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

- Build the Swift window-tracking helper with an explicit `-target ...-apple-macos12.0` instead of letting swiftc stamp the build machine's OS, so the overlay attaches to mpv on older macOS (e.g. Ventura) instead of crashing at load
- Fold the standalone build-macos-helper.sh into prepare-build-assets.mjs and update docs/tests to match

.agents/skills/subminer-release/SKILL.md

@@ -0,0 +1,34 @@
+---
+name: subminer-release
+description: Prepare, cut, publish, or repair SubMiner stable and prerelease releases. Use for hands-on release work; do not use for general release questions.
+---
+
+# SubMiner release
+
+Carry out the requested release phase using the repository's current release process.
+
+## Source of truth
+
+Read `docs/RELEASING.md` completely before changing files or release state. Treat it as canonical. Read `changes/README.md` when the work touches change fragments or generated release notes.
+
+Do not copy release commands or policy into this skill. If this skill disagrees with the release guide, follow the guide and reconcile the skill before handoff.
+
+## Workflow
+
+1. Identify whether the request is for a stable release, prerelease, release preparation, publication, or repair.
+2. Inspect the current branch, worktree status, package version, pending change fragments, relevant tags, and latest CI state before making changes.
+3. Follow the matching procedure in `docs/RELEASING.md` in order. Review generated changelog and release-note Markdown before it can be committed or published.
+4. Run every required gate for the requested release phase. Do not treat a cheaper test lane as a substitute for the documented release gate.
+5. Before a stable tag, confirm the package and tag versions match and no pending `changes/*.md` fragments remain. Preserve fragments for prereleases as documented.
+6. Report the resulting version, completed checks, local commit and tag state, remote publication state, skipped platform checks, and any remaining manual work.
+
+## Authorization boundaries
+
+- A request to prepare a release stops before commit, tag, push, or remote publication unless the user also authorizes those actions.
+- A clear request to cut or publish a release includes the documented commit, tag, and push steps. Ask before the first remote mutation when the wording is ambiguous.
+- Do not edit an existing GitHub release, publish to the AUR, change secrets, or alter signing configuration unless the user explicitly requests that operation.
+- Do not switch branches without consent.
+
+## Stop conditions
+
+Stop and report the blocker when required CI or a release gate fails, authentication is missing, versions disagree, required artifacts are absent, or the worktree contains unexpected changes that overlap the release. Do not tag or publish a partially verified release.

.gitignore

@@ -49,6 +49,7 @@ tests/*
 !.agents/skills/
 .agents/skills/*
 !.agents/skills/subminer-change-verification/
+!.agents/skills/subminer-release/
 !.agents/skills/subminer-scrum-master/
 .agents/skills/subminer-change-verification/*
 !.agents/skills/subminer-change-verification/SKILL.md
@@ -56,6 +57,8 @@ tests/*
 .agents/skills/subminer-change-verification/scripts/*
 !.agents/skills/subminer-change-verification/scripts/classify_subminer_diff.sh
 !.agents/skills/subminer-change-verification/scripts/verify_subminer_change.sh
+.agents/skills/subminer-release/*
+!.agents/skills/subminer-release/SKILL.md
 .agents/skills/subminer-scrum-master/*
 !.agents/skills/subminer-scrum-master/SKILL.md
 favicon.png

changes/dedupe-embedded-subtitle-extraction.md

@@ -0,0 +1,4 @@
+type: fixed
+area: subtitles
+
+- Prevented embedded subtitle parsing from starving network playback: mounted SMB/NFS media now uses deduplicated mpv live text, while duplicate extraction requests for local media share one ffmpeg process.

changes/fix-macos-helper-deployment-target.md

@@ -0,0 +1,4 @@
+type: fixed
+area: overlay
+
+- The macOS window-tracking helper is now built for macOS 12.0+, so the overlay attaches to mpv on older systems (previously the helper required the macOS version of the build machine and crashed on e.g. Ventura, leaving the overlay stuck on "Overlay loading").

