Remotion Rule: Get Video Duration

What it is

This is a Remotion skill rule for getting the duration of a video file in seconds using Mediabunny. When building dynamic Remotion compositions that incorporate external video files, you need to know the video duration to set the composition length correctly. Mediabunny provides a reliable way to read this metadata.

The rule is part of the official Remotion Agent Skill collection for AI coding assistants (Claude Code, Cursor, OpenAI Codex) working on React-based programmatic video projects.

How it saves time or tokens

Without this rule, an AI assistant might suggest using ffprobe, a custom ffmpeg command, or unreliable JavaScript-based approaches to read video duration. Mediabunny is the recommended Remotion approach, handling format detection and metadata extraction consistently. The rule eliminates trial-and-error by providing the correct implementation on the first attempt.

How to use

1. Install the Remotion skills collection:

npx skills add remotion-dev/skills

1. The rule activates automatically when your AI assistant detects video duration queries in a Remotion project.

1. Use the provided pattern to read video duration before configuring your composition.

Example

import { getVideoMetadata } from '@remotion/media-utils';

// Get video duration in a calculate-metadata function
export const calculateMetadata = async () => {
  const metadata = await getVideoMetadata(
    'https://example.com/video.mp4'
  );

  return {
    durationInFrames: Math.ceil(metadata.durationInSeconds * 30),
    fps: 30,
    width: metadata.width,
    height: metadata.height,
  };
};

// Use in composition
import { Composition } from 'remotion';
import { MyVideo } from './MyVideo';

export const Root = () => {
  return (
    <Composition
      id='MyVideo'
      component={MyVideo}
      calculateMetadata={calculateMetadata}
      width={1920}
      height={1080}
      fps={30}
      durationInFrames={1}
    />
  );
};

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This tool integrates with standard development workflows and requires minimal configuration to get started. It is available as open-source software with documentation and community support through the official repository. The project follows semantic versioning for stable releases.

For teams evaluating this tool, the key advantage is reducing manual work in repetitive tasks. The automation provided by the built-in features means less custom code to maintain and fewer integration points to manage. This translates directly to lower maintenance costs and faster iteration cycles.

Common pitfalls

• The getVideoMetadata function works with URLs and local file paths; ensure the video file is accessible from the build environment.
• Duration is returned in seconds (floating point); multiply by fps and ceil to get durationInFrames for Remotion compositions.
• Some video formats may not report duration in metadata headers; for these files, the function may need to download more of the file before returning.