The first signs of music and video as one was in 1894.
"In 1894, sheet music publishers Edward B. Marks and Joe Stern hired electrician George Thomas and various performers to promote sales of their song "The Little Lost Child". Using a magic lantern, Thomas projected a series of still images on a screen simultaneous to live performances. This would become a popular form of entertainment known as the illustrated song, the first step toward music video." (Source): WikipediaAs time has moved on bands have started to use their music videos as a way of advertising and promoting their songs, rather than for the entertainment aspects and purpose's.
An example of this would be 'Lady Gaga - Telephone.'
- Diet Coke - Cans are used as rollers in Lady Gaga's hair
- Virgin Mobile - A phone is snatched from a butch prison yard toughie's waistband
- Wonder Bread & Miracle Whip - Those are the magic ingredients in sandwiches made by Gaga
- Polaroid - A camera is used to photograph Beyonce
This helps show that music videos can be used to help promote other products, such as; Lady Gaga drinking a can of coke in one of her videos. As well as promoting their own music. This is called 'product placement.' Product placement grows in Music Videos link
MTV was formed in 1981 is an American network based in New York. It was brought in to try and help music artists promote their music and was a massive success, as it still is today.