changes/fix-secondary-subtitle-duplication.md

@@ -1,4 +1,4 @@
 type: fixed
 area: overlay
 
-- Secondary subtitles now parse the selected ASS/SRT/VTT source with the primary subtitle deduplication pipeline, preventing layered animation text from appearing several times in the overlay, mined cards, and statistics. Long ASS lines repeated as dialogue and positioned signs are also collapsed when they differ only in whitespace or terminal punctuation. Dense multi-row sign layouts no longer become one concatenated secondary line. Live mpv text remains the fallback for unreadable tracks and applies full-line duplicate filtering before display.
+- Secondary subtitles now parse the selected ASS/SRT/VTT source with the primary subtitle deduplication pipeline, preventing layered animation text from appearing several times in the overlay, mined cards, and statistics. Fragmented ASS karaoke keeps spaces authored at event boundaries instead of joining every word together. Long ASS lines repeated as dialogue and positioned signs are also collapsed when they differ only in whitespace or terminal punctuation. Dense multi-row sign layouts no longer become one concatenated secondary line. Live mpv text remains the fallback for unreadable tracks and applies full-line duplicate filtering before display.

changes/remove-secondary-subtitle-display-limit.md

@@ -0,0 +1,4 @@
+type: fixed
+area: overlay
+
+- Secondary subtitle overlays now show every rendered line instead of clipping text after roughly four lines.

docs-site/development.md

@@ -6,7 +6,7 @@ For internal architecture/workflow guidance, use `docs/README.md` at the repo ro
 
 - [Bun](https://bun.sh)
 - A system `lua` interpreter for `bun run test:launcher` / `bun run test:plugin:src`
-- macOS builds compile a Swift helper via `scripts/build-macos-helper.sh` (skip with `SUBMINER_SKIP_MACOS_HELPER_BUILD=1`)
+- macOS builds compile a Swift helper via `scripts/prepare-build-assets.mjs` (skip with `SUBMINER_SKIP_MACOS_HELPER_BUILD=1`)
 
 ## Setup
 

docs-site/mining-workflow.md

@@ -108,9 +108,11 @@ The secondary bar is a compact top-strip region in the same overlay window. It s
 - Quick comprehension checks without leaving the mining flow.
 - Auto-populating the translation field on mined cards - when a card is created, SubMiner uses the secondary subtitle text as the translation field value (unless AI translation is configured to override it).
 
+For local media, SubMiner can parse supported embedded secondary tracks into timed cues. For remote URLs and files on network mounts, it uses mpv's live secondary subtitle text instead of scanning the media with ffmpeg.
+
 It is controlled by `secondarySub` configuration and shares its lifecycle with the main overlay window. Cycle which track feeds it with `Shift+J`.
 
-SubMiner collapses duplicate ASS layers in parsed secondary tracks. Long lines repeated as dialogue and positioned signs are treated as the same line when they differ only in whitespace or terminal punctuation. Dense multi-row sign layouts, such as translated timetables, are excluded instead of being concatenated into the secondary bar. When SubMiner must use mpv's live text as a fallback, it still filters full-line duplicates while preserving short repeated dialogue.
+SubMiner collapses duplicate ASS layers in parsed secondary tracks. Exact repeated lines collapse at any length, while distinct simultaneous short lines remain separate. Long dialogue and positioned-sign copies also collapse when they differ only in whitespace or terminal punctuation. Dense multi-row sign layouts, such as translated timetables, are excluded instead of being concatenated into the secondary bar.
 
 ### Display Modes
 

docs/architecture/subtitle-overlay-priming.md

@@ -97,11 +97,12 @@ coming and prefetching would otherwise idle for the rest of the cue.
 
 ## Secondary Subtitle Flow
 
-- `secondary-sub-text` remains the immediate fallback, so unreadable and remote subtitle sources
-  still appear without waiting for file resolution.
-- Parsed secondary text and the live fallback share a flattened-line identity for long lines. This
-  removes dialogue/sign repetitions that differ only in whitespace or terminal punctuation while
-  retaining short repeated lines that can represent authored dialogue without source metadata.
+- `secondary-sub-text` remains the immediate fallback, so unreadable subtitle sources, remote URLs,
+  and files on network mounts still appear without waiting for file resolution. Embedded-track
+  extraction is skipped for those sources to avoid competing with playback for network bandwidth.
+- Parsed secondary text and the live fallback remove exact repeated lines at any length. A
+  flattened-line identity also removes long dialogue/sign repetitions that differ only in
+  whitespace or terminal punctuation, while distinct simultaneous short lines remain separate.
 - `secondary-subtitle-track.ts` resolves `secondary-sid` against mpv's track list. External tracks
   are read directly; supported embedded text tracks are extracted through the same ffmpeg-backed
   source resolver used by primary subtitle prefetching.

