Passing Pipe Streams to Concat - Demux

const express = require('express')
const mongoose = require('mongoose')
const path = require('path')
const { spawn } = require('child_process')
const { v1: uuidv1 } = require('uuid')
const fs = require('fs')

const allVideoMergeRouter = express.Router()

allVideoMergeRouter.post('/', (req, res) =>
{
    const videoPaths = req.body['video_file_path_list']
    if(!videoPaths || videoPaths.length === 0)
    {
        return res.json({
            status: "error",
            message: "File paths missing"
        })
    }

    const gridfsbucket = new mongoose.mongo.GridFSBucket(mongoose.connection.db, {
        chunkSizeBytes: 1024,
        bucketName: 'filesBucket'
    })

    const mergedVideoName = uuidv1() + '.mp4'
    const mergedVideoPath = 'public/upload/' +  mergedVideoName

    let myList = ''
    let pipeCount = 3
    const pipes = ['pipe', 'pipe', 'pipe']

    const finalVideoStreams = videoPaths.map(videoPath => {
        if(!videoPath.startsWith('public/upload/'))
        {
            return res.json({
                status: "error",
                message: "File not found"
            })
        }
        else if(path.extname(videoPath) !== '.mp4')
        {
            return res.json({
                status: "error",
                message: "Video File is not a .mp4 file"
            })
        }
        const videoStream = gridfsbucket.openDownloadStreamByName(videoPath.substring(14))
        const cmd1 = spawn('ffmpeg', ['-i', 'pipe:0', '-acodec', 'aac', '-vcodec', 'libx264', '-s', '1920x1080', '-r', '60', '-video_track_timescale', '90000', '-f', 'ismv', 'pipe:1'],
        {stdio: ['pipe', 'pipe', 'pipe']})
        videoStream.pipe(cmd1.stdin)
        myList = myList + "file 'pipe:" + pipeCount + "'\n"
        pipeCount++
        pipes.push('pipe')
        return cmd1.stdout
    })

    fs.writeFileSync(__dirname + '/../data/' + mergedVideoName + '.txt', myList)

    const command = spawn('ffmpeg', ['-f', 'concat', '-safe', '0', '-protocol_whitelist', 'file,pipe', '-i', 'data/' + mergedVideoName + '.txt', '-c', 'copy', '-f', 'ismv', 'pipe:1'], {
        stdio: pipes
    })
    for(let i = 3; i<pipeCount; i++)
    {
        finalVideoStreams[i-3].pipe(command.stdio[i])
    }

    command.stdout.pipe(gridfsbucket.openUploadStream(mergedVideoName)).
    on('error', err => {
        return res.json({
            status: 'error',
            message: err.message
        })
    }).
    on('finish', () => {
        return res.json({
            status: "ok",
            message: "Merged All Video Successfully",
            file_path: mergedVideoPath
        })
    })

    command.stderr.on('data', (dt) => {
        console.log('data: ' + dt)
    })
})

module.exports = allVideoMergeRouter