History of music videos..

1926-1959: Talkies, soundies and shorts

• Featured many bands, vocalists and dancers.
• Sing-along short cartoons called Screen Songs, which invited audiences to sing along to popular songs by "following the bouncing ball", which is similar to a modern karaoke machine.
• Early 1930s cartoons featured popular musicians performing their hit songs on-camera in live-action segments during the cartoons.
• in the mid-1940s, musician Louis Jordan made short films for his songs, some of which were spliced together into a feature film Lookout Sister.
• Musical films were another important precursor to music video, and several well-known music videos have imitated the style of classic Hollywood musicals from the 1930s to the 1950s. 

1960–1973: Promotional clips and others

• Late 1950's the Scopitone, a visual jukebox, was invented in France. Many french artists produced short films using this.
• In 1964, The Beatles starred in their first feature film.
• The Rolling Stones appeared in many promotional clips for their songs in the 1960s.
• During late 1972–73 David Bowie featured in a series of promotional films directed by pop photographer Mick Rock.
• Country music historian Bob Millard wrote that JMI had pioneered the country music video concept by "producing a 3-minute film" to go along with Williams' song.

1974–1980 – Beginnings of music television

• The Australian TV shows Countdown and Sounds, both of which premiered in 1974, were significant in developing and popularizing the music video genre in Australia and other countries.

• The long-running British TV show Top of the Pops began playing music videos in the late 1970s, although the BBC placed strict limits on the number of 'outsourced' videos TOTP could use. Therefore a good video would increase a song's sales as viewers hoped to see it again the following week.
• In 1980, David Bowie scored his first UK number one in nearly a decade thanks to director David Mallet's eye catching promo for "Ashes to Ashes".

1981–1991: Music videos go mainstream

• In 1981, the U.S. video channel MTV launched, airing "Video Killed the Radio Star" and beginning an era of 24-hour-a-day music on television.
• In 1983, one of the most successful, influential and iconic music videos of all time was released: the nearly 14-minute-long video for Michael Jackson's song "Thriller", directed by John Landis.
• On March 5, 1983, Country Music Television, or CMT, was launched,created and founded by Glenn D. Daniels and uplinked from the Video World Productions facility in Hendersonville, Tennessee.
• The Canadian music channel MuchMusic was launched in 1984.
• In 1984, MTV also launched the MTV Video Music Awards, an annual awards event that would come to underscore MTV's importance in the music industry.
• In 1985, MTV launched the channel VH1, featuring softer music, and meant to cater to an older demographic than MTV. MTV Europe was launched in 1987, and MTV Asia in 1991.
• Another important development in music videos was the launch of The Chart Show on the UK's Channel 4 in 1986. This was a program which consisted entirely of music videos.

1992–2004: Rise of the directors

• In November 1992, MTV began listing directors with the artist and song credits, reflecting the fact that music videos had increasingly become an auteur's medium.
• Two of the videos directed by Romanek in 1995 are notable for being two of the three most expensive music videos of all time: Michael and Janet Jackson's "Scream", which cost $7 million to produce, and Madonna's "Bedtime Story", which cost $5 million.

2005–present: The Internet becomes video-friendly

• 2005 saw the launch of the website YouTube, which made the viewing of online video much faster and easier; Google Videos, Yahoo! Video, Facebook and MySpace's video functionality, use similar technology.
• n 2009, 30 Seconds to Mars' music video "Kings and Queens" was uploaded to popular video-sharing website YouTube on the same day of its release, where it has garnered over one hundred million views.

Now, many music videos are used to sell the song or the artist, especially mainstream artists.