fix(subtitles): improve secondary subtitle extraction and display (#215)

src/main.ts

@@ -588,9 +588,10 @@ import {
 import { buildSubtitleSidebarSourceKey } from './main/runtime/subtitle-prefetch-source';
 import { createSubtitlePrefetchInitController } from './main/runtime/subtitle-prefetch-init';
 import {
+  createCachedInternalSubtitleTrackExtractor,
   loadSubtitleSourceText,
-  extractInternalSubtitleTrackToTempFile,
 } from './main/runtime/internal-subtitle-extraction';
+import { createRemoteMediaPathDetector } from './main/runtime/network-media-path';
 import { applyCharacterDictionarySelection } from './main/character-dictionary-selection';
 import { getSubsyncConfig } from './subsync/utils';
 
@@ -2054,10 +2055,13 @@ const subtitlePrefetchInitController = createSubtitlePrefetchInitController({
     }
   },
 });
+const cachedInternalSubtitleTrackExtractor = createCachedInternalSubtitleTrackExtractor();
+const detectRemoteMediaPath = createRemoteMediaPathDetector();
 const resolveActiveSubtitleSidebarSourceHandler = createResolveActiveSubtitleSidebarSourceHandler({
   getFfmpegPath: () => configService.getConfig().subsync.ffmpeg_path.trim() || 'ffmpeg',
+  isRemoteMediaPath: detectRemoteMediaPath,
   extractInternalSubtitleTrack: (ffmpegPath, videoPath, track) =>
-    extractInternalSubtitleTrackToTempFile(ffmpegPath, videoPath, track),
+    cachedInternalSubtitleTrackExtractor.extract(ffmpegPath, videoPath, track),
   logDebug: (message) => logger.debug(message),
 });
 
@@ -2086,8 +2090,8 @@ const refreshSubtitlePrefetchFromActiveTrackHandler =
     // Remote media has no extractable on-disk track to fall back to, so a transient
     // resolve miss (sid briefly 'no', a cycle onto an embedded stream track) would
     // otherwise drop a working cue list for the rest of the episode.
-    shouldKeepExistingCuesOnMissingSource: (videoPath) =>
-      isYoutubeMediaPath(videoPath) || isRemoteMediaPath(videoPath),
+    shouldKeepExistingCuesOnMissingSource: async (videoPath) =>
+      isYoutubeMediaPath(videoPath) || (await detectRemoteMediaPath(videoPath)),
     subtitlePrefetchInitController,
     resolveActiveSubtitleSidebarSource: (input) => resolveActiveSubtitleSidebarSourceHandler(input),
     logDebug: (message) => logger.debug(message),
@@ -3962,6 +3966,7 @@ const {
       appState.yomitanSettingsWindow = null;
     },
     stopJellyfinRemoteSession: () => stopJellyfinRemoteSession(),
+    cleanupInternalSubtitleTrackCache: () => cachedInternalSubtitleTrackExtractor.clear(),
     cleanupYoutubeSubtitleTempDirs: () => youtubeFlowRuntime.cleanupSubtitleTempDirs(),
     cleanupYoutubeMediaCache: () => youtubeMediaCache.cleanup(),
     cleanupJellyfinSubtitleCache: () => cleanupJellyfinSubtitleCache(),
@@ -4522,6 +4527,7 @@ const {
         appState.activeParsedSubtitleMediaPath,
       );
       if ((normalizedPath || null) !== previousPath) {
+        cachedInternalSubtitleTrackExtractor.clear();
         secondarySubtitleTrackController.reset();
         const resetSubtitlePayload = { text: '', tokens: null };
         const frequencyDictionary = configService.getConfig().subtitleStyle.frequencyDictionary;

src/main/main-wiring.test.ts

@@ -183,7 +183,10 @@ test('remote media keeps parsed cues when the active subtitle source cannot be r
   )?.groups?.body;
 
   assert.ok(actionBlock);
-  assert.match(actionBlock, /isYoutubeMediaPath\(videoPath\) \|\| isRemoteMediaPath\(videoPath\)/);
+  assert.match(
+    actionBlock,
+    /isYoutubeMediaPath\(videoPath\) \|\| \(await detectRemoteMediaPath\(videoPath\)\)/,
+  );
 });
 
