ffmpeg.FS('readFile', 'output.mp4') error. Check if the path exists

import React, { useRef } from 'react';
import { createFFmpeg, fetchFile } from '@ffmpeg/ffmpeg/dist/ffmpeg.min.js';

const VideoTextEditor = () => {
const videoFileRef = useRef(null);
const fontFileRef = useRef(null);

const addTextAtTime = async (videoFile, fontFile, outputPath, text, timeInSeconds) => {
const ffmpegInstance = createFFmpeg({ log: true });
await ffmpegInstance.load();
return new Promise(async(resolve, reject) => {
ffmpegInstance.FS('writeFile', 'input.mp4', new Uint8Array(videoFile, 0, videoFile.byteLength));
ffmpegInstance.FS('writeFile', 'font.ttf', new Uint8Array(fontFile, 0, fontFile.byteLength));

ffmpegInstance.run(
'-i', 'input.mp4',
'-vf', `drawtext=fontfile=font.ttf:text='${text}':fontsize=24:fontcolor=white:x=(w-text_w)/2:y=(h-text_h)/2:enable='between(t,${timeInSeconds},${timeInSeconds + 1})'`,
'output.mp4'
)
.then(() => {
const outputFileName = 'output.mp4';
// ffmpegInstance.FS('mkdir', '/input');
const data = ffmpegInstance.FS('readFile', outputFileName);
const outputUrl = URL.createObjectURL(new Blob([data.buffer], { type: 'video/mp4' }));
console.log(outputUrl);

resolve(outputUrl);
})
.catch((error) => {
reject(error);
});
});
};

const handleAddText = () => {
const videoFile = videoFileRef.current.files[0];
const fontFile = fontFileRef.current.files[0];

if (!videoFile || !fontFile) {
console.error('Please select a video file and a font file.');
return;
}

const videoPath = URL.createObjectURL(videoFile);
const outputPath = '/path/to/output/video.mp4';
const text = 'Your text here';
const timeInSeconds = 10; // Add text at 10 seconds mark

addTextAtTime(videoFile, fontFile, outputPath, text, timeInSeconds)
.then((outputUrl) => {
console.log('Text added successfully at the specified time.');
// Use the outputUrl as needed (e.g., display the video in a element)
})
.catch((error) => {
console.error('Error adding text:', error);
});
};

return (

);
};

export default VideoTextEditor;

this is my code in react and i am getting the above error again and again in ffmpeg.
whyyy????
any help....