Diegetic Switch

A pop song or other piece of music is being played diegetically (that is, it's in the scene, played on someone's radio or otherwise). As the scene fades out, the music shifts to a non-diegetic version of... the same song that was just playing.

Contrast Left the Background Music On.

Anime

 * Sayuri's recital in The Place Promised in Our Early Days starts off as just her playing in the classroom, but shifts to the full version of her theme tune after the first verse.
 * Five Centimeters Per Second has the famous J-ballad "One More Time, One More Chance" playing first muffled through tinny speakers in a convenience store and then at full clarity volume through the ending montage.
 * Kara no Kyoukai tends to do this.
 * Kyoske's violin-playing in episode 5 of Puella Magi Madoka Magica. Interestingly, when the music starts, only the violin (actually, a viola) is heard; when Kyoske stops playing and the switch occurs, the track continues into a full orchestra.

Films -- Animation

 * The Disney dub track for Laputa Castle in The Sky has this happen to Pazu's bugle call.
 * Shrek 2 does this near the climax. The Fairy Godmother sings "Holding Out for a Hero" at the grand ball to celebrate Princess Fiona's wedding. Then the camera cuts to Shrek, Donkey, and Puss in Boots Storming the Castle, with the song continuing to play as background music. The point of view switches back and forth for the entire duration of the song.
 * Nine has Somewhere Over the Rainbow start playing on a scratchy phonograph operated by 3 and 4 after, and the song gradually loses its phonograph-like qualities as the scene continues until it is heard free of the dampening, static, and occasional skipping that occur when it first starts up. It also plays for a bit free of in-world sound effects over it. This continues while 5 discovers that  , leading to somewhat humorous/Nightmare Fuel-eriffic Soundtrack Dissonance while  . The song ends the instant the phonograph's needle is knocked off.
 * The songs "You'll Be In My Heart" and "On My Way" from their respective films Tarzan and Brother Bear both start out being sung by one of the film's main characters, but when the chorus starts, it moves into the background and is now sung by an offscreen singer. Curiously enough, both films had their songs written by Phil Collins.
 * The ending song from Mulan starts out being sung by Mushu and the Fa family ancestors, but then segues into the film's closing credits.
 * "Sun Do Shine (reprise)" from Rock a Doodle.