 test('jellyfin subtitle preload seeds the tokenization prefetch directly', () => {
@@ -860,3 +863,18 @@ test('subtitle sidebar snapshot prefers cached YouTube parsed cues before active
       snapshotBlock.indexOf('resolveActiveSubtitleSidebarSourceHandler'),
   );
 });
+
+test('main process guards internal subtitle extraction with the remote media detector', () => {
+  const source = readMainSource();
+  const resolverWiring = source.match(
+    /const resolveActiveSubtitleSidebarSourceHandler = createResolveActiveSubtitleSidebarSourceHandler\(\{(?<body>[\s\S]*?)\n\}\);/,
+  )?.groups?.body;
+
+  assert.ok(resolverWiring);
+  assert.match(source, /const detectRemoteMediaPath = createRemoteMediaPathDetector\(\);/);
+  assert.match(resolverWiring, /isRemoteMediaPath:\s*detectRemoteMediaPath/);
+  assert.match(
+    resolverWiring,
+    /extractInternalSubtitleTrack:[\s\S]*cachedInternalSubtitleTrackExtractor\.extract/,
+  );
+});

src/main/runtime/app-lifecycle-actions.test.ts

@@ -43,6 +43,7 @@ test('on will quit cleanup handler runs all cleanup steps', () => {
     destroyYomitanSettingsWindow: () => calls.push('destroy-yomitan-settings-window'),
     clearYomitanSettingsWindow: () => calls.push('clear-yomitan-settings-window'),
     stopJellyfinRemoteSession: () => calls.push('stop-jellyfin-remote'),
+    cleanupInternalSubtitleTrackCache: () => calls.push('cleanup-internal-subtitles'),
     cleanupYoutubeSubtitleTempDirs: () => calls.push('cleanup-youtube-subtitles'),
     cleanupYoutubeMediaCache: () => calls.push('cleanup-youtube-media'),
     cleanupJellyfinSubtitleCache: () => calls.push('cleanup-jellyfin-subtitles'),
@@ -50,10 +51,11 @@ test('on will quit cleanup handler runs all cleanup steps', () => {
   });
 
   cleanup();
-  assert.equal(calls.length, 34);
+  assert.equal(calls.length, 35);
   assert.equal(calls[0], 'destroy-tray');
   assert.equal(calls[calls.length - 1], 'stop-discord-presence');
   assert.ok(calls.includes('cleanup-jellyfin-subtitles'));
+  assert.ok(calls.includes('cleanup-internal-subtitles'));
   assert.ok(calls.includes('clear-windows-visible-overlay-poll'));
   assert.ok(calls.includes('clear-linux-mpv-fullscreen-overlay-refresh-timeouts'));
   assert.ok(calls.includes('cleanup-youtube-subtitles'));
@@ -97,6 +99,7 @@ test('on will quit cleanup handler cleans jellyfin subtitle cache when stopping
       calls.push('stop-jellyfin-remote');
       throw new Error('stop failed');
     },
+    cleanupInternalSubtitleTrackCache: () => calls.push('cleanup-internal-subtitles'),
     cleanupYoutubeSubtitleTempDirs: () => calls.push('cleanup-youtube-subtitles'),
     cleanupYoutubeMediaCache: () => calls.push('cleanup-youtube-media'),
     cleanupJellyfinSubtitleCache: () => calls.push('cleanup-jellyfin-subtitles'),
@@ -104,7 +107,11 @@ test('on will quit cleanup handler cleans jellyfin subtitle cache when stopping
   });
 
   assert.throws(() => cleanup(), /stop failed/);
-  assert.deepEqual(calls, ['stop-jellyfin-remote', 'cleanup-jellyfin-subtitles']);
+  assert.deepEqual(calls, [
+    'stop-jellyfin-remote',
+    'cleanup-jellyfin-subtitles',
+    'cleanup-internal-subtitles',
+  ]);
 });
 
 test('should restore windows on activate requires initialized runtime and no windows', () => {

src/main/runtime/app-lifecycle-actions.ts

@@ -29,6 +29,7 @@ export function createOnWillQuitCleanupHandler(deps: {
   destroyYomitanSettingsWindow: () => void;
   clearYomitanSettingsWindow: () => void;
   stopJellyfinRemoteSession: () => void;
+  cleanupInternalSubtitleTrackCache: () => void;
   cleanupYoutubeSubtitleTempDirs: () => void;
   cleanupYoutubeMediaCache: () => void;
   cleanupJellyfinSubtitleCache: () => void;
@@ -67,7 +68,11 @@ export function createOnWillQuitCleanupHandler(deps: {
     try {
       deps.stopJellyfinRemoteSession();
     } finally {
-      deps.cleanupJellyfinSubtitleCache();
+      try {
+        deps.cleanupJellyfinSubtitleCache();
+      } finally {
+        deps.cleanupInternalSubtitleTrackCache();
+      }
     }
     deps.cleanupYoutubeSubtitleTempDirs();
     deps.cleanupYoutubeMediaCache();

src/main/runtime/app-lifecycle-main-cleanup.test.ts

@@ -72,6 +72,7 @@ test('cleanup deps builder returns handlers that guard optional runtime objects'
     clearYomitanSettingsWindow: () => calls.push('clear-yomitan-settings-window'),
 
