fix(subtitles): suppress ASS font texture artifacts

- Filter clipped glyph runs and alpha-texture effects from parsed ASS cues
- Add regression coverage for repeated-glyph and per-character texture signs

src/core/services/subtitle-cue-parser.test.ts

@@ -1250,6 +1250,41 @@ test('parseSubtitleCues drops symbol-font glyph decoration from a reconstructed
   assert.equal(cues[0]?.text, 'sotto mimi ni ateru to');
 });
 
+test('parseSubtitleCues drops clipped repeated-glyph texture text', () => {
+  const content = [
+    '[Events]',
+    'Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text',
+    "Dialogue: 10,0:00:01.00,0:00:04.00,Default,,0,0,0,,I'm blocking them.",
+    'Dialogue: 2,0:00:01.00,0:00:04.00,MarySigns,,0,0,0,,{\\pos(960,80)\\fnSerangkaian Pattern Regular\\clip(800,20,1120,140)}LLLLLLLLLLLLLLLLLLLLLLLL',
+    'Dialogue: 3,0:00:01.00,0:00:04.00,MarySigns,,0,0,0,,{\\pos(960,150)\\fnSF Pro Display}Enter a message',
+  ].join('\n');
+
+  assert.deepEqual(
+    parseSubtitleCues(content, 'test.ass').map((cue) => cue.text),
+    ["I'm blocking them.", 'Enter a message'],
+  );
+});
+
+test('parseSubtitleCues drops per-character alpha texture text', () => {
+  const content = [
+    '[Events]',
+    'Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text',
+    "Dialogue: 10,0:00:01.00,0:00:04.00,Default,Girl,0,0,0,,So Doloris was actually Uika-chan from sumimi! That's amazing!",
+    "Dialogue: 2,0:00:01.00,0:00:04.00,MarySigns,,0,0,0,,{\\pos(960,240)\\fnCinzel}Hanasakigawa Girl's School",
+    'Dialogue: 3,0:00:01.00,0:00:04.00,MarySigns,,0,0,0,,{\\pos(960,300)\\fnSplit splat splodge\\clip(800,200,1120,400)}d{\\2a1}s{\\2a0}h{\\2a1}f{\\2a0}k{\\2a1}h{\\2a0}f{\\2a1}s{\\2a0}d{\\2a1}f{\\2a0}e',
+    'Dialogue: 3,0:00:01.00,0:00:04.00,MarySigns,,0,0,0,,{\\pos(980,340)\\fnSplit splat splodge}f {\\2a1}a',
+    'Dialogue: 4,0:00:01.00,0:00:04.00,MarySigns,,0,0,0,,{\\pos(960,360)\\fnGrain SemiBold}5{\\2a1}X{\\2a0}N{\\2a1}T{\\2a0}f{\\2a1}I{\\2a0}g{\\2a1}F{\\2a0}B{\\2a1}?{\\2a0}k{\\2a1}u{\\2a0}C{\\2a1}m',
+  ].join('\n');
+
+  assert.deepEqual(
+    parseSubtitleCues(content, 'test.ass').map((cue) => cue.text),
+    [
+      "So Doloris was actually Uika-chan from sumimi! That's amazing!",
+      "Hanasakigawa Girl's School",
+    ],
+  );
+});
+
 test('parseSubtitleCues separates overlapping positioned English lyric sequences', () => {
   const fragments = [
     ['my', 642, '0:00:01.00', '0:00:04.05'],

src/core/services/subtitle-cue-parser.ts

@@ -964,6 +964,69 @@ function staticFontOverride(cue: AnnotatedSubtitleCue): string | null {
   return font;
 }
 
+const MIN_TEXTURE_GLYPH_RUN = 8;
+const MIN_TEXTURE_ALPHA_OVERRIDES = 6;
+
+function hasStaticOverride(cue: AnnotatedSubtitleCue, expectedName: string): boolean {
+  return cue.overrides.some(
+    (command) => !command.animated && command.name.toLowerCase() === expectedName,
+  );
+}
+
+/**
+ * Some ASS signs feed placeholder glyphs through a texture font instead of drawing the
+ * texture as a vector. A long clipped single-glyph run or frequent changing secondary
+ * alpha tags identifies the effect without guessing from its visible text or font name.
+ */
+function isAssFontTextureSeed(cue: AnnotatedSubtitleCue): boolean {
+  if (staticFontOverride(cue) === null || fragmentPosition(cue) === null) {
+    return false;
+  }
+
+  const glyphs = [...compactCueMatchText(cue)];
+  const isClippedRepeatedGlyphRun =
+    glyphs.length >= MIN_TEXTURE_GLYPH_RUN &&
+    glyphs.every((glyph) => glyph === glyphs[0]) &&
+    (hasStaticOverride(cue, 'clip') || hasStaticOverride(cue, 'iclip'));
+  if (isClippedRepeatedGlyphRun) {
+    return true;
+  }
+
+  const secondaryAlpha = cue.overrides.filter(
+    (command) => !command.animated && command.name.toLowerCase() === '2a',
+  );
+  if (secondaryAlpha.length < MIN_TEXTURE_ALPHA_OVERRIDES) {
+    return false;
+  }
+  const alphaValues = secondaryAlpha.map((command) => command.args.toLowerCase());
+  return alphaValues.every((value, index) => index === 0 || value !== alphaValues[index - 1]);
+}
+
+function assFontTextureGroupKey(cue: AnnotatedSubtitleCue): string | null {
+  const font = staticFontOverride(cue);
+  return font === null
+    ? null
+    : `${assEventGroupKey(cue)}\0${cue.startTime}\0${cue.endTime}\0${font}`;
+}
+
+function removeAssFontTextureEvents(events: ParsedAssEvents): ParsedAssEvents {
+  // Short pieces can share the seeded font effect without carrying enough tags to identify
+  // themselves. Limit propagation to the exact style, actor, time span, and font group.
+  const textureGroups = new Set(
+    events.dialogue
+      .filter(isAssFontTextureSeed)
+      .map(assFontTextureGroupKey)
+      .filter((key): key is string => key !== null),
+  );
+  return {
+    dialogue: events.dialogue.filter((cue) => {
+      const key = assFontTextureGroupKey(cue);
+      return key === null || !textureGroups.has(key);
+    }),
+    comments: events.comments,
+  };
+}
+
 /**
  * Generated lyric effects often layer decoration over the real syllables: single letters
  * positioned above each glyph, animated in, and rendered through a `\fn` override to a
@@ -1434,7 +1497,8 @@ function parseAnnotatedAssEvents(content: string): ParsedAssEvents {
 }
 
 function parseAnnotatedAssCues(content: string): AnnotatedSubtitleCue[] {
-  return recoverFragmentOnlyAssLines(recoverCanonicalAssEvents(parseAnnotatedAssEvents(content)));
+  const events = removeAssFontTextureEvents(parseAnnotatedAssEvents(content));
+  return recoverFragmentOnlyAssLines(recoverCanonicalAssEvents(events));
 }
 
 export function parseAssCues(content: string): SubtitleCue[] {