composing music

i want to compose music video is for school and will be used on YouTube and the school website. Therefore, I need to make sure that you are the one who is composing this music and this has never been used before or given to anyone. If we agree on the music you did, I will need you to sign a paper that states you allow me to use your music and credits will be given to you ( this is a must by the professor.) As been stated before the music I need is about a video where it's a bit calm and cheerful and by the end it turns sad or less cheerful (whatever you see works well.) Attached is a sample of a music that is about the same idea of what I am looking for. Thanks in advance. [login to view URL] [login to view URL] [login to view URL]