     stopJellyfinRemoteSession: () => calls.push('stop-jellyfin-remote'),
+    cleanupInternalSubtitleTrackCache: () => calls.push('cleanup-internal-subtitles'),
     cleanupYoutubeSubtitleTempDirs: () => calls.push('cleanup-youtube-subtitles'),
     cleanupYoutubeMediaCache: () => calls.push('cleanup-youtube-media'),
     cleanupJellyfinSubtitleCache: () => calls.push('cleanup-jellyfin-subtitles'),
@@ -95,6 +96,7 @@ test('cleanup deps builder returns handlers that guard optional runtime objects'
   assert.ok(calls.includes('destroy-first-run-window'));
   assert.ok(calls.includes('destroy-yomitan-settings-window'));
   assert.ok(calls.includes('stop-jellyfin-remote'));
+  assert.ok(calls.includes('cleanup-internal-subtitles'));
   assert.ok(calls.includes('cleanup-youtube-subtitles'));
   assert.ok(calls.includes('cleanup-youtube-media'));
   assert.ok(calls.includes('cleanup-jellyfin-subtitles'));
@@ -152,6 +154,7 @@ test('cleanup deps builder skips destroyed yomitan window', () => {
     getYomitanSettingsWindow: () => null,
     clearYomitanSettingsWindow: () => {},
     stopJellyfinRemoteSession: () => {},
+    cleanupInternalSubtitleTrackCache: () => {},
     cleanupYoutubeSubtitleTempDirs: () => {},
     cleanupYoutubeMediaCache: () => {},
     cleanupJellyfinSubtitleCache: () => {},
@@ -204,6 +207,7 @@ test('cleanup deps builder skips global shortcut cleanup before app ready', () =
     getYomitanSettingsWindow: () => null,
     clearYomitanSettingsWindow: () => {},
     stopJellyfinRemoteSession: () => {},
+    cleanupInternalSubtitleTrackCache: () => {},
     cleanupYoutubeSubtitleTempDirs: () => {},
     cleanupYoutubeMediaCache: () => {},
     cleanupJellyfinSubtitleCache: () => {},

src/main/runtime/app-lifecycle-main-cleanup.ts

@@ -58,6 +58,7 @@ export function createBuildOnWillQuitCleanupDepsHandler(deps: {
   clearYomitanSettingsWindow: () => void;
 
   stopJellyfinRemoteSession: () => void;
+  cleanupInternalSubtitleTrackCache: () => void;
   cleanupYoutubeSubtitleTempDirs: () => void;
   cleanupYoutubeMediaCache: () => void;
   cleanupJellyfinSubtitleCache: () => void;
@@ -144,6 +145,7 @@ export function createBuildOnWillQuitCleanupDepsHandler(deps: {
     },
     clearYomitanSettingsWindow: () => deps.clearYomitanSettingsWindow(),
     stopJellyfinRemoteSession: () => deps.stopJellyfinRemoteSession(),
+    cleanupInternalSubtitleTrackCache: () => deps.cleanupInternalSubtitleTrackCache(),
     cleanupYoutubeSubtitleTempDirs: () => deps.cleanupYoutubeSubtitleTempDirs(),
     cleanupYoutubeMediaCache: () => deps.cleanupYoutubeMediaCache(),
     cleanupJellyfinSubtitleCache: () => deps.cleanupJellyfinSubtitleCache(),

src/main/runtime/composers/startup-lifecycle-composer.test.ts

@@ -49,6 +49,7 @@ test('composeStartupLifecycleHandlers returns callable startup lifecycle handler
       getYomitanSettingsWindow: () => null,
       clearYomitanSettingsWindow: () => {},
       stopJellyfinRemoteSession: async () => {},
+      cleanupInternalSubtitleTrackCache: () => {},
       cleanupYoutubeSubtitleTempDirs: () => {},
       cleanupYoutubeMediaCache: () => {},
       cleanupJellyfinSubtitleCache: () => {},

src/main/runtime/internal-subtitle-extraction.test.ts

@@ -6,6 +6,7 @@ import process from 'node:process';
 import test from 'node:test';
 import {
   buildFfmpegSubtitleExtractionArgs,
+  createCachedInternalSubtitleTrackExtractor,
   extractInternalSubtitleTrackToTempFile,
   parseTrackId,
 } from './internal-subtitle-extraction';
@@ -22,6 +23,65 @@ test('parseTrackId rejects negative track ids', () => {
   assert.equal(parseTrackId(' -2 '), null);
 });
 
