fix(plex): support no-burn transcode subtitles

lib/mpv/player/player_base.dart

@@ -46,6 +46,8 @@ abstract class PlayerBase with PlayerStreamControllersMixin implements Player {
   int _lastEmitMs = 0;
   int _lastCacheStateMs = 0;
   int _positionMs = 0;
+  Duration _timelineOffset = Duration.zero;
+  Duration? _timelineDuration;
   int _nextPropId = 0;
   final Map<int, String> _propIdToName = {};
 
@@ -142,13 +144,13 @@ abstract class PlayerBase with PlayerStreamControllersMixin implements Player {
 
       case 'time-pos':
         if (value is num) {
-          _positionMs = (value * 1000).round();
+          final pos = _toTimelinePosition(Duration(milliseconds: (value * 1000).round()));
+          _positionMs = pos.inMilliseconds;
           // Only allocate Duration + copyWith + emit at ~4Hz (250ms).
           // Raw int is stored every tick so synchronous reads via _positionMs stay current.
           final nowMs = _throttleSw.elapsedMilliseconds;
           if (nowMs - _lastEmitMs >= 250) {
             _lastEmitMs = nowMs;
-            final pos = Duration(milliseconds: _positionMs);
             _state = _state.copyWith(position: pos);
             positionController.add(pos);
           }
@@ -157,7 +159,7 @@ abstract class PlayerBase with PlayerStreamControllersMixin implements Player {
 
       case 'duration':
         if (value is num) {
-          final duration = Duration(milliseconds: (value * 1000).toInt());
+          final duration = _timelineDuration ?? _toTimelinePosition(Duration(milliseconds: (value * 1000).toInt()));
           _state = _state.copyWith(duration: duration);
           durationController.add(duration);
         }
@@ -174,7 +176,7 @@ abstract class PlayerBase with PlayerStreamControllersMixin implements Player {
           final nowMs = _throttleSw.elapsedMilliseconds;
           if (nowMs - _lastCacheStateMs < 250) break;
           _lastCacheStateMs = nowMs;
-          final buffer = Duration(milliseconds: (value * 1000).toInt());
+          final buffer = _toTimelinePosition(Duration(milliseconds: (value * 1000).toInt()));
           _state = _state.copyWith(buffer: buffer);
           bufferController.add(buffer);
           // Synthesize a single range for players without demuxer-cache-state (ExoPlayer).
@@ -295,7 +297,7 @@ abstract class PlayerBase with PlayerStreamControllersMixin implements Player {
     // Extract cache-end for the single buffer duration (replaces demuxer-cache-time)
     final cacheEnd = cacheState['cache-end'] as num?;
     if (cacheEnd != null) {
-      final buffer = Duration(milliseconds: (cacheEnd * 1000).toInt());
+      final buffer = _toTimelinePosition(Duration(milliseconds: (cacheEnd * 1000).toInt()));
       _state = _state.copyWith(buffer: buffer);
       bufferController.add(buffer);
     }
@@ -311,8 +313,8 @@ abstract class PlayerBase with PlayerStreamControllersMixin implements Player {
           if (start != null && end != null) {
             ranges.add(
               BufferRange(
-                start: Duration(milliseconds: (start * 1000).toInt()),
-                end: Duration(milliseconds: (end * 1000).toInt()),
+                start: _toTimelinePosition(Duration(milliseconds: (start * 1000).toInt())),
+                end: _toTimelinePosition(Duration(milliseconds: (end * 1000).toInt())),
               ),
             );
           }
@@ -491,18 +493,35 @@ abstract class PlayerBase with PlayerStreamControllersMixin implements Player {
   }
 
   @protected
-  void resetPlaybackProgress(Duration position) {
+  void configureTimeline({Duration offset = Duration.zero, Duration? duration}) {
+    _timelineOffset = offset;
+    _timelineDuration = duration;
+  }
+
+  @protected
+  Duration sourceSeekPosition(Duration timelinePosition) {
+    final sourcePosition = timelinePosition - _timelineOffset;
+    return sourcePosition.isNegative ? Duration.zero : sourcePosition;
+  }
+
+  Duration _toTimelinePosition(Duration sourcePosition) {
+    return sourcePosition + _timelineOffset;
+  }
+
+  @protected
+  void resetPlaybackProgress(Duration sourcePosition) {
+    final position = _toTimelinePosition(sourcePosition);
     _positionMs = position.inMilliseconds;
     _state = _state.copyWith(
       completed: false,
       position: position,
-      duration: Duration.zero,
+      duration: _timelineDuration ?? Duration.zero,
       buffer: Duration.zero,
       bufferRanges: const [],
     );
     completedController.add(false);
     positionController.add(position);
-    durationController.add(Duration.zero);
+    durationController.add(_timelineDuration ?? Duration.zero);
     bufferController.add(Duration.zero);
     bufferRangesController.add(const []);
   }