It seems that a film is anything that may be put in a projector that will modulate the emerging beam of light.
“People often ask me: ‘Can you hear what you write? Are you surprised by what you write?’ The thing that surprises me is never the sound — I’m not a sound composer, I don’t go for special effects like that — what surprises me is how the piece speaks, how it unfolds and tells its story. That’s always a surprise.”
Harrison Birtwhistle