A good friend of mine, Jen Blood, approached me a few months ago asking for a piano musing that she could use to market her book, All the Blue-Eyed Angels. It sounded like a fun project so I said yes (this is often how I make decisions :) ). She sent me the roughdraft of the video, and I asked for a few adjectives to describe what the music should sound like. She responded, "dark, haunting, Gothic, mysterious, romantic, old New England, suspenseful, tragic, sensual... " :-)
With my piano musings, I sit down, press record, make up a piece on the spot, and press stop. Sometimes I publish that version, other times I might re-record 2-3 times to clarify my thinking a bit. It was a bit different with a video because I had to watch the video while I was playing, so it took a few more tries to get things lined up pretty well - I remember trying to crescendo to the image of the house being on fire. It was fun!
Months later, her book has apparently been selling very well - she even charted on Amazon! She's come up with a sequel called Sins of the Father, and has taken the opportunity to re-market the first book with a new trailer, containing the same music. It's been really fun to see the book(s) taking off!