diff --git a/src/components/TrimControl.tsx b/src/components/TrimControl.tsx
index d48bdd69..a66d0fc5 100644
--- a/src/components/TrimControl.tsx
+++ b/src/components/TrimControl.tsx
@@ -25,7 +25,11 @@ export default function TrimControl({ recipe, onChange, duration, file }: Props)
     recipe.trimStart.toString()
   );
 
-  const { waveform, isLoading: waveformLoading } = useAudioWaveform(file);
+  const {
+    waveform,
+    status: waveformStatus,
+    isLoading: waveformLoading,
+  } = useAudioWaveform(file);
   const hasAudio = waveform.length > 0;
 
   useEffect(() => {
@@ -235,6 +239,30 @@ export default function TrimControl({ recipe, onChange, duration, file }: Props)
           />
         </div>
       )}
+
+      {file && (
+        <div className="space-y-1">
+          {waveformStatus === "disabled" ? (
+            <div
+              role="img"
+              aria-label="Audio waveform preview disabled for large file"
+              className="flex h-16 w-full items-center justify-center rounded-md border border-[var(--border)] bg-[var(--surface)] px-3"
+            >
+              <p className="font-heading text-center text-[10px] text-[var(--muted)]">
+                Waveform preview is disabled for very large files to keep the
+                editor responsive.
+              </p>
+            </div>
+          ) : (
+            <WaveformCanvas
+              samples={waveform}
+              loading={waveformLoading}
+              hasAudio={hasAudio}
+            />
+          )}
+        </div>
+      )}
+
       <div className="flex gap-3">
         <div className="flex-1">
           <label
diff --git a/src/components/__tests__/TrimControl.test.tsx b/src/components/__tests__/TrimControl.test.tsx
new file mode 100644
index 00000000..04b18e06
--- /dev/null
+++ b/src/components/__tests__/TrimControl.test.tsx
@@ -0,0 +1,78 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import "@testing-library/jest-dom/vitest";
+import { render, screen } from "@testing-library/react";
+import TrimControl from "../TrimControl";
+import { DEFAULT_RECIPE } from "@/lib/constants";
+import type { UseAudioWaveformResult } from "@/hooks/useAudioWaveform";
+
+vi.mock("@/hooks/useAudioWaveform", () => ({
+  useAudioWaveform: vi.fn(),
+}));
+
+import { useAudioWaveform } from "@/hooks/useAudioWaveform";
+
+const mockedHook = vi.mocked(useAudioWaveform);
+
+function setWaveform(result: UseAudioWaveformResult) {
+  mockedHook.mockReturnValue(result);
+}
+
+function renderTrim(file: File | null) {
+  return render(
+    <TrimControl
+      recipe={DEFAULT_RECIPE}
+      onChange={() => {}}
+      duration={10}
+      file={file}
+    />
+  );
+}
+
+const sampleFile = new File(["video-bytes"], "clip.mp4", { type: "video/mp4" });
+
+beforeEach(() => {
+  mockedHook.mockReset();
+});
+
+describe("TrimControl waveform fallback", () => {
+  it("renders the disabled placeholder for very large files", () => {
+    setWaveform({ waveform: [], status: "disabled", isLoading: false });
+
+    renderTrim(sampleFile);
+
+    expect(
+      screen.getByLabelText("Audio waveform preview disabled for large file")
+    ).toBeInTheDocument();
