That movie is called "Passion" and it has Barbara Hershey in it (as Grainger's mother). Can't remeber who played Grainger.
About his recordings, apparently he felt that ordinary transcriptions of folk songs left so much out, and produced a false impression, when singers had all sorts of interesting, but hard to transcribe, effects in their singing. He called it "the impress of personality".
I also have read that he collected music from the Pacific Islands and New Zealand Maori, which he was fascinated by.