Films -- Live-Action

 * In Interview With the Vampire, Lestat turns on the radio at the end to start the end credits music. Naturally, it's "Sympathy for the Devil".
 * At the end of Clerks II, the song "Misery" by Soul Asylum is actually played from a stereo from off camera and only switches to non-diagetic once the credits kick in.
 * Happens several times in Love Actually, most notably in the scene where the Prime Minister dances to the radio.
 * "That's How You Know" in Enchanted probably counts: The musical accompaniment starts as being just a couple of street musicians, but quickly expands to a full orchestra without one actually being present.
 * Return of the Jedi ends with a celebratory song by the Ewoks, which blends into a glorious choral crescendo well out of the little aliens' vocal range. (At least it used to.)
 * Stranger Than Fiction has a beautiful case with "Whole Wide World". The protagonist is playing and singing it for his would-be girlfriend. When the audio cuts to the original Wreckless Eric version, loud and triumphant.
 * This happens in Star Trek II the Wrath of Khan at the end of Spock's funeral, in which Scotty plays "Amazing Grace" on the bagpipes, and the tune is taken up by the soundtrack as the scene cuts to an exterior of the ship and Spock's casket being fired into space.
 * The new Star Trek also does this. Young Kirk fires up some Beastie Boys on his uncle's "antique" car's stereo. The music continues even after said car has fallen into a quarry.
 * The Welsh lullaby in Empire of the Sun goes from being sung by Christian Bale's character to playing with choral backup after the character has stopped singing.
 * Last Action Hero may have lampshaded this. Slater interrupts a conversation to notice the background music on the radio. (Bringing closure to one of the movie's running gags, it's Mozart.) It hits crescendo at the following scene change.
 * Even better, the hard rock playing during one of the chase scenes is coming from Slater's tape deck -- and he changes the tape mid-chase!
 * Grosse Pointe Blank goes from diegetic to nondiegetic and back again. Martin Blank's car radio is playing the sentimental beginning of "Live and Let Die" (the Paul McCartney song from the movie) as he pulls up to his childhood home. Stopping the car, he looks up and sees in shock that the house has been turned into a convenience store. The background music blasts Axl Rose's screaming metal version of "Live and Let Die". As Martin wanders into the store, the metal BGM is replaced with the store's Muzak version of the same song.
 * In John Woo's The Killer, Jenny's song from near the beginning of the movie is played on the soundtrack in instrumental several scenes later when Ah Jong saves the blinded Jenny from the muggers and he's telling her about how not everyone is untrustworthy. It plays again for Inspector Li after he is taken off the case, signifying that he's come to care about Jenny as well.
 * In the original Highlander Movie, Kurgan sings a very bad rendition of Frank Sinatra's "New York, New York", which then segues into a Queen version of the song. (For the record, there is no full Queen version of the song. The Highlander snippet is all that's known to exist.)
 * Happens twice in The Cable Guy. While dueling with Matthew Broderick at Medieval Times, the Cable Guy references a Star Trek episode and begins humming the soundtrack. The film's soundtrack quickly picks it up. Later, the Cable Guy sticks Owen Wilson's mouth over a hand dryer, says he looks like Dizzy Gillespie, and starts singing "Salt Peanuts," causing the actual song to start playing on the soundtrack.
 * Occurs in the The Hangover with the song "Who Let The Dogs Out".
 * Evil Aliens has one of the characters climbing into a combine harvester, and putting on a tape of "Motivational Farming Music", leading to a slightly distorted rendition of The Wurzels. Once the song hits the chorus, it goes from being just on the tape to being the scene's background music as well. It doesn't end well (very much NSFW).
 * The seventh Harry Potter movie, Harry Potter and The Deathly Hallows, does this rather well, actually.
 * In Top Gun, Goose is playing and singing "Great Balls of Fire" and then the scene cuts to Maverick and Charlie riding a motorcycle while the Jerry Lee Lewis version plays as nondiegetic music.
 * Done in Sahara during the boat trip along the niger river. The music goes from soundtrack, to the moored boat's radio. Later, after the heroes launch the boat again, the different tune on the radio shifts into soundtrack once more as the boat speeds away along the river.
 * xXx has Rammstein's "Feuer Frei!" in the background of a chase scene -- and when the spy runs through a doorway in an alley he's suddenly in the middle of a Rammstein concert, and guess what they're playing?
 * Reds has this with the song "I Don't Want to Play in Your Yard," where a character is singing it and playing it on a banjo. Cue to the next scene, where it's played by an orchestra, in a different key, with a shot of Louise and Eugene walking on the beach.
 * The 2002 The Importance of Being Earnest opens with Algernon playing the movie's theme tune on a piano, which quickly flows into a full orchestra playing the same theme as the background to a chase scene.
 * Tony Gatlif does this in both Korkuro and Gadjo Dilo.
 * A variation of this in The Sorcerers Apprentice. While trying to impress a girl, Dave (the titular apprentice and a Hollywood Nerd) rigs tesla coils to discharge at a cage with Dave and the girl inside. The discharges make sounds that turn out to be playing "Secrets" by OneRepublic, a song previously heard on the radio. The actual song quickly picks up in the background, not through the radio this time.

