fix(subtitles): render Korean glyphs on the MPV path via bundled Hangul font

GoNotoCurrent lacks Hangul syllables, and the Android libmpv build has no
fontconfig/system-font fallback, so libass could not resolve any Korean
glyph and subtitles rendered as boxes. Ship a Hangul subset of
GoNotoKurrent-Regular beside the default font in the extracted subtitle
fonts directory; libass picks it up as fallback by glyph coverage.

close #1932

lib/mpv/font_loader.dart

@@ -6,11 +6,28 @@ import 'package:path_provider/path_provider.dart';
 import '../utils/app_logger.dart';
 
 /// Extracts font files from Flutter assets to the cache directory for
-/// comprehensive Unicode coverage (including CJK characters) for libass subtitles.
+/// comprehensive Unicode coverage (including CJK and Hangul characters) for
+/// libass subtitles.
+///
+/// GoNotoCurrent (the primary font) covers every common script except Korean,
+/// and the Android libmpv build has no fontconfig/system-font fallback, so
+/// libass can only find glyphs in this directory. The Hangul subset next to
+/// it provides the missing syllables: generated from GoNotoKurrent-Regular
+/// (satbyy/go-noto-universal v7.0) via fontTools.subset, keeping Hangul
+/// Syllables, Jamo, compat Jamo, and common Hangul punctuation.
 class SubtitleFontLoader {
   static const String _fontAssetPath = 'assets/go-noto-current-regular.ttf';
   static const String _fontName = 'Go Noto Current-Regular';
 
+  /// Hangul-only subset of Go Noto Kurrent-Regular (see class docs).
+  static const String _hangulFontAssetPath = 'assets/go-noto-kurrent-hangul.ttf';
+
+  /// Font files extracted to the subtitle fonts directory, in extraction order.
+  static const List<(String, String)> _fonts = [
+    (_fontAssetPath, 'go-noto-current-regular.ttf'),
+    (_hangulFontAssetPath, 'go-noto-kurrent-hangul.ttf'),
+  ];
+
   /// In-memory cache of the resolved font directory. The filesystem work
   /// (temp dir lookup, existence checks, asset extraction) is idempotent per
   /// process — caching the result skips ~20ms on every subsequent Player
@@ -30,10 +47,10 @@ class SubtitleFontLoader {
         await fontDir.create(recursive: true);
       }
 
-      final fontFile = File(path.join(fontDir.path, 'go-noto-current-regular.ttf'));
-
-      if (!await fontFile.exists()) {
-        final fontData = await rootBundle.load(_fontAssetPath);
+      for (final (assetPath, fileName) in _fonts) {
+        final fontFile = File(path.join(fontDir.path, fileName));
+        if (await fontFile.exists()) continue;
+        final fontData = await rootBundle.load(assetPath);
         await fontFile.writeAsBytes(fontData.buffer.asUint8List());
       }
 

pubspec.yaml

@@ -146,6 +146,7 @@ flutter:
     - assets/seerr_mark.svg
     - assets/mdblist_mark.svg
     - assets/go-noto-current-regular.ttf
+    - assets/go-noto-kurrent-hangul.ttf
     - assets/shaders/nvscaler/
     - assets/shaders/artcnn/
     - assets/shaders/anime4k/

test/mpv/font_loader_test.dart

@@ -0,0 +1,57 @@
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:path/path.dart' as p;
+import 'package:path_provider_platform_interface/path_provider_platform_interface.dart';
+import 'package:plezy/mpv/font_loader.dart';
+
+import '../test_helpers/io_fakes.dart';
+
+/// Guards the subtitle-font extraction contract: libass on Android MPV has no
+/// fontconfig/system fallback, so every script must ship inside the one
+/// directory this loader produces. Losing a font here silently regresses
+/// glyph coverage for subtitles (e.g. #1932, Korean Hangul).
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+
+  late Directory tempRoot;
+  late PathProviderPlatform originalPlatform;
+
+  setUp(() {
+    originalPlatform = PathProviderPlatform.instance;
+    tempRoot = Directory.systemTemp.createTempSync('font_loader_test');
+    PathProviderPlatform.instance = FakePathProvider(tempRoot);
+  });
+
+  tearDown(() {
+    PathProviderPlatform.instance = originalPlatform;
+    tempRoot.deleteSync(recursive: true);
+  });
+
+  // loadSubtitleFont() caches its result per process, so only this test may
+  // trigger extraction.
+
+  test('extracts the default and Hangul fonts into one directory', () async {
+    final fontDir = await SubtitleFontLoader.loadSubtitleFont();
+
+    expect(fontDir, isNotNull);
+    final dir = Directory(fontDir!);
+    expect(dir.existsSync(), isTrue);
+
+    for (final fileName in ['go-noto-current-regular.ttf', 'go-noto-kurrent-hangul.ttf']) {
+      final fontFile = File(p.join(fontDir, fileName));
+      expect(fontFile.existsSync(), isTrue, reason: '$fileName missing');
+      final bytes = fontFile.readAsBytesSync();
+      expect(bytes.length, greaterThan(0), reason: '$fileName empty');
+      // TrueType magic: 0x00010000. Catches a corrupt/truncated asset.
+      expect(bytes.sublist(0, 4), Uint8List.fromList([0x00, 0x01, 0x00, 0x00]));
+    }
+  });
+
+  test('default font name stays Go Noto Current-Regular', () {
+    // configureSubtitleFonts() sets sub-font to this exact name; libass falls
+    // back to the Hangul subset for Korean glyphs.
+    expect(SubtitleFontLoader.fontName, 'Go Noto Current-Regular');
+  });
+}