Remotion Rule: Get Audio Duration

What it is

This Remotion rule instructs AI coding agents on how to get the duration of an audio file in seconds using Mediabunny within Remotion projects. Knowing the exact audio duration is essential for synchronizing video compositions with background music, voiceovers, or sound effects.

The rule targets developers using AI assistants to build Remotion video projects that need frame-accurate audio synchronization.

How it saves time or tokens

Without this rule, AI agents often guess at audio durations or suggest incorrect APIs for measuring them. The rule provides the exact Mediabunny function call and demonstrates how to convert the duration into frame counts for Remotion compositions, eliminating debugging time.

How to use

1. Add the Remotion audio duration rule to your project's AI configuration.
2. Ask your AI assistant to create a composition that matches the length of an audio file.
3. The agent uses Mediabunny to measure the duration and sets the composition's durationInFrames accordingly.

Example

import { getAudioDurationInSeconds } from '@remotion/media-utils';
import { Composition, Audio, staticFile } from 'remotion';

// Calculate composition duration from audio length
const fps = 30;

export const RemotionRoot: React.FC = () => {
  return (
    <Composition
      id='AudioVideo'
      component={AudioVideo}
      fps={fps}
      width={1920}
      height={1080}
      calculateMetadata={async () => {
        const duration = await getAudioDurationInSeconds(
          staticFile('voiceover.mp3')
        );
        return {
          durationInFrames: Math.ceil(duration * fps),
        };
      }}
    />
  );
};

const AudioVideo: React.FC = () => (
  <Audio src={staticFile('voiceover.mp3')} />
);

Related on TokRepo

• AI Tools for Video -- video creation and editing tools for developers
• AI Tools for Automation -- automation tools for media workflows

Common pitfalls

• getAudioDurationInSeconds is async and must be called inside calculateMetadata or a delayRender block, not during render.
• Supported formats depend on the browser and FFmpeg availability. MP3 and WAV are universally supported; OGG may not work in all environments.
• Audio files in the public directory must be referenced with staticFile(). Direct file paths cause rendering failures in production.