Live-Action TV

 * Lost is fond of this. Three Dog Night's "Shambala" was played as Source Music (on an 8-track in the Volkswagen bus) in "Tricia Tanaka is Dead", and then it faded into an orchestral version of same as background music. They did the same with "La Mer" when Shannon sang it at the end of "Whatever the Case May Be". In "One of Us," Petula Clark's "Downtown" goes from playing on Juliet's CD player to playing non-diegetically over a montage of ensuing events. In season six's episode "Sundown" we have Claire singing "Catch a Falling Star" and then later a spooky version is played during a slo-mo sequence.
 * In the Top Gear Bolivia special, Jeremy Clarkson brings along his iPod. During one driving segment, he starts up a song (ostensibly Will Young's "Grace"), which switches into full-blown background music when the view switches from inside the car to outside. (Clarkson having a crush on Will Young is an in-program joke, so this may be a little editorial humor.)
 * Something similar happens in the Vietnam special, in which James May's off-key rendition of "Little Honda" is thankfully drowned out by the Beach Boys' version of the real thing.
 * And in the Botswana special, during a montage of Richard tearfully trying to fix his beloved (waterlogged) Oliver, a sad song begins playing in the background... And then the camera zooms out and you see that it's coming from Hammond's walkie-talkie, and it's actually Jeremy playing tragic songs on what appears to be an ipod. He and James then giggle and howl along to the music, explaining Hammond's frown.
 * "Hold On I'm Coming" by Sam & Dave in the pilot episode of White Collar. It starts out playing on a cassette in the truck the protagonist steals after escaping from prison, then gets taken up by the soundtrack after the camera cuts to an exterior shot of the truck.
 * Bones: in "The Goop on the Girl", Angela turns up the radio to get an annoying intern to shut up. The song playing, "Snowfall" by Ingrid Michaelson, then becomes the soundtrack for the montage of Angela sculpting the likeness of a suspect.
 * The episode "Someone to Watch Over Me" of Battlestar Galactica Reimagined used this trope quite a bit, when a pianist's music would suddenly be heard underscoring other scenes.
 * Inverted in Going Straight. As Fletcher finally steels himself to start an honest job for the first time in his life, the suitably dramatic overture to The Yeomen of the Guard accompanies his determined walk to his new workplace. Cut to the workplace in question, where the radio is playing the same piece.
 * In "Chuck vs. the Best Friend", Jeff and Lester ("Jeffster") are performing a Hollywood Tone Deaf cover of Toto's "Africa." We then see an important moment between two other characters, and suddenly instead of hearing Lester we're hearing Toto, being played as background music.
 * Done again in "Chuck vs. the Ring", in which it transitions from the Jeffster! (and backing string quartet) version of "Mr. Roboto" to a version orchestrated by the house composer, to the original Styx version, back to Jeffster.
 * Non-Jeffster example: the use of "Don't Look Back in Anger" in "Chuck vs. the Alma Mater"
 * Another non-Jeffster example: Chuck psyching Morgan up by humming The Imperial March, inspiring Morgan to join in. Cut to Morgan opening up a pair of doors, with the full Imperial March blaring in the soundtrack.
 * In a reverse of the trope, one episode of Twin Peaks came back from commercial (with the standard "bridging" music), which was then playing on the car stereo that the next scene faded in on.
 * House has the last scene playing a song on House's iPod, then accidentally cutting to the Hava Nagila. Then, after turning off his iPod, the song returns as background music.
 * Happens in Life On Mars, in the first episode, with the title song: it starts out on the iPod (diegetic), then we don't hear it anymore as the hero gets hit with the car and struggles to stay conscious. Then, as he drifts off, we hear bits of the track coming through (nondiegetic) until it bursts into full volume as he arrives completely in 1973 (nondiegetic). Then it goes quieter and diegetic again as he approaches his car and it's playing on 8-track. It's quietly under his conversation with the policeman by the car (still diegetic) but then goes louder and nondiegetic as he wanders off through Manchester. The last finishing quiet bits of the track continue to play nondiegetically as he enters the police station and looks around.
 * In the Quantum Leap episode "Play It Again, Seymour", Sam shares a jail cell with a man who is drunkenly singing "You, You, You". When the scene changes, the singing becomes better and a backup band comes in, and it continues to play softly under the action.
 * In the the last act of the The West Wing episode "Commencement", the song "Angel" by Massive Attack is playing at the party where the main action takes place, and continues to play uninterrupted over inter-spliced scenes set in other locations where other characters are engaging in their own still-unsolved plot threads (Donna and Amy arguing, Leo meeting with the Joint Chiefs, CJ and Danny picking apart a story, etc.) while the main plot/cliffhanger is set up. The alignment of specific lyrics with specific scenes is chosen symbolically.
 * The Wire, as a rule, only uses Source Music, with the exemption of the montages in the season finales. However, there is an occasion in the second season where music from a radio is overlaid across several scenes.
 * In the episode "Light" of Stargate Universe, we hear a somber violin piece play on Dr. Rush's iPod speaker dock before the music and scene switch into a montage of the rest of the Destiny's crew bracing itself for a fiery death in the sun that the ship is plummeting into.
 * The BBC adaptation of Little Dorrit focuses on a scene between Amy Dorrit and her uncle Frederick, both of whom are missing their former life in and around the Marshalsea. Frederick is a clarinettist, and supported himself playing his instrument prior to William Dorrit's unexpected inheritance of his vast fortune. Frederick has obviously been told off for playing his beloved instrument by Fanny, who has taken it away from him on a previous occasion. He begins to play as Amy leaves the room to go and see her father. The tune he is playing swells to become the background music.
 * In the Stargate Atlantis episode "Critical Mass", Teyla sings a song at a funeral while tense action packed scenes are taking place around the city. As the scene switches between locations, the song continues as background music.
 * A variation occurs in the Castle episode "Home is Where The Heart Stops". Richard Castle is humming a tune when he unexpectedly gets in a fight. His action sequence theme song follows the tune of his humming.
 * Done to brilliant effect in the ER episode "Be Still My Heart", where the ER staff are having a Valentine's Day party in the reception area with Pigeonhead's "Battleflag" blaring loudly from the radio. Carter goes down the back hallway to the patient rooms to check why a patient hasn't been discharged, and the music becomes muffled with distance, still diegetic. And then he gets stabbed in the back by said schizophrenic patient and left to bleed on the floor. The second the knife goes in, the music seamlessly transitions from the distant, tinny-sounding BGM to a full, clear, non-diegetic soundtrack -- which is exactly as loud as the radio is back in the reception area, and Carter's cries for help are drowned out by it, letting the viewer realize that no one can hear him because they can't hear him either.

