> Your app is living off the work of artists and making it in a way that gives them a way to profit from it costs you nothing, so it is the right thing to do.

The app just find the music on free sources, probably published by the artists themselves or their agents. How is that living off their work and where do the nuclear developer receive money from the nuclear app users in the process?

You read "living of" as a monetary value, that isn't what I meant. That particular app is useless without musicians that upload stuff for free, meaning the fact that musicians do that is of existential importance for it.

And that means such an app enters a certain relationship with these musicians. This relationship can be symbiotic (good) or parasitic (bad).