This song is infinitely long.
The Song exists in a Platonic world of ideas, across all of time. It can't exist in the real world because it can't be stored in a file, since the file would also be infinitely big.
But every time you click play a small piece of code will ask "how does The Song sound right now?" And it will generate, on the fly, a stream for you.
If two people click play at the same time, they'll hear the same song. But if 5 minutes later someone else clicks play, they won't hear the same first 5 minutes that the two other people have already listened to — those notes are now in the past. Instead, the person will simply join an ongoing song, and hear the same notes everyone else is hearing.
If you could go back in time, you could listen to The Song the moment you were born. Or when you fell in love for the first time.
A more technical explanation is that The song is generative, but the chords, notes, and pauses being generated are determined by the time when they play. So it can be generated for any period of time, past or future.
If you ask the code "how will The Song sound like on February 1st 2033?", it will know the answer.
But that would spoil the surprise, wouldn't it?