Add remotion-video skill (#1)

* Add remotion-video skill Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019yhnsd9RDz7jDSUUX7oEcH * Add Phase 2 templates to remotion-video skill Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019yhnsd9RDz7jDSUUX7oEcH * Fix captions template background; document browser flag after test render Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019yhnsd9RDz7jDSUUX7oEcH * Add audio/voiceover template (Phase 3), tested with real render Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019yhnsd9RDz7jDSUUX7oEcH * Document font loading and its network requirement; captions-over-video verified Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_019yhnsd9RDz7jDSUUX7oEcH --------- Co-authored-by: Claude <noreply@anthropic.com>
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+---
+name: remotion-video
+description: Create videos from React code with Remotion. Use when the user asks to make, animate, preview, or render a video, motion graphic, intro, caption, or social clip using code.
+---
+
+# Remotion Video
+
+Remotion makes videos out of React components. Each frame is a web page. Render them in order and you get an MP4.
+
+## Core ideas
+- **Composition**: one video. Has `width`, `height`, `fps`, `durationInFrames`.
+- **Frame**: `useCurrentFrame()` returns the current frame number. All animation is a function of the frame.
+- **`interpolate`**: maps a frame range to a value range (fade, slide).
+- **`spring`**: natural bouncy motion.
+- **`Sequence`**: shows children only during a frame range.
+- **`AbsoluteFill`**: full-screen layer; stack them for backgrounds.
+- **`Audio` / `OffthreadVideo` / `Img`**: media. Put files in `public/` and load with `staticFile("name.mp3")`.
+
+## Workflow
+1. **Plan first.** Ask or decide: length (seconds), size (1920x1080, or 1080x1920 for vertical), fps (30), and the scenes. Keep scenes to a short list.
+2. **Set up** (skip if the project exists):
+   ```
+   npx create-video@latest
+   cd <project> && npm install
+   ```
+3. **Write** compositions in `src/`, register them in `src/Root.tsx`.
+4. **Preview**: `npm run dev` (opens Remotion Studio).
+5. **Render**: `npx remotion render <CompositionId> out/video.mp4`
+   Still frame: `npx remotion still <CompositionId> out/frame.png --frame=30`
+6. **Verify**: render one still first, check it looks right, then render the full video.
+
+## Starter example
+`src/Root.tsx`
+```tsx
+import { Composition } from "remotion";
+import { Hello } from "./Hello";
+
+export const RemotionRoot = () => (
+  <Composition
+    id="Hello"
+    component={Hello}
+    durationInFrames={150}
+    fps={30}
+    width={1920}
+    height={1080}
+    defaultProps={{ title: "Hello, world" }}
+  />
+);
+```
+
+`src/Hello.tsx`
+```tsx
+import { AbsoluteFill, interpolate, spring, useCurrentFrame, useVideoConfig } from "remotion";
+
+export const Hello = ({ title }: { title: string }) => {
+  const frame = useCurrentFrame();
+  const { fps } = useVideoConfig();
+  const opacity = interpolate(frame, [0, 30], [0, 1], { extrapolateRight: "clamp" });
+  const scale = spring({ frame, fps, config: { damping: 12 } });
+
+  return (
+    <AbsoluteFill style={{ backgroundColor: "#0b1020", justifyContent: "center", alignItems: "center" }}>
+      <h1 style={{ color: "white", fontSize: 120, opacity, transform: `scale(${scale})` }}>{title}</h1>
+    </AbsoluteFill>
+  );
+};
+```
+
+## Rules of thumb
+- Never animate with CSS transitions, `setTimeout`, or CSS animations. They don't render per frame. Drive everything from `useCurrentFrame()`.
+- Always pass `extrapolateRight: "clamp"` to `interpolate` unless you want values to keep growing.
+- Seconds to frames: `seconds * fps`.
+- Use `<Sequence from={..} durationInFrames={..}>` to order scenes; `<Series>` to chain them.
+- Load fonts with `@remotion/google-fonts` so they are ready before rendering.
+- Keep props in `defaultProps` so the user can edit text in the Studio.
+- Rendering needs Chromium and ffmpeg (Remotion installs/handles these); first render can be slow.
+
+## Fonts
+Google Fonts: `npm i @remotion/google-fonts`, then
+```tsx
+import { loadFont } from "@remotion/google-fonts/Inter";
+const { fontFamily } = loadFont();   // use as style={{ fontFamily }}
+```
+It downloads the font while rendering, so the machine needs internet access to fonts.googleapis.com. If the render fails with "Failed to load font", the network is blocking it: use a local font file in `public/` with `@remotion/fonts` (`loadFont({ family, url: staticFile("x.woff2") })`) or a system font. (Not verified in the sandbox where this skill was tested, which had no access to Google.)
