1. youtube-dl -a lista.txt // Download all lectures with youtube-dl from file `lista.txt`
2. for f in *.mp4; do ffmpeg -i "$f" -vn "$(basename "$f" .mp4).mp3"; done // convert all mp4 to mp3
(2. ffmpeg -i input.mp4 -f mp3 -ab 192000 -vn output.mp3)
3. ffmpeg -i output.mp3 -af "highpass=f=200, lowpass=f=3000" output_clean.mp3 // reduce noice (https://superuser.com/questions/733061/reduce-background-noise-and-optimize-the-speech-from-an-audio-clip-using-ffmpeg)
4. ffmpeg -i output_clean.mp3 -af silenceremove=1:0:-50dB output_stripped.mp3 // remove silent bits from the mp3
5. normalize audio?? (https://superuser.com/a/323127/643639)

6. PROFIT??