fix(subtitles): navigate by sanitized cues across ASS animation

- Route subtitle navigation through parsed cue boundaries
- Treat explicit short seeks as subtitle priming events

src/core/services/index.ts

@@ -50,6 +50,10 @@ export {
 } from './tokenizer/yomitan-parser-runtime';
 export { syncYomitanDefaultAnkiServer } from './tokenizer/yomitan-parser-runtime';
 export { createSubtitleProcessingController } from './subtitle-processing-controller';
+export {
+  resolveSanitizedSubtitleSeekCommand,
+  subtitleCueSeekTime,
+} from './subtitle-cue-navigation';
 export { createFrequencyDictionaryLookup } from './frequency-dictionary';
 export { createJlptVocabularyLookup } from './jlpt-vocab';
 export {

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

@@ -0,0 +1,87 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {
+  resolveSanitizedSubtitleSeekCommand,
+  subtitleCueSeekTime,
+} from './subtitle-cue-navigation';
+
+test('next subtitle navigation skips generated ASS events and seeks to the next sanitized cue', () => {
+  const cues = [
+    {
+      startTime: 10,
+      endTime: 13,
+      text: 'first lyric',
+      source: 'canonical-ass' as const,
+      animationStartTime: 9.7,
+      animationEndTime: 13.4,
+    },
+    {
+      startTime: 13,
+      endTime: 16,
+      text: 'second lyric',
+      source: 'canonical-ass' as const,
+      animationStartTime: 12.7,
+      animationEndTime: 16.4,
+    },
+  ];
+
+  assert.deepEqual(resolveSanitizedSubtitleSeekCommand(['sub-seek', 1], cues, 10.2), [
+    'seek',
+    13.08,
+    'absolute+exact',
+  ]);
+});
+
+test('next subtitle navigation treats simultaneous sanitized cues as one line boundary', () => {
+  const cues = [
+    { startTime: 10, endTime: 13, text: 'romaji' },
+    { startTime: 10.02, endTime: 13, text: 'English' },
+    { startTime: 13, endTime: 16, text: 'next romaji' },
+    { startTime: 13.02, endTime: 16, text: 'Next English' },
+  ];
+
+  assert.deepEqual(resolveSanitizedSubtitleSeekCommand(['sub-seek', 1], cues, 10.1), [
+    'seek',
+    13.08,
+    'absolute+exact',
+  ]);
+});
+
+test('next subtitle navigation advances past the latest overlapping lyric', () => {
+  const cues = [
+    { startTime: 10, endTime: 14, text: 'exiting lyric' },
+    { startTime: 13, endTime: 16, text: 'current lyric' },
+    { startTime: 16, endTime: 19, text: 'next lyric' },
+  ];
+
+  assert.deepEqual(resolveSanitizedSubtitleSeekCommand(['sub-seek', 1], cues, 13.2), [
+    'seek',
+    16.08,
+    'absolute+exact',
+  ]);
+});
+
+test('previous subtitle navigation leaves the current cue and seeks to the prior cue', () => {
+  const cues = [
+    { startTime: 10, endTime: 12, text: 'first line' },
+    { startTime: 13, endTime: 16, text: 'current line' },
+  ];
+
+  assert.deepEqual(resolveSanitizedSubtitleSeekCommand(['sub-seek', -1], cues, 14.5), [
+    'seek',
+    10.08,
+    'absolute+exact',
+  ]);
+});
+
+test('subtitle navigation falls back when no sanitized destination exists', () => {
+  const cues = [{ startTime: 10, endTime: 13, text: 'only line' }];
+
+  assert.equal(resolveSanitizedSubtitleSeekCommand(['sub-seek', 1], cues, 10.2), null);
+  assert.equal(resolveSanitizedSubtitleSeekCommand(['seek', 5], cues, 10.2), null);
+});
+
+test('sidebar cue seeks share the boundary-safe sanitized cue timestamp', () => {
+  assert.equal(subtitleCueSeekTime({ startTime: 1, endTime: 2, text: 'line' }), 1.08);
+  assert.equal(subtitleCueSeekTime({ startTime: 1, endTime: 1.04, text: 'short' }), 1.03);
+});

