Download and process YouTube videos with nbb

ytdl.cljs

(ns ytdl
  (:require ["ytdl-core$default" :as ytdl]
            ["fluent-ffmpeg$default" :as FFmpeg]
            ["fs" :as fs]
            [promesa.core :as p]))

(defn save 
  "Fetches a YouTube url and writes it to a file."
  [url name]
  (p/let [stream (ytdl url)]
    (.pipe stream (fs/createWriteStream name))))

(defn ffmpeg 
  "Creates ffmpeg command to extract audio and apply dynamic compression."
  [url threshold ratio makeup]
  (.audioFilters (FFmpeg url)
                 (js->clj
                  {:filter  "acompressor"
                   :options {:threshold (str threshold "dB")
                             :ratio     ratio
                             :makeup    makeup}})))

(comment
  
  (ffmpeg "https://www.youtube.com/watch?v=x24fLxur-2o" -40 20 10)

  (save "https://www.youtube.com/watch?v=x24fLxur-2o"  "maps.mp4")
  
  )

ytdl.js

const http = require('http')
const fs = require('fs')
const { PassThrough } = require('stream')
const path = require('path')
const ytdl = require('ytdl-core')
const FFmpeg = require('fluent-ffmpeg')

const stream = function streamify (uri, opt) {
  opt = {
    ...opt,
    videoFormat: 'mp4',
    quality: 'lowest',
    audioFormat: 'mp3',
    filter (format) {
      return format.container === opt.videoFormat && format.audioBitrate
    }
  }

  const video = ytdl(uri, opt)
  const { file, audioFormat } = opt
  const stream = file ? fs.createWriteStream(file) : new PassThrough()
  
  const ffmpeg = FFmpeg(video).audioFilters(
    {
      filter: 'acompressor',
      options: { threshold: '-40dB', ratio: 20,  makeup: 8 }
    }
  )

  process.nextTick(() => {
    const output = ffmpeg.format(audioFormat).pipe(stream)

    ffmpeg.once('error', error => stream.emit('error', error))
    output.once('error', error => {
      video.end()
      stream.emit('error', error)
    })
  })

  stream.video = video
  stream.ffmpeg = ffmpeg

  return stream
}


http.createServer(demo).listen(3000)

async function demo (req, res) {
  try {
    for await (const chunk of stream(`https://www.youtube.com/watch?v=BKHImVMWq3o`)) {
      res.write(chunk)
    }
    res.end()
  } catch (err) {
    console.error(err)
    if (!res.headersSent) {
      res.writeHead(500)
      res.end('internal system error')
    }
  }
}

console.log('open http://localhost:3000 for audio stream')