As @spaceballoon said, it's just like youtube. You can make a music video if you wish (or have the time/skill), but people don't seem to mind if you just upload an album cover or eye catching related thumbnail. Don't forget to use a WAV when making the video (when you import audio) because if you import an mp3 into a video project your editing software will convert it back to WAV then encode it again when rendering, so you'll lose quality.