+test('cached internal subtitle extraction shares concurrent and repeated track requests', async () => {
+  let extractionCalls = 0;
+  let cleanupCalls = 0;
+  let resolveExtraction:
+    | ((result: { path: string; cleanup: () => Promise<void> }) => void)
+    | undefined;
+  const firstExtraction = new Promise<{ path: string; cleanup: () => Promise<void> }>((resolve) => {
+    resolveExtraction = resolve;
+  });
+  const extractor = createCachedInternalSubtitleTrackExtractor({
+    extract: async () => {
+      extractionCalls += 1;
+      if (extractionCalls === 1) {
+        return firstExtraction;
+      }
+      return {
+        path: `/tmp/subtitle-${extractionCalls}.ass`,
+        cleanup: async () => {
+          cleanupCalls += 1;
+        },
+      };
+    },
+  });
+  const request = () =>
+    extractor.extract('ffmpeg', '/Volumes/media/episode.mkv', {
+      'ff-index': 3,
+      codec: 'ass',
+    });
+
+  const concurrent = Array.from({ length: 6 }, request);
+  assert.equal(extractionCalls, 1);
+  if (!resolveExtraction) {
+    throw new Error('extraction did not start');
+  }
+  resolveExtraction({
+    path: '/tmp/subtitle-1.ass',
+    cleanup: async () => {
+      cleanupCalls += 1;
+    },
+  });
+
+  const results = await Promise.all(concurrent);
+  assert.deepEqual(
+    results.map((result) => result?.path),
+    Array.from({ length: 6 }, () => '/tmp/subtitle-1.ass'),
+  );
+  await Promise.all(results.map((result) => result?.cleanup()));
+  assert.equal(cleanupCalls, 0);
+
+  assert.equal((await request())?.path, '/tmp/subtitle-1.ass');
+  assert.equal(extractionCalls, 1);
+
+  extractor.clear();
+  await new Promise((resolve) => setImmediate(resolve));
+  assert.equal(cleanupCalls, 1);
+  assert.equal((await request())?.path, '/tmp/subtitle-2.ass');
+  assert.equal(extractionCalls, 2);
+});
+
 test('extractInternalSubtitleTrackToTempFile times out stalled ffmpeg process', async () => {
   const root = fs.mkdtempSync(path.join(os.tmpdir(), 'subminer-ffmpeg-timeout-'));
   const videoPath = path.join(root, 'video.mkv');

src/main/runtime/internal-subtitle-extraction.ts

@@ -35,6 +35,17 @@ export type MpvSubtitleTrackLike = {
   'external-filename'?: unknown;
 };
 
+export type ExtractedInternalSubtitleTrack = {
+  path: string;
+  cleanup: () => Promise<void>;
+};
+
+export type InternalSubtitleTrackExtractor = (
+  ffmpegPath: string,
+  videoPath: string,
+  track: MpvSubtitleTrackLike,
+) => Promise<ExtractedInternalSubtitleTrack | null>;
+
 const DEFAULT_EXTRACTION_TIMEOUT_MS = 30_000;
 
 export function parseTrackId(value: unknown): number | null {
@@ -80,7 +91,7 @@ export async function extractInternalSubtitleTrackToTempFile(
   videoPath: string,
   track: MpvSubtitleTrackLike,
   options: { extractionTimeoutMs?: number; spawnArgsOverride?: string[] } = {},
-): Promise<{ path: string; cleanup: () => Promise<void> } | null> {
+): Promise<ExtractedInternalSubtitleTrack | null> {
   const ffIndex = parseTrackId(track['ff-index']);
   const codec = typeof track.codec === 'string' ? track.codec : null;
   const extension = codecToExtension(codec ?? undefined);
@@ -145,3 +156,69 @@ export async function extractInternalSubtitleTrackToTempFile(
     },
   };
 }
+
+type CachedExtraction = {
+  promise: Promise<ExtractedInternalSubtitleTrack | null>;
+};
+
+function buildCachedExtractionKey(
+  ffmpegPath: string,
+  videoPath: string,
+  track: MpvSubtitleTrackLike,
+): string {
+  const codec = typeof track.codec === 'string' ? track.codec : null;
+  return JSON.stringify([ffmpegPath, videoPath, parseTrackId(track['ff-index']), codec]);
+}
+
+const releaseCachedExtraction = async (): Promise<void> => {};
+
+/**
+ * Owns extracted subtitle files for the active media and shares one extraction between callers.
+ * Caller cleanup releases only its view; clear removes the owned files on media changes or quit.
+ */
+export function createCachedInternalSubtitleTrackExtractor(
+  deps: { extract?: InternalSubtitleTrackExtractor } = {},
+): {
+  extract: InternalSubtitleTrackExtractor;
+  clear: () => void;
+} {
+  const extractTrack = deps.extract ?? extractInternalSubtitleTrackToTempFile;
+  const extractions = new Map<string, CachedExtraction>();
+
+  const extract: InternalSubtitleTrackExtractor = async (ffmpegPath, videoPath, track) => {
+    const key = buildCachedExtractionKey(ffmpegPath, videoPath, track);
+    let cached = extractions.get(key);
+    if (!cached) {
+      const next: CachedExtraction = {
+        promise: extractTrack(ffmpegPath, videoPath, track),
+      };
+      cached = next;
+      extractions.set(key, next);
+      void next.promise.catch(() => {
+        if (extractions.get(key) === next) {
+          extractions.delete(key);
+        }
+      });
+    }
+
+    const result = await cached.promise;
+    if (extractions.get(key) !== cached || !result) {
+      return null;
+    }
+
+    return {
+      path: result.path,
+      cleanup: releaseCachedExtraction,
+    };
+  };
+
+  const clear = (): void => {
+    const staleExtractions = [...extractions.values()];
+    extractions.clear();
+    for (const extraction of staleExtractions) {
+      void extraction.promise.then((result) => result?.cleanup()).catch(() => undefined);
+    }
+  };
+
+  return { extract, clear };
+}

