---
name: calculate-metadata
description: Dynamically set composition duration, dimensions, and props
metadata:
  tags: calculateMetadata, duration, dimensions, props, dynamic
---

# 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 `getMediaMetadata()` function from the mediabunny/metadata skill to get the video duration:

```tsx
import { CalculateMetadataFunction } from 'remotion';
import { getMediaMetadata } from '../get-media-metadata';

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

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

## Matching dimensions of a video

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

  return {
    durationInFrames: Math.ceil(durationInSeconds * 30),
    width: dimensions?.width ?? 1920,
    height: dimensions?.height ?? 1080,
  };
};
```

## Setting duration based on multiple videos

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

  const totalDuration = allMetadata.reduce((sum, meta) => sum + meta.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
