My online store is being developed so that I can sell mp3 downloads of hypnosis sessions for home use. How do I encode the mp3's so that they can't be copied again once downloaded??
It's almost impossible to stop people who want to copy your audio. If their sound adapter doesn't just let them record via "what you hear" or "Stereo mix", then they can always string an audio cable between two jacks (output and input, might need two audio devices but hey) and record it in 'analog' with little to no loss of quality, and no way for DRM to stop it.
My advice would be to give up now and spend your time and energies on something more useful, and you wouldn't be the first:
Hope that helps...
No. What you are asking is an impossible task, something that has been attempted by many since the birth of stored audio. A computer has to read the data, so however you encrypt it it will at some point exist unencrypted - at which point it's trivial to grab it. Even if you had a perfect encryption that can't ever be copied, you can use a loopback cable, or virtual loopback, to copy the sound perfectly and re-encode it.
On the other hand, perhaps you could offer a "taster" mp3 that hypnotises people into not copying your files ;)