src/main/runtime/network-media-path.test.ts

@@ -0,0 +1,64 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { createRemoteMediaPathDetector } from './network-media-path';
+
+test('remote media detector recognizes mounted network filesystems', async () => {
+  const detectRemoteMedia = createRemoteMediaPathDetector({
+    platform: 'darwin',
+    readMountOutput: async () =>
+      [
+        '/dev/disk3s5 on /System/Volumes/Data (apfs, local, journaled)',
+        '//viewer@media/jellyfin on /Volumes/jellyfin (smbfs, nodev, nosuid)',
+      ].join('\n'),
+  });
+
+  assert.equal(await detectRemoteMedia('/Volumes/jellyfin/movie.mkv'), true);
+  assert.equal(await detectRemoteMedia('/Volumes/jellyfin-another/movie.mkv'), false);
+  assert.equal(await detectRemoteMedia('/Users/viewer/movie.mkv'), false);
+});
+
+test('remote media detector recognizes Linux network mount output', async () => {
+  const detectRemoteMedia = createRemoteMediaPathDetector({
+    platform: 'linux',
+    readMountOutput: async () =>
+      '//media/jellyfin on /mnt/Jellyfin\\040Media type cifs (rw,relatime)',
+  });
+
+  assert.equal(await detectRemoteMedia('/mnt/Jellyfin Media/movie.mkv'), true);
+});
+
+test('remote media detector shares its mount lookup between concurrent callers', async () => {
+  let mountReads = 0;
+  const detectRemoteMedia = createRemoteMediaPathDetector({
+    platform: 'darwin',
+    readMountOutput: async () => {
+      mountReads += 1;
+      return '//viewer@media/jellyfin on /Volumes/jellyfin (smbfs, nodev, nosuid)';
+    },
+  });
+
+  const results = await Promise.all(
+    Array.from({ length: 6 }, () => detectRemoteMedia('/Volumes/jellyfin/movie.mkv')),
+  );
+
+  assert.deepEqual(
+    results,
+    Array.from({ length: 6 }, () => true),
+  );
+  assert.equal(mountReads, 1);
+});
+
+test('remote media detector recognizes URLs and Windows UNC paths without reading mounts', async () => {
+  let mountReads = 0;
+  const detectRemoteMedia = createRemoteMediaPathDetector({
+    platform: 'win32',
+    readMountOutput: async () => {
+      mountReads += 1;
+      return '';
+    },
+  });
+
+  assert.equal(await detectRemoteMedia('https://media.example/movie.mkv'), true);
+  assert.equal(await detectRemoteMedia('\\\\media-server\\jellyfin\\movie.mkv'), true);
+  assert.equal(mountReads, 0);
+});

