It is likely the film soundtrack came into existence about the same time as films themselves. Early films were silent, but were released with cue sheets or scores so that individual theater houses could play music, recorded or live, at appropriate places in the film. The first reels of 1961's West Side Story and 2001's Moulin Rouge! follow the practice of the era of silent film by beginning with an orchestra playing the opening theme. With the advent of talkies in 1927, music was optically integrated into the actual film itself, and the wide world of film soundtracks was born.
The score to a film is also known as its background music. This is arguably the most common type of music heard on a film soundtrack, is music composed and placed to enhance the desired emotion of a scene, be it positive or negative. The actors on screen are talking and moving normally, that is, they are neither singing nor dancing nor interacting with the music in any way (except in cases of a spoof). A person watching the movie may not be aware that anything is playing, but might comment on the poorness or flatness of a scene should the music be removed. The background music is usually orchestrated without meaningful vocals (with the exception of some chanting), and somewhat formless, based heavily on musical peaks and troughs that highlight the scene but which otherwise may be nonsensical or even boring when played alone.
Most background music follows a general pattern of instrumentation and technique to achieve whatever ends the composer desires. Common examples of such devices used in background music include trilling violins to indicate suspense, legato flutes to convey peaceful or pastoral setting, trumpet fanfares for military or martial scenes, and drumming for tribal events.
Movies with notable soundtracks consisting mainly of background music include the Lord of the Rings movie trilogy (Howard Shore, composer), Star Wars (John Williams, composer), The Mission (Ennio Morricone, composer) and The Piano (Michael Nyman, composer).
A title song is a theme, usually sung to lyrics, and associated with a particular movie that is heard in toto during the credits and rarely anywhere else in the film, except in the case of musicals. Usually the title song is composed for the movie itself, but sometimes existing pieces are used, especially when a current movie is set in a recent era that possessed stereotypical music, such as disco. The singer of the title theme is usually unrelated to the movie itself, with Barbra Streisand being a notable exception.
Title songs are, by and large, vague in their references to the film’s particulars, focusing instead on general themes of love, loss, and betrayal. These songs often go on to be commercial successes even if the movie was forgettable, though the fate of both movie and title song are intertwined. One wonders if "My Heart Will Go On" would have become such a hit had not Titanic succeeded as well as it did. The same can be said for "I Will Always Love You" and its corresponding movie The Bodyguard.
Occasionally, a film will have both a popular orchestrated theme and a sung theme. The James Bond films all feature the James Bond theme as well as a movie-specific title song, such as Carly Simon's The Spy who Loved Me (Nobody Does it Better).
Closely related to a movie’s background music is the theme(s) of the movie. A theme is a particular melodic or rhythmic motif that appears in the music whenever a certain event, usually the presence or entrance of a major character, occurs (see leitmotif). Themes differ from background music in that they are usually tuneful and will stand alone if removed from the context of the movie. Also unlike background music, the song may often have purposeful lyrics.
The theme is usually repeated throughout the course of the film. Sometimes, it is introduced early and manipulated with regards to tempo, key, and instrumentation to fit the particular mood. For example, an upbeat theme may be played in a minor mode if the character it is associated with suffers or dies. It may be slowed down for a romantic moment or sped up for stressful emotions. It may be placed in counterpoint with another theme to show a relationship. A theme may also be hinted at as a character develops and be finally played in full when the character reaches a peak. For example, in the Attack of the Clones, when Anakin Skywalker makes the choice to exact revenge on the people who killed his mother, the Imperial March from Star Wars is played in full for the first time that movie.
A single movie may have one or many strong themes. Often, a movie will have a primary theme played during the opening and/or closing credits that is not heard in totality anywhere else in the film. In certain cases, this song may be sung (usually by a popular singer unrelated to the rest of the film) during the credits, but instrumented when inserted into the film. This is called the title song and is discussed later. A film may have an orchestrated theme as well as a title song, composed by different people with different results. Often, one will succeed commercially while the other will fail.
The theme of a film may eventually come to symbolize a character or the film itself, to the point where the original purpose of the theme may be lost. The opening strains of Also sprach Zarathustra and Blue Danube Waltz by Richard Strauss are inextricably linked to 2001: A Space Odyssey, though few can remember when in the film the themes were first played. Themes are usually titled for the movie they occur in, such as The Theme from Schindler's List or Theme from the Magnificent Seven, and may be distinguished as to why they occur, such as the Love Theme from Romeo and Juliet.
Many films made in the 1940s through 1960s especially were screen-based adaptations of popular stage musicals. Several films of this time originated as musicals, some of which were later adapted to the stage (e.g., Lerner and Loewe's Gigi). Besides the sung portions, there is also background, or "incidental," music used to underscore dialogue (as in stage musicals); this background music may be more prominent in film musicals, because of the greater capacity to have scenes of transition or with special effects. Whereas spoken films (e.g., Gone with the Wind) may at times use recurring themes in the background music, the underscoring, including dance music, in a film (or stage) musical is usually more specifically derived from themes that occur in the vocal numbers.
