Encryption prevents one and only one thing

Ed Felton discusses the myths of encryption

Encryption prevents one and only one thing - decryption without knowledge of the secret key.

But if you want to play the content, you have to decrypt it. And this means two things. First, the decrypted content will exist on the customer’s premises, where it can be readily copied. Second, the decryption key (and any other knowledge needed to decrypt) will exist on the customer’s premises, where it can be reverse-engineered.

Hopefully one day all the tech advisers to the wankers at the big Record and Movie Companies relise this
and then they won't bother putting digital rights management(DRM) software on our CDs and DVDs.