It is a very curious and relatively delicate issue. I have heard that for example a song protected with copyright "you could not even hum it" ... How is it possible? ... It sounds more like a metaphor but if the author demands then It is possible. What madness!
I think you can hum or sing any song to yourself but you can't publicly perform it as in organize a concert and sell tickets without compensating the copyright owner for that.
A few days ago in one of Maduro's campaigns he sang a very popular song just in that situation that you describe. In front of a hundred people the song "Me importas tu"(I care about you), without any kind of public reproduction permits. For dictators, copyright does not apply.