diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7f53cf1f83..4b994f283e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -132,6 +132,7 @@ jobs:
           __tests__/unit/homepage-demo-accessibility.test.ts
           __tests__/unit/linkified-text.test.ts
           __tests__/unit/loom-import-ui.test.ts
+          __tests__/unit/media-format-converter-selection.test.ts
           __tests__/unit/media-format-converter.test.ts
           __tests__/unit/media-player-store-refs.test.ts
           __tests__/unit/playback-store.test.ts
diff --git a/apps/web/__tests__/unit/media-format-converter-selection.test.ts b/apps/web/__tests__/unit/media-format-converter-selection.test.ts
new file mode 100644
index 0000000000..df4dbb0d65
--- /dev/null
+++ b/apps/web/__tests__/unit/media-format-converter-selection.test.ts
@@ -0,0 +1,144 @@
+// @vitest-environment jsdom
+
+import { act, createElement } from "react";
+import { createRoot, type Root } from "react-dom/client";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { MediaFormatConverter } from "@/components/tools/MediaFormatConverter";
+
+vi.mock("@cap/ui", () => ({
+	Button: ({ children, ...props }: React.ComponentProps<"button">) =>
+		createElement("button", { type: "button", ...props }, children),
+}));
+vi.mock("next/link", () => ({
+	default: ({ children, ...props }: React.ComponentProps<"a">) =>
+		createElement("a", props, children),
+}));
+vi.mock("next/navigation", () => ({
+	usePathname: () => "/tools/convert/mp4-to-webm",
+	useRouter: () => ({ push: vi.fn() }),
+}));
+vi.mock("@/app/utils/analytics", () => ({ trackEvent: vi.fn() }));
+vi.mock("@remotion/media-parser", async (importOriginal) => ({
+	...(await importOriginal<typeof import("@remotion/media-parser")>()),
+	mediaParserController: () => ({ abort: vi.fn() }),
+	parseMedia: () => Promise.resolve({ durationInSeconds: 1 }),
+}));
+vi.mock("@remotion/webcodecs", async (importOriginal) => ({
+	...(await importOriginal<typeof import("@remotion/webcodecs")>()),
+	convertMedia: vi.fn(),
+}));
+
+describe("media converter file selection", () => {
+	let container: HTMLDivElement;
+	let root: Root;
+
+	beforeEach(async () => {
+		vi.stubGlobal("IS_REACT_ACT_ENVIRONMENT", true);
+		vi.stubGlobal("MediaRecorder", { isTypeSupported: () => true });
+		container = document.createElement("div");
+		document.body.append(container);
+		root = createRoot(container);
+		await act(async () =>
+			root.render(
+				createElement(MediaFormatConverter, {
+					initialConversionPath: "mp4-to-webm",
+				}),
+			),
+		);
+	});
+
+	afterEach(async () => {
+		await act(async () => root.unmount());
+		container.remove();
+		delete (ArrayBuffer.prototype as { resize?: () => void }).resize;
+		vi.unstubAllGlobals();
+	});
+
+	const selectFile = async (container: HTMLElement, file: File) => {
+		const input = container.querySelector("input[type=file]");
+		if (!(input instanceof HTMLInputElement)) throw new Error("Missing input");
+		Object.defineProperty(input, "files", {
+			configurable: true,
+			value: [file],
+		});
+		await act(async () =>
+			input.dispatchEvent(new Event("change", { bubbles: true })),
+		);
+	};
+
+	it.each([
+		["invalid type", new File(["wrong"], "notes.txt", { type: "text/plain" })],
+		["oversized", new File(["x"], "huge.mp4", { type: "video/mp4" })],
+	])(
+		"clears the previous video after an %s replacement",
+		async (reason, replacement) => {
+			if (reason === "oversized") {
+				Object.defineProperty(replacement, "size", {
+					value: 500 * 1024 * 1024 + 1,
+				});
+			}
+			await selectFile(
+				container,
+				new File(["video"], "first.mp4", { type: "video/mp4" }),
+			);
+			expect(container.textContent).toContain("first.mp4");
+			await selectFile(container, replacement);
+			expect(container.textContent).not.toContain("first.mp4");
+			expect(container.textContent).not.toContain("Convert to WEBM");
+		},
+	);
+
+	it("keeps the active file when an invalid replacement is dropped during conversion", async () => {
+		const { convertMedia } = await import("@remotion/webcodecs");
+		let finishConversion: (blob: Blob) => void = () => {};
+		vi.mocked(convertMedia).mockResolvedValueOnce({
+			save: () =>
+				new Promise<Blob>((resolve) => {
+					finishConversion = resolve;
+				}),
+		} as Awaited<ReturnType<typeof convertMedia>>);
+		vi.stubGlobal("VideoDecoder", class {});
+		vi.stubGlobal("AudioDecoder", class {});
+		Object.defineProperty(ArrayBuffer.prototype, "resize", {
+			configurable: true,
+			value: vi.fn(),
+		});
+		vi.stubGlobal(
+			"URL",
+			class extends URL {
+				static createObjectURL = vi.fn(() => "blob:converted");
+				static revokeObjectURL = vi.fn();
+			},
+		);
+
+		await selectFile(
+			container,
+			new File(["video"], "first.mp4", { type: "video/mp4" }),
+		);
+		const convertButton = [...container.querySelectorAll("button")].find(
+			(button) => button.textContent?.includes("Convert to WEBM"),
+		);
+		await act(async () => {
+			convertButton?.click();
+		});
+		expect(container.textContent).toContain("Converting...");
+
+		const dropZone = container.querySelector("[class*='border-dashed']");
+		if (!dropZone) throw new Error("Missing drop zone");
+		const drop = new Event("drop", { bubbles: true });
+		Object.defineProperty(drop, "dataTransfer", {
+			value: {
+				files: [new File(["wrong"], "notes.txt", { type: "text/plain" })],
+			},
+		});
+		await act(async () => dropZone.dispatchEvent(drop));
+		await act(async () =>
+			finishConversion(new Blob(["converted"], { type: "video/webm" })),
+		);
+
+		expect(container.textContent).toContain("first.mp4");
+		expect(container.textContent).toContain("Conversion complete!");
+		expect(container.textContent).toContain("Download WEBM");
+		expect(container.textContent).not.toContain("Please select a MP4 file.");
+	});
+});
diff --git a/apps/web/components/tools/MediaFormatConverter.tsx b/apps/web/components/tools/MediaFormatConverter.tsx
index fd184a168c..47f419b3a3 100644
--- a/apps/web/components/tools/MediaFormatConverter.tsx
+++ b/apps/web/components/tools/MediaFormatConverter.tsx
@@ -251,8 +251,15 @@ export const MediaFormatConverter = ({
 	};
 
 	const validateAndSetFile = (selectedFile: File) => {
+		if (isConverting) return;
+
 		setError(null);
+		setFile(null);
+		if (outputUrl) {
+			URL.revokeObjectURL(outputUrl);
+		}
 		setOutputUrl(null);
+		recordedChunksRef.current = [];
 
 		const expectedMimeType = getMimeType(currentSourceFormat);
 
@@ -974,6 +981,7 @@ export const MediaFormatConverter = ({
 				<input
 					type="file"
 					accept={getAcceptAttribute(currentSourceFormat)}
+					disabled={isConverting}
 					className="hidden"
 					onChange={handleFileChange}
 					ref={fileInputRef}