I have confusion about the multicast addresses, I have read an example which is given by.

Suppose two applications have been built to send audio over a network. One application accepts and digitizes an audio input stream, and then sends the resulting frame across the network to other application. The second application receives the digitized audio from the network, converts it back to the audio signal and plays the result over a speaker. Unless the two applications use broadcast to send frames, no other computers on the network will receive a copy of the frame. Multicasting provides an excellent solution to the problems of allowing some computers to participate in audio transmission. To use multicasting , a multicast address must be chosen for the audio application. And the receiving application passes the multicast address to the network interface. The interface begins to accept the packets sent to that address.

Question: how this multicast address is chosen, how the receiving application knows that the sender using this specific destination address for the audio frames.