feat: hotkey for subtitle offset

lib/models/settings/video_player_settings.dart

@@ -36,6 +36,8 @@ enum VideoHotKeys {
   takeScreenshot,
   takeScreenshotClean,
   toggleSubtitles,
+  subtitleOffsetBackward,
+  subtitleOffsetForward,
   exit;
 
   const VideoHotKeys();
@@ -63,6 +65,8 @@ enum VideoHotKeys {
       VideoHotKeys.takeScreenshot => context.localized.takeScreenshot,
       VideoHotKeys.takeScreenshotClean => context.localized.takeScreenshotClean,
       VideoHotKeys.toggleSubtitles => context.localized.toggleSubtitles,
+      VideoHotKeys.subtitleOffsetBackward => 'Subtitle backward',
+      VideoHotKeys.subtitleOffsetForward => 'Subtitle forward',
       VideoHotKeys.exit => context.localized.exit,
     };
   }
@@ -312,6 +316,10 @@ Map<VideoHotKeys, KeyCombination> get _defaultVideoHotKeys => {
           VideoHotKeys.takeScreenshotClean =>
             KeyCombination(key: LogicalKeyboardKey.keyG, modifier: LogicalKeyboardKey.controlLeft),
           VideoHotKeys.toggleSubtitles => KeyCombination(key: LogicalKeyboardKey.keyT),
+          VideoHotKeys.subtitleOffsetBackward =>
+            KeyCombination(key: LogicalKeyboardKey.arrowLeft, modifier: LogicalKeyboardKey.controlLeft),
+          VideoHotKeys.subtitleOffsetForward =>
+            KeyCombination(key: LogicalKeyboardKey.arrowRight, modifier: LogicalKeyboardKey.controlLeft),
           VideoHotKeys.exit => KeyCombination(key: LogicalKeyboardKey.escape),
         },
     };

lib/providers/settings/video_player_settings_provider.dart

@@ -19,6 +19,8 @@ final videoPlayerSettingsProvider =
   return VideoPlayerSettingsProviderNotifier(ref);
 });
 
+final subtitleTimingOffsetProvider = StateProvider<Duration>((ref) => Duration.zero);
+
 final playbackRateProvider = StateProvider<double>((ref) => 1.0);
 
 class VideoPlayerSettingsProviderNotifier extends StateNotifier<VideoPlayerSettingsModel> {

lib/screens/video_player/components/video_player_subtitle_offset_indicator.dart

@@ -0,0 +1,79 @@
+import 'package:flutter/material.dart';
+
+import 'package:async/async.dart';
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:iconsax_plus/iconsax_plus.dart';
+
+import 'package:fladder/providers/settings/video_player_settings_provider.dart';
+
+class VideoPlayerSubtitleOffsetIndicator extends ConsumerStatefulWidget {
+  const VideoPlayerSubtitleOffsetIndicator({super.key});
+
+  @override
+  ConsumerState<ConsumerStatefulWidget> createState() => _VideoPlayerSubtitleOffsetIndicatorState();
+}
+
+class _VideoPlayerSubtitleOffsetIndicatorState extends ConsumerState<VideoPlayerSubtitleOffsetIndicator> {
+  late Duration currentOffset = ref.read(subtitleTimingOffsetProvider);
+
+  bool showIndicator = false;
+  late final timer = RestartableTimer(const Duration(seconds: 1), () {
+    setState(() {
+      showIndicator = false;
+    });
+  });
+
+  @override
+  void dispose() {
+    showIndicator = false;
+    timer.cancel();
+    super.dispose();
+  }
+
+  @override
+  Widget build(BuildContext context) {
+    ref.listen(
+      subtitleTimingOffsetProvider,
+      (previous, next) {
+        if (previous == next) return;
+        setState(() {
+          showIndicator = true;
+          currentOffset = next;
+        });
+        timer.reset();
+      },
+    );
+
+    return IgnorePointer(
+      child: AnimatedOpacity(
+        duration: const Duration(milliseconds: 250),
+        opacity: showIndicator ? 1 : 0,
+        child: Center(
+          child: Container(
+            decoration: BoxDecoration(
+              color: Colors.black.withValues(alpha: 0.85),
+              borderRadius: BorderRadius.circular(16),
+            ),
+            child: Padding(
+              padding: const EdgeInsets.all(16.0),
+              child: Row(
+                mainAxisSize: MainAxisSize.min,
+                spacing: 12,
+                children: [
+                  const Icon(IconsaxPlusLinear.textalign_left),
+                  Text(_subtitleDelayLabel(currentOffset)),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+  }
+}
+
+String _subtitleDelayLabel(Duration offset) {
+  final absMilliseconds = offset.inMilliseconds.abs();
+  final sign = offset.inMilliseconds >= 0 ? '+' : '-';
+  return 'Subtitle $sign${absMilliseconds}ms';
+}

