diff --git a/playwright.config.ts b/playwright.config.ts
index d268975b..53e7ef0c 100644
--- a/playwright.config.ts
+++ b/playwright.config.ts
@@ -4,5 +4,6 @@ export default defineConfig({
 	testDir: "./tests/e2e",
 	timeout: 120_000, // GIF encoding is CPU-bound; give it room
 	retries: 0,
+	workers: 1,
 	reporter: "list",
 });
diff --git a/src/components/video-editor/SettingsPanel.tsx b/src/components/video-editor/SettingsPanel.tsx
index 5cac5737..0db5deea 100644
--- a/src/components/video-editor/SettingsPanel.tsx
+++ b/src/components/video-editor/SettingsPanel.tsx
@@ -1466,6 +1466,7 @@ export function SettingsPanel({
 			<div className="flex-shrink-0 p-4 pt-3 border-t border-white/5 bg-[#09090b]">
 				<div className="flex items-center gap-2 mb-3">
 					<button
+						data-testid={getTestId("mp4-format-button")}
 						onClick={() => onExportFormatChange?.("mp4")}
 						className={cn(
 							"flex-1 flex items-center justify-center gap-1.5 py-2 rounded-lg border transition-all text-xs font-medium",
diff --git a/src/hooks/useScreenRecorder.ts b/src/hooks/useScreenRecorder.ts
index dc9758fb..f14be62f 100644
--- a/src/hooks/useScreenRecorder.ts
+++ b/src/hooks/useScreenRecorder.ts
@@ -408,6 +408,14 @@ export function useScreenRecorder(): UseScreenRecorderReturn {
 		}
 	});
 
+	const safeHideCountdownOverlay = useCallback(async (runId: number) => {
+		try {
+			await window.electronAPI.hideCountdownOverlay(runId);
+		} catch (error) {
+			console.warn("Failed to hide countdown overlay:", error);
+		}
+	}, []);
+
 	useEffect(() => {
 		let cleanup: (() => void) | undefined;
 
@@ -450,7 +458,7 @@ export function useScreenRecorder(): UseScreenRecorderReturn {
 			webcamRecorder.current = null;
 			teardownMedia();
 		};
-	}, [teardownMedia]);
+	}, [teardownMedia, safeHideCountdownOverlay]);
 
 	const safeShowCountdownOverlay = async (value: number, runId: number) => {
 		try {
@@ -477,14 +485,6 @@ export function useScreenRecorder(): UseScreenRecorderReturn {
 		}
 	};
 
-	const safeHideCountdownOverlay = async (runId: number) => {
-		try {
-			await window.electronAPI.hideCountdownOverlay(runId);
-		} catch (error) {
-			console.warn("Failed to hide countdown overlay:", error);
-		}
-	};
-
 	const isCountdownRunActive = (runId?: number) =>
 		runId === undefined || countdownRunId.current === runId;
 
diff --git a/src/utils/getTestId.ts b/src/utils/getTestId.ts
index 453f7c99..b724240f 100644
--- a/src/utils/getTestId.ts
+++ b/src/utils/getTestId.ts
@@ -1,4 +1,8 @@
-export type TestId = `gif-size-button-${string}` | "export-button" | `gif-format-button`;
+export type TestId =
+	| `gif-size-button-${string}`
+	| "export-button"
+	| "gif-format-button"
+	| "mp4-format-button";
 
 export function getTestId(testId: TestId) {
 	return `testId-${testId}`;
diff --git a/tests/e2e/gif-export.spec.ts b/tests/e2e/gif-export.spec.ts
index d1fa3f7a..222a0ff4 100644
--- a/tests/e2e/gif-export.spec.ts
+++ b/tests/e2e/gif-export.spec.ts
@@ -3,6 +3,12 @@ import os from "node:os";
 import path from "node:path";
 import { fileURLToPath } from "node:url";
 import { _electron as electron, expect, test } from "@playwright/test";
+import {
+	closeElectronApp,
+	copyFixtureToRecordings,
+	interceptExportSave,
+	readCapturedExportBuffer,
+} from "./helpers";
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url));
 const ROOT = path.join(__dirname, "../..");
@@ -49,27 +55,11 @@ test("exports a GIF from a loaded video", async () => {
 		// main process is ESM and Playwright runs the callback via eval(), which
 		// has no dynamic-import hook.  We retrieve and write the file below after
 		// the export finishes.
-		await app.evaluate(({ ipcMain }) => {
-			ipcMain.removeHandler("save-exported-video");
-			ipcMain.handle(
-				"save-exported-video",
-				(_event: Electron.IpcMainInvokeEvent, buffer: ArrayBuffer) => {
-					(globalThis as Record<string, unknown>)["__testExportData"] =
-						Buffer.from(buffer).toString("base64");
-					return { success: true, path: "pending" };
-				},
-			);
-		});
+		await interceptExportSave(app);
 
