Music Video Syndrome

Back in the early 1980s, when MTV was new, people who directed music videos tried to catch eyes by cutting (shifting the scene) quickly to the rhythm of the music and using other special effects. The movement in them also tended to be in time to the song because doing it any other way would distract from the music.

Music Video Syndrome is when media that are not music videos are cut to resemble music videos. The actions onscreen correlate and are edited to be in rhythm with the song playing in the background, which is usually something recognisable and popular, though classical music can be used instead (in particular 1812 Overture, the Ode to Joy, "Fur Elise," or Amazing Freaking Grace). Bonus points if the theme of the lyrics relate to the actions being shown onscreen. The plot may progress through this song, but this may happen through actions that are timed perfectly to the song being played.

This first became noticeable in television shows in The Eighties. It became more common when TV production studios and record companies became closely related: not only was it easier to get rights to the song, but using the song was Product Placement: a show with Music Video Syndrome can sometimes sell songs as well as actual music videos.

Commercials and trailers get Music Video Syndrome, too - after all, music videos are commercials. They just have value of their own. Commercials often deliberately invoke this; you can tell if that's happened when the artist is credited at the beginning of the commercial.

Film

 * Quentin Tarantino films can invoke this with use of pop-culture references and general oddness. Most famous is the "Little Green Bag" sequence from Reservoir Dogs.
 * Averted as well by the film Cast Away. While Tom Hanks's character is stranded on the desert island (the bulk of the movie), there is no background music at all.
 * Rocky III and IV, during opening sequences and Training Montages.
 * Lampshaded in the SpongeBob SquarePants episode "The Krusty Krab Training Video", with similar BGM.
 * The Hangover has this, especially in the first act.
 * "Head Over Heels" during Donnie Darko's first scene in the school.
 * Also "Never Tear Us Apart" over the opening scene in the director's cut, though the theatrical cut replaced this with Killing Moon since Richard Kelly couldn't afford the rights to the former. And again with the dance scene cut to match "West End Girls" perfectly, though for the same reason the song is replaced with "Notorious" in both versions.
 * Very noticeable in Catwoman during the basketball scene.
 * Basically all of Moulin Rouge.
 * Zack Snyder's Sucker Punch fit this trope nicely, especially in the opening sequence, the prologue of the film set to lead actress Emily Browning's cover of "Sweet Dreams (Are Made of This)" by the Eurythmics.

