Rolling Stone: Legend wrote the song without visiting the set, seeing the film, or even the scene it would appear in. He'd only heard about the Django movie plot. He'd heard that Tarantino preferred listening to cassettes. Legend said "... we converted the digital material into a cassette and I wrote him a note and I said, ‘I wrote this song for your film, wanted to know if you would use it.'” In an interview, Tarantino said, “If I had gotten a link or something to plug into my computer, I would have thrown that shit away..."
Rolling Stone: Legend wrote the song without visiting the set, seeing the film, or even the scene it would appear in. He'd only heard about the Django movie plot. He'd heard that Tarantino preferred listening to cassettes. Legend said "... we converted the digital material into a cassette and I wrote him a note and I said, ‘I wrote this song for your film, wanted to know if you would use it.'” In an interview, Tarantino said, “If I had gotten a link or something to plug into my computer, I would have thrown that shit away..."
[Edit: additional quote]