Video demo

scripts/demo films a web app and writes demo-out/ into that project's workspace: per scene an mp4 with voice-over, a poster, retina stills, plus full-tour.mp4, manifest.json and index.html. All local. The engine runs from this skill; nothing is installed into the app being filmed.

Non-negotiables

Each of these cost a run or a user's patience.

1. A pinned build, never a dev server. Its module graph belongs to whoever is editing source. Copy it somewhere private and verify its API base by reading the bundle. A URL with no repo behind it is site mode; a URL on localhost is a dev server and is never filmed. 2. In build mode, mock every request in-process and pin the clock. A corpus gets published, and a real account publishes real people's addresses. site mode trades both away knowingly: public pages only. 3. Own your port and output directory. The studio refuses to adopt a server it did not start. Never pkill by pattern. 4. 1080p60 video, 2x stills. They are separate settings. 4K video judders because throughput is a fixed pixels-per-second budget. 5. Do the gesture, then narrate while pushed in on the result. One subject per line. Never narrate before the subject exists. Where the app has its own timer — an undo window, a toast — the gesture goes inside it and the words after, or the film shows a feature that does not work. 6. One scene, then stop and ask (step 8). It caught four defects before twenty-six more scenes were filmed. 7. Read the PNG, every time. A scene that passes while framing the wrong thing is a failure, and only an eye on the still catches it. 8. Nothing is final until they say so. Any note about the words, the framing, the pace, what is covered or the voice is a re-film, not a negotiation: change it and film it again. They cannot see what you can, so "too long", "zoom in more" and "stop zooming so much" are all complete instructions, and a scene is cheap to shoot twice.

Workflow

1. Pick the mode from what you were given. Do not ask. An http(s) URL on a public host is site, workspace ~/.video-demo/<host>/. A URL on localhost or a private address is a dev server: find the repo behind it and treat the request as that repo. No URL means the repo you are in, so walk up and look for a web app (a package.json with a build script beside a Vite, React Router, Next, Astro, SvelteKit or Remix config). Exactly one is build; several, ask which; none, ask for a URL or a path. A workspace whose .origin already names this repo is reused, not scaffolded again. Say the mode and the workspace path in one line and carry on. 2. scripts/doctor.sh, then set yourself up before asking anything else of the user. They installed a skill; they did not sign up to run three scripts. Say what is missing in one line, say what you propose to install and roughly how big it is, and run it once they agree. scripts/install.sh covers the engine and Chromium (about 250MB) and installs ffmpeg too where a package manager allows it; scripts/install-voice.sh is the voice (~350MB), and filming silent is a fine answer if they would rather not. Never install anything without asking, and never hand them a doctor report to interpret. Two things it will not do, and nor should you: upgrade their Node, because which tool owns it is theirs to know, and run sudo, because a password prompt in a script nobody is watching just hangs. In both cases the script prints the one command and you pass it on. 3. Discover, writing nothing. site: open the URL and read it, for what the page is for, the three things worth showing, and what is stable enough to point at. If it lands on a sign-in, stop: a signed-in app is filmed from its repo, so ask for that or for a public URL. build: the build command copied verbatim out of package.json; the output directory from the framework's config; any absolute API host in .env* (it goes in build.forbid); the key the theme boot script reads; an existing fixture API or MSW handlers; data-testid density; routes with no credential. 4. scripts/scaffold.mjs <appRoot>, or scripts/scaffold.mjs --site <url>. Neither writes anything into the app. 5. Fill in the workspace's demo.config.ts. A required field still unknown means discovery is not done. [config.md](references/config.md) 6. build only: write mock.ts and seed/. Reuse the repo's own data fixtures where it has them, but never a file that imports @playwright/test: two copies in one run is an error Playwright refuses, and it fails the whole corpus rather than the one scene that did it. Then DEMO_VOICE=0 scripts/demo --grep smoke. Reuse the repo's fixture API if it has one ([mocking.md](references/mocking.md)). Read the still: signed in, seeded data, right theme, no login page. Read the capture line. Fix until both are right, then write demo/ui.ts with only what the smoke run proved. 7. Film what they asked for, at the scope they asked for it. A named feature is one scene: write it, film it, hand it over. Do not answer "record the search on the home page" with a ten-scene proposal, and do not quietly widen the ask because the product has more in it. Only when the request is the whole product do you propose 6 to 10 scenes, each a title and a one-line blurb in tour order, and ask which to film first. 8. STOP. Film that one scene with voice. Verify the spoken count matches the say calls, nothing overran, the rate held. Read every still. Give the user the mp4 path and ask about the writing's register, the zoom scale, the pacing and the voice. Write nothing else until they answer. 9. Then batches of three or four via --grep; the manifest merges. Read the stills after every batch. DEMO_BUILD=0 scripts/demo skips the rebuild while iterating on a scene — twenty seconds instead of four minutes; drop it for the run that produces the corpus. 10. Full run with DEMO_TRACE_FRAMES=1, then scripts/gaps.mjs and open demo-out/index.html. Report the capture table and any slow clips.

A scene

scene('tasks', { title: 'Your to-dos, beside your calendar', blurb: '...' },
  async ({ actor, page, shot }) => {
    await actor.click(page.getByRole('radio', { name: 'Today' }));
    await actor.settle();
    await actor.spotlight(
      row('Send Sam the feedback'),
      'And this one is from yesterday that I never got to, so it is flagged.',
      { scale: 1.8, stay: true }
    );
    await shot('overdue');
    await actor.unfocus();
  });

spotlight takes the narration mark, then moves camera and cursor over the line's opening words. Scale by subject: panel ~1.4, row ~1.7, single control ~2. A line about the whole screen gets a plain say and no zoom. unfocus is a hint rather than a movement: the camera only comes out when something needs it wide, so consecutive beats about the same region glide instead of bouncing. [scenes.md](references/scenes.md) · [narration.md](references/narration.md)

Never

Subtitles (the voice is the channel). Cloud TTS (the film is of private data). Playwright's recordVideo (no control of rate, size or start; the recorder replaces it). 4K as a default. Music, intro cards or cross-fades. Scenes generated from a route crawl: a scene is choreography with a point. Retries: a retried scene is a different film.

Also

[capture.md](references/capture.md) before changing any capture number. [runs.md](references/runs.md) for builds, isolation and the manifest. [troubleshooting.md](references/troubleshooting.md) when a run dies or a shot looks wrong. The engine runs from this skill, so a fix to engine/ reaches every project on the machine at once: edit it there, and nothing needs propagating.