History of music videos

In 1894 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.

Music video's have changed a lot over the years, the first music video ever to be released as a promotional video was Bohemian Rhapsody, and that was released in 1975.
Over the years the quality of the music videos has changed, now when watching music videos on YouTube their is an option for you to change the quality of the video ranging from 144p 1080p.  

Compare this video -

To this one -

You can tell the difference straight away from watching the two clips.