Songs are assets of value to their authors and singers and there will always be demand.
Songs produces income from various sources, such as: radios, iradios, TV, internet, movies, ads, etc.
There is no replacement for music as a product, but technology has created new consumption and revenue models.
Projections are for growing revenues over the next few years through streaming and decrease for mechanical reproduction.
The valuation of musical assets may be performed by Income Approach or Market Approach.
The author of the song and the singer have distinct royalties.