i can't anwser this question for certain or direct experience but from what i've gathered through the years is that each film is different. but it's important, i think, to consider how times have changed from past to present... for instance let's take a tv series from the 80s or early 90s in which some television series may have had music that was written & composed by a singular person or more likely than not several people working together. in this case, from what i know, it depends on who has creative control over the music direction and selection to be used; this could be say, a writer and producer of the show who came up with the story and other primary aspects of the series. if say, this particular person was given control over music and other creative aspects of the series due to his or her expertise and perhaps previous works, then from what i know, this person would also single handedly choose the composers, writers, and performers of the music because, well especially at this time, music was considered an absolute integral part of what was on srceen. in this case, this person would sometimes choose a select composer to write with side by side composing and offering input to bring out the qualities that they heard in this composers previous work, but adapted to a singular feeling and style that would perfectly match his or her creative intention for the series... they could write together and most likely before this develop somewhat of a very solid working relationship to be comfortable to work; achieved through meetings to get a feel for each other just like friends used to, going out to eat, talking films, music, etc. once this was established, they would work together and write. the person would articulate the feeling and mood of the music to be made and clearly somehow communicate what they wanted the compositions to feel like, including, tones, tempos, rhythms, and other musical descriptors. the two would then work together to find the right singers and other performers bringing them in to find just the right match... they would work together and make something truly memorable.... fast forward to the present day, things seem to have changed drastically. finances have seemed to take presidence over creativity and with all the technology available and sound libraries in circulation. i would think that most things on a screen just use pre recordded music from a library made by anyone and everyone. you can tell because everything basically sounds the same and has no emotive feeling anymore. it's mostly just very loud, generic, and is highly processed with effects to make thunderous bassy sounds that make watching a movie unbearable and shreeking fx that could be very disturbing to some. it seems this is so large spread nowadays that it doesn't matter because there is nothing else to compare it to. i'm sure there could be many exceptions to this, but i think you would mostly find that in smaller movies and things made from unknown people or someone from an older generation who still have some pull to make decesions today. i am not really sure, this is just purely my opinion; very long and obtuse. i imagine there could be some very interesting and emotive works but they are all unknown some even made in secret with no one elese every seeing or hearing anything except for a handful of friends and family, if that...