lib/screens/video_player/video_player_controls.dart

@@ -31,6 +31,7 @@ import 'package:fladder/screens/video_player/components/video_player_quality_con
 import 'package:fladder/screens/video_player/components/video_player_screenshot_indicator.dart';
 import 'package:fladder/screens/video_player/components/video_player_seek_indicator.dart';
 import 'package:fladder/screens/video_player/components/video_player_speed_indicator.dart';
+import 'package:fladder/screens/video_player/components/video_player_subtitle_offset_indicator.dart';
 import 'package:fladder/screens/video_player/components/video_player_volume_indicator.dart';
 import 'package:fladder/screens/video_player/components/video_progress_bar.dart';
 import 'package:fladder/screens/video_player/components/video_volume_slider.dart';
@@ -182,6 +183,7 @@ class _DesktopControlsState extends ConsumerState<DesktopControls> {
                 ),
                 VideoPlayerSeekIndicator(controller: _seekController),
                 const VideoPlayerVolumeIndicator(),
+                const VideoPlayerSubtitleOffsetIndicator(),
                 const VideoPlayerBrightnessIndicator(),
                 const VideoPlayerSpeedIndicator(),
                 const VideoPlayerScreenshotIndicator(),
@@ -1000,6 +1002,8 @@ class _DesktopControlsState extends ConsumerState<DesktopControls> {
     final mediaSegments = ref.read(playBackModel.select((value) => value?.mediaSegments));
     final position = ref.read(mediaPlaybackProvider).position;
     final playing = ref.read(mediaPlaybackProvider.select((value) => value.playing));
+    final subtitlesEnabled = ref.read(playBackModel)?.mediaStreams?.defaultSubStreamIndex != null &&
+        ref.read(playBackModel)!.mediaStreams!.defaultSubStreamIndex != -1;
 
     MediaSegment? segment = mediaSegments?.atPosition(position);
 
@@ -1064,6 +1068,16 @@ class _DesktopControlsState extends ConsumerState<DesktopControls> {
       case VideoHotKeys.toggleSubtitles:
         _toggleSubtitles();
         return true;
+      case VideoHotKeys.subtitleOffsetBackward:
+        if (!subtitlesEnabled) return false;
+        ref.read(subtitleTimingOffsetProvider.notifier).update((state) => state + const Duration(milliseconds: -250));
+        ref.read(videoPlayerProvider).shiftSubtitleOffset(const Duration(milliseconds: -250));
+        return true;
+      case VideoHotKeys.subtitleOffsetForward:
+        if (!subtitlesEnabled) return false;
+        ref.read(subtitleTimingOffsetProvider.notifier).update((state) => state + const Duration(milliseconds: 250));
+        ref.read(videoPlayerProvider).shiftSubtitleOffset(const Duration(milliseconds: 250));
+        return true;
       case VideoHotKeys.seekForwardInstant:
         final seekForwardSeconds =
             ref.read(userProvider.select((value) => value?.userSettings?.skipForwardDuration.inSeconds ?? 30));

lib/wrappers/media_control_wrapper.dart

@@ -553,6 +553,8 @@ class MediaControlsWrapper extends BaseAudioHandler implements VideoPlayerContro
   Future<int> setSubtitleTrack(SubStreamModel? model, PlaybackModel playbackModel) async =>
       await _player?.setSubtitleTrack(model, playbackModel) ?? -1;
 
+  Future<void> shiftSubtitleOffset(Duration offset) async => _player?.shiftSubtitleOffset(offset);
+
   Future<void> setVolume(double volume) async => _player?.setVolume(volume);
 
   @override

lib/wrappers/players/base_player.dart

@@ -39,6 +39,7 @@ abstract class BasePlayer {
   Future<Uint8List?> takeScreenshot();
   Future<int> setSubtitleTrack(SubStreamModel? model, PlaybackModel playbackModel);
   Future<int> setAudioTrack(AudioStreamModel? model, PlaybackModel playbackModel);
+  Future<void> shiftSubtitleOffset(Duration offset) async {}
   void applySubtitleSettings(SubtitleSettingsModel settings) {}
 
   Uri? isValidUrl(String input) {

lib/wrappers/players/lib_mpv.dart

@@ -27,6 +27,7 @@ class LibMPV extends BasePlayer {
   mpv.Player? _player;
   VideoController? _controller;
   String _currentSubtitleCodec = '';
+  Duration _subtitleOffset = Duration.zero;
 
   final StreamController<PlayerState> _stateController = StreamController.broadcast();
   @override
@@ -526,6 +527,15 @@ class LibMPV extends BasePlayer {
             )
           : null;
 
+  @override
+  Future<void> shiftSubtitleOffset(Duration offset) async {
+    if (_player?.platform is! mpv.NativePlayer) return;
+
+    _subtitleOffset += offset;
+    final nativePlayer = _player!.platform as dynamic;
+    await nativePlayer.setProperty('sub-delay', (_subtitleOffset.inMilliseconds / 1000).toStringAsFixed(3));
+  }
+
   @override
   Future<void> setVolume(double volume) async {
     _fadeTimer?.cancel();