I use Spotify for all my music needs and was wondering if there was some way to write an app that would allow me to access the music from Spotify and slow songs down and loop portions of the songs. I am a musician, and something like this would help with practicing.
If it can be done, a brief outline of what I'd need to do would be appreciated.
Separately, would this be legal?
You'd have to write that application yourself using libspotify. However, I'm fairly certain the Terms of Service for libspotify disallow modifying the audio. I'm not sure if slowing down counts as "modifying" - that's probably a question for a lawyer.