My understanding was that the copyright law changed in the 70's to match the rest of the world. You don't have to file. As soon as you write something, you hold the copyright to it, until you transfer it to someone. Then they hold it for a duration stated in the contract, or for a maximum of 35 years, at which time you have five years to file to get them back. (Unless you waived this right in your contract.)
However, if you want to take someone to court, it turns into a "his word against yours" situation without a filed and registered copyright. If he registers the copyright in 2015 and you've got a book bearing your name as the author and a copyright stamp from 2012, with royalty checks and printed reviews in major newspapers from 2012, the judge or jury might laugh him out of court. But if all you have to protect yourself is the manuscript, a string of emails, and a video trailer which doesn't include the hijacked content, it will be harder to prove. So even if the judge finds in your favor, the award will be smaller.
If you're at all nervous that someone is going to steal your stuff, register with the copyright office. It's a lot cheaper and easier than taking on an army of entertainment lawyers.
Then again I'm not a lawyer, I'm just an author who just attended a copyright law seminar. I could be completely wrong here, so please correct me.