feat(playback): report Embedded MPV file chapters on the timeline

Observe mpv `chapter-list` in the macOS and Windows addons and the
frame-copy helper, carry it as `EmbeddedMpvSession.chapters`, and map it
to `PlayerTimelineSegment[]` for `app-player-controls` when the host
passes no catch-up segments. A closing-credits chapter now times the
Up next card.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/electron-backend-e2e/src/embedded-mpv-chapters.e2e.ts

@@ -0,0 +1,129 @@
+import { readFileSync, writeFileSync } from 'fs';
+import { join } from 'path';
+import {
+    channelItemByTitle,
+    closeElectronApp,
+    expect,
+    goToDashboard,
+    importM3uPlaylistFromNativeDialog,
+    launchElectronApp,
+    openSettings,
+    openSettingsSection,
+    saveSettings,
+    test,
+    workspaceRoot,
+} from './electron-test-fixtures';
+import {
+    createLocalMediaServer,
+    installEmbeddedMpvSessionCapture,
+} from './embedded-mpv-frame-copy-packaged-fixtures';
+
+/**
+ * mpv's `chapter-list` must reach the shared controls: the chaptered fixture
+ * (Intro 0 s, Episode 5 s, Credits 24 s of 30 s) is drawn as three titled
+ * timeline segments. Frame-copy is the Embedded MPV engine that mounts
+ * `app-player-controls`; the test skips where that runtime is unavailable.
+ */
+test('@playback @electron @embedded-mpv frame-copy draws file chapters on the timeline', async ({
+    dataDir,
+}) => {
+    const media = await createLocalMediaServer({
+        body: readFileSync(
+            join(
+                workspaceRoot,
+                'apps/web-e2e/src/fixtures/playback/episode-chapters.webm'
+            )
+        ),
+        resourcePath: '/episode-chapters.webm',
+        contentType: 'video/webm',
+    });
+    const app = await launchElectronApp(dataDir, {
+        env: {
+            IPTVNATOR_ENABLE_EMBEDDED_MPV_EXPERIMENT: '1',
+            IPTVNATOR_ENABLE_EMBEDDED_MPV_FRAME_COPY: '1',
+            IPTVNATOR_EMBEDDED_MPV_ALLOW_HOMEBREW: '1',
+        },
+    });
+    try {
+        const support = await app.mainWindow.evaluate(() =>
+            window.electron.getEmbeddedMpvSupport()
+        );
+        test.skip(
+            !support.supported || support.engine !== 'frame-copy',
+            `Frame-copy runtime unavailable: ${JSON.stringify(support)}`
+        );
+        await openSettings(app.mainWindow);
+        await openSettingsSection(app.mainWindow, 'playback');
+        await app.mainWindow.getByTestId('select-video-player').click();
+        await app.mainWindow.getByTestId('embedded-mpv').click();
+        await saveSettings(app.mainWindow);
+        await goToDashboard(app.mainWindow);
+
+        const playlist = join(dataDir, 'chapters.m3u');
+        writeFileSync(
+            playlist,
+            `#EXTM3U\n#EXTINF:-1,Chaptered fixture\n${media.url}\n`
+        );
+        await installEmbeddedMpvSessionCapture(app);
+        await importM3uPlaylistFromNativeDialog(app, playlist);
+        await channelItemByTitle(app.mainWindow, 'Chaptered fixture')
+            .first()
+            .click();
+
+        // The local frame-copy runtime can fail its first frame-view
+        // initialization; one user Retry recovers it (see player-theme).
+        await expect
+            .poll(() =>
+                app.mainWindow.evaluate(
+                    () =>
+                        (window.__packagedEmbeddedMpvSessions?.at(-1)?.chapters
+                            ?.length ?? 0) > 0 ||
+                        !!document.querySelector('.embedded-mpv-player__stalled')
+                ),
+                { timeout: 20000 }
+            )
+            .toBe(true);
+        const stalled = app.mainWindow.locator('.embedded-mpv-player__stalled');
+        if (await stalled.isVisible()) {
+            await stalled.getByRole('button', { name: 'Retry' }).click();
+        }
+
+        await expect
+            .poll(
+                () =>
+                    app.mainWindow.evaluate(
+                        () =>
+                            window.__packagedEmbeddedMpvSessions?.at(-1)
+                                ?.chapters ?? []
+                    ),
+                { timeout: 20000 }
+            )
+            .toEqual([
+                { timeSeconds: 0, title: 'Intro' },
+                { timeSeconds: 5, title: 'Episode' },
+                { timeSeconds: 24, title: 'Credits' },
+            ]);
+
+        const segments = app.mainWindow.locator(
+            'app-player-controls .player-controls__timeline-segment'
+        );
+        await expect(segments).toHaveCount(3);
+        await expect
+            .poll(() =>
+                segments.evaluateAll((elements) =>
+                    elements.map((element) => ({
+                        title: element.getAttribute('data-segment-title'),
+                        left: Math.round(parseFloat(element.style.left)),
+                    }))
+                )
+            )
+            .toEqual([
+                { title: 'Intro', left: 0 },
+                { title: 'Episode', left: 17 },
+                { title: 'Credits', left: 80 },
+            ]);
+    } finally {
+        await closeElectronApp(app);
+        await media.close();
+    }
+});