docs/knowledge-base/catalog.md

@@ -19,7 +19,7 @@ Read when: finding internal docs or checking verification status
 | Quality scorecard | `docs/knowledge-base/quality.md` | active | 2026-03-13 | quality grades and gaps |
 | Workflow index | `docs/workflow/README.md` | active | 2026-08-13 | execution map |
 | Planning guide | `docs/workflow/planning.md` | active | 2026-05-23 | lightweight vs execution plans |
-| Agent skills | `docs/workflow/agent-skills.md` | active | 2026-08-13 | repo-local workflow skill ownership |
+| Agent skills | `docs/workflow/agent-skills.md` | active | 2026-08-23 | repo-local workflow skill ownership |
 | Verification guide | `docs/workflow/verification.md` | active | 2026-08-13 | maintained verification lanes |
 | Release guide | `docs/RELEASING.md` | active | 2026-05-23 | release checklist |
 

docs/workflow/agent-skills.md

@@ -3,7 +3,7 @@
 # Agent Skills
 
 Status: active
-Last verified: 2026-08-13
+Last verified: 2026-08-23
 Owner: Kyle Yasuda
 Read when: using, adding, or changing a repo-local agent workflow skill
 
@@ -12,6 +12,9 @@ Read when: using, adding, or changing a repo-local agent workflow skill
 - `.agents/skills/subminer-change-verification/`
   - Selects the cheapest sufficient repo-native verification lane.
   - Defers command ownership to `package.json` and `docs/workflow/verification.md`.
+- `.agents/skills/subminer-release/`
+  - Prepares, cuts, publishes, or repairs stable and prerelease releases.
+  - Defers release procedure and policy to `docs/RELEASING.md`.
 
 Repo-local workflows stay as standalone skills. Do not add plugin packaging, marketplace metadata, or compatibility shims unless the workflow is intentionally being distributed beyond this repository.
 

package.json

@@ -2,7 +2,7 @@
   "name": "subminer",
   "productName": "SubMiner",
   "desktopName": "SubMiner.desktop",
-  "version": "0.19.4-beta.3",
+  "version": "0.19.4-beta.4",
   "description": "All-in-one sentence mining overlay with AnkiConnect and dictionary integration",
   "packageManager": "bun@1.3.5",
   "main": "dist/main-entry.js",

release/prerelease-notes.md

@@ -6,39 +6,41 @@
 ### Added
 
 - Library Merge & Reassignment
-  - Duplicate library entries for the same show can now be merged: pick entries in "Select" mode and use "Merge Selected" to combine their sessions, mined cards, and watch time onto one card.
-  - Episodes can be moved to a different library entry with a per-episode "→" button, fixing cases where a stray filename split off its own entry; manual assignments now survive later filename parsing, Jellyfin refreshes, and season repair, and other episodes in the same folder pick up the same fix automatically unless they already belong elsewhere.
-  - Exact AniList matches with compatible seasons now merge automatically, and likely (fuzzy) matches surface as a dismissible "Possible duplicate" suggestion instead of merging silently; entries with conflicting seasons are left alone either way.
+  - Duplicate library cards for the same show can be combined: select entries in "Select" mode and use "Merge Selected" to combine their sessions, mined cards, and watch time onto one card.
+  - Episodes can be moved to a different entry with a per-episode "→" button, fixing stray files that split off their own entry; manual assignments now survive later filename parsing, Jellyfin refreshes, and season repair.
+  - Exact AniList matches with compatible seasons merge automatically, while likely (fuzzy) matches surface as a dismissible "Possible duplicate" suggestion instead of merging silently.
 
 - Duplicate Line Cleanup
-  - The Vocabulary tab's new **Duplicates** button scans a chosen time window for the repeated-line bursts described under Fixed below and collapses each burst to a single line once you confirm it; a matching `subminer stats cleanup --duplicate-lines` command (with `--dry-run` and `--lookback-days <n>`) is available from the terminal.
+  - The Vocabulary tab's new **Duplicates** button scans a chosen time window for the repeated-line bursts described under Fixed below and collapses each burst to a single line once confirmed.
+  - A matching `subminer stats cleanup --duplicate-lines` command (with `--dry-run` and `--lookback-days <n>`) is available from the terminal.
   - Only the affected subtitle lines and the vocabulary counts they inflated are touched; watch time and lines-seen totals are left as recorded.
 
