fix(cli): fail video snapshots without FFmpeg

packages/cli/src/commands/snapshot.test.ts

@@ -1,5 +1,10 @@
 import { describe, expect, it } from "vitest";
-import { computeSnapshotTimes, parseZoomScale, tailFrameTime } from "./snapshot.js";
+import {
+  computeSnapshotTimes,
+  parseZoomScale,
+  requireSnapshotFfmpeg,
+  tailFrameTime,
+} from "./snapshot.js";
 
 // --zoom's crop-region math (selector bbox + padding + clamp, exact region
 // form, no-match error) is owned by and tested in
@@ -79,3 +84,15 @@ describe("parseZoomScale (--zoom-scale)", () => {
     expect(parseZoomScale("-1")).toBe(3);
   });
 });
+
+describe("requireSnapshotFfmpeg", () => {
+  it("rejects video snapshot extraction when FFmpeg is unavailable", () => {
+    expect(() => requireSnapshotFfmpeg(undefined)).toThrow(
+      /FFmpeg is required to extract video frames for snapshots/,
+    );
+  });
+
+  it("preserves the resolved FFmpeg executable", () => {
+    expect(requireSnapshotFfmpeg("C:\\tools\\ffmpeg.exe")).toBe("C:\\tools\\ffmpeg.exe");
+  });
+});

packages/cli/src/commands/snapshot.ts

@@ -17,7 +17,7 @@ import { resolveProject } from "../utils/project.js";
 import { normalizeErrorMessage } from "../utils/errorMessage.js";
 import { serveStaticProjectHtml } from "../utils/staticProjectServer.js";
 import { c } from "../ui/colors.js";
-import { findFFmpeg } from "../browser/ffmpeg.js";
+import { findFFmpeg, getFFmpegInstallHint } from "../browser/ffmpeg.js";
 import { parseAngle, type Camera } from "./motionShotLayout.js";
 import type { Example } from "./_examples.js";
 
@@ -60,6 +60,13 @@ function orbitStageSource(): string {
  * `hyperframes snapshot` indefinitely. */
 const FFMPEG_EXTRACT_TIMEOUT_MS = 30_000;
 
+export function requireSnapshotFfmpeg(ffmpegPath: string | undefined): string {
+  if (ffmpegPath) return ffmpegPath;
+  throw new Error(
+    `FFmpeg is required to extract video frames for snapshots. ${getFFmpegInstallHint()}`,
+  );
+}
+
 /**
  * Extract a single frame from a video file at `timeSeconds` via FFmpeg.
  * Used to work around Chrome-headless's inability to reliably seek
@@ -73,8 +80,7 @@ async function extractVideoFrameToBuffer(
   const tmp = mkdtempSync(join(tmpdir(), "hf-snapshot-frame-"));
   const outPath = join(tmp, "frame.png");
   try {
-    const ffmpegPath = findFFmpeg();
-    if (!ffmpegPath) return null;
+    const ffmpegPath = requireSnapshotFfmpeg(findFFmpeg());
     // `-ss` before `-i` performs a fast keyframe seek; adequate for snapshot accuracy
     // (±1 frame) and orders of magnitude faster than the decode-and-scan alternative.
     const args = ["-hide_banner", "-loglevel", "error"];