As Tom and I have mentioned several times on the main show, if you release your music under Creative Commons, you can always license your work to someone else under a non-CC license. For example, if you release under BY-SA, you can contract with a film producer for them to use your music without the film producer having the release under BY-SA (which they would have to normally do under the ShareAlike provision, aka SA).
1. If at all possible, get a lawyer.
While not technically a member of the attorney guild just yet, you're right to be skeptical of my intentions here. It is, however, the most important of these suggestions. There are a lot of reasons why getting an attorney is important, but I'll give you two of the most important.
First, if the lawyer screws up, you an sue them for malpractice. If you screw up the contract yourself, sue yourself. Let me know how that goes.
Second, the laws are different in different jurisdictions. Copyright might be federal in the US, but occasionally there are circuit splits. You may very well know the New York contract and copyright interpretations, but if the film maker is in California, it's possible California law might apply.
2. Define everything.
Certain words have specific meanings in copyright and contract law, but if you're negotiating on behalf of yourself, you probably don't know those meanings. If you force the other side to get all of the meanings in the contract, at least you aren't being left in the dark about the meaning.
3. Assume you will be going to court later.
While writing things down can have some positives aside from just having something to hand a judge, if you have no intention of ever suing anyone, there's not much reason to spend time negotiating a contract. Just license your work under the WTFPL or CC0 and save everybody the hassle.
4. Don't act like you know what you are doing.
This mostly applies if the other side as a lawyer. Courts generally do not look kindly upon lawyers taking advantage of lay people. It's true that this presupposes that you're going to be in court later, but see #3. If a lawyer knows you don't know contract law, they will have to explain things to you. This is very important. If you do not understand the contract, there is no contract. A contract is a meeting of the minds and if you don't understand, there is no meeting of the minds. It's true that you would have to prove in court that you didn't understand, but if you didn't, this probably won't be hard. If you acted like you knew what you were doing, there is going to be a ton of evidence against you.
5. Assume the worst.
In most cases, the lawyer on the other side is going to be happy you are doing this. Lawyers are by nature pessimistic creatures. Licenses are all about damage control. If you assume the worst, you'll hammer out all the details while negotiating and you'll avoid court later on. But see #3.
6. Understand that most oral contracts are enforceable.
There are plenty of exceptions, like real estate contracts, but most oral contracts are enforceable. If you agree to something on the phone, don't expect to weasel out of it. That said, proving there was an oral contract is often hard.
7. Write it down.
This might be obvious, but you don't want to get in a he-said, she-said battle in court.
8. Make sure the other party knows you license under CC.
For one thing, if you've licensed under CC, you won't be able to give an exclusive license. Now, you might be able to do some things exclusive. For example, you could contract away the right to further sub-license. Again using the example of the film maker where you've released under BY-SA. You could specify that you would not license another film maker for proprietary use. What you could not do is say that your song will never appear in another film, because BY-SA films would still be allowed.
9. Don't forget about trademarks and trade secrets.
If a film maker is licensing your music, it's unlikely that you'll be potentially revealing any trade secrets. If the film is a documentary though, particularly one where certain individuals are portrayed in a negative light, they may not want you telling anybody about that. While this is really their issue and not your issue, just because the other person doesn't have a case doesn't mean you won't get a threatening letter. Additionally, if you violate their community norms, they may lambaste you which could tarnish your career if it's a popular film maker. If you are coming from a community, like CC, that values sharing, you might not think of this. Just be aware that if you are dealing with a non-CC film maker, they may not feel the same about sharing as you.
10. Ask for help.
Help is available from organizations like Volunteer Lawyers for the Arts. They don't appear to have affiliates in all 50 states, but many states and a few countries have affiliates. If you are in a state that doesn't have a VLA, ask me and I'll see if I can help you find someone.
It's true I probably could have folded this into #1. However, you are always supposed to start and end strong, and I really cannot emphasize how complicated the law is. This is why you should choose CC if you haven't already!
Remember, contract law is different in different parts of the USA and of course in different parts of the world, so see #1!
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