+    expect(
+      screen.getByText(/disabled for very large files/i)
+    ).toBeInTheDocument();
+    // The canvas waveform must not render in the disabled state.
+    expect(screen.queryByLabelText("Audio waveform")).not.toBeInTheDocument();
+  });
+
+  it("renders the waveform canvas for normal files", () => {
+    setWaveform({
+      waveform: [0.1, 0.5, 0.9],
+      status: "ready",
+      isLoading: false,
+    });
+
+    renderTrim(sampleFile);
+
+    expect(screen.getByLabelText("Audio waveform")).toBeInTheDocument();
+    expect(
+      screen.queryByText(/disabled for very large files/i)
+    ).not.toBeInTheDocument();
+  });
+
+  it("does not render any waveform UI when no file is selected", () => {
+    setWaveform({ waveform: [], status: "idle", isLoading: false });
+
+    renderTrim(null);
+
+    expect(
+      screen.queryByText(/disabled for very large files/i)
+    ).not.toBeInTheDocument();
+    expect(screen.queryByLabelText("Audio waveform")).not.toBeInTheDocument();
+  });
+});
diff --git a/src/hooks/__tests__/useAudioWaveform.test.tsx b/src/hooks/__tests__/useAudioWaveform.test.tsx
new file mode 100644
index 00000000..df9ad2f7
--- /dev/null
+++ b/src/hooks/__tests__/useAudioWaveform.test.tsx
@@ -0,0 +1,133 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { renderHook, waitFor, act } from "@testing-library/react";
+import { useAudioWaveform } from "../useAudioWaveform";
+import { MAX_WAVEFORM_FILE_SIZE_BYTES } from "@/lib/constants";
+
+// --- Test doubles -----------------------------------------------------------
+
+type FakeAudioBuffer = { getChannelData: () => Float32Array };
+
+class FakeAudioContext {
+  static instances: FakeAudioContext[] = [];
+  static decodeImpl: () => Promise<FakeAudioBuffer> = async () => ({
+    getChannelData: () => new Float32Array([0, 0.25, 0.5, 0.75, 1]),
+  });
+
+  decodeAudioData = vi.fn(() => FakeAudioContext.decodeImpl());
+  close = vi.fn(async () => {});
+
+  constructor() {
+    FakeAudioContext.instances.push(this);
+  }
+}
+
+/**
+ * Builds a minimal File stand-in. The hook only touches `file.size` and
+ * `file.slice(...).arrayBuffer()`, so we expose spies for both to assert that
+ * the full file is never read for oversized inputs.
+ */
+function makeFile(size: number, readBytes: () => Promise<ArrayBuffer>) {
+  const arrayBuffer = vi.fn(readBytes);
+  const slice = vi.fn(() => ({ arrayBuffer }) as unknown as Blob);
+  return { size, slice, arrayBuffer } as unknown as File;
+}
+
+function deferred<T>() {
+  let resolve!: (value: T) => void;
+  const promise = new Promise<T>((res) => {
+    resolve = res;
+  });
+  return { promise, resolve };
+}
+
+beforeEach(() => {
+  FakeAudioContext.instances = [];
+  FakeAudioContext.decodeImpl = async () => ({
+    getChannelData: () => new Float32Array([0, 0.25, 0.5, 0.75, 1]),
+  });
+  vi.stubGlobal("AudioContext", FakeAudioContext);
+});
+
+afterEach(() => {
+  vi.unstubAllGlobals();
+  vi.clearAllMocks();
+});
+
+// --- Tests ------------------------------------------------------------------
+
+describe("useAudioWaveform", () => {
+  it("is idle when no file is provided", async () => {
