You obviously [might] have transferred a song to/from a friend via Bluetooth, iR or wifi, most likely the music file is MP3.
In the early days of the last decade (2010s), some of us even carried an extra device like a portable MP3 Player and the richer kids an iPod today thanks to how powerful our phones have become, we don't need an MP3 player anymore.
It is very easy to say that MP3 players are dead, they died in the last decade. But the MP3 file format might not make it past this decade(2020s) too. As our phones become even more powerful and access to the internet becomes easier, we might not need to save offline copies of our favourite songs the old school way of MP3 players. Music streaming services like Spotify are already becoming the preferred way to carry our digital music with us.
Some Advantages of Music Streaming
1. One playlist across devices: You can switch devices and listen to the same songs you love. No stress of transferring music files across your various devices. Same songs on your PC/Mac, Smart TV and Phones, up-to-date and synchronized all the time.
2. Discover good music effortlessly: Spotify and co have a very nice way of recommending songs you might like. You will be amazed by how much good stuff is out there from their unlimited collection of songs.
3. Support your creatives . : Oh! Yeah!! Music streaming can reduce piracy and help our musicians earn more form their hard work.
4. HQ Music: Expect High Audio Quality from music streaming services. If you ain't getting that maybe you have some data saving settings turned on.
By the end of 2020s (2029) MP3 files might just become vintage like... (do you remember the 3GP video format?). Welcome to 2020 and enjoy technology. Bye-bye for now.