The Function of a Music Video

The function of a music video is to convey a message across to the audience that may not be entirely obvious in the song, or something that the artist want's to bring in that creatively that wasn't necessarily in the song.
Most music videos contain:

• A Narrative - The story within the video that expresses the song so the audience can watch the song visually
• The singer/band - So the fan-base can see the artist and/or a new audience can see who the video is by
• Advertising - There has been a rise in music videos selling out to big brands so the brands can get their names out there and the artist gets paid £££££££££

Depending on the genre there are common features in music videos

Rock

Rock videos tend to stay in a single set, and feature just the band, playing their instruments. 

The lead singer is normally at the front, for the focus of the audience.

This is a classic format that's been done from the Rolling Stones to Green Day.

Pop
Pop videos tend to be more spontaneous compared to rock. If there isn't a set narrative the artist may go for a more 'artistic' approach e.g. Madonna, Gaga, Miley Cyrus, Cher. My Heart Will Go On & Applause both feature focus on the main singers whilst things happen around them. Clips from the Titanic brake up Celine Dion's shots whereas weird stuff and dancing breaks up Lady Gaga's.

R&B

R&B videos tend to have more of a sexualised nature about them. This could partly be due to the fact a lot of the songs are about sex/drugs/clubs/cars and whatnot. On the left we see Frank Oceans video Novacane. Although he has women on a bed behind him, the effects are so heavy that you can barely see them, along with a Giant Panda (to replicate how high he is). On the right however Usher has heavy scenes of slightly aggressive sexual stuff. They contrast quite a lot.

Iconic Music Videos

These two videos are very iconic now. Michael Jacksons Thriller (Left) is normally #1 on most websites charts of iconic music videos. Beyonce's Single Ladies was made in 2009 so it's still very new(ish).
Both videos have iconic dances so maybe that's the key for a huge video.

First Music Video

This was the 'first' music video ever filmed, edited and released. The video is Bessie Smith - St Louis Blues.
The video was released in 1929 for a short film that she featured in and the video, like My Heart Will Go On features Bessie singing along with clips from the film.