Mickey Mousing

Composers often start writing their music just before the editing starts so that they can see the scenes and mould the music around them. However by mickey mousing the sound is synchronised with the visuals. Therefore the music is sometimes recorded before the film. Mickey mousing was first introduced in 1928 when steamboat willie was created. This short film was an experiment by Walt Disney with as main character, you guessed it, Mickey Mouse. The main purpose of mickey mousing is to underline the visuals.

Mickey mousing can be achieved in numerus ways. The most common one is where the movie is following the sound (most of the times animated) in for example steamboat willie. The highest point of this development was in 1940 with the movie Fantasia where the movie score is so important it's even introduced in the opening scene. 

It's also possible that the music is following the visuals while it's still synchronised if this happens certain movements of characters are often tied to certain instruments and rhythms (the skeleton dance 1929). 

In not animated movies mickey mousing can still be a thing but it's not so common, in the 1935 movie ''the informer'' however there was music playing on the set and the actor had to follow the music. 

Mickey mousing can also be achieved by editing this technic is commonly used by so called ''vidding'' where already existing movies or series are edited to follow a song or tune