 ### Fixed
 
 - Subtitle Duplication from Karaoke & Animated Signs
-  - Typeset ASS karaoke and animated signs no longer flood the overlay, subtitle sidebar, immersion history, mined cards, or stats with repeated glyph fragments or per-frame duplicates; the complete authored line is recovered instead, without merging genuinely repeated dialogue or separately positioned signs. Dialogue spoken while a song's animation is on screen is kept intact instead of being replaced by the lyric, and lyric transitions (including seeking into the middle of a line) resolve to the clean line instead of a stray entrance or exit frame.
-  - The secondary overlay now shares the same deduplication logic as the primary overlay, including collapsing lines that only differ by whitespace or trailing punctuation, so layered animation text and dense multi-row sign layouts no longer appear duplicated or garbled there or in what gets mined.
-  - Sidebar navigation now moves between the clean, sanitized lyric lines instead of the raw generated animation events, and selecting an overlapping lyric keeps the right line selected.
-  - Vocabulary stats no longer count every animation frame of a karaoke opening as a separate line, which previously could push an OP lyric to the top of "Top Repeated Words."
+  - Typeset ASS karaoke and animated signs no longer flood the overlay, subtitle sidebar, immersion history, mined cards, or stats with repeated glyph fragments or per-frame duplicates; the complete authored line is recovered instead, without merging genuinely repeated dialogue or separately positioned signs.
+  - Fragmented karaoke now preserves the spaces the author placed between words instead of joining them together, and lyric transitions (including seeking into the middle of a line) resolve to the clean line instead of a stray entrance or exit frame.
+  - The secondary overlay shares the same deduplication logic as the primary overlay, including collapsing lines that differ only by whitespace or trailing punctuation, and sidebar navigation moves between clean lyric lines while keeping the right line selected.
 
 - Anki Media Generation
-  - Sentence-audio generation no longer times out on slow network-mounted video files with many subtitle and font streams (bounded probing plus a two-minute extraction budget), and a failed extraction now reports a clear error instead of a raw `ENOENT`.
+  - Sentence-audio generation no longer times out on slow network-mounted video files with many subtitle and font streams, and a failed extraction now reports a clear error instead of a raw `ENOENT`.
   - Mined audio and animated AVIF clips now capture the subtitle line you actually mined, instead of whatever line happened to be on screen once slow audio extraction finished.
 
 - Character Dictionary Performance & Notifications
-  - Character dictionary generation, merged rebuilds, and imports no longer freeze the app on large dictionaries, and cached results (including character portraits) are reused across launches instead of regenerating everything every time. Portraits also now display correctly if their cache finishes loading after subtitles have already started showing.
+  - Character dictionary generation, merged rebuilds, and imports no longer freeze the app on large dictionaries, and cached results (including character portraits) are reused across launches instead of regenerating everything every time.
+  - Portraits also now display correctly if their cache finishes loading after subtitles have already started showing.
   - Desktop progress notifications, including on Linux AppImage installs, now update in place instead of flickering closed and reopening.
 
 - Overlay Reliability
   - Overlay modals (settings, stats, etc.) now open promptly on the first shortcut press, including on repeated sessions on Windows, and appear above fullscreen mpv on macOS instead of switching Spaces or opening off-screen.
+  - The macOS window-tracking helper is now built for macOS 12.0+, so the overlay attaches to mpv on older systems like Ventura instead of crashing and getting stuck on "Overlay loading."
   - The overlay no longer gets stuck on "Overlay loading" indefinitely if mpv's connection stalls; it now retries and shows an actionable error after 30 seconds.
-  - Fixed native Wayland drag-and-drop from file managers like Thunar, so subtitle and video files dropped on the overlay reach mpv.
-  - Fixed system-wide mouse lag on Windows caused by the overlay's click-through handling and repeated mpv window lookups.
+  - Fixed native Wayland drag-and-drop from file managers like Thunar, and fixed system-wide mouse lag on Windows caused by the overlay's click-through handling.
 
 - Stats Dashboard
   - Deletes, library merges, video moves, and AniList reassignments no longer freeze the stats dashboard or rebuild lifetime totals from scratch; large deletes that used to take minutes now finish in milliseconds.
-  - Vocabulary totals and charts now count all tracked vocabulary instead of just the first page, new-word history uses corrected daily rollups, calendar labels respect time zones west of UTC, and vocabulary cards refresh automatically after editing the word exclusion list (with a Retry option if a load fails).
+  - Vocabulary totals and charts now count all tracked vocabulary instead of just the first page, and new-word history uses corrected daily rollups.
+  - Calendar labels respect time zones west of UTC, and vocabulary cards refresh automatically after editing the word exclusion list (with a Retry option if a load fails).
 
