YouTube.js/examples/download/ffmpeg/index.js

/**
 * Mux audio and video into a single stream.
 * 
 * This example requires ffmpeg-static package or some other ffmpeg binary installed on your system.
 */

// import Innertube from 'youtubei.js';
const Innertube = require('../../../lib/Innertube');
const ffmpeg = require('ffmpeg-static');

const cp = require('child_process');


(async () => {

  // instantiate the library
  const yt = await new Innertube();

  // get video info
  const info = await yt.getInfo('bUHZ2k9DYHY');

  // get the best video stream
  const video = info.download({
    quality: 'bestefficiency',
    format: 'any',
    type: 'video',
  });

  // get the best audio stream
  const audio = info.download({
    quality: 'bestefficiency',
    format: 'any',
    type: 'audio',
  });

  // create a ffmpeg instance
  const ffmpeg_process = cp.spawn(ffmpeg, [
    // remove ffmpeg's banner spam
    '-hide_banner',
    // inputs
    '-i', 'pipe:3',
    '-i', 'pipe:4',
    // map the streams
    '-map', '0:a',
    '-map', '1:v',
    // keep the original encodings
    '-c', 'copy',
    // output format
    '-f', 'matroska',
    // force write to file 
    '-y', 'stream.mkv'
  ], {
    windowsHide: true,
    stdio: [
      // inherit stdio, stdin and stdout
      'inherit', 'inherit', 'inherit',
      // pipe:3, pipe:4
      'pipe', 'pipe'
    ]
  });

  // pipe the streams to ffmpeg
  audio.pipe(ffmpeg_process.stdio[3]);
  video.pipe(ffmpeg_process.stdio[4]);

})();