apps/electron-backend-e2e/src/embedded-mpv-frame-copy-packaged.e2e.ts

@@ -360,12 +360,23 @@ test.describe('Packaged Linux embedded MPV frame-copy runtime', () => {
                 resourcePath: '/stream-stats-switch.webm',
                 contentType: 'video/webm',
             });
+            const chapteredMedia = await createLocalMediaServer({
+                body: readFileSync(
+                    join(
+                        __dirname,
+                        '../../web-e2e/src/fixtures/playback/episode-chapters.webm'
+                    )
+                ),
+                resourcePath: '/chapters.webm',
+                contentType: 'video/webm',
+            });
             media = {
                 url: mediaServer.url,
                 close: async () => {
                     await Promise.all([
                         mediaServer.close(),
                         alternateMedia.close(),
+                        chapteredMedia.close(),
                     ]);
                 },
             };
@@ -415,6 +426,33 @@ test.describe('Packaged Linux embedded MPV frame-copy runtime', () => {
                     });
             }
 
+            // mpv's `chapter-list` reaches the renderer session (it draws the
+            // timeline segments and times the Up next card), and the next
+            // file starts without the previous file's chapters.
+            await launchedFrameCopyApp.mainWindow.evaluate(
+                async ({ sessionId, streamUrl }) => {
+                    await window.electron.loadEmbeddedMpvPlayback(sessionId, {
+                        streamUrl,
+                        title: 'Chaptered episode',
+                        isLive: false,
+                    });
+                },
+                { sessionId: created.id, streamUrl: chapteredMedia.url }
+            );
+            await expect
+                .poll(
+                    () => getLatestSession(launchedFrameCopyApp, created.id),
+                    { timeout: 15000 }
+                )
+                .toMatchObject({
+                    streamUrl: chapteredMedia.url,
+                    chapters: [
+                        { timeSeconds: 0, title: 'Intro' },
+                        { timeSeconds: 5, title: 'Episode' },
+                        { timeSeconds: 24, title: 'Credits' },
+                    ],
+                });
+
             // Audio-only replacements must not retain the previous video size.
             await launchedFrameCopyApp.mainWindow.evaluate(
                 async ({ sessionId, streamUrl }) => {
@@ -433,6 +471,7 @@ test.describe('Packaged Linux embedded MPV frame-copy runtime', () => {
                 )
                 .toMatchObject({
                     streamUrl: audioMedia.url,
+                    chapters: [],
                     videoWidth: 0,
                     videoHeight: 0,
                     stats: {

apps/electron-backend/native/helper/mpv_frame_helper.cpp

@@ -55,6 +55,12 @@ struct TrackInfo {
     bool forced = false;
 };
 
+/* One entry of mpv's `chapter-list`: start time and optional title. */
+struct ChapterInfo {
+    double timeSeconds = 0;
+    std::string title;
+};
+
 struct SnapshotState {
     std::string status = "idle";
     double positionSeconds = 0;
@@ -118,6 +124,7 @@ struct SnapshotState {
     int64_t selectedAudioTrackId = -1;
     std::vector<TrackInfo> subtitleTracks;
     int64_t selectedSubtitleTrackId = -1;
+    std::vector<ChapterInfo> chapters;
     double playbackSpeed = 1;
     std::string aspectOverride = "no";
     bool recordingActive = false;
@@ -187,6 +194,21 @@ std::string tracksJson(const std::vector<TrackInfo>& tracks,
     return out;
 }
 
