Streaming Music and being able to keep them as your personel files

The Tidal app on iOS (and I imagine Android, though I've never tried it) allows you to download content to your device to be able to play it locally without an internet connection (such as when you're on a plane).  It does need to periodically authenticate with the Tidal servers, though I don't know how often that happens, you could probably keep your offline files offline for at least a week and have them still work, but eventually they're going to stop playing until you allow Tidal to connect to the internet and authenticate you still have a valid subscription.  

@dweller 

Sure, you could do that, but you'd have to time the track breaks just right, then you have to convert what will probably be a raw .WAV file into something more usable, input all of the metadata manually for each track, and go through a lot of hassle when it would be easier to just buy the album from HDTracks or iTunes if you want to keep it forever and move it across multiple devices.

When you sign up for a streaming service you are't buying the music, you're buying access to play any of the music from their catalog for as long as you maintain your membership.  If you want to keep the music you need to buy the album from a service that offers that.

@dweller 

Sure, that's not fundamentally different from using the tape loop with a tape recorder back in the old days to record from a turntable or a tuner.  

You're not going to end up with a bit-perfect copy of the original though, and it's not going to have any of the metadata that makes it easy to manage in a portable player.  

It's also a bit more dubious from an ethical stance - making mix tapes and copies for personal use of music you already own or that's being broadcast freely over the airwaves is one thing, doing it to make permanent copies of music from a streaming service where the royalties to the artists are paid per stream/play is another.