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

@@ -0,0 +1,98 @@
+import type { SubtitleCue } from './subtitle-cue-parser';
+
+const CUE_START_GROUP_TOLERANCE_SECONDS = 0.05;
+const CUE_BOUNDARY_SEEK_OFFSET_SECONDS = 0.08;
+const CUE_END_GUARD_SECONDS = 0.01;
+
+type CueGroup = {
+  startTime: number;
+  endTime: number;
+  cue: SubtitleCue;
+};
+
+function isValidCue(cue: SubtitleCue): boolean {
+  return (
+    Number.isFinite(cue.startTime) && Number.isFinite(cue.endTime) && cue.endTime > cue.startTime
+  );
+}
+
+function groupCueBoundaries(cues: readonly SubtitleCue[]): CueGroup[] {
+  const sorted = cues.filter(isValidCue).sort((left, right) => {
+    return left.startTime - right.startTime || left.endTime - right.endTime;
+  });
+  const groups: CueGroup[] = [];
+
+  for (const cue of sorted) {
+    const current = groups.at(-1);
+    if (current && cue.startTime - current.startTime <= CUE_START_GROUP_TOLERANCE_SECONDS) {
+      current.endTime = Math.max(current.endTime, cue.endTime);
+      continue;
+    }
+    groups.push({ startTime: cue.startTime, endTime: cue.endTime, cue });
+  }
+
+  return groups;
+}
+
+/** A small offset avoids asking mpv to render exactly on a subtitle boundary. */
+export function subtitleCueSeekTime(cue: SubtitleCue): number {
+  return Math.max(
+    cue.startTime,
+    Math.min(cue.endTime - CUE_END_GUARD_SECONDS, cue.startTime + CUE_BOUNDARY_SEEK_OFFSET_SECONDS),
+  );
+}
+
+/**
+ * Translate mpv subtitle-line navigation onto parsed cues. Generated ASS karaoke can
+ * contain hundreds of subtitle events for one visible line, while the parsed list has
+ * already collapsed those events into the authored lines the user expects to navigate.
+ */
+export function resolveSanitizedSubtitleSeekCommand(
+  command: readonly (string | number)[],
+  cues: readonly SubtitleCue[],
+  currentTimeSec: number,
+): (string | number)[] | null {
+  if (
+    command.length < 2 ||
+    command[0] !== 'sub-seek' ||
+    (command[1] !== -1 && command[1] !== 1) ||
+    !Number.isFinite(currentTimeSec)
+  ) {
+    return null;
+  }
+
+  const groups = groupCueBoundaries(cues);
+  if (groups.length === 0) {
+    return null;
+  }
+
+  let activeIndex = -1;
+  for (const [index, group] of groups.entries()) {
+    if (group.startTime <= currentTimeSec && group.endTime > currentTimeSec) {
+      activeIndex = index;
+    }
+  }
+
+  let destination: CueGroup | undefined;
+  if (command[1] === 1) {
+    destination =
+      activeIndex >= 0
+        ? groups[activeIndex + 1]
+        : groups.find((group) => group.startTime > currentTimeSec);
+  } else if (activeIndex >= 0) {
+    destination = groups[activeIndex - 1];
+  } else {
+    for (let index = groups.length - 1; index >= 0; index -= 1) {
+      const group = groups[index]!;
+      if (group.startTime < currentTimeSec) {
+        destination = group;
+        break;
+      }
+    }
+  }
+
+  if (!destination) {
+    return null;
+  }
+  return ['seek', subtitleCueSeekTime(destination.cue), 'absolute+exact'];
+}

src/main.ts

@@ -312,6 +312,7 @@ import {
   promoteSettingsWindowAboveOverlay,
   registerGlobalShortcuts as registerGlobalShortcutsCore,
   replayCurrentSubtitleRuntime,
+  resolveSanitizedSubtitleSeekCommand,
   resolveJellyfinPlaybackPlanRuntime,
   runStartupBootstrapRuntime,
   saveJellyfinSubtitleDelay,
@@ -1958,6 +1959,31 @@ let linuxVisibleOverlayOwnerBindingKey: string | null = null;
 let linuxVisibleOverlayWindowModeSwitchToken = 0;
 let subtitleSidebarRequestedOpen = false;
 const SEEK_THRESHOLD_SECONDS = 3;
+const EXPLICIT_SEEK_INTENT_TTL_MS = 2000;
+let explicitSeekIntentExpiresAtMs = 0;
+
+function isExplicitMpvSeekCommand(command: readonly (string | number)[]): boolean {
+  return command[0] === 'seek' || command[0] === 'sub-seek';
+}
+
+function sendRendererMpvCommand(rawCommand: (string | number)[]): void {
+  const command =
+    resolveSanitizedSubtitleSeekCommand(
+      rawCommand,
+      appState.activeParsedSubtitleCues,
+      appState.mpvClient?.currentTimePos ?? Number.NaN,
+    ) ?? rawCommand;
+  if (isExplicitMpvSeekCommand(command)) {
+    explicitSeekIntentExpiresAtMs = Date.now() + EXPLICIT_SEEK_INTENT_TTL_MS;
+  }
+  sendMpvCommandRuntime(appState.mpvClient, command);
+}
+
+function consumeExplicitSeekIntent(): boolean {
+  const pending = explicitSeekIntentExpiresAtMs >= Date.now();
+  explicitSeekIntentExpiresAtMs = 0;
+  return pending;
+}
 