+std::string chaptersJson(const std::vector<ChapterInfo>& chapters) {
+    std::string out = "[";
+    bool first = true;
+    for (const ChapterInfo& chapter : chapters) {
+        JsonWriter writer;
+        writer.num("timeSeconds", chapter.timeSeconds);
+        if (!chapter.title.empty()) writer.str("title", chapter.title);
+        if (!first) out += ',';
+        first = false;
+        out += writer.finish();
+    }
+    out += ']';
+    return out;
+}
+
 /* Compose the `stats` object of the snapshot event. Always emitted, even when
  * empty: the adapter merges snapshot events field by field, so an omitted key
  * would leave the previous stream's numbers in place across a channel switch.
@@ -262,6 +284,9 @@ std::string composeSnapshotLocked() {
     } else {
         writer.nullValue("selectedSubtitleTrackId");
     }
+    /* Always emitted: the adapter merges snapshot events field by field, so
+     * an omitted key would keep the previous file's chapters. */
+    writer.raw("chapters", chaptersJson(s.chapters));
     writer.num("playbackSpeed", s.playbackSpeed);
     writer.str("aspectOverride", s.aspectOverride);
     writer.raw("stats", composeStatsJsonLocked());
@@ -383,6 +408,41 @@ void updateTracksFromNode(const mpv_node& trackListNode) {
     g_state.snapshot.subtitleTracks = std::move(subs);
 }
 
+/* mpv `chapter-list`: an array of { time, title? } maps in file order. */
+void updateChaptersFromNode(const mpv_node& chapterListNode) {
+    std::vector<ChapterInfo> chapters;
+    if (chapterListNode.format == MPV_FORMAT_NODE_ARRAY &&
+        chapterListNode.u.list) {
+        for (int i = 0; i < chapterListNode.u.list->num; i++) {
+            const mpv_node& entry = chapterListNode.u.list->values[i];
+            if (entry.format != MPV_FORMAT_NODE_MAP || !entry.u.list) continue;
+            ChapterInfo chapter;
+            bool hasTime = false;
+            const mpv_node_list& map = *entry.u.list;
+            for (int k = 0; k < map.num; k++) {
+                const char* key = map.keys[k];
+                const mpv_node& value = map.values[k];
+                if (!key) continue;
+                if (std::strcmp(key, "time") == 0 &&
+                    value.format == MPV_FORMAT_DOUBLE) {
+                    chapter.timeSeconds = value.u.double_;
+                    hasTime = std::isfinite(chapter.timeSeconds);
+                } else if (std::strcmp(key, "time") == 0 &&
+                           value.format == MPV_FORMAT_INT64) {
+                    chapter.timeSeconds = (double)value.u.int64;
+                    hasTime = true;
+                } else if (std::strcmp(key, "title") == 0 &&
+                           value.format == MPV_FORMAT_STRING &&
+                           value.u.string) {
+                    chapter.title = value.u.string;
+                }
+            }
+            if (hasTime) chapters.push_back(std::move(chapter));
+        }
+    }
+    g_state.snapshot.chapters = std::move(chapters);
+}
+
 bool parseTrackSelection(const char* value, int64_t& out) {
     if (!value) return false;
     char* end = nullptr;
@@ -436,6 +496,9 @@ void handlePropertyChange(const mpv_event_property& property) {
     } else if (name == "track-list" && property.format == MPV_FORMAT_NODE &&
                property.data) {
         updateTracksFromNode(*static_cast<mpv_node*>(property.data));
+    } else if (name == "chapter-list" &&
+               property.format == MPV_FORMAT_NODE && property.data) {
+        updateChaptersFromNode(*static_cast<mpv_node*>(property.data));
     } else if (name == "aid" && property.format == MPV_FORMAT_STRING &&
                property.data) {
         int64_t selected = -1;
@@ -536,6 +599,7 @@ void runMpvEventLoop() {
                     s.selectedAudioTrackId = -1;
                     s.subtitleTracks.clear();
                     s.selectedSubtitleTrackId = -1;
+                    s.chapters.clear();
                     g_state.loadedPath = false;
                     markDirtyLocked();
                     break;
@@ -1115,6 +1179,8 @@ int main(int argc, char** argv) {
                          MPV_FORMAT_STRING);
     mpv_observe_property(g_state.mpv, 24, "audio-params/samplerate",
                          MPV_FORMAT_INT64);
+    /* File chapters draw the timeline segments and mark closing credits. */
+    mpv_observe_property(g_state.mpv, 25, "chapter-list", MPV_FORMAT_NODE);
 
