sox-example.js

const fs = require('fs');
const {
  spawn
} = require('child_process')
const soxStream = require('sox-stream')

const songPath = './audio/songs/Modern Attempt - TrackTribe.mp3'
const fxPath = './audio/fx/Boo! Sound Effect (128 kbps).mp3'
const output = 'output.mp3'

const inputStream = fs.createReadStream(songPath)
const outputStream = fs.createWriteStream(output)
const main = inputStream
  .pipe(soxStream({
    input: {
      type: 'mp3',
      // volume: 0.8
    },
    output: {
      type: 'mp3'
    }
  }))

const args = [
  '-t', 'mp3',
  '-m', '-',
  '-t', 'mp3',
  fxPath,
  '-t', 'mp3',
  '-'
]

const {
  stderr,
  stdout,
  stdin
} = spawn('sox', args)

stdout.pipe(outputStream)
stderr.on('data', msg => console.log('error', msg.toString()))

main.pipe(stdin)