feat: timeline thumbnail on dpad key-repeat

close #805

lib/widgets/video_controls/desktop_video_controls.dart

@@ -1,3 +1,4 @@
+import 'dart:async';
 import 'dart:io' show Platform;
 
 import 'package:flutter/material.dart';
@@ -171,6 +172,11 @@ class DesktopVideoControlsState extends State<DesktopVideoControls> {
   LogicalKeyboardKey? _seekDirection; // Current direction being held
   int _seekRepeatCount = 0; // Consecutive key repeats for acceleration
 
+  // Preview thumbnail during sustained dpad/keyboard seeking
+  bool _showKeyRepeatThumbnail = false;
+  Timer? _keyRepeatThumbnailTimer;
+  static const _keyRepeatThumbnailTimeout = Duration(milliseconds: 400);
+
   // Content strip state
   bool _contentStripVisible = false;
   final GlobalKey<ContentStripState> _contentStripKey = GlobalKey<ContentStripState>();
@@ -214,6 +220,7 @@ class DesktopVideoControlsState extends State<DesktopVideoControls> {
 
   @override
   void dispose() {
+    _keyRepeatThumbnailTimer?.cancel();
     _prevItemFocusNode.dispose();
     _prevChapterFocusNode.dispose();
     _skipBackFocusNode.dispose();
@@ -429,6 +436,24 @@ class DesktopVideoControlsState extends State<DesktopVideoControls> {
   void _resetSeekState() {
     _seekDirection = null;
     _seekRepeatCount = 0;
+    _keyRepeatThumbnailTimer?.cancel();
+    _keyRepeatThumbnailTimer = null;
+    if (_showKeyRepeatThumbnail) {
+      setState(() => _showKeyRepeatThumbnail = false);
+    }
+  }
+
+  /// Show the timeline preview thumbnail during sustained key-repeat seeking.
+  /// Arms a short timer that hides the thumbnail once repeats stop.
+  void _triggerKeyRepeatThumbnail() {
+    if (!_showKeyRepeatThumbnail) {
+      setState(() => _showKeyRepeatThumbnail = true);
+    }
+    _keyRepeatThumbnailTimer?.cancel();
+    _keyRepeatThumbnailTimer = Timer(_keyRepeatThumbnailTimeout, () {
+      if (!mounted) return;
+      setState(() => _showKeyRepeatThumbnail = false);
+    });
   }
 
   /// Calculate seek multiplier based on repeat count (stepped tiers)
@@ -490,6 +515,7 @@ class DesktopVideoControlsState extends State<DesktopVideoControls> {
       }
       if (event is KeyRepeatEvent) {
         _seekRepeatCount++;
+        _triggerKeyRepeatThumbnail();
       }
 
       final isForward = key == LogicalKeyboardKey.arrowRight;
@@ -680,6 +706,7 @@ class DesktopVideoControlsState extends State<DesktopVideoControls> {
               onFocusChange: _onFocusChange,
               enabled: canInteract,
               thumbnailDataBuilder: widget.thumbnailDataBuilder,
+              showKeyRepeatThumbnail: _showKeyRepeatThumbnail,
             ),
           ],
           // Row 2: Playback controls and options

lib/widgets/video_controls/widgets/timeline_slider.dart

@@ -37,6 +37,11 @@ class TimelineSlider extends StatefulWidget {
   /// Optional callback that returns thumbnail image bytes for a given timestamp.
   final Uint8List? Function(Duration time)? thumbnailDataBuilder;
 
+  /// When true, show the preview thumbnail at the current playback position.
+  /// Intended for sustained dpad/keyboard seeking where the decoder cannot
+  /// keep up with accumulated seeks. Single presses should leave this false.
+  final bool showKeyRepeatThumbnail;
+
   const TimelineSlider({
     super.key,
     required this.position,
@@ -51,6 +56,7 @@ class TimelineSlider extends StatefulWidget {
     this.onFocusChange,
     this.enabled = true,
     this.thumbnailDataBuilder,
+    this.showKeyRepeatThumbnail = false,
   });
 
   @override
@@ -153,6 +159,13 @@ class _TimelineSliderState extends State<TimelineSlider> {
             final fraction = ((_mousePosition! - _sliderPadding) / trackWidth).clamp(0.0, 1.0);
             final time = Duration(milliseconds: (fraction * durationMs).round());
             tooltip = _buildTooltip(sliderWidth, _mousePosition!, time);
+          } else if (widget.showKeyRepeatThumbnail && widget.thumbnailDataBuilder != null) {
+            // Preview thumbnail at the current playback position while the
+            // user holds a dpad/keyboard direction. The decoder lags behind
+            // rapid seeks, so the BIF thumbnail is the only live feedback.
+            final fraction = (widget.position.inMilliseconds / durationMs).clamp(0.0, 1.0);
+            final px = _sliderPadding + fraction * trackWidth;
+            tooltip = _buildTooltip(sliderWidth, px, widget.position);
           }
         }
 

lib/widgets/video_controls/widgets/video_timeline_bar.dart

@@ -41,6 +41,10 @@ class VideoTimelineBar extends StatelessWidget {
   /// Optional callback that returns thumbnail image bytes for a given timestamp.
   final Uint8List? Function(Duration time)? thumbnailDataBuilder;
 
+  /// When true, show the preview thumbnail at the current playback position
+  /// (used during sustained dpad/keyboard key-repeat seeking).
+  final bool showKeyRepeatThumbnail;
+
   const VideoTimelineBar({
     super.key,
     required this.player,
@@ -55,6 +59,7 @@ class VideoTimelineBar extends StatelessWidget {
     this.enabled = true,
     this.showFinishTime = false,
     this.thumbnailDataBuilder,
+    this.showKeyRepeatThumbnail = false,
   });
 
   @override
@@ -164,6 +169,7 @@ class VideoTimelineBar extends StatelessWidget {
       onFocusChange: onFocusChange,
       enabled: enabled,
       thumbnailDataBuilder: thumbnailDataBuilder,
+      showKeyRepeatThumbnail: showKeyRepeatThumbnail,
     );
   }
 }