 - Linux Launcher Thumbnails
   - Fixed missing MKV thumbnails in the Linux rofi picker when the system thumbnailer only registers legacy Matroska MIME aliases.

scripts/build-macos-helper.sh

@@ -1,54 +0,0 @@
-#!/bin/bash
-# Build macOS window tracking helper binary
-
-set -e
-
-SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-SWIFT_SOURCE="$SCRIPT_DIR/get-mpv-window-macos.swift"
-OUTPUT_DIR="$SCRIPT_DIR/../dist/scripts"
-OUTPUT_BINARY="$OUTPUT_DIR/get-mpv-window-macos"
-OUTPUT_SOURCE_COPY="$OUTPUT_DIR/get-mpv-window-macos.swift"
-
-fallback_to_source() {
-  echo "Falling back to source fallback: $OUTPUT_SOURCE_COPY"
-  mkdir -p "$OUTPUT_DIR"
-  cp "$SWIFT_SOURCE" "$OUTPUT_SOURCE_COPY"
-}
-
-build_swift_helper() {
-  echo "Compiling macOS window tracking helper..."
-  if ! command -v swiftc >/dev/null 2>&1; then
-    echo "swiftc not found in PATH; skipping compilation."
-    return 1
-  fi
-
-  if ! swiftc -O "$SWIFT_SOURCE" -o "$OUTPUT_BINARY"; then
-    return 1
-  fi
-
-  chmod +x "$OUTPUT_BINARY"
-  echo "✓ Built $OUTPUT_BINARY"
-  return 0
-}
-
-# Optional skip flag for non-macOS CI/dev environments
-if [[ "${SUBMINER_SKIP_MACOS_HELPER_BUILD:-}" == "1" ]]; then
-  echo "Skipping macOS helper build (SUBMINER_SKIP_MACOS_HELPER_BUILD=1)"
-  fallback_to_source
-  exit 0
-fi
-
-# Only build on macOS
-if [[ "$(uname)" != "Darwin" ]]; then
-  echo "Skipping macOS helper build (not on macOS)"
-  fallback_to_source
-  exit 0
-fi
-
-# Create output directory
-mkdir -p "$OUTPUT_DIR"
-
-# Compile Swift script to binary, fallback to source if unavailable or compilation fails
-if ! build_swift_helper; then
-  fallback_to_source
-fi

scripts/prepare-build-assets.mjs

@@ -1,4 +1,5 @@
 import fs from 'node:fs';
+import os from 'node:os';
 import path from 'node:path';
 import { execFileSync } from 'node:child_process';
 import { fileURLToPath } from 'node:url';
@@ -52,6 +53,16 @@ function fallbackToMacosSource() {
   process.stdout.write(`Staged macOS helper source fallback: ${macosHelperSourceCopyPath}\n`);
 }
 
+// Pin the minimum macOS to the app's own floor (Electron's `minos`). Without an
+// explicit target, swiftc stamps the build machine's OS version as the binary's
+// minimum and the helper fails to load on older systems (#213). The arch stays
+// the host's, matching the single-arch app electron-builder packages here.
+const MACOS_HELPER_DEPLOYMENT_TARGET = '12.0';
+
+function macosHelperTarget() {
+  return `${os.arch() === 'x64' ? 'x86_64' : 'arm64'}-apple-macos${MACOS_HELPER_DEPLOYMENT_TARGET}`;
+}
+
 function shouldSkipMacosHelperBuild() {
   return process.env.SUBMINER_SKIP_MACOS_HELPER_BUILD === '1';
 }
@@ -72,9 +83,13 @@ function buildMacosHelper() {
   ensureDir(scriptsOutputDir);
 
   try {
-    execFileSync('swiftc', ['-O', macosHelperSourcePath, '-o', macosHelperBinaryPath], {
-      stdio: 'inherit',
-    });
+    execFileSync(
+      'swiftc',
+      ['-O', '-target', macosHelperTarget(), macosHelperSourcePath, '-o', macosHelperBinaryPath],
+      {
+        stdio: 'inherit',
+      },
+    );
     fs.chmodSync(macosHelperBinaryPath, 0o755);
     process.stdout.write(`Built macOS helper: ${macosHelperBinaryPath}\n`);
   } catch (error) {

scripts/prepare-build-assets.test.ts

@@ -8,7 +8,7 @@ test('macOS helper build creates dist scripts directory before swiftc output', (
   const buildFunctionIndex = source.indexOf('function buildMacosHelper()');
   assert.notEqual(buildFunctionIndex, -1);
 