src/main/runtime/network-media-path.ts

@@ -0,0 +1,142 @@
+import { execFile } from 'node:child_process';
+import path from 'node:path';
+import process from 'node:process';
+import { resolveSubtitleSourcePath } from './subtitle-prefetch-source';
+
+const DEFAULT_MOUNT_CACHE_TTL_MS = 5_000;
+const NETWORK_FILESYSTEM_TYPES = new Set([
+  '9p',
+  'afpfs',
+  'cifs',
+  'davfs',
+  'davfs2',
+  'fuse.sshfs',
+  'nfs',
+  'nfs4',
+  'smbfs',
+  'sshfs',
+  'webdav',
+]);
+
+function isRemoteUrl(value: string): boolean {
+  try {
+    const url = new URL(value);
+    return url.protocol === 'http:' || url.protocol === 'https:';
+  } catch {
+    return false;
+  }
+}
+
+function decodeMountPath(value: string): string {
+  return value.replace(/\\([0-7]{3})/g, (_match, digits: string) =>
+    String.fromCharCode(Number.parseInt(digits, 8)),
+  );
+}
+
+function parseNetworkMountPaths(output: string): string[] {
+  const networkMountPaths: string[] = [];
+  for (const line of output.split('\n')) {
+    const optionsStart = line.lastIndexOf(' (');
+    if (optionsStart < 0) continue;
+
+    let mountDescription = line.slice(0, optionsStart);
+    const options = line.slice(optionsStart + 2, line.indexOf(')', optionsStart));
+    const linuxTypeSeparator = mountDescription.lastIndexOf(' type ');
+    const filesystemType = (
+      linuxTypeSeparator >= 0
+        ? mountDescription.slice(linuxTypeSeparator + ' type '.length)
+        : (options.split(',').at(0) ?? '')
+    )
+      .trim()
+      .toLowerCase();
+    if (!NETWORK_FILESYSTEM_TYPES.has(filesystemType)) continue;
+
+    if (linuxTypeSeparator >= 0) {
+      mountDescription = mountDescription.slice(0, linuxTypeSeparator);
+    }
+    const mountSeparator = mountDescription.indexOf(' on ');
+    if (mountSeparator < 0) continue;
+    networkMountPaths.push(
+      path.posix.normalize(decodeMountPath(mountDescription.slice(mountSeparator + 4).trim())),
+    );
+  }
+  return networkMountPaths;
+}
+
+function readMountOutput(platform: NodeJS.Platform): Promise<string> {
+  if (platform === 'win32') return Promise.resolve('');
+  const command = platform === 'darwin' ? '/sbin/mount' : 'mount';
+  return new Promise((resolve, reject) => {
+    execFile(
+      command,
+      [],
+      { encoding: 'utf8', timeout: 1_000, maxBuffer: 1024 * 1024 },
+      (error, stdout) => {
+        if (error) {
+          reject(error);
+          return;
+        }
+        resolve(stdout);
+      },
+    );
+  });
+}
+
+function isPathWithinMount(filePath: string, mountPath: string): boolean {
+  const relativePath = path.posix.relative(mountPath, filePath);
+  return (
+    relativePath === '' ||
+    (relativePath !== '..' &&
+      !relativePath.startsWith(`..${path.posix.sep}`) &&
+      !path.posix.isAbsolute(relativePath))
+  );
+}
+
+export type RemoteMediaPathDetector = (mediaPath: string) => Promise<boolean>;
+
+export function createRemoteMediaPathDetector(
+  deps: {
+    platform?: NodeJS.Platform;
+    readMountOutput?: () => Promise<string>;
+    now?: () => number;
+    mountCacheTtlMs?: number;
+  } = {},
+): RemoteMediaPathDetector {
+  const platform = deps.platform ?? process.platform;
+  const getMountOutput = deps.readMountOutput ?? (() => readMountOutput(platform));
+  const now = deps.now ?? Date.now;
+  const mountCacheTtlMs = deps.mountCacheTtlMs ?? DEFAULT_MOUNT_CACHE_TTL_MS;
+  let mountCache: { expiresAt: number; networkMountPaths: Promise<readonly string[]> } | undefined;
+
+  const getNetworkMountPaths = (): Promise<readonly string[]> => {
+    const currentTime = now();
+    if (mountCache && currentTime < mountCache.expiresAt) {
+      return mountCache.networkMountPaths;
+    }
+
+    const networkMountPaths = getMountOutput()
+      .then(parseNetworkMountPaths)
+      .catch(() => []);
+    mountCache = {
+      expiresAt: currentTime + mountCacheTtlMs,
+      networkMountPaths,
+    };
+    return networkMountPaths;
+  };
+
+  return async (mediaPath): Promise<boolean> => {
+    const source = mediaPath.trim();
+    if (!source) return false;
+    if (isRemoteUrl(source)) return true;
+
+    const filePath = resolveSubtitleSourcePath(source);
+    if (platform === 'win32') {
+      return filePath.startsWith('\\\\');
+    }
+    if (!path.posix.isAbsolute(filePath)) return false;
+
+    const networkMountPaths = await getNetworkMountPaths();
+    const normalizedPath = path.posix.normalize(filePath);
+    return networkMountPaths.some((mountPath) => isPathWithinMount(normalizedPath, mountPath));
+  };
+}

src/main/runtime/subtitle-prefetch-runtime.test.ts

@@ -101,6 +101,32 @@ test('subtitle prefetch runtime preserves parsed cues when YouTube active track
   assert.deepEqual(calls, []);
 });
 
