einundzwanzig-verein/videos/.opencode/skills/remotion-best-practices/rules/compositions.md

---
name: compositions
description: Defining compositions, stills, folders, default props and dynamic metadata
metadata:
  tags: composition, still, folder, props, metadata
---

A `<Composition>` defines the component, width, height, fps and duration of a renderable video.

It normally is placed in the `src/Root.tsx` file.

```tsx
import { Composition } from "remotion";
import { MyComposition } from "./MyComposition";

export const RemotionRoot = () => {
  return (
    <Composition
      id="MyComposition"
      component={MyComposition}
      durationInFrames={100}
      fps={30}
      width={1080}
      height={1080}
    />
  );
};
```

## Default Props

Pass `defaultProps` to provide initial values for your component.  
Values must be JSON-serializable (`Date`, `Map`, `Set`, and `staticFile()` are supported).

```tsx
import { Composition } from "remotion";
import { MyComposition, MyCompositionProps } from "./MyComposition";

export const RemotionRoot = () => {
  return (
    <Composition
      id="MyComposition"
      component={MyComposition}
      durationInFrames={100}
      fps={30}
      width={1080}
      height={1080}
      defaultProps={{
        title: "Hello World",
        color: "#ff0000",
      } satisfies MyCompositionProps}
    />
  );
};
```

Use `type` declarations for props rather than `interface` to ensure `defaultProps` type safety.

## Folders

Use `<Folder>` to organize compositions in the sidebar.  
Folder names can only contain letters, numbers, and hyphens.

```tsx
import { Composition, Folder } from "remotion";

export const RemotionRoot = () => {
  return (
    <>
      <Folder name="Marketing">
        <Composition id="Promo" /* ... */ />
        <Composition id="Ad" /* ... */ />
      </Folder>
      <Folder name="Social">
        <Folder name="Instagram">
          <Composition id="Story" /* ... */ />
          <Composition id="Reel" /* ... */ />
        </Folder>
      </Folder>
    </>
  );
};
```

## Stills

Use `<Still>` for single-frame images. It does not require `durationInFrames` or `fps`.

```tsx
import { Still } from "remotion";
import { Thumbnail } from "./Thumbnail";

export const RemotionRoot = () => {
  return (
    <Still
      id="Thumbnail"
      component={Thumbnail}
      width={1280}
      height={720}
    />
  );
};
```

## Calculate Metadata

Use `calculateMetadata` to make dimensions, duration, or props dynamic based on data.

```tsx
import { Composition, CalculateMetadataFunction } from "remotion";
import { MyComposition, MyCompositionProps } from "./MyComposition";

const calculateMetadata: CalculateMetadataFunction<MyCompositionProps> = async ({
  props,
  abortSignal,
}) => {
  const data = await fetch(`https://api.example.com/video/${props.videoId}`, {
    signal: abortSignal,
  }).then((res) => res.json());

  return {
    durationInFrames: Math.ceil(data.duration * 30),
    props: {
      ...props,
      videoUrl: data.url,
    },
  };
};

export const RemotionRoot = () => {
  return (
    <Composition
      id="MyComposition"
      component={MyComposition}
      durationInFrames={100} // Placeholder, will be overridden
      fps={30}
      width={1080}
      height={1080}
      defaultProps={{ videoId: "abc123" }}
      calculateMetadata={calculateMetadata}
    />
  );
};
```

The function can return `props`, `durationInFrames`, `width`, `height`, `fps`, and codec-related defaults. It runs once before rendering begins.