rendering layer.
   ///
   /// On macOS, this controls the Metal layer visibility.

lib/mpv/player/player_base.dart

@@ -668,6 +668,15 @@ abstract class PlayerBase with PlayerStreamControllersMixin implements Player {
   // ignore: no-empty-block - base no-op, overridden by platform subclasses
   Future<void> setAudioPassthrough(bool enabled) async {}
 
+  /// mpv loudnorm targeting streaming-style loudness; mirrored by the
+  /// Android ExoPlayer effect parameters in AudioNormalizationEffect.kt.
+  static const _loudnormFilter = 'loudnorm=I=-14:TP=-3:LRA=4';
+
+  @override
+  Future<void> setAudioNormalization(bool enabled) async {
+    await setProperty('af', enabled ? _loudnormFilter : '');
+  }
+
   @override
   // ignore: no-empty-block - base no-op, overridden by platform subclasses
   Future<void> setLogLevel(String level) async {}