fix(overlay): collapse karaoke syllable spam in secondary subtitles (#139)

changes/secondary-sub-karaoke-collapse.md

@@ -0,0 +1,4 @@
+type: fixed
+area: overlay
+
+- Fixed secondary subtitles stacking dozens of one-syllable lines down the screen during karaoke-typeset openings/endings, which made the hover-pause band cover the whole video: karaoke-like event spam is now collapsed into a single deduped line, and the secondary subtitle area is height-capped so it always stays a strip at the top.

src/renderer/style.css

@@ -1842,6 +1842,10 @@ body.layer-modal #overlay {
   text-align: center;
   font-size: 24px;
   line-height: 1.5;
+  /* Backstop: pathological tracks (karaoke typesetting, sign spam) must never grow
+     the hover-pause band beyond a top strip. ~4 lines at line-height 1.5. */
+  max-height: 6em;
+  overflow: hidden;
   color: #ffffff;
   -webkit-text-stroke: 0.45px rgba(0, 0, 0, 0.7);
   paint-order: stroke fill;

src/renderer/subtitle-render.test.ts

@@ -11,6 +11,7 @@ import {
   getFrequencyRankLabelForToken,
   getJlptLevelLabelForToken,
   normalizeSubtitle,
+  prepareSecondarySubtitleLines,
   sanitizeSubtitleHoverTokenColor,
   shouldRenderTokenizedSubtitle,
 } from './subtitle-render.js';
@@ -1404,3 +1405,43 @@ test('subtitle annotation CSS underlines JLPT tokens without changing token colo
     /body\.layer-visible\s+#secondarySubContainer\s*\{[^}]*display:\s*none/i,
   );
 });
+
+test('prepareSecondarySubtitleLines collapses karaoke syllable spam into one deduped line', () => {
+  // Karaoke-typeset OP/ED: one ASS event per syllable, duplicated across layers,
+  // joined with \N by mpv's secondary-sub-text.
+  const karaoke = ['ya', 'This', 'ya', 'This', 'ya', 'This', 'no', 'ma', 'ups', 'ma', 'ups'].join(
+    '\\N',
+  );
+
+  assert.deepEqual(prepareSecondarySubtitleLines(karaoke), ['ya This no ma ups']);
+});
+
+test('prepareSecondarySubtitleLines keeps normal dialogue lines intact', () => {
+  const dialogue = ' I never expected this. \\N\\N But here we are. ';
+
+  assert.deepEqual(prepareSecondarySubtitleLines(dialogue), [
+    'I never expected this.',
+    'But here we are.',
+  ]);
+});
+
+test('prepareSecondarySubtitleLines does not collapse many long simultaneous lines', () => {
+  const lines = Array.from({ length: 9 }, (_, i) => `This is a full sentence number ${i}.`);
+
+  assert.deepEqual(prepareSecondarySubtitleLines(lines.join('\\N')), lines);
+});
+
+test('prepareSecondarySubtitleLines strips ASS override tags and handles empty input', () => {
+  assert.deepEqual(prepareSecondarySubtitleLines('{\\an8}Sign text'), ['Sign text']);
+  assert.deepEqual(prepareSecondarySubtitleLines(''), []);
+  assert.deepEqual(prepareSecondarySubtitleLines('{\\an8}'), []);
+});
+
+test('secondary subtitle root CSS caps height so hover-pause band stays a top strip', () => {
+  const srcCssPath = path.join(process.cwd(), 'src', 'renderer', 'style.css');
+  const cssText = fs.readFileSync(srcCssPath, 'utf-8');
+
+  const secondaryRootBlock = extractClassBlock(cssText, '#secondarySubRoot');
+  assert.match(secondaryRootBlock, /max-height:\s*6em;/);
+  assert.match(secondaryRootBlock, /overflow:\s*hidden;/);
+});

src/renderer/subtitle-render.ts

@@ -652,6 +652,43 @@ function renderPlainTextPreserveLineBreaks(root: ParentNode, text: string): void
   root.appendChild(fragment);
 }
 
+// Karaoke-typeset OP/ED tracks emit one ASS event per syllable (duplicated across
+// layers), and mpv's secondary-sub-text joins every active event with newlines —
+// rendering those verbatim stacks dozens of tiny lines down the screen and turns the
+// hover-pause band into a full-screen trap.
+const KARAOKE_MIN_LINE_COUNT = 8;
+const KARAOKE_MAX_MEDIAN_LINE_LENGTH = 4;
+
+function isKaraokeLikeLineSet(lines: string[]): boolean {
+  if (lines.length < KARAOKE_MIN_LINE_COUNT) return false;
+  const lengths = lines.map((line) => line.length).sort((a, b) => a - b);
+  const median = lengths[Math.floor(lengths.length / 2)] ?? 0;
+  return median <= KARAOKE_MAX_MEDIAN_LINE_LENGTH;
+}
+
+export function prepareSecondarySubtitleLines(text: string): string[] {
+  const normalized = normalizeSubtitle(text, true, false);
+
+  if (!normalized) return [];
+
+  const lines = normalized
+    .split('\n')
+    .map((line) => line.trim())
+    .filter((line) => line.length > 0);
+  if (!isKaraokeLikeLineSet(lines)) {
+    return lines;
+  }
+
+  const seen = new Set<string>();
+  const unique: string[] = [];
+  for (const line of lines) {
+    if (seen.has(line)) continue;
+    seen.add(line);
+    unique.push(line);
+  }
+  return [unique.join(' ')];
+}
+
 export function createSubtitleRenderer(ctx: RendererContext) {
   let lastPrimarySubtitleRenderKey: string | null = null;
   let lastPrimarySubtitleNormalizedText: string | null = null;
@@ -750,15 +787,7 @@ export function createSubtitleRenderer(ctx: RendererContext) {
     ctx.dom.secondarySubRoot.replaceChildren();
     if (!text) return;
 
-    const normalized = text
+    const lines = prepareSecondarySubtitleLines(text);
-      .replace(/\\N/g, '\n')
-      .replace(/\\n/g, '\n')
-      .replace(/\{[^}]*\}/g, '')
-      .trim();
-
-    if (!normalized) return;
-
-    const lines = normalized.split('\n');
     for (let i = 0; i < lines.length; i += 1) {
       const line = lines[i];
       if (line) {