+test('subtitle prefetch runtime preserves parsed cues when a network mount source is unresolved', async () => {
+  const calls: string[] = [];
+  const refresh = createRefreshSubtitlePrefetchFromActiveTrackHandler({
+    getMpvClient: () => ({
+      connected: true,
+      requestProperty: async (name) => (name === 'path' ? '/Volumes/jellyfin/movie.mkv' : null),
+    }),
+    getLastObservedTimePos: () => 12,
+    subtitlePrefetchInitController: {
+      cancelPendingInit: () => {
+        calls.push('cancel');
+      },
+      initSubtitlePrefetch: async () => {
+        calls.push('init');
+      },
+    },
+    resolveActiveSubtitleSidebarSource: async () => null,
+    shouldKeepExistingCuesOnMissingSource: async (videoPath) =>
+      videoPath.startsWith('/Volumes/jellyfin/'),
+  });
+
+  await refresh();
+
+  assert.deepEqual(calls, []);
+});
+
 test('subtitle prefetch runtime does not extract internal subtitle tracks from remote media urls', async () => {
   let extracted = false;
   const resolveSource = createResolveActiveSubtitleSidebarSourceHandler({
@@ -131,6 +157,34 @@ test('subtitle prefetch runtime does not extract internal subtitle tracks from r
   assert.equal(extracted, false);
 });
 
+test('subtitle prefetch runtime does not extract internal subtitle tracks from network mounts', async () => {
+  let extracted = false;
+  const resolveSource = createResolveActiveSubtitleSidebarSourceHandler({
+    getFfmpegPath: () => 'ffmpeg-custom',
+    isRemoteMediaPath: async (videoPath) => videoPath.startsWith('/Volumes/jellyfin/'),
+    extractInternalSubtitleTrack: async () => {
+      extracted = true;
+      return null;
+    },
+  });
+
+  const resolved = await resolveSource({
+    currentExternalFilenameRaw: null,
+    currentTrackRaw: {
+      type: 'sub',
+      id: 3,
+      'ff-index': 7,
+      codec: 'ass',
+    },
+    trackListRaw: [],
+    sidRaw: 3,
+    videoPath: '/Volumes/jellyfin/movie.mkv',
+  });
+
+  assert.equal(resolved, null);
+  assert.equal(extracted, false);
+});
+
 test('subtitle prefetch refresh logs a warning when source resolution throws', async () => {
   const warnings: string[] = [];
   const refresh = createRefreshSubtitlePrefetchFromActiveTrackHandler({

src/main/runtime/subtitle-prefetch-runtime.ts

@@ -17,6 +17,8 @@ type ActiveSubtitleSidebarSource = {
   cleanup?: () => Promise<void>;
 };
 
+type RemoteMediaPathDetector = (mediaPath: string) => boolean | Promise<boolean>;
+
 function parseTrackId(value: unknown): number | null {
   if (typeof value === 'number' && Number.isInteger(value)) {
     return value;
@@ -28,7 +30,7 @@ function parseTrackId(value: unknown): number | null {
   return null;
 }
 
-function isRemoteMediaPath(value: string): boolean {
+function isRemoteMediaUrl(value: string): boolean {
   try {
     const url = new URL(value);
     return url.protocol === 'http:' || url.protocol === 'https:';
@@ -86,6 +88,7 @@ function getActiveSubtitleTrack(
 
 export function createResolveActiveSubtitleSidebarSourceHandler(deps: {
   getFfmpegPath: () => string;
+  isRemoteMediaPath?: RemoteMediaPathDetector;
   extractInternalSubtitleTrack: (
     ffmpegPath: string,
     videoPath: string,
@@ -126,7 +129,8 @@ export function createResolveActiveSubtitleSidebarSourceHandler(deps: {
       return { path: externalFilename, sourceKey: externalFilename };
     }
 
-    if (isRemoteMediaPath(input.videoPath)) {
+    const isRemoteMediaPath = deps.isRemoteMediaPath ?? isRemoteMediaUrl;
+    if (await isRemoteMediaPath(input.videoPath)) {
       deps.logDebug?.('[subtitle-prefetch] skipping internal subtitle extraction for remote media');
       return null;
     }
@@ -156,7 +160,7 @@ export function createRefreshSubtitlePrefetchFromActiveTrackHandler(deps: {
     requestProperty: (name: string) => Promise<unknown>;
   } | null;
   getLastObservedTimePos: () => number;
-  shouldKeepExistingCuesOnMissingSource?: (videoPath: string) => boolean;
+  shouldKeepExistingCuesOnMissingSource?: (videoPath: string) => boolean | Promise<boolean>;
   subtitlePrefetchInitController: SubtitlePrefetchInitController;
   resolveActiveSubtitleSidebarSource: (
     input: Parameters<ReturnType<typeof createResolveActiveSubtitleSidebarSourceHandler>>[0],
@@ -195,7 +199,7 @@ export function createRefreshSubtitlePrefetchFromActiveTrackHandler(deps: {
         videoPath,
       });
       if (!resolvedSource) {
-        if (deps.shouldKeepExistingCuesOnMissingSource?.(videoPath) === true) {
+        if ((await deps.shouldKeepExistingCuesOnMissingSource?.(videoPath)) === true) {
           deps.logDebug?.(
             '[subtitle-prefetch] no active subtitle source resolved; keeping existing cues',
           );

src/renderer/style.css

@@ -1928,10 +1928,6 @@ 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

@@ -1424,11 +1424,8 @@ test('subtitle annotation CSS underlines JLPT tokens without changing token colo
   );
 });
 