+
+## Common problems
+- **Can't download the browser (no internet / locked-down machine)**: point Remotion at an installed Chromium:
+  `npx remotion render <Id> out/video.mp4 --browser-executable=/path/to/chromium --chrome-mode=chrome-for-testing`
+- **Blank/white frames**: an asset path is wrong; use `staticFile()`.
+- **Flicker**: an image or font not loaded; use `<Img>` and `@remotion/google-fonts`.
+- **Slow render**: lower resolution/fps while testing, or use `--concurrency`.
+
+## Templates
+Copy-paste starting points. Read the one that fits:
+- `templates/captions.md` - words highlighted in time with speech
+- `templates/charts.md` - animated bar chart
+- `templates/intro-outro.md` - title card + chaining scenes with `Series`
+- `templates/audio-voiceover.md` - background music, voiceover, auto video length
+- `templates/vertical.md` - 1080x1920 clips for Reels/TikTok/Shorts
+
+## Docs
+https://www.remotion.dev/docs
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+# Template: Audio, music and voiceover
+
+Put sound files in `public/` (mp3 or wav). Load them with `staticFile()`.
+
+`src/Narrated.tsx`
+```tsx
+import { AbsoluteFill, Audio, Sequence, interpolate, staticFile, useVideoConfig } from "remotion";
+import { getAudioDurationInSeconds } from "@remotion/media-utils";
+import type { CalculateMetadataFunction } from "remotion";
+
+type Props = { title: string; voice: string; music: string };
+
+// Make the video exactly as long as the voiceover (+1 second of padding).
+export const calcNarratedMetadata: CalculateMetadataFunction<Props> = async ({ props }) => {
+  const seconds = await getAudioDurationInSeconds(staticFile(props.voice));
+  return { durationInFrames: Math.ceil((seconds + 1) * 30) };
+};
+
+export const Narrated = ({ title, voice, music }: Props) => {
+  const { fps, durationInFrames } = useVideoConfig();
+  return (
+    <AbsoluteFill style={{ background: "#0b1020", justifyContent: "center", alignItems: "center" }}>
+      <h1 style={{ color: "white", fontSize: 110 }}>{title}</h1>
+
+      {/* Background music: quiet, fades out over the last second. */}
+      <Audio
+        src={staticFile(music)}
+        volume={(f) => interpolate(f, [durationInFrames - fps, durationInFrames], [0.15, 0], { extrapolateLeft: "clamp", extrapolateRight: "clamp" })}
+      />
+
+      {/* Voiceover starts half a second in, full volume. */}
+      <Sequence from={Math.round(fps * 0.5)}>
+        <Audio src={staticFile(voice)} volume={1} />
+      </Sequence>
+    </AbsoluteFill>
+  );
+};
+```
+
+Register it (note `calculateMetadata`):
+```tsx
+<Composition
+  id="Narrated"
+  component={Narrated}
+  calculateMetadata={calcNarratedMetadata}
+  durationInFrames={300}   // placeholder, replaced by calculateMetadata
+  fps={30} width={1920} height={1080}
+  defaultProps={{ title: "My story", voice: "voice.mp3", music: "music.mp3" }}
+/>
+```
+
+Install: `npm i @remotion/media-utils`
+
+Getting a voiceover
+- Record yourself, or generate speech with a text-to-speech service, and save as `public/voice.mp3`. Never commit API keys; keep them in environment variables.
+- Pair with `templates/captions.md`: feed it word timings from a transcription of the same file.
+
+Rules
+- Music volume 0.1-0.2 so the voice stays clear.
+- `<Sequence from={...}>` delays when a sound starts.
+- Audio is only in the final render (mp4). Stills (`remotion still`) have no sound.
+- Check the sound made it in: `ffprobe out/video.mp4` should list an `Audio:` stream.
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+# Template: Captions
+
+Words appear in time with speech. Give each word a start time in seconds.
+
+`src/Captions.tsx`
+```tsx
+import { AbsoluteFill, useCurrentFrame, useVideoConfig } from "remotion";
+
+type Word = { text: string; start: number; end: number }; // seconds
+
+export const Captions = ({ words, background = "#111" }: { words: Word[]; background?: string }) => {
+  const frame = useCurrentFrame();
+  const { fps } = useVideoConfig();
+  const t = frame / fps;
+
+  // Show a window of up to 5 words around the current one.
+  const current = words.findIndex((w) => t >= w.start && t < w.end);
+  const i = current === -1 ? 0 : current;
+  const visible = words.slice(Math.floor(i / 5) * 5, Math.floor(i / 5) * 5 + 5);
+
+  return (
+    <AbsoluteFill style={{ backgroundColor: background, justifyContent: "flex-end", alignItems: "center", paddingBottom: 200 }}>
+      <div style={{ fontSize: 72, fontWeight: 800, color: "white", textShadow: "0 4px 12px black", textAlign: "center", maxWidth: "80%" }}>
+        {visible.map((w, k) => (
+          <span key={k} style={{ color: t >= w.start && t < w.end ? "#ffd400" : "white", marginRight: 16 }}>
+            {w.text}
+          </span>
+        ))}
+      </div>
+    </AbsoluteFill>
+  );
+};
+```
+
+Tips
+- Get word times from a transcription tool (e.g. `@remotion/captions` or Whisper) and save them as JSON in `public/`.