 const autoplaySubtitlePrimingRuntime = createAutoplaySubtitlePrimingRuntime({
   getCurrentMediaPath: () => appState.currentMediaPath,
@@ -4580,6 +4606,7 @@ const {
     reportJellyfinRemoteProgress: (forceImmediate) => {
       void reportJellyfinRemoteProgress(forceImmediate);
     },
+    consumeExplicitSeek: () => consumeExplicitSeekIntent(),
     onTimePosUpdate: (time) => {
       const delta = time - lastObservedTimePos;
       if (subtitlePrefetchService && (delta > SEEK_THRESHOLD_SECONDS || delta < 0)) {
@@ -5485,8 +5512,7 @@ const { registerIpcRuntimeHandlers } = composeIpcRuntimeHandlers({
     showPlaybackFeedback: (text: string) => showConfiguredPlaybackFeedback(text),
     replayCurrentSubtitle: () => replayCurrentSubtitleRuntime(appState.mpvClient),
     playNextSubtitle: () => playNextSubtitleRuntime(appState.mpvClient),
-    sendMpvCommand: (rawCommand: (string | number)[]) =>
-      sendMpvCommandRuntime(appState.mpvClient, rawCommand),
+    sendMpvCommand: (rawCommand: (string | number)[]) => sendRendererMpvCommand(rawCommand),
     getMpvClient: () => appState.mpvClient,
     isMpvConnected: () => Boolean(appState.mpvClient && appState.mpvClient.connected),
     hasRuntimeOptionsManager: () => appState.runtimeOptionsManager !== null,

src/main/runtime/mpv-main-event-actions.test.ts

@@ -358,6 +358,30 @@ test('time-pos handler forces Jellyfin progress when mpv position jumps', () =>
   ]);
 });
 
+test('time-pos handler treats an explicit short jump as a seek', () => {
+  const updateKinds: string[] = [];
+  let explicitSeekPending = false;
+  const timeHandler = createHandleMpvTimePosChangeHandler({
+    recordPlaybackPosition: () => {},
+    reportJellyfinRemoteProgress: () => {},
+    refreshDiscordPresence: () => {},
+    maybeRunAnilistPostWatchUpdate: async () => {},
+    consumeExplicitSeek: () => {
+      const pending = explicitSeekPending;
+      explicitSeekPending = false;
+      return pending;
+    },
+    onTimePosUpdate: (_time, kind) => updateKinds.push(kind),
+  });
+
+  timeHandler({ time: 10 });
+  explicitSeekPending = true;
+  timeHandler({ time: 11.5 });
+  timeHandler({ time: 11.6 });
+
+  assert.deepEqual(updateKinds, ['initial', 'seek', 'playback']);
+});
+
 test('time-pos handler passes fresh playback time to AniList post-watch', async () => {
   const watchedSeconds: unknown[] = [];
   const timeHandler = createHandleMpvTimePosChangeHandler({

src/main/runtime/mpv-main-event-actions.ts

@@ -141,14 +141,16 @@ export function createHandleMpvTimePosChangeHandler(deps: {
   maybeRunAnilistPostWatchUpdate?: (options?: AnilistPostWatchRunOptions) => Promise<void>;
   logError?: (message: string, error: unknown) => void;
   onTimePosUpdate?: (time: number, kind: TimePosUpdateKind) => void;
+  consumeExplicitSeek?: () => boolean;
 }) {
   let lastObservedTime: number | null = null;
 