     g_state.pipeline.onGenerationChanged = [](const std::string& name,
                                               int width, int height,

apps/electron-backend/native/src/embedded_mpv.mm

@@ -91,6 +91,12 @@ struct AudioTrack {
     bool forced = false;
 };
 
+// One entry of mpv's `chapter-list`: start time and optional title.
+struct Chapter {
+    double timeSeconds = 0.0;
+    std::string title;
+};
+
 struct SessionSnapshot {
     SessionStatus status = SessionStatus::Idle;
     double positionSeconds = 0.0;
@@ -108,6 +114,7 @@ struct SessionSnapshot {
     int64_t selectedAudioTrackId = -1;
     std::vector<AudioTrack> subtitleTracks;
     int64_t selectedSubtitleTrackId = -1;
+    std::vector<Chapter> chapters;
     double playbackSpeed = 1.0;
     std::string aspectOverride = "no";
     // Stream diagnostics for the player's info popover. Sentinels mean "mpv
@@ -1087,6 +1094,44 @@ void updateAudioTracksFromNode(SessionSnapshot& snapshot, const mpv_node& node)
     );
 }
 
+// mpv `chapter-list`: an array of { time, title? } maps in file order.
+void updateChaptersFromNode(SessionSnapshot& snapshot, const mpv_node& node)
+{
+    snapshot.chapters.clear();
+    if (node.format != MPV_FORMAT_NODE_ARRAY ||
+        !node.u.list ||
+        !node.u.list->values) {
+        return;
+    }
+
+    for (int index = 0; index < node.u.list->num; index += 1) {
+        const mpv_node& chapterNode = node.u.list->values[index];
+        if (chapterNode.format != MPV_FORMAT_NODE_MAP) {
+            continue;
+        }
+
+        const mpv_node* timeNode = getNodeMapValue(chapterNode, "time");
+        if (!timeNode) {
+            continue;
+        }
+        Chapter chapter;
+        if (timeNode->format == MPV_FORMAT_DOUBLE) {
+            chapter.timeSeconds = timeNode->u.double_;
+        } else if (timeNode->format == MPV_FORMAT_INT64) {
+            chapter.timeSeconds = static_cast<double>(timeNode->u.int64);
+        } else {
+            continue;
+        }
+        if (!std::isfinite(chapter.timeSeconds)) {
+            continue;
+        }
+        if (const mpv_node* titleNode = getNodeMapValue(chapterNode, "title")) {
+            chapter.title = readNodeString(*titleNode);
+        }
+        snapshot.chapters.push_back(chapter);
+    }
+}
+
 void updateSubtitleTracksFromNode(SessionSnapshot& snapshot, const mpv_node& node)
 {
     updateTracksFromNode(
@@ -1228,6 +1273,7 @@ void runEventLoop(const std::shared_ptr<Session>& session)
                 session->snapshot.selectedAudioTrackId = -1;
                 session->snapshot.subtitleTracks.clear();
                 session->snapshot.selectedSubtitleTrackId = -1;
+                session->snapshot.chapters.clear();
                 session->loadedPath = false;
                 break;
             case MPV_EVENT_FILE_LOADED:
@@ -1354,6 +1400,16 @@ void runEventLoop(const std::shared_ptr<Session>& session)
                     break;
                 }
 
+                if (propertyName == "chapter-list" &&
+                    property->format == MPV_FORMAT_NODE &&
+                    property->data) {
+                    updateChaptersFromNode(
+                        session->snapshot,
+                        *static_cast<mpv_node*>(property->data)
+                    );
+                    break;
+                }
+
                 if (propertyName == "aid" &&
                     property->format == MPV_FORMAT_STRING &&
                     property->data) {
@@ -1993,6 +2049,8 @@ Napi::Value CreateSession(const Napi::CallbackInfo& info)
         "audio-params/samplerate",
         MPV_FORMAT_INT64
     );
+    // File chapters draw the timeline segments and mark closing credits.
+    mpv_observe_property(session->handle, 23, "chapter-list", MPV_FORMAT_NODE);
 
     session->running.store(true);
     session->eventThread = std::thread(runEventLoop, session);
@@ -2818,6 +2876,21 @@ Napi::Value GetSessionSnapshot(const Napi::CallbackInfo& info)
     }
     result.Set("subtitleTracks", subtitleTracks);
 
