Use this to download this category as MP3 with youtube-dl:
declare -a list=("https://www.youtube.com/channel/UCgkhWgBGRp0sdFy2MHDWfSg" "https://www.youtube.com/user/numberphile/videos" "https://www.youtube.com/channel/UCYO_jab_esuFRV4b17AJtAw/videos" "https://www.youtube.com/channel/UC1_uAIS3r8Vu6JjXWvastJg/videos" "https://www.youtube.com/channel/UCpbU7mXDloketKRA92AcW7Q/videos" "https://www.youtube.com/channel/UCpCSAcbqs-sjEVfk_hMfY9w/videos")
for val in ${list[@]}; do
name=$(basename "$val")
if [ -e $name ]
then
continue
fi
mkdir $name
cd $name
youtube-dl -f mp3-128 $val
cd ..
done