   return ({ time }: { time: number }): void => {
+    const explicitSeek = deps.consumeExplicitSeek?.() ?? false;
     const updateKind: TimePosUpdateKind =
       lastObservedTime === null
         ? 'initial'
-        : isSeekLikeTimeChange(lastObservedTime, time)
+        : explicitSeek || isSeekLikeTimeChange(lastObservedTime, time)
           ? 'seek'
           : 'playback';
     const forceImmediate = updateKind === 'seek';

src/main/runtime/mpv-main-event-bindings.ts

@@ -79,6 +79,7 @@ export function createBindMpvMainEventHandlersHandler(deps: {
   recordMediaDuration: (durationSec: number) => void;
   reportJellyfinRemoteProgress: (forceImmediate: boolean) => void;
   onTimePosUpdate?: (time: number) => void;
+  consumeExplicitSeek?: () => boolean;
   onFullscreenChange?: (fullscreen: boolean) => void;
   recordPauseState: (paused: boolean) => void;
 
@@ -172,6 +173,7 @@ export function createBindMpvMainEventHandlersHandler(deps: {
       refreshDiscordPresence: () => deps.refreshDiscordPresence(),
       maybeRunAnilistPostWatchUpdate: (options) => deps.maybeRunAnilistPostWatchUpdate(options),
       logError: (message, error) => deps.logSubtitleTimingError(message, error),
+      consumeExplicitSeek: deps.consumeExplicitSeek,
       onTimePosUpdate: (time, updateKind) => {
         deps.onTimePosUpdate?.(time);
         if (updateKind === 'playback') return;

src/main/runtime/mpv-main-event-main-deps.ts

@@ -86,6 +86,7 @@ export function createBuildBindMpvMainEventHandlersMainDepsHandler(deps: {
   resetAnilistMediaGuessState: () => void;
   reportJellyfinRemoteProgress: (forceImmediate: boolean) => void;
   onTimePosUpdate?: (time: number) => void;
+  consumeExplicitSeek?: () => boolean;
   onFullscreenChange?: (fullscreen: boolean) => void;
   updateSubtitleRenderMetrics: (patch: Record<string, unknown>) => void;
   refreshDiscordPresence: () => void;
@@ -334,6 +335,7 @@ export function createBuildBindMpvMainEventHandlersMainDepsHandler(deps: {
     },
     reportJellyfinRemoteProgress: (forceImmediate: boolean) =>
       deps.reportJellyfinRemoteProgress(forceImmediate),
+    consumeExplicitSeek: deps.consumeExplicitSeek,
     onTimePosUpdate: (time: number) => {
       // Timing history is a viewing log: after a real backward seek, a rewatched
       // canonical line should enter it again. Immersion stats keep their

src/renderer/modals/subtitle-sidebar.ts

@@ -4,6 +4,7 @@ import type {
   SubtitleMiningContext,
   SubtitleSidebarSnapshot,
 } from '../../types';
+import { subtitleCueSeekTime } from '../../core/services/subtitle-cue-navigation.js';
 import type { ModalStateReader, RendererContext } from '../context';
 import { syncOverlayMouseIgnoreState } from '../overlay-mouse-ignore.js';
 import {
@@ -14,7 +15,6 @@ import {
 
 const MANUAL_SCROLL_HOLD_MS = 1500;
 const ACTIVE_CUE_LOOKAHEAD_SEC = 0.18;
-const CLICK_SEEK_OFFSET_SEC = 0.08;
 const SNAPSHOT_POLL_INTERVAL_MS = 80;
 const EMBEDDED_SIDEBAR_MIN_WIDTH_PX = 240;
 const EMBEDDED_SIDEBAR_MAX_RATIO = 0.45;
@@ -392,12 +392,7 @@ export function createSubtitleSidebarModal(
   }
 
   function seekToCue(cue: SubtitleCue): void {
-    const targetTime = Math.min(cue.endTime - 0.01, cue.startTime + CLICK_SEEK_OFFSET_SEC);
-    window.electronAPI.sendMpvCommand([
-      'seek',
-      Math.max(cue.startTime, targetTime),
-      'absolute+exact',
-    ]);
+    window.electronAPI.sendMpvCommand(['seek', subtitleCueSeekTime(cue), 'absolute+exact']);
   }
 
   function getCueRowLabel(cue: SubtitleCue): string {