 		// Copy the test fixture into the app's recordings directory so it passes
 		// the path security check in set-current-video-path.
-		const userDataDir = await app.evaluate(({ app: electronApp }) => {
-			return electronApp.getPath("userData");
-		});
-		const recordingsDir = path.join(userDataDir, "recordings");
-		testVideoInRecordings = path.join(recordingsDir, "test-sample.webm");
-		fs.mkdirSync(recordingsDir, { recursive: true });
-		fs.copyFileSync(TEST_VIDEO, testVideoInRecordings);
+		testVideoInRecordings = await copyFixtureToRecordings(app, TEST_VIDEO, "test-sample.webm");
 
 		try {
 			await hudWindow.evaluate((videoPath: string) => {
@@ -107,10 +97,7 @@ test("exports a GIF from a loaded video", async () => {
 		});
 
 		// ── 7. Write the captured buffer from the main-process global to disk.
-		const base64 = await app.evaluate(
-			() => (globalThis as Record<string, unknown>)["__testExportData"] as string,
-		);
-		fs.writeFileSync(outputPath, Buffer.from(base64, "base64"));
+		fs.writeFileSync(outputPath, await readCapturedExportBuffer(app));
 
 		// ── 8. Verify the file on disk is a valid GIF.
 		expect(fs.existsSync(outputPath), `GIF not found at ${outputPath}`).toBe(true);
@@ -126,7 +113,7 @@ test("exports a GIF from a loaded video", async () => {
 		const stats = fs.statSync(outputPath);
 		expect(stats.size).toBeGreaterThan(1024); // at least 1 KB
 	} finally {
-		await app.close();
+		await closeElectronApp(app);
 		if (fs.existsSync(outputPath)) {
 			fs.unlinkSync(outputPath);
 		}
diff --git a/tests/e2e/helpers.ts b/tests/e2e/helpers.ts
new file mode 100644
index 00000000..8ad886a1
--- /dev/null
+++ b/tests/e2e/helpers.ts
@@ -0,0 +1,70 @@
+import fs from "node:fs";
+import path from "node:path";
+import type { ElectronApplication } from "@playwright/test";
+
+export async function waitForProcessExit(
+	child: ReturnType<ElectronApplication["process"]>,
+	timeoutMs: number,
+) {
+	if (child.exitCode !== null || child.killed) return;
+
+	await Promise.race([
+		new Promise<void>((resolve) => child.once("exit", () => resolve())),
+		new Promise<void>((resolve) => setTimeout(resolve, timeoutMs)),
+	]);
+}
+
+export async function closeElectronApp(app: ElectronApplication) {
+	const child = app.process();
+	await app
+		.evaluate(({ app: electronApp }) => {
+			electronApp.exit(0);
+		})
+		.catch(() => {
+			// App may already be closing.
+		});
+	await waitForProcessExit(child, 2_000);
+	if (child.exitCode === null && !child.killed) {
+		child.kill("SIGKILL");
+		await waitForProcessExit(child, 2_000);
+	}
+}
+
+export async function interceptExportSave(app: ElectronApplication) {
+	await app.evaluate(({ ipcMain }) => {
+		ipcMain.removeHandler("save-exported-video");
+		ipcMain.handle(
+			"save-exported-video",
+			(_event: Electron.IpcMainInvokeEvent, buffer: ArrayBuffer) => {
+				(globalThis as Record<string, unknown>)["__testExportData"] =
+					Buffer.from(buffer).toString("base64");
+				return { success: true, path: "pending" };
+			},
+		);
+	});
+}
+
+export async function copyFixtureToRecordings(
+	app: ElectronApplication,
+	fixturePath: string,
+	fileName: string,
+) {
+	const userDataDir = await app.evaluate(({ app: electronApp }) => {
+		return electronApp.getPath("userData");
+	});
+	const recordingsDir = path.join(userDataDir, "recordings");
+	const targetPath = path.join(recordingsDir, fileName);
+	fs.mkdirSync(recordingsDir, { recursive: true });
+	fs.copyFileSync(fixturePath, targetPath);