+    const { result } = renderHook(() => useAudioWaveform(null));
+    await waitFor(() => expect(result.current.status).toBe("idle"));
+    expect(result.current.waveform).toEqual([]);
+    expect(result.current.isLoading).toBe(false);
+  });
+
+  it("extracts a waveform for files within the size threshold", async () => {
+    const file = makeFile(1024, () => Promise.resolve(new ArrayBuffer(8)));
+
+    const { result } = renderHook(() => useAudioWaveform(file, 5));
+
+    await waitFor(() => expect(result.current.status).toBe("ready"));
+    expect(result.current.waveform).toHaveLength(5);
+    expect(result.current.isLoading).toBe(false);
+    // Reads through a bounded slice, never the raw File in one shot.
+    expect(file.slice).toHaveBeenCalledWith(0, MAX_WAVEFORM_FILE_SIZE_BYTES);
+    expect(FakeAudioContext.instances).toHaveLength(1);
+  });
+
+  it("skips extraction and reports 'disabled' for very large files", async () => {
+    const file = makeFile(MAX_WAVEFORM_FILE_SIZE_BYTES + 1, () =>
+      Promise.resolve(new ArrayBuffer(8))
+    );
+
+    const { result } = renderHook(() => useAudioWaveform(file));
+
+    await waitFor(() => expect(result.current.status).toBe("disabled"));
+    expect(result.current.waveform).toEqual([]);
+    // The whole point of #1013: the oversized file is never read into memory.
+    expect(file.slice).not.toHaveBeenCalled();
+    expect(file.arrayBuffer).not.toHaveBeenCalled();
+    expect(FakeAudioContext.instances).toHaveLength(0);
+  });
+
+  it("respects a custom size threshold", async () => {
+    const file = makeFile(2048, () => Promise.resolve(new ArrayBuffer(8)));
+
+    const { result } = renderHook(() => useAudioWaveform(file, 96, 1024));
+
+    await waitFor(() => expect(result.current.status).toBe("disabled"));
+    expect(file.slice).not.toHaveBeenCalled();
+  });
+
+  it("reports 'error' when decoding fails", async () => {
+    FakeAudioContext.decodeImpl = () => Promise.reject(new Error("bad audio"));
+    const file = makeFile(1024, () => Promise.resolve(new ArrayBuffer(8)));
+
+    const { result } = renderHook(() => useAudioWaveform(file));
+
+    await waitFor(() => expect(result.current.status).toBe("error"));
+    expect(result.current.waveform).toEqual([]);
+  });
+
+  it("cancels in-flight work and does not update state after unmount", async () => {
+    const gate = deferred<ArrayBuffer>();
+    const file = makeFile(1024, () => gate.promise);
+
+    const { result, unmount } = renderHook(() => useAudioWaveform(file));
+
+    await waitFor(() => expect(result.current.status).toBe("loading"));
+
+    unmount();
+
+    // Resolve the pending read *after* unmount — the hook must bail out before
+    // creating an AudioContext or advancing to "ready".
+    await act(async () => {
+      gate.resolve(new ArrayBuffer(8));
+      await Promise.resolve();
+    });
+
+    expect(result.current.status).toBe("loading");
+    expect(FakeAudioContext.instances).toHaveLength(0);
+  });
+});
diff --git a/src/hooks/useAudioWaveform.ts b/src/hooks/useAudioWaveform.ts
index 25ed57d5..cb1ece4d 100644
--- a/src/hooks/useAudioWaveform.ts
+++ b/src/hooks/useAudioWaveform.ts
@@ -1,9 +1,28 @@
 "use client";
 
