fluent-ffmpeg merge audio with video

merge-ffmpeg.js

const command = ffmpeg()
const commandArray = []
command.addInput(`./best.mp4`)
command.addInput(`./best2.wav`)
commandArray.push(`[1]volume=0.1[a1]`)
command.addInput(`./voiceover.mp3`)
commandArray.push(`[2]volume=0.9[a2]`)
let ffmpegKeys = '[a1][a2]amix=inputs=2[a]'

commandArray.push(ffmpegKeys)
command.complexFilter(commandArray)
command.addOptions(['-map 0:v', '-map [a]', '-c:v copy'])
.format('mp4')
.on('error', (error) => {
  console.log(error)    
})
.on('end', function() {
  console.log('Merging finished !');
})
.save('./merged.mp4');

like this:

import ffmpeg from 'fluent-ffmpeg'

function merge(video, audio) {
    ffmpeg()
        .addInput(video)
        .addInput(audio)
        .addOptions(['-map 0:v', '-map 1:a', '-c:v copy'])
        .format('mp4')
        .on('error', error => console.log(error))
        .on('end', console.log(' finished !'))
        .saveToFile('merged.mp4')
}
merge('./video.mp4', './audio.webm')

Hi! I get this error, I've been looking for a long time how to merge audio and video and it's taking a while

This is my code:

const audioStream = ytdl(URL as string, {
          filter: 'audioonly',
          quality: 'highestaudio',
        })

        const videoStream = ytdl(URL as string, {
          filter: (format) =>
            format.hasVideo &&
            (format.container === 'mp4' || format.container === 'webm'),
          quality: qualityOption,
        })


        const combinedStream = new PassThrough()

        // Usar ffmpeg para combinar video y audio y enviar la salida directamente al objeto de respuesta (res)
        ffmpeg()
          .input(videoStream)
          .input(audioStream)
          .addOptions(['-map 0:v', '-map 1:a', '-c:v copy'])
          .format('mp4')
          .on('error', (error) => {
            console.error('Error durante la combinación:', error)
            res.status(500).json({ error: 'Error durante la combinación de video y audio' })
          })
          .on('end', () => {
            console.log('Combinación de video y audio completada con éxito.')
          })
          .pipe(combinedStream, { end: true })

        // Transmitir la salida combinada al objeto de respuesta (res)
        combinedStream.pipe(res, { end: true })

        res.setHeader('Content-Type', 'video/mp4')

This is the error:

    at proto.mergeAdd.proto.addInput.proto.input (E:\proyectos\download_mp3\down_media\node_modules\fluent-ffmpeg\lib\options\inputs.js:42:15)
    at downloadMedia (webpack-internal:///(api)/./src/pages/api/downloadMedia.ts:57:91)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)```
    

Basically it is an error because ffmpeg does not allow more than one entry.

any help is welcome, thank's.