+    auto chapters = Napi::Array::New(env, snapshot.chapters.size());
+    for (size_t index = 0; index < snapshot.chapters.size(); index += 1) {
+        const Chapter& chapter = snapshot.chapters[index];
+        auto chapterObject = Napi::Object::New(env);
+        chapterObject.Set(
+            "timeSeconds",
+            Napi::Number::New(env, chapter.timeSeconds)
+        );
+        if (!chapter.title.empty()) {
+            chapterObject.Set("title", Napi::String::New(env, chapter.title));
+        }
+        chapters.Set(index, chapterObject);
+    }
+    result.Set("chapters", chapters);
+
     result.Set(
         "playbackSpeed",
         Napi::Number::New(env, snapshot.playbackSpeed)

apps/electron-backend/native/src/embedded_mpv_wid_common.h

@@ -112,6 +112,12 @@ struct AudioTrack {
     bool forced = false;
 };
 
+/** One entry of mpv's `chapter-list`: start time and optional title. */
+struct Chapter {
+    double timeSeconds = 0.0;
+    std::string title;
+};
+
 struct SessionSnapshot {
     SessionStatus status = SessionStatus::Idle;
     double positionSeconds = 0.0;
@@ -125,6 +131,8 @@ struct SessionSnapshot {
     int64_t selectedAudioTrackId = -1;
     std::vector<AudioTrack> subtitleTracks;
     int64_t selectedSubtitleTrackId = -1;
+    /** libmpv backend only; the Linux `--wid` poller does not read it. */
+    std::vector<Chapter> chapters;
     double playbackSpeed = 1.0;
     std::string aspectOverride = "no";
     /** Stream diagnostics for the player's info popover. Sentinels mean "not
@@ -1400,6 +1408,42 @@ void updateAudioTracksFromNode(SessionSnapshot& snapshot, const mpv_node& node)
     }
 }
 
+/** mpv `chapter-list`: an array of { time, title? } maps in file order. */
+void updateChaptersFromNode(SessionSnapshot& snapshot, const mpv_node& node)
+{
+    snapshot.chapters.clear();
+    if (node.format != MPV_FORMAT_NODE_ARRAY || !node.u.list ||
+        !node.u.list->values) {
+        return;
+    }
+
+    for (int index = 0; index < node.u.list->num; index += 1) {
+        const mpv_node& chapterNode = node.u.list->values[index];
+        if (chapterNode.format != MPV_FORMAT_NODE_MAP) {
+            continue;
+        }
+        const mpv_node* timeNode = getNodeMapValue(chapterNode, "time");
+        if (!timeNode) {
+            continue;
+        }
+        Chapter chapter;
+        if (timeNode->format == MPV_FORMAT_DOUBLE) {
+            chapter.timeSeconds = timeNode->u.double_;
+        } else if (timeNode->format == MPV_FORMAT_INT64) {
+            chapter.timeSeconds = static_cast<double>(timeNode->u.int64);
+        } else {
+            continue;
+        }
+        if (!std::isfinite(chapter.timeSeconds)) {
+            continue;
+        }
+        if (const mpv_node* titleNode = getNodeMapValue(chapterNode, "title")) {
+            chapter.title = readNodeString(*titleNode);
+        }
+        snapshot.chapters.push_back(chapter);
+    }
+}
+
 void updateSubtitleTracksFromNode(SessionSnapshot& snapshot, const mpv_node& node)
 {
     snapshot.subtitleTracks = readTracksOfType(node, "sub");
@@ -1498,6 +1542,7 @@ void runEventLoop(std::shared_ptr<Session> session)
                 session->snapshot.status = SessionStatus::Loading;
                 session->snapshot.error.clear();
                 session->snapshot.clearStreamStats();
+                session->snapshot.chapters.clear();
                 break;
             case MPV_EVENT_FILE_LOADED:
                 session->snapshot.status =
@@ -1580,6 +1625,10 @@ void runEventLoop(std::shared_ptr<Session> session)
                         *static_cast<mpv_node*>(property->data);
                     updateAudioTracksFromNode(session->snapshot, node);
                     updateSubtitleTracksFromNode(session->snapshot, node);
+                } else if (name == "chapter-list" && property->format == MPV_FORMAT_NODE) {
+                    updateChaptersFromNode(
+                        session->snapshot,
+                        *static_cast<mpv_node*>(property->data));
                 } else if (name == "aid") {
                     const char* rawValue = property->format == MPV_FORMAT_STRING
                         ? *static_cast<char**>(property->data)
@@ -1918,6 +1967,8 @@ Napi::Value CreateSession(const Napi::CallbackInfo& info)
         session->handle, 21, "audio-params/channels", MPV_FORMAT_STRING);
     mpv_observe_property(
         session->handle, 22, "audio-params/samplerate", MPV_FORMAT_INT64);
+    /* File chapters draw the timeline segments and mark closing credits. */
+    mpv_observe_property(session->handle, 23, "chapter-list", MPV_FORMAT_NODE);
 
