WizzardX's guide for extracting audio from YouTube videos
From A Reyvateil's Wiki
1) Download the video in the highest available quality:
youtube-dl -bt 'http://www.youtube.com/watch?v=LccFzYsrVY0'
This downloads a file called "Ar_Tonelico_II_JPN_Final_Boss_P03_05_Replekia_Battle-LccFzYsrVY0.mp4"
2) Extract audio, and convert to mp3 (btw, it's originally in aac format, but you asked for mp3):
ffmpeg -i Ar_Tonelico_II_JPN_Final_Boss_P03_05_Replekia_Battle-LccFzYsrVY0.mp4 \ Ar_Tonelico_II_JPN_Final_Boss_P03_05_Replekia_Battle-LccFzYsrVY0.mp3