 import { useEffect, useState } from "react";
+import { MAX_WAVEFORM_FILE_SIZE_BYTES } from "@/lib/constants";
 
 const DEFAULT_BAR_COUNT = 96;
 
+/**
+ * Lifecycle of a waveform extraction request:
+ * - `idle`     — no file selected.
+ * - `loading`  — reading/decoding audio.
+ * - `ready`    — `waveform` holds the downsampled peaks.
+ * - `disabled` — file exceeds the size threshold; extraction was skipped to
+ *                keep memory bounded (#1013). UI should show a placeholder.
+ * - `error`    — decoding failed or Web Audio is unavailable.
+ */
+export type WaveformStatus = "idle" | "loading" | "ready" | "disabled" | "error";
+
+export interface UseAudioWaveformResult {
+  waveform: number[];
+  status: WaveformStatus;
+  /** Convenience flag, retained for backward compatibility. */
+  isLoading: boolean;
+}
+
 type BrowserWindow = Window &
   typeof globalThis & {
     webkitAudioContext?: typeof AudioContext;
@@ -27,12 +46,23 @@ function downsampleWaveform(channelData: Float32Array, barCount: number): number
   return peaks.map((peak) => peak / maxPeak);
 }
 
+/**
+ * Extracts a low-resolution audio waveform from a media file.
+ *
+ * Memory safety (#1013): files larger than `maxFileSizeBytes` are not read into
+ * memory at all — the hook reports `status: "disabled"` and the caller renders a
+ * placeholder instead. Within the threshold the audio is read through a bounded
+ * `Blob.slice` so the amount of data handed to `decodeAudioData` never exceeds
+ * the threshold, even if the underlying file grows unexpectedly. Small files
+ * (the common case) are read in full exactly as before — no behavioural change.
+ */
 export function useAudioWaveform(
   file: File | null,
-  barCount = DEFAULT_BAR_COUNT
-) {
+  barCount = DEFAULT_BAR_COUNT,
+  maxFileSizeBytes = MAX_WAVEFORM_FILE_SIZE_BYTES
+): UseAudioWaveformResult {
   const [waveform, setWaveform] = useState<number[]>([]);
-  const [isLoading, setIsLoading] = useState(false);
+  const [status, setStatus] = useState<WaveformStatus>("idle");
 
   useEffect(() => {
     let isCancelled = false;
@@ -41,7 +71,14 @@ export function useAudioWaveform(
     async function extractWaveform() {
       if (!file) {
         setWaveform([]);
-        setIsLoading(false);
+        setStatus("idle");
+        return;
+      }
+
+      // Hard memory guard: never pull a multi-gigabyte file into the heap.
+      if (file.size > maxFileSizeBytes) {
+        setWaveform([]);
+        setStatus("disabled");
         return;
       }
 
@@ -50,41 +87,49 @@ export function useAudioWaveform(
 
       if (!AudioContextCtor) {
         setWaveform([]);
-        setIsLoading(false);
+        setStatus("error");
         return;
       }
 
-      setIsLoading(true);
+      setWaveform([]);
+      setStatus("loading");
 
       try {
+        // Read at most `maxFileSizeBytes`. For files within the threshold this
+        // is the whole file (unchanged); the slice bounds the allocation so we
+        // never decode more than the threshold's worth of bytes.
+        const audioBytes = await file.slice(0, maxFileSizeBytes).arrayBuffer();
+        if (isCancelled) return;
+
         audioContext = new AudioContextCtor();
-        const audioBuffer = await audioContext.decodeAudioData(
-          await file.arrayBuffer()
-        );
+        const audioBuffer = await audioContext.decodeAudioData(audioBytes);
+        if (isCancelled) return;
+
         const channelData = audioBuffer.getChannelData(0);
         const peaks = downsampleWaveform(channelData, barCount);
 
         if (!isCancelled) {
           setWaveform(peaks);
+          setStatus("ready");
         }
       } catch {
         if (!isCancelled) {
           setWaveform([]);
+          setStatus("error");
         }
       } finally {
         await audioContext?.close();
-        if (!isCancelled) {
-          setIsLoading(false);
-        }
       }
     }
 
     extractWaveform();
 
+    // Cancellation: a new file, a changed bar count, or an unmount stops the
+    // in-flight read/decode and prevents state updates on a dead component.
     return () => {
       isCancelled = true;
     };
-  }, [barCount, file]);
+  }, [barCount, file, maxFileSizeBytes]);
 
-  return { waveform, isLoading };
+  return { waveform, status, isLoading: status === "loading" };
 }
diff --git a/src/lib/constants.ts b/src/lib/constants.ts
index e713f779..93707580 100644
--- a/src/lib/constants.ts
+++ b/src/lib/constants.ts
@@ -3,6 +3,19 @@ import { RECIPE_VERSION } from "./types"
 
 export const SPEED_STEPS = [0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 4] as const;
 
+/**
+ * Upper bound (in bytes) on the file size for which audio waveform extraction
+ * is attempted. The app accepts uploads up to 2 GB, but decoding a file of that
+ * size with the Web Audio API reads the whole thing into memory (raw buffer +
+ * decoded PCM), which spikes the heap and crashes browser tabs (#1013).
+ *
+ * Files at or below this threshold are decoded as before; larger files skip
+ * waveform extraction and fall back to a static placeholder so the editor stays
+ * responsive. 300 MB keeps the worst-case waveform allocation bounded while
+ * still covering the vast majority of real-world clips.
+ */
+export const MAX_WAVEFORM_FILE_SIZE_BYTES = 300 * 1024 * 1024;
+
 export const DEFAULT_RECIPE: EditRecipe = {
   preset: "vertical-9-16",
   customWidth: 1920,