diff --git a/src/main.ts b/src/main.ts
index 8412708..2034e8a 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -7,6 +7,7 @@ import axios from 'axios';
 import { autoUpdater } from 'electron-updater';
 import { compareUpdateVersions, isNewerUpdateVersion, normalizeUpdateVersion } from './main/domain/update-version-utils';
 import { writeFileAtomicSync } from './main/infra/fs-atomic';
+import { parseDuration, formatDuration, formatDurationDashed } from './main/infra/duration';
 import { CustomClip, MergeGroupItem, MergeGroup, QueueItem, DownloadProgress, DownloadResult } from './types';
 import {
     setDebugLogFn, initToolDirs,
@@ -1073,38 +1074,6 @@ function appendDebugLog(message: string, details?: unknown): void {
 setDebugLogFn(appendDebugLog);
 initToolDirs(TOOLS_STREAMLINK_DIR, TOOLS_FFMPEG_DIR, () => app.getPath('temp'));
 
-// ==========================================
-// DURATION HELPERS
-// ==========================================
-function parseDuration(duration: string): number {
-    let seconds = 0;
-    const hours = duration.match(/(\d+)h/);
-    const minutes = duration.match(/(\d+)m/);
-    const secs = duration.match(/(\d+)s/);
-
-    if (hours) seconds += parseInt(hours[1]) * 3600;
-    if (minutes) seconds += parseInt(minutes[1]) * 60;
-    if (secs) seconds += parseInt(secs[1]);
-
-    return seconds;
-}
-
-function formatDuration(seconds: number): string {
-    if (!isFinite(seconds) || seconds < 0) return '00:00:00';
-    const h = Math.floor(seconds / 3600);
-    const m = Math.floor((seconds % 3600) / 60);
-    const s = Math.floor(seconds % 60);
-    return `${h.toString().padStart(2, '0')}:${m.toString().padStart(2, '0')}:${s.toString().padStart(2, '0')}`;
-}
-
-function formatDurationDashed(seconds: number): string {
-    if (!isFinite(seconds) || seconds < 0) return '00-00-00';
-    const h = Math.floor(seconds / 3600);
-    const m = Math.floor((seconds % 3600) / 60);
-    const s = Math.floor(seconds % 60);
-    return `${h.toString().padStart(2, '0')}-${m.toString().padStart(2, '0')}-${s.toString().padStart(2, '0')}`;
-}
-
 const claimedFilenames = new Set<string>();
 const itemClaimedFilenames = new Map<string, Set<string>>();
 
diff --git a/src/main/infra/duration.test.ts b/src/main/infra/duration.test.ts
new file mode 100644
index 0000000..f776ff7
--- /dev/null
+++ b/src/main/infra/duration.test.ts
@@ -0,0 +1,65 @@
+import { test, expect, describe } from 'vitest';
+import { parseDuration, formatDuration, formatDurationDashed } from './duration';
+
+describe('parseDuration', () => {
+    test('1h2m3s = 3723', () => {
+        expect(parseDuration('1h2m3s')).toBe(3723);
+    });
+    test('45m = 2700', () => {
+        expect(parseDuration('45m')).toBe(2700);
+    });
+    test('10s = 10', () => {
+        expect(parseDuration('10s')).toBe(10);
+    });
+    test('empty string = 0', () => {
+        expect(parseDuration('')).toBe(0);
+    });
+    test('unknown format = 0', () => {
+        expect(parseDuration('abcdef')).toBe(0);
+    });
+    test('partial 2h = 7200', () => {
+        expect(parseDuration('2h')).toBe(7200);
+    });
+    test('h and s without m = 3601', () => {
+        expect(parseDuration('1h1s')).toBe(3601);
+    });
+});
+
+describe('formatDuration', () => {
+    test('3723 = 01:02:03', () => {
+        expect(formatDuration(3723)).toBe('01:02:03');
+    });
+    test('0 = 00:00:00', () => {
+        expect(formatDuration(0)).toBe('00:00:00');
+    });
+    test('negative = 00:00:00', () => {
+        expect(formatDuration(-1)).toBe('00:00:00');
+    });
+    test('Infinity = 00:00:00', () => {
+        expect(formatDuration(Infinity)).toBe('00:00:00');
+    });
+    test('NaN = 00:00:00', () => {
+        expect(formatDuration(NaN)).toBe('00:00:00');
+    });
+    test('3600 = 01:00:00', () => {
+        expect(formatDuration(3600)).toBe('01:00:00');
+    });
+    test('86399 = 23:59:59', () => {
+        expect(formatDuration(86399)).toBe('23:59:59');
+    });
+    test('fractional seconds floored', () => {
+        expect(formatDuration(3723.9)).toBe('01:02:03');
+    });
+});
+
+describe('formatDurationDashed', () => {
+    test('3723 = 01-02-03', () => {
+        expect(formatDurationDashed(3723)).toBe('01-02-03');
+    });
+    test('negative = 00-00-00', () => {
+        expect(formatDurationDashed(-1)).toBe('00-00-00');
+    });
+    test('NaN = 00-00-00', () => {
+        expect(formatDurationDashed(NaN)).toBe('00-00-00');
+    });
+});
diff --git a/src/main/infra/duration.ts b/src/main/infra/duration.ts
new file mode 100644
index 0000000..e2aa5ec
--- /dev/null
+++ b/src/main/infra/duration.ts
@@ -0,0 +1,28 @@
+export function parseDuration(duration: string): number {
+    let seconds = 0;
+    const hours = duration.match(/(\d+)h/);
+    const minutes = duration.match(/(\d+)m/);
+    const secs = duration.match(/(\d+)s/);
+
+    if (hours) seconds += parseInt(hours[1]) * 3600;
+    if (minutes) seconds += parseInt(minutes[1]) * 60;
+    if (secs) seconds += parseInt(secs[1]);
+
+    return seconds;
+}
+
+export function formatDuration(seconds: number): string {
+    if (!isFinite(seconds) || seconds < 0) return '00:00:00';
+    const h = Math.floor(seconds / 3600);
+    const m = Math.floor((seconds % 3600) / 60);
+    const s = Math.floor(seconds % 60);
+    return `${h.toString().padStart(2, '0')}:${m.toString().padStart(2, '0')}:${s.toString().padStart(2, '0')}`;
+}
+
+export function formatDurationDashed(seconds: number): string {
+    if (!isFinite(seconds) || seconds < 0) return '00-00-00';
+    const h = Math.floor(seconds / 3600);
+    const m = Math.floor((seconds % 3600) / 60);
+    const s = Math.floor(seconds % 60);
+    return `${h.toString().padStart(2, '0')}-${m.toString().padStart(2, '0')}-${s.toString().padStart(2, '0')}`;
+}