I did something similar for myself a while back, to put the transcript in a text file. It's a five line bash script that uses youtube-dl to get the closed captions and cleans up the formatting.

  #!/bin/bash
  link="$1"
  fn="captions"
  youtube-dl --output $fn.%(ext)s --write-auto-sub --skip-download $link
  sed '/-->/d' $fn.en.vtt | sed '/<c>/d' | sed '/^[[:space:]]\*$/d' | uniq > $fn.txt