Music

 * On Orbital's Orbital 2 album, the beginning of "Planet of the Shapes" has the song playing diegetically on a vinyl record player in the background, complete with crackling sound effects. Then at the end, there's a Record Needle Scratch as it segues into "Lush 3.1", which is also briefly heard diegetically.
 * The intro to Pink Floyd's "Wish You Were Here" was produced so as to make it sound like Dave Gilmour was playing along with a record player.

Music Videos

 * The video for Sunset Strippers - Falling Stars starts with a guy listening to the song on his MP 3 player, before switching to non-diegetic form.
 * The video for "19-2000" by Gorillaz begins with this.
 * The video for "Queen of Hearts" by Fucked Up has this, played on a boombox before switching.

Video Games

 * In Devil May Cry 4, during first cutscene fight with Dante, Nero throws off his headphones when he decides it is time to get serious. The music which is heard from headphones becomes background music for the rest of the scene. Scene in question.
 * Persona 3 plays with it a bit. The background theme in the opening cutscene (called "Burn My Dread") is first heard from Main Character's headphones, then it switches to being a full-fledged BGM for a minute, and then heard again from headphones.
 * In the Left 4 Dead series, a player character may turn on a jukebox. Doing this attracts a horde of zombies, but instead of the typical horde background music playing, the music from the jukebox will be heard instead, even if it's out of the practical range of the jukebox.
 * In The Legend of Zelda Ocarina of Time, Saria's Song is first heard diegetically, directing your path through the Lost Woods maze. After you learn the song on the Ocarina, it becomes permanent background music there.
 * The intro to Borderlands seems to invert this; the music starts off very distant and once the bus enters the scene, the music is at full volume from the inside of the bus.
 * The background music from one of the final missions of Ace Combat 5 The Unsung War is Captain Andersen playing the Award Bait Song "The Journey Begins" over his aircraft carrier's loudspeaker, and as such it actually sounds like it's coming through a loudspeaker - though after about a minute, it fades into a non-diegetic version of the song.

Western Animation

 * During the Sad Times Montage which opens Season 2 of The Venture Bros., the music which backs the entire montage is eventually revealed to be the techno track which is playing at the rave where Brock tracks down Doctor Venture.
 * In ThunderCats (2011)
 * This is often employed with Wilykit as a provider of flute music, only for a more orchestral version of her piece to begin immediately after she finishes or the camera cuts away.
 * In "Song of the Petalars" Ethereal Choir is in-universe singing by the Petalars that flows into a more expansive theme after they finish singing.
 * Subverted in RWBY. In the opening scenes of the very first episode, Ruby's clearly listening to "This Will Be The Day" via headphones until she decides to interrupt the robbery of the Dust shop.  After she follows one of the Mooks through the shop window, the music switches from a tinny playback version to a high-quality version -- until we hear the "click" of Ruby turning off her player, the music stops -- and the action begins.