-  const swiftcIndex = source.indexOf("execFileSync('swiftc'", buildFunctionIndex);
+  const swiftcIndex = source.indexOf("'swiftc'", buildFunctionIndex);
   assert.notEqual(swiftcIndex, -1);
 
   const ensureDirIndex = source.lastIndexOf('ensureDir(scriptsOutputDir)', swiftcIndex);
@@ -18,3 +18,10 @@ test('macOS helper build creates dist scripts directory before swiftc output', (
     'buildMacosHelper must create dist/scripts before swiftc writes the helper binary',
   );
 });
+
+// Regression guard for #213: an untargeted swiftc stamps the build machine's OS
+// version as the helper's minimum, so released builds refuse to load on older macOS.
+test('macOS helper is compiled with an explicit deployment target', () => {
+  assert.match(source, /-target/);
+  assert.match(source, /apple-macos\$\{MACOS_HELPER_DEPLOYMENT_TARGET\}/);
+});

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

@@ -853,6 +853,10 @@ function parseAnnotatedAssEvents(content: string): ParsedAssEvents {
 
   for (const line of lines) {
     const trimmed = line.trim();
+    // Event text can end in an authored space. Fragmented karaoke commonly uses that
+    // space to retain word boundaries when its separately positioned events are joined
+    // back into a line, so only remove indentation before slicing the event fields.
+    const eventLine = line.trimStart();
 
     if (trimmed.startsWith('[') && trimmed.endsWith(']')) {
       inEventsSection = trimmed.toLowerCase() === '[events]';
@@ -883,9 +887,9 @@ function parseAnnotatedAssEvents(content: string): ParsedAssEvents {
       continue;
     }
 
-    const eventPrefix = trimmed.startsWith(ASS_DIALOGUE_PREFIX)
+    const eventPrefix = eventLine.startsWith(ASS_DIALOGUE_PREFIX)
       ? ASS_DIALOGUE_PREFIX
-      : trimmed.startsWith(ASS_COMMENT_PREFIX)
+      : eventLine.startsWith(ASS_COMMENT_PREFIX)
         ? ASS_COMMENT_PREFIX
         : null;
     if (!eventPrefix) {
@@ -896,7 +900,7 @@ function parseAnnotatedAssEvents(content: string): ParsedAssEvents {
       continue;
     }
 
-    const fields = trimmed.slice(eventPrefix.length).split(',');
+    const fields = eventLine.slice(eventPrefix.length).split(',');
     if (
       fieldIndex.start >= fields.length ||
       fieldIndex.end >= fields.length ||

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/secondary-subtitle-track.test.ts

@@ -181,6 +181,41 @@ test('ASS fragment karaoke stays separated by style with authored word spacing',
   assert.equal(findActiveSubtitleText(parseSubtitleCues(ass, 'ending.ass'), 8.5), 'Iwanttogo');
 });
 
+test('ASS fragment karaoke preserves word spaces authored at event boundaries', () => {
+  const fragments = [
+    'The ',
+    'shoot',
+    'ing ',
+    'stars ',
+    'arc',
+    'ing ',
+    'across ',
+    'the ',
+    'sky ',
+    'I ',
+    'wish ',
+    'upon,',
+  ];
+  const events: string[] = [];
+  for (const layer of [0, 1]) {
+    fragments.forEach((fragment, index) => {
+      events.push(
+        `Dialogue: ${layer},0:00:01.00,0:00:04.00,op_english,,0,0,0,,{\\pos(${100 + index * 40},110)\\t(0,200,\\fscx110)}${fragment}`,
+      );
+    });
+  }
+  const ass = [
+    '[Events]',
+    'Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text',
+    ...events,
+  ].join('\n');
+
+  assert.equal(
+    findActiveSubtitleText(parseSubtitleCues(ass, 'bravern-s01e10.ass'), 2),
+    'The shooting stars arcing across the sky I wish upon,',
+  );
+});
+
 test('findActiveSubtitleText keeps a complete reconstructed line over entrance fragments', () => {
   const current = {
     startTime: 1,

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;
   });
 }