Live-Action TV

 * Cold Case. Mostly appears in flashbacks, using period music from the time the current case takes place in, with the exception of one ending song (also using period music).
 * Just about every scripted drama on MTV, fittingly enough.
 * Found a lot on Scrubs.
 * Subverted in an episode of Lost, when morose music plays over the end of one episode, only to shut off abruptly. The show then cuts to Hurley, who curses, as the batteries on his CD player have run out. The episode closes in silence except for the sound of the waves.
 * The show did end on a "music video" a few times in the first half of the first season, and once using "These Arms of Mine" in season 2. Usually, the music was being played on Hurley's CD player or the turntable in the Swan station.
 * Averted on The Sopranos mostly. David Chase had wanted to only use "in-universe" music, but sometimes music plays with no apparent source. When this does occur, the music underscores and emphasizes the emotional effect. "The Beast In Me" playing over the end sequence and credits of the first episode, for example.
 * An especially good one is the season three premiere's use of the Peter Gunn theme song and "Every Breath You Take" played simultaneously. The two songs have exactly the same beat and work surprisingly well together.
 * As noted before, it happens on House, where almost every episode ends with a song juxtaposed with showing the patient of the week cured from the mysterious disease, although it is sometimes averted with House himself playing either the guitar or the piano in the end of certain episodes.
 * Battlestar Galactica averts the trope by almost never using music outside of that composed for the series. (One of the few exceptions before the third season was using the old TV show's theme as the Colonial Anthem.) The trope is subverted in the two-part season 3 finale, when hear a chord repeated several times that no one else can—including, at one point, from a radio that's just producing static. (At one point,   yells out "Will someone shut that frakking music off?!", in a scene that you can't look away from, like a trainwreck.) Eventually, the chord blooms into a full-fledged song, and they discover it's . The main riff of this version is present in the score from the first episode of the season, though, and is led up to by a surrealistic, almost hippie-commune-drug-fueled-orgy treatment of the song in the scene immediately preceding it. It should be noted that Ronald Moore, the head writer, had wanted to include the song on the show for some time. All of this together manages to play straight, avert, subvert, and justify the trope.
 * Three-quarters of all scripted shows on the WB, UPN, and/or CW, ever.
 * "Tonight's artists featured on Smallville include...."
 * Supernatural, however, has managed to avert this trope. The creator, Eric Kripke, refuses to use what he calls the "anemic pop songs" that the other shows use in montages at the ends of their episodes. They only use classic rock, which the fans really enjoy. They will have an opening montage, but it's not cut to fit the rhythm of the background music, which is just that: background music.
 * Mocked on an episode of Conan O'Brien, where a handsome young intern repeatedly enters the set to "Welcome To My Life" by A Simple Plan, completely with the camera zooming in on his and Conan's longing expressions...and then the intern says something mundane, and leaves.
 * The season 2 finale of Millennium featured an entire act portraying Laura Means' mental breakdown, arranged as a music video for Patti Smith's "Land".
 * CSI did this with subjects like autopsies and lab work.
 * Quite common on Alias, and used to varying effect, from generic slow-motion action scene to genuinely awesome or heartfelt moments. One instance of this was in the season 1 finale, when, with all the audio fading out and the haunting music of Natalie Merchant's "My Skin" playing over it.
 * Averted by Joss Whedon in the naturalistic Buffy episode "The Body" in which no music can be heard (save for a few ambient tuba arpeggios) and each act is essentially comprised of a single scene.
 * Other episodes of Buffy and Angel, however, played the trope straight.
 * Miami Vice was pitched as "MTV Cops", and turned this into an art form, with two similar sequences in the Pilot - one in the first half and one in the second half.
 * Sons of Anarchy is a little guilty of this.
 * Freaks and Geeks often justified its use of this. The show featured a lot of scenes set to music, but it was usually music that the characters were declared fans of and often was important to the plot (ie. Lindsay and The Grateful Dead, Nick and Rush). Setting the show in 1980 meant the creators could use the music they loved growing up and keep the network from shoehorning in the latest songs from the hottest acts.
 * Mostly averted by The Wire, which had a rule that artificial music could only appear in the final montage sequence of each season. Though apparently it took them a little while to nail down, as an early episode features drug kingpin Avon Barksdale approaching a group of his gang members with music playing from nowhere.
 * Homicide: Life on the Street used this quite often, particularly in Seasons Three to Six. Many of the songs worked well and were made of a nice combination of obscure classics, modern hits and classic rock.
 * The Big Bang Theory parodies this trope, with Sheldon and Raj dramatically staring at a board, whilst the camera moves to the tune of "Eye of the Tiger".
 * Parodied on Thirty Rock after Angie's reality show fakes a reconciliation with Liz and Tracy after a fight using (naturally) a musical montage.
 * Taken Up to Eleven in True Blood, where music rises dramatically for about twenty seconds and then fades bluntly out again as

Professional Wrestling

 * Common in Professional Wrestling, with its entrance music, promotional packages, flashbacks, and so on. WWE actually licenses a reasonably popular song for each of its pay-per-views, two in the case of Wrestlemania.

Web Comic

 * Homestuck. Pretty much any panel with a [S] in the name will create an instant simultaneous Crowning Moment of Awesome/Crowning Music of Awesome combo.

Web Original

 * This series of online comic videos seems to be slipping in and out of this trope. Compare this video with this one.

Western Animation

 * The Simpsons has been doing this a lot in the more recent seasons, what seems like once per episode at this point.