Maybe ，you can try as

  const ffmpeg = spawn('ffmpeg', [
    '-i', 'pipe:0',
    '-c:v', 'libx264',
    '-preset', 'veryfast',
    '-maxrate', '3000k',
    '-bufsize', '6000k',
    '-pix_fmt', 'yuv420p',
    '-g', '50',
    '-f', 'flv',
    'rtmp://a.rtmp.youtube.com/live2/MY_KEY'
  ]);

remove the first '-f flv'