-test('prepareSecondarySubtitleLines preserves short stacks without layer metadata', () => {
+test('prepareSecondarySubtitleLines collapses exact short copies in stacks', () => {
   assert.deepEqual(prepareSecondarySubtitleLines('Your\\NYour\\NYour\\NYour\\Nmosaic'), [
-    'Your',
-    'Your',
-    'Your',
     'Your',
     'mosaic',
   ]);
@@ -1438,6 +1435,15 @@ test('prepareSecondarySubtitleLines preserves short stacks without layer metadat
   ]);
 });
 
+test('prepareSecondarySubtitleLines collapses exact short sign copies beside dialogue', () => {
+  const liveText = "And for today's sports festival...\nEntrance\nEntrance";
+
+  assert.deepEqual(prepareSecondarySubtitleLines(liveText), [
+    "And for today's sports festival...",
+    'Entrance',
+  ]);
+});
+
 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.
@@ -1448,10 +1454,10 @@ test('prepareSecondarySubtitleLines collapses karaoke syllable spam into one ded
   assert.deepEqual(prepareSecondarySubtitleLines(karaoke), ['ya This no ma ups']);
 });
 
-test('prepareSecondarySubtitleLines preserves repeated short dialogue without layer metadata', () => {
+test('prepareSecondarySubtitleLines collapses exact repeated short lines', () => {
   const dialogue = ['Wait', 'Wait', 'Wait'];
 
-  assert.deepEqual(prepareSecondarySubtitleLines(dialogue.join('\\N')), dialogue);
+  assert.deepEqual(prepareSecondarySubtitleLines(dialogue.join('\\N')), ['Wait']);
 });
 
 test('prepareSecondarySubtitleLines collapses punctuation variants of a full-sentence fallback', () => {
@@ -1469,6 +1475,10 @@ test('prepareSecondarySubtitleLines preserves short simultaneous dialogue withou
   assert.deepEqual(prepareSecondarySubtitleLines(dialogue.join('\\N')), dialogue);
 });
 
+test('prepareSecondarySubtitleLines preserves distinct short lines with internal whitespace', () => {
+  assert.deepEqual(prepareSecondarySubtitleLines('AB\\NA B'), ['AB', 'A B']);
+});
+
 test('prepareSecondarySubtitleLines keeps normal dialogue lines intact', () => {
   const dialogue = ' I never expected this. \\N\\N But here we are. ';
 
@@ -1490,13 +1500,13 @@ test('prepareSecondarySubtitleLines strips ASS override tags and handles empty i
   assert.deepEqual(prepareSecondarySubtitleLines('{\\an8}'), []);
 });
 
-test('secondary subtitle root CSS caps height so hover-pause band stays a top strip', () => {
+test('secondary subtitle root CSS does not clip long subtitle stacks', () => {
   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;/);
+  assert.doesNotMatch(secondaryRootBlock, /max-height\s*:/);
+  assert.doesNotMatch(secondaryRootBlock, /overflow\s*:\s*hidden/);
 });
 
 test('applySubtitleStyle sets known-word maturity color variables', () => {

src/renderer/subtitle-render.ts

@@ -667,12 +667,17 @@ function isKaraokeLikeLineSet(lines: string[]): boolean {
 }
 
 function collapseFullLineFallbackCopies(lines: string[]): string[] {
-  const seen = new Set<string>();
+  const seenExact = new Set<string>();
+  const seenFlattened = new Set<string>();
   return lines.filter((line) => {
-    const identity = flattenedSecondarySubtitleLineIdentity(line);
-    if (!identity) return true;
-    if (seen.has(identity)) return false;
-    seen.add(identity);
+    const exactIdentity = line.normalize('NFKC');
+    if (seenExact.has(exactIdentity)) return false;
+    seenExact.add(exactIdentity);
+
+    const flattenedIdentity = flattenedSecondarySubtitleLineIdentity(line);
+    if (!flattenedIdentity) return true;
+    if (seenFlattened.has(flattenedIdentity)) return false;
+    seenFlattened.add(flattenedIdentity);
     return true;
   });
 }