Andrew Goodwin identified a number of key features which distinguish the music video as a form, before you understand his theory you need to understand some key terminology. If you click on the key terms you will be taken to videos which best illustrate these terms
Illustrate: Images used to represent the meanings of the lyrics and genre (this is the most common feature of a music video) this is very often literal.
Disjuncture: When the meaning of the song is completely ignored
Amplify: Meanings and effects are manipulated and constantly shown throughout the video and shown to the audience (basically repetition).