+- `background` is the backdrop when there is no video. Pass `"transparent"` when layering over a video.
+- Layer it over the video: `<AbsoluteFill><OffthreadVideo src={staticFile("clip.mp4")} /><Captions words={words} background="transparent" /></AbsoluteFill>`.
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+# Template: Animated bar chart
+
+Bars grow one after another.
+
+`src/BarChart.tsx`
+```tsx
+import { AbsoluteFill, spring, useCurrentFrame, useVideoConfig } from "remotion";
+
+type Bar = { label: string; value: number };
+
+export const BarChart = ({ data, color = "#4f8cff" }: { data: Bar[]; color?: string }) => {
+  const frame = useCurrentFrame();
+  const { fps } = useVideoConfig();
+  const max = Math.max(...data.map((d) => d.value));
+
+  return (
+    <AbsoluteFill style={{ backgroundColor: "#0b1020", padding: 120, justifyContent: "flex-end" }}>
+      <div style={{ display: "flex", alignItems: "flex-end", gap: 40, height: 700 }}>
+        {data.map((d, i) => {
+          const grow = spring({ frame: frame - i * 6, fps, config: { damping: 15 } });
+          return (
+            <div key={d.label} style={{ flex: 1, textAlign: "center", color: "white", fontSize: 36 }}>
+              <div style={{ height: (d.value / max) * 600 * grow, background: color, borderRadius: 8 }} />
+              <div style={{ marginTop: 16 }}>{d.label}</div>
+            </div>
+          );
+        })}
+      </div>
+    </AbsoluteFill>
+  );
+};
+```
+
+Tips
+- Delay each bar with `frame - i * 6` (6 frames apart).
+- For lines, animate `strokeDashoffset` on an SVG path using `interpolate`.
+- Keep numbers readable: show the value as text, rounded.
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+# Template: Title intro / outro card
+
+A short card (2-3 seconds) with a title and subtitle. Use at the start or end.
+
+`src/TitleCard.tsx`
+```tsx
+import { AbsoluteFill, interpolate, spring, useCurrentFrame, useVideoConfig } from "remotion";
+
+export const TitleCard = ({ title, subtitle }: { title: string; subtitle?: string }) => {
+  const frame = useCurrentFrame();
+  const { fps, durationInFrames } = useVideoConfig();
+  const rise = spring({ frame, fps, config: { damping: 14 } });
+  const fadeOut = interpolate(frame, [durationInFrames - 15, durationInFrames], [1, 0], {
+    extrapolateLeft: "clamp",
+    extrapolateRight: "clamp",
+  });
+
+  return (
+    <AbsoluteFill style={{ background: "linear-gradient(135deg,#1b2a6b,#0b1020)", justifyContent: "center", alignItems: "center", opacity: fadeOut }}>
+      <h1 style={{ color: "white", fontSize: 130, margin: 0, transform: `translateY(${(1 - rise) * 60}px)`, opacity: rise }}>{title}</h1>
+      {subtitle && <p style={{ color: "#9fb3ff", fontSize: 48, opacity: rise }}>{subtitle}</p>}
+    </AbsoluteFill>
+  );
+};
+```
+
+Chain with the main video using `<Series>`:
+```tsx
+<Series>
+  <Series.Sequence durationInFrames={90}><TitleCard title="My Video" /></Series.Sequence>
+  <Series.Sequence durationInFrames={600}><MainScene /></Series.Sequence>
+  <Series.Sequence durationInFrames={90}><TitleCard title="Thanks for watching" /></Series.Sequence>
+</Series>
+```
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+# Template: Vertical clips (Reels / TikTok / Shorts)
+
+Same code, different size. Register a vertical composition:
+
+```tsx
+<Composition
+  id="Vertical"
+  component={MyScene}
+  width={1080}
+  height={1920}
+  fps={30}
+  durationInFrames={30 * 30} // 30 seconds
+/>
+```
+
+Render: `npx remotion render Vertical out/vertical.mp4`
+
+Rules
+- Keep text inside the **safe zone**: about 150px from the top, 350px from the bottom (apps cover those parts with buttons and captions), and 60px from the sides.
+- Use big text (60px+). Phone screens are small.
+- Keep clips under 60 seconds (Shorts limit); 15-30 seconds does best.
+- Use `useVideoConfig()` for width/height instead of hard-coding, so the same scene works wide and tall.
+- Put captions in the lower-middle, above the bottom safe zone (see captions.md).