Using youtube-dl to download audio and convert it to m4a with ffmpeg. (the file downloaded as it is won't play on iTunes for some reason. So I decided to convert it with ffmpeg with -acodec copy)

youtube2audio.sh

#!/bin/bash

# Setting default quality to 256kb
quality=141

# See if url is provided
url=$1
if [ -z $url ]; then
  echo "Need a URL"
  exit
fi

# See if 256kb is available. If not, setting quality to 128kb.
is256kb=$(youtube-dl -F $url | grep 141)
if [ -z is256kb ]; then
  echo "256kb not available. Downloading lower quality..."
  quality=140
fi

# Getting and setting the title
original=$(youtube-dl --get-filename -f $quality $url)
title=${original:0:${#original}-16}".m4a"
echo "Processing $title"

# Download the audio file
youtube-dl -f $quality $url > /dev/null

# Converting the audio file to playable file with ffmpeg and then move it to Music folder
ffmpeg -v 0 -i "$original" -acodec copy "$title"

mv "$title" ~/Music
rm "$original"

echo "$title created."