node command-line script that uses ffmpeg to cut a video into clips in one command

fclips.js

#! /usr/bin/env node

// created by Malcolm Ocean (malcolmocean.com) mid-2021, published Jan 2023
// CC-BY-SA license

// call as fclips.js source.mp4 list.txt
// where list.txt contains lines like
// 59:36 to 1:00:53
// (millis allowed)

const fs = require('fs')
const argv = require('minimist')(process.argv.slice(2))
async function execShellCommand(cmd) {
  console.log(cmd)
  const exec = require('child_process').exec
  return new Promise((resolve, reject) => {
    exec(cmd, (error, stdout, stderr) => {
     if (error) {
       console.warn(error || stderr)
       return reject(error || stderr)
     }
     // sometimes stderr even when goes fine
     resolve(stdout || stderr)
   })
  })
}


async function ffmpegClip (inputFile, outputFilename, ss, t) {
  const copyMaybe = /\.(mp3|m4a|aac|ogg)$/.test(inputFile) ? '-c copy' : ''
  return execShellCommand(`ffmpeg -ss ${ss} -i '${inputFile}' -t ${t} ${copyMaybe} ${outputFilename}`)
}

async function ffmpegConcat (inputListFilename, outputFilename) {
  return execShellCommand(`ffmpeg -f concat -i '${inputListFilename}' -c copy "${outputFilename}"`)
}

if (!argv._.length) {
  return console.log(`How to use: 
    fclips media.mp4 list.txt

    where list.txt has the format
    0:00 to 10:34
    15:29 to 1:02:11
    `)
}
console.log("argv", argv)
const list = String(fs.readFileSync(argv._[1])).split('\n').filter(line => !line.startsWith('#'))
const randTempName = Math.random().toString('36').replace(/[0-9.]/g, '').substr(0,5)
const inputFilename = argv._[0]
console.log("inputFilename", inputFilename)
const clipListFilename = randTempName + '_list.txt'
console.log("clipListFilename", clipListFilename)
const ext = inputFilename.replace(/.*\./, '')
console.log("ext", ext)

function hmsToSeconds (hms) {
  const millis = /\./.test(hms) ? parseInt(hms.replace(/.*\./, '')) : 0
  hms = hms.replace(/\..*/, '')
  const a = hms.split(':').reverse()
  return (+a[2] || 0) * 60 * 60 + (+a[1]) * 60 + (+a[0]) + millis/1000
}

async function doStuff () {
  if (argv.nodelete) {console.log('no delete')}
  let totalTime = 0
  let outputFiles = []
  for (var n in list) {
    const line = list[n].trim()
    if (!line) {continue}
    if (line.startsWith('#')) {continue}
    const ss = line.replace(/ +to .*/, '')
    const to = line.replace(/.* to +/, '')
    const t = hmsToSeconds(to) - hmsToSeconds(ss)
    totalTime += t
    const outputFilename = `${randTempName}_${n}.${ext}`
    outputFiles.push(outputFilename)
    await ffmpegClip(inputFilename, outputFilename, ss, t)
  }
  console.log('totalTime = ' + totalTime + ' seconds')
  const clipList = outputFiles.map(x => 'file ' + x).join('\n')+'\n'
  fs.writeFileSync(clipListFilename, clipList)
  const finalOutputFilename = `clips from ${inputFilename}`
  await ffmpegConcat(clipListFilename, finalOutputFilename)
  if (argv.nodelete) {return}
  for (var filename of outputFiles) {
    await execShellCommand(`rm ${filename}`)
  }
  await execShellCommand(`rm ${clipListFilename}`)
}

doStuff().then(() => console.log('complete'), err => console.log('err', err))