feat(player): configurable play/pause fade duration

The play/pause volume fade was hardcoded to 175ms, which delays the
actual mpv pause until the fade completes and makes toggling playback
feel sluggish compared to native players like mpc/mpv.

Expose the fade length as a 'Play/pause fade duration' setting (0-1000ms)
shown beneath the existing fade toggle. A value of 0 (or any duration
shorter than one fade step) now skips the fade entirely and hits mpv
immediately for an instant, snappy response. Default stays at 175ms to
preserve current behaviour.

Author: JenteJan

lib/l10n/app_en.arb

@@ -984,6 +984,10 @@
   "@settingsPlayerPlayPauseFadeTitle": {},
   "settingsPlayerPlayPauseFadeDesc": "Fade volume in and out when playing or pausing",
   "@settingsPlayerPlayPauseFadeDesc": {},
+  "settingsPlayerPlayPauseFadeDurationTitle": "Play/pause fade duration",
+  "@settingsPlayerPlayPauseFadeDurationTitle": {},
+  "settingsPlayerPlayPauseFadeDurationDesc": "How long the volume fade takes when playing or pausing. Lower values feel snappier; set to 0 for an instant response.",
+  "@settingsPlayerPlayPauseFadeDurationDesc": {},
   "settingsPlayerBufferSizeDesc": "Configure the buffer size for video playback, determining how much data is loaded into the cache.",
   "@settingsPlayerBufferSizeDesc": {},
   "settingsPlayerTitle": "Player",

lib/models/settings/video_player_settings.dart

@@ -108,6 +108,7 @@ abstract class VideoPlayerSettingsModel with _$VideoPlayerSettingsModel {
     @Default(true) bool enableReplayGain,
     @Default(ReplayGainVolumeLevel.quiet) ReplayGainVolumeLevel replayGainVolumeLevel,
     @Default(true) bool enablePlayPauseFade,
+    @Default(175) int playPauseFadeDurationMs,
     @Default(true) bool enableCrossfade,
     @Default(400) int crossfadeDurationMs,
   }) = _VideoPlayerSettingsModel;

lib/models/settings/video_player_settings.freezed.dart

@@ -187,6 +187,9 @@ class VideoPlayerSettingsProviderNotifier extends StateNotifier<VideoPlayerSetti
 
   void setEnablePlayPauseFade(bool value) => state = state.copyWith(enablePlayPauseFade: value);
 
+  void setPlayPauseFadeDurationMs(int value) =>
+      state = state.copyWith(playPauseFadeDurationMs: value.clamp(0, 1000));
+
   void setReplayGainVolumeLevel(ReplayGainVolumeLevel value) => state = state.copyWith(replayGainVolumeLevel: value);
 
   void setEnableCrossfade(bool value) {

lib/models/settings/video_player_settings.g.dart

@@ -437,6 +437,44 @@ class _PlayerSettingsPageState extends ConsumerState<PlayerSettingsPage> {
                     onChanged: (value) => provider.setEnablePlayPauseFade(value),
                   ),
                 ),
+              if (currentPlayer == PlayerOptions.libMPV && videoSettings.enablePlayPauseFade)
+                Padding(
+                  padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
+                  child: Column(
+                    crossAxisAlignment: CrossAxisAlignment.start,
+                    children: [
+                      Text(
+                        context.localized.settingsPlayerPlayPauseFadeDurationTitle,
+                        style: Theme.of(context).textTheme.titleLarge,
+                      ),
+                      Padding(
+                        padding: const EdgeInsets.only(bottom: 8),
+                        child: Text(
+                          context.localized.settingsPlayerPlayPauseFadeDurationDesc,
+                          style: Theme.of(context).textTheme.bodyMedium,
+                        ),
+                      ),
+                      Row(
+                        children: [
+                          Expanded(
+                            child: FladderSlider(
+                              min: 0,
+                              max: 1000,
+                              value: videoSettings.playPauseFadeDurationMs.toDouble(),
+                              divisions: 40,
+                              onChanged: (value) => provider.setPlayPauseFadeDurationMs(value.round()),
+                            ),
+                          ),
+                          const SizedBox(width: 12),
+                          Text(
+                            '${videoSettings.playPauseFadeDurationMs} ms',
+                            style: Theme.of(context).textTheme.bodyLarge,
+                          ),
+                        ],
+                      ),
+                    ],
+                  ),
+                ),
               if (currentPlayer == PlayerOptions.libMPV)
                 SettingsListTile(
                   label: Text(context.localized.settingsPlayerBufferSizeTitle),

lib/providers/settings/video_player_settings_provider.dart

@@ -46,7 +46,7 @@ class LibMPV extends BasePlayer {
   double _preferredVolume = 100;
   int _crossfadeGeneration = 0;
   Timer? _fadeTimer;
-  Duration get playPauseFadeDuration => const Duration(milliseconds: 175);
+  Duration get playPauseFadeDuration => Duration(milliseconds: _settings.playPauseFadeDurationMs);
 
   @override
   Future<void> init(VideoPlayerSettingsModel settings) async {
@@ -372,17 +372,22 @@ class LibMPV extends BasePlayer {
 
     _fadeTimer?.cancel();
 
-    if (!_settings.enablePlayPauseFade) {
+    const stepMs = 16;
+    final steps = playPauseFadeDuration.inMilliseconds ~/ stepMs;
+
+    // Skip the fade entirely when disabled or the configured duration is too
+    // short to produce at least one step. This makes play/pause hit mpv
+    // immediately for a snappy, mpc-like response.
+    if (!_settings.enablePlayPauseFade || steps <= 0) {
       if (fadingIn) {
+        player.setVolume(_preferredVolume);
         player.play();
       } else {
         player.pause();
       }
       return;
     }
 
-    const stepMs = 16;
-    final steps = playPauseFadeDuration.inMilliseconds ~/ stepMs;
     final stepSize = _preferredVolume / steps;
 
     if (fadingIn) player.play();