Bart Venneker is experimenting with "tap" files. A tap file contains the digital data from a compact cassette that is used in a Datassette. With a PC you can transfer the tap file to a real compact cassette. And with a special interface you can connect a standard cassette player to the Commodore C64. In the video you can see how the system works (Dutch language).

Video about the use of the C64 Tape Interface.