Thats great, but just fire up a program like Audacity, set the input to "Stereo Mix" or "Wave Out" depending on your machine, press record then press play.
Now, with video it is harder since wmp and the like can write directly to video memory, but most of the binary stream formats for video have been reversed. I point you to the MMS devouring SDP among others.
My point here is if it is played back on your local machine, then the content can be captured. The best you can do is encrypt it. For audio, there isn't even much point to that. You just inconvienience (sp?) the pirate