     session->running.store(true);
     session->eventThread = std::thread(runEventLoop, session);
@@ -2624,6 +2675,17 @@ Napi::Value GetSessionSnapshot(const Napi::CallbackInfo& info)
         result.Set("selectedSubtitleTrackId", env.Null());
     }
     writeTracks(env, result, "subtitleTracks", snapshot.subtitleTracks);
+    auto chapters = Napi::Array::New(env, snapshot.chapters.size());
+    for (size_t index = 0; index < snapshot.chapters.size(); index += 1) {
+        const Chapter& chapter = snapshot.chapters[index];
+        auto chapterObject = Napi::Object::New(env);
+        chapterObject.Set("timeSeconds", Napi::Number::New(env, chapter.timeSeconds));
+        if (!chapter.title.empty()) {
+            chapterObject.Set("title", Napi::String::New(env, chapter.title));
+        }
+        chapters.Set(index, chapterObject);
+    }
+    result.Set("chapters", chapters);
     result.Set("playbackSpeed", Napi::Number::New(env, snapshot.playbackSpeed));
     result.Set("aspectOverride", Napi::String::New(env, snapshot.aspectOverride));
     writeStreamStats(env, result, snapshot);

apps/electron-backend/src/app/services/embedded-mpv-chapters.util.spec.ts

@@ -0,0 +1,36 @@
+import { normalizeEmbeddedMpvChapters } from './embedded-mpv-chapters.util';
+
+describe('normalizeEmbeddedMpvChapters', () => {
+    it('keeps valid chapters and trims titles', () => {
+        expect(
+            normalizeEmbeddedMpvChapters([
+                { timeSeconds: 0, title: ' Intro ' },
+                { timeSeconds: 12.5 },
+                { timeSeconds: 40, title: '' },
+            ])
+        ).toEqual([
+            { timeSeconds: 0, title: 'Intro' },
+            { timeSeconds: 12.5 },
+            { timeSeconds: 40 },
+        ]);
+    });
+
+    it('drops malformed entries', () => {
+        expect(
+            normalizeEmbeddedMpvChapters([
+                null,
+                'chapter',
+                { title: 'No time' },
+                { timeSeconds: -1 },
+                { timeSeconds: Number.NaN },
+                { timeSeconds: '10' },
+                { timeSeconds: 5, title: 7 },
+            ])
+        ).toEqual([{ timeSeconds: 5 }]);
+    });
+
+    it('treats a missing field from an older binary as no chapters', () => {
+        expect(normalizeEmbeddedMpvChapters(undefined)).toEqual([]);
+        expect(normalizeEmbeddedMpvChapters({})).toEqual([]);
+    });
+});