+	return targetPath;
+}
+
+export async function readCapturedExportBuffer(app: ElectronApplication) {
+	const base64 = await app.evaluate(
+		() => (globalThis as Record<string, unknown>)["__testExportData"] as string,
+	);
+	if (typeof base64 !== "string" || base64.length === 0) {
+		throw new Error("__testExportData was not set or is invalid");
+	}
+	return Buffer.from(base64, "base64");
+}
diff --git a/tests/e2e/mp4-export.spec.ts b/tests/e2e/mp4-export.spec.ts
new file mode 100644
index 00000000..9d002c5a
--- /dev/null
+++ b/tests/e2e/mp4-export.spec.ts
@@ -0,0 +1,86 @@
+import fs from "node:fs";
+import os from "node:os";
+import path from "node:path";
+import { fileURLToPath } from "node:url";
+import { _electron as electron, expect, test } from "@playwright/test";
+import {
+	closeElectronApp,
+	copyFixtureToRecordings,
+	interceptExportSave,
+	readCapturedExportBuffer,
+} from "./helpers";
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+const ROOT = path.join(__dirname, "../..");
+const MAIN_JS = path.join(ROOT, "dist-electron/main.js");
+const TEST_VIDEO = path.join(__dirname, "../fixtures/sample.webm");
+
+test("exports an MP4 from a loaded video", async () => {
+	const outputPath = path.join(os.tmpdir(), `test-mp4-export-${Date.now()}.mp4`);
+	let testVideoInRecordings = "";
+
+	const app = await electron.launch({
+		args: [MAIN_JS, "--no-sandbox", "--enable-unsafe-swiftshader"],
+		env: {
+			...process.env,
+			HEADLESS: process.env["HEADLESS"] ?? "true",
+		},
+	});
+
+	app.process().stdout?.on("data", (d) => process.stdout.write(`[electron] ${d}`));
+	app.process().stderr?.on("data", (d) => process.stderr.write(`[electron] ${d}`));
+
+	try {
+		const hudWindow = await app.firstWindow({ timeout: 60_000 });
+		await hudWindow.waitForLoadState("domcontentloaded");
+		await interceptExportSave(app);
+
+		testVideoInRecordings = await copyFixtureToRecordings(app, TEST_VIDEO, "test-sample-mp4.webm");
+
+		try {
+			await hudWindow.evaluate(async (videoPath: string) => {
+				await window.electronAPI.setCurrentVideoPath(videoPath);
+				await window.electronAPI.switchToEditor();
+			}, testVideoInRecordings);
+		} catch {
+			// Expected: switchToEditor closes the HUD window.
+		}
+
+		const editorWindow = await app.waitForEvent("window", {
+			predicate: (w) => w.url().includes("windowType=editor"),
+			timeout: 15_000,
+		});
+
+		await editorWindow.reload();
+		await editorWindow.waitForLoadState("domcontentloaded");
+		await expect(editorWindow.getByText("Loading video...")).not.toBeVisible({
+			timeout: 15_000,
+		});
+
+		await editorWindow.getByTestId("testId-mp4-format-button").click();
+		await editorWindow.getByTestId("testId-export-button").click();
+
+		await expect(editorWindow.getByText("Video exported successfully")).toBeVisible({
+			timeout: 90_000,
+		});
+
+		fs.writeFileSync(outputPath, await readCapturedExportBuffer(app));
+		expect(fs.existsSync(outputPath), `MP4 not found at ${outputPath}`).toBe(true);
+
+		const header = Buffer.alloc(12);
+		const fd = fs.openSync(outputPath, "r");
+		fs.readSync(fd, header, 0, 12, 0);
+		fs.closeSync(fd);
+
+		expect(header.subarray(4, 8).toString("ascii")).toBe("ftyp");
+		expect(fs.statSync(outputPath).size).toBeGreaterThan(1024);
+	} finally {
+		await closeElectronApp(app);
+		if (fs.existsSync(outputPath)) {
+			fs.unlinkSync(outputPath);
+		}
+		if (testVideoInRecordings && fs.existsSync(testVideoInRecordings)) {
+			fs.unlinkSync(testVideoInRecordings);
+		}
+	}
+});