# Remotion Rule: Calculate Metadata

> Remotion skill rule: Dynamically set composition duration, dimensions, and props. Part of the official Remotion Agent Skill for programmatic video in React.

## Install

Save the content below to `.claude/skills/` or append to your `CLAUDE.md`:

## Quick Use

```bash
npx skills add remotion-dev/skills
```

This rule activates automatically when working with calculate metadata in a Remotion project.

---

## Intro

Dynamically set composition duration, dimensions, and props. Part of the [Remotion AI Skill](https://tokrepo.com/en/workflows/57997ead-c8fa-409c-916f-28bbc0adc8d9) — the official Agent Skill for programmatic video creation in React.

**Best for**: Developers using Remotion for calculate metadata
**Works with**: Claude Code, OpenAI Codex, Cursor

---

## Rule Content

# Using calculateMetadata

Use `calculateMetadata` on a `<Composition>` to dynamically set duration, dimensions, and transform props before rendering.

```tsx
<Composition
  id="MyComp"
  component={MyComponent}
  durationInFrames={300}
  fps={30}
  width={1920}
  height={1080}
  defaultProps={{ videoSrc: "https://remotion.media/video.mp4" }}
  calculateMetadata={calculateMetadata}
/>
```

## Setting duration based on a video

Use the [`getVideoDuration`](./get-video-duration.md) and [`getVideoDimensions`](./get-video-dimensions.md) skills to get the video duration and dimensions:

```tsx
import { CalculateMetadataFunction } from "remotion";
import { getVideoDuration } from "./get-video-duration";

const calculateMetadata: CalculateMetadataFunction<Props> = async ({
  props,
}) => {
  const durationInSeconds = await getVideoDuration(props.videoSrc);

  return {
    durationInFrames: Math.ceil(durationInSeconds * 30),
  };
};
```

## Matching dimensions of a video

Use the [`getVideoDimensions`](./get-video-dimensions.md) skill to get the video dimensions:

```tsx
import { CalculateMetadataFunction } from "remotion";
import { getVideoDuration } from "./get-video-duration";
import { getVideoDimensions } from "./get-video-dimensions";

const calculateMetadata: CalculateMetadataFunction<Props> = async ({
  props,
}) => {
  const dimensions = await getVideoDimensions(props.videoSrc);

  return {
    width: dimensions.width,
    height: dimensions.height,
  };
};
```

## Setting duration based on multiple videos

```tsx
const calculateMetadata: CalculateMetadataFunction<Props> = async ({
  props,
}) => {
  const metadataPromises = props.videos.map((video) =>
    getVideoDuration(video.src),
  );
  const allMetadata = await Promise.all(metadataPromises);

  const totalDuration = allMetadata.reduce(
    (sum, durationInSeconds) => sum + durationInSeconds,
    0,
  );

  return {
    durationInFrames: Math.ceil(totalDuration * 30),
  };
};
```

## Setting a default outName

Set the default output filename based on props:

```tsx
const calculateMetadata: CalculateMetadataFunction<Props> = async ({
  props,
}) => {
  return {
    defaultOutName: `video-${props.id}.mp4`,
  };
};
```

## Transforming props

Fetch data or transform props before rendering:

```tsx
const calculateMetadata: CalculateMetadataFunction<Props> = async ({
  props,
  abortSignal,
}) => {
  const response = await fetch(props.dataUrl, { signal: abortSignal });
  const data = await response.json();

  return {
    props: {
      ...props,
      fetchedData: data,
    },
  };
};
```

The `abortSignal` cancels stale requests when props change in the Studio.

## Return value

All fields are optional. Returned values override the `<Composition>` props:

- `durationInFrames`: Number of frames
- `width`: Composition width in pixels
- `height`: Composition height in pixels
- `fps`: Frames per second
- `props`: Transformed props passed to the component
- `defaultOutName`: Default output filename
- `defaultCodec`: Default codec for rendering

---

## Source & Thanks

> Created by [Remotion](https://github.com/remotion-dev). Licensed under MIT.
> [remotion-dev/skills](https://github.com/remotion-dev/skills) — Rule: `calculate-metadata`

Part of the [Remotion AI Skill](https://tokrepo.com/en/workflows/57997ead-c8fa-409c-916f-28bbc0adc8d9) collection on TokRepo.

---
Source: https://tokrepo.com/en/workflows/994d2298-c7f5-4f57-a9e9-6a7d28dcc490
Author: Skill Factory