apps/electron-backend/src/app/services/embedded-mpv-chapters.util.ts

@@ -0,0 +1,33 @@
+import type { EmbeddedMpvChapter } from '@iptvnator/shared/interfaces';
+
+/**
+ * Validate the addon's or helper's `chapters` snapshot field before it
+ * reaches the renderer: an older binary omits it, and a malformed entry must
+ * not draw a segment. Order is left to the renderer's timeline mapping.
+ */
+export function normalizeEmbeddedMpvChapters(
+    value: unknown
+): EmbeddedMpvChapter[] {
+    if (!Array.isArray(value)) {
+        return [];
+    }
+    const chapters: EmbeddedMpvChapter[] = [];
+    for (const entry of value) {
+        if (!entry || typeof entry !== 'object') {
+            continue;
+        }
+        const { timeSeconds, title } = entry as Record<string, unknown>;
+        if (
+            typeof timeSeconds !== 'number' ||
+            !Number.isFinite(timeSeconds) ||
+            timeSeconds < 0
+        ) {
+            continue;
+        }
+        const trimmedTitle = typeof title === 'string' ? title.trim() : '';
+        chapters.push(
+            trimmedTitle ? { timeSeconds, title: trimmedTitle } : { timeSeconds }
+        );
+    }
+    return chapters;
+}

apps/electron-backend/src/app/services/embedded-mpv-frame-copy-protocol.ts

@@ -53,6 +53,7 @@ export function createInitialSnapshot(): NativeEmbeddedMpvSessionSnapshot {
         selectedAudioTrackId: null,
         subtitleTracks: [],
         selectedSubtitleTrackId: null,
+        chapters: [],
         playbackSpeed: 1,
         aspectOverride: 'no',
         recording: { active: false },

apps/electron-backend/src/app/services/embedded-mpv-native.service.spec.ts

@@ -83,6 +83,7 @@ interface MockSnapshot {
     streamUrl: string;
     audioTracks?: never[];
     selectedAudioTrackId?: number | null;
+    chapters?: Array<{ timeSeconds: number; title?: string }>;
     stats?: {
         fps?: number;
         videoBitrateBps?: number;
@@ -580,6 +581,24 @@ describe('EmbeddedMpvNativeService power blocker', () => {
         });
     });
 
+    it('passes validated file chapters through to the renderer session', () => {
+        startSession('s1', snapshot('playing'));
+        addon.getSessionSnapshot.mockReturnValue(
+            snapshot('playing', {
+                chapters: [
+                    { timeSeconds: 0, title: 'Intro' },
+                    { timeSeconds: Number.NaN, title: 'Broken' },
+                    { timeSeconds: 1320, title: 'Credits' },
+                ],
+            })
+        );
+
+        expect(service.setVolume('s1', 1)?.chapters).toEqual([
+            { timeSeconds: 0, title: 'Intro' },
+            { timeSeconds: 1320, title: 'Credits' },
+        ]);
+    });
+
     it('omits the stats key entirely when the engine reports none', () => {
         // An empty object would make the renderer render an empty popover
         // instead of hiding the info button.

apps/electron-backend/src/app/services/embedded-mpv-native.service.ts

@@ -14,6 +14,7 @@ import App from '../app';
 import {
     EmbeddedMpvAudioTrack,
     EmbeddedMpvBounds,
+    EmbeddedMpvChapter,
     EmbeddedMpvCapabilities,
     EmbeddedMpvRecordingStartOptions,
     EmbeddedMpvRecordingState,
@@ -56,6 +57,7 @@ import {
     resolveFrameCopyHelperPath,
 } from './embedded-mpv-frame-copy-platform.util';
 import type { EmbeddedMpvFrameCopyRuntimeMode } from './embedded-mpv-frame-copy-runtime';
+import { normalizeEmbeddedMpvChapters } from './embedded-mpv-chapters.util';
 import {
     EMBEDDED_MPV_EXPERIMENT_ENV,
     isEmbeddedMpvFeatureEnabled,
@@ -71,6 +73,7 @@ export interface NativeEmbeddedMpvSessionSnapshot {
     selectedAudioTrackId?: number | null;
     subtitleTracks?: EmbeddedMpvSubtitleTrack[];
     selectedSubtitleTrackId?: number | null;
+    chapters?: EmbeddedMpvChapter[];
     playbackSpeed?: number;
     aspectOverride?: string;
     videoWidth?: number;
@@ -1237,6 +1240,7 @@ export class EmbeddedMpvNativeService {
                 typeof snapshot.selectedSubtitleTrackId === 'number'
                     ? snapshot.selectedSubtitleTrackId
                     : null,
+            chapters: normalizeEmbeddedMpvChapters(snapshot.chapters),
             playbackSpeed:
                 typeof snapshot.playbackSpeed === 'number'
                     ? snapshot.playbackSpeed