readFile throws the exception "Check if the path exists"

[KathRains]

Hi,
I'm trying to cut 2 fragments of video and then concatenate them into one.
This is my code:

        const extension = 'move', start = 0.9, length = 7;
        const name = 'asdf'
        const fileContent = await fetchFile(fileData);
        ffmpeg.FS('writeFile', name, fileContent);

        await ffmpeg.run('-t', start, '-i', name, '-map', '0', '-c', 'copy', `output1.${extension}`);
        await ffmpeg.run('-ss', start + length, '-i', name, '-map', '0', '-c', 'copy', `output2.${extension}`);

        const filesList = [`file output1.${extension}`, `file output2.${extension}`];

        ffmpeg.FS('writeFile', 'filesList.txt', filesList.join('\n'));

        await ffmpeg.run('-f', 'concat', '-safe', '0', '-i', 'filesList.txt',  `outputResult.${extension}`);

        const data = ffmpeg.FS('readFile', `outputResult.${extension}`); // <------------- this line throws the exception
        const newUrl = URL.createObjectURL(new Blob([data.buffer], { type: fileData.type }));

This command works but it's very slow, it takes more than 30 seconds to cut a piece of 1 sec length:

await ffmpeg.run('-i', name, '-ss', '0', '-to', '1', `output1.${extension}`);

I'm not very familiar with ffmpeg itself so maybe there is some obvious mistake that I've made?

Thanks!

UPD
I was able to run without any exceptions the following code but the concatenation was superslow (about 1 minute for 2 seconds) and I had a very strange exception on the readFile:

        await ffmpeg.run('-ss', '0', '-i', name, 
                        '-codec', 'copy', '-map', '0', '-to', lengthString, `output1.${extension}`)
        await ffmpeg.run('-ss', toString, '-i', name, 
                        '-codec', 'copy', '-map', '0', `output2.${extension}`)

        const filesList = [`file output1.${extension}`, `file output2.${extension}`];

        ffmpeg.FS('writeFile', 'filesList.txt', filesList.join('\n'));

        await ffmpeg.run('-f', 'concat', '-safe', '0', '-i', 'filesList.txt',  `outputResult.${extension}`);

        const data = ffmpeg.FS('readRile', `outputResult.${extension}`);

createFFmpeg.js:167 Uncaught (in promise) Error: Oops, something went wrong in FS operation.
    at Object.FS (createFFmpeg.js:167)
    at _callee2$ (ffmpegTest.js:59)<== my file
    at tryCatch (runtime.js:45)
    at Generator.invoke [as _invoke] (runtime.js:271)
    at Generator.prototype.<computed> [as next] (runtime.js:97)
    at asyncGeneratorStep (asyncToGenerator.js:3)
    at _next (asyncToGenerator.js:25)
    at es.es6.js:240
    at batchedUpdates$1 (react-dom.development.js:24353)
    at batch (es.es6.js:240)

[KathRains]

For those who can face the same problem. I found the working solution:

        await ffmpeg.run('-i', name, '-ss', '0', '-to', start.toString(), '-c', 'copy', 'output1.mov');
        await ffmpeg.run('-i', name, '-ss', (start + length).toString(), '-c', 'copy', 'output2.mov');

        
        const filesList = [`file output1.mov`, `file output2.mov`];
        ffmpeg.FS('writeFile', 'filesList.txt', filesList.join('\n'));

        await ffmpeg.run('-f', 'concat', '-safe', '0', '-i', 'filesList.txt', '-c', 'copy', 'result.mov');
        const data = ffmpeg.FS('readFile', 'result.mov');

[seiwonpark]

BE CAUTIOUS to use ffmpeg options.

You might have put mismatching options in ffmpeg.run()

I was facing this issue because of following options.

await ffmpeg.run(
    '-i', 'video.mp4',
    '-r', '20',
    '-vf', // 'scale=500:-1',            <--------       I had to pass value for `-vf`
    '-f', 'gif',
    fileName
);