In the filmmaking process, the music editor is a person who works closely with the composer and the film’s production company to organize, document and time the music cues for a given film project.
While the composer/conductor leads the recording, the music editor will be off to the side keeping track of what is being recorded and when.
A music editor is also responsible for compiling the temp track used as the film’s temporary soundtrack (see The Temp Track for details about this feature of film music).
A music editor will, as a general rule, be present during the recording sessions and document (i.e. keep track of) each cue as it is recorded and may also have the responsibility of generating the click track for a particular cue (see The Click Track).
Putting a film’s soundtrack together is definitely a team effort, to say the least.