Not the OP here, but briefly, the technique uses a little statistical cleverness and the ability to examine a running program to help identify which part of the Spotify program produces the unencrypted bytes of the track it is playing. It then taps into that part of the program, and copies these bytes to a file. That file then contains playable audio. (This data must be unencrypted in order to meaningfully feed the digital-to-analog converter of the playback computer.)