The modern film musical fell out of popularity after the 1960s. Nevertheless, film musicals occasionally have been produced since that time, such as A Little Night Music, Victor/Victoria, Chicago, and Moulin Rouge!. Lately Hollywood seems to produce more musicals as animated films (see below), while Bollywood still embraces the live-action film musical as a viable genre.
Significant differences can exist between the stage and film versions of musicals, not only in the plot and details of the script (e.g., On a Clear Day You Can See Forever), but also in the constitution or even creators of the musical numbers (e.g., The Best Little Whorehouse in Texas). Sometimes the original creators of a stage musical have little or no connection with the film version once the film rights have been bought.
The recordings presented on a soundtrack album from a film musical may not always correspond with the version shown on screen. The album may include numbers omitted from the final cut, may include additional verses or passages not heard in the film, may substitute a different recording or mix of a number, or may omit certain passages within a number. The way dialogue is interpolated can present a different version in the recording from the film.
A standard practice in filming musicals is to have the score with vocals recorded in advance, and then to have the actors lip sync to a playing of the recording while they are in front of the camera. (It is rare in film musicals to film a scene as a "live" performance with orchestra.) This practice allows for other voices to be used for the sung portions than those of the featured actors. Perhaps the most famous off-camera singing voice used for dubbing in filmed musicals is that of Marni Nixon. Part of the craft of editing pre-recorded vocal portions into the film is to make sure that they merge effectively and seamlessly with the surrounding dialogue.
Related to the above is the genre of filmed operas (that is, vocal musical works that are sung virtually throughout, traditionally originating on stage). Many filmed operas are made from live performances in a theatrical setting. Some filmed operas, however, are made on location, and therefore require lip-synchronization. In this case, often the singers themselves serve as the actors, but sometimes professional actors use those singers' voices before the camera.
Existing in a similar place, but different class, as the score are the so-called songs from the movie, which will be abbreviated SftM for now. SftM are discrete songs, almost always not composed specifically for the movie, heard during the course of the movie itself. A SftM may either be background music or semi-interactive. (Soviet cinematography traditionally relied heavily on songs with lyrics, even in non-musical films.)
An SftM used as background music functions much in the same way as an orchestrated piece would. It is added external to the movie and used to heighten the mood. The main difference is its existing as a full, independent song without being a theme (and thus played only once during the film), though a piece such as Shaft would traverse that boundary.
A semi-interactive SftM is a song playing in the context of the movie, such as the background music in a club or a tune heard on the radio of a character’s car. When a semi-interactive SftM is playing, it functions as background music, so it would be rare to see a gang fight scene with a giddy SftM unless the director were going for irony.
The average movie soundtrack will contain eight or so SftM by popular artists tangentially or unrelated to the film itself. Forrest Gump's soundtrack is one of the best selling of all times and reads almost like a laundry list of popular tunes from the Baby Boomer generation.
Most animated films produced by Disney are musicals. Indeed, almost every feature-length animated feature which is not anime is a musical, although Pixar's animated features are not musicals. Animated films share all basic characteristics with their live-action counterparts, except that the incidental music is more likely to be novel, i.e. in the tradition of non-musical film scores.
Title songs from animated musicals do sometimes go on to become commercially successful, a fact capitalized on by such singers as Elton John (The Lion King) and Celine Dion (Beauty and the Beast). The glory days of the Disney song might be considered to have come during the tenure of Alan Menken and Howard Ashman.
A somewhat recent invention, songs inspired by the movie are almost always not actually played in the movie itself. Instead, as the title suggests, they are derivative of the musical, cultural, social, etc. themes of the film. This seems to be done primarily to capitalize on the success of a particular film. After the soundtrack to The Lion King was released to great acclaim, Disney released the follow-up album Rhythm of the Pridelands.
Most of these classical works have enjoyed tremendous popularity following the release of a movie featuring them extensively:
Some of these songs had been released before the movie, but had found little success only to become popular once featured in the movie. Other songs were released alongside the film or were briefly re-popularized some years after their initial peak. (This list does not include songs associated with a cinematic opera or musical.)
Most of these theme songs occur at least once during a climax during the movie, and are often played during the opening and/or closing credits; the close association between the highlights of a movie and a particular song, especially when the two are marketed together (as in a music video), means that songs can find new audiences. For example, Quentin Tarantino's use of "La La Means I Love You" and 1970s Philly soul group The Delfonics led to a renaissance in hipness for the band some fifteen years after their mainstream success ended.