You can use Spotify to sync (or copy) a selection of local tracks from your computer to an iPhone, iPod touch, iPad, or Android device. Just follow these steps:
Open Spotify on your computer and create a playlist that contains the local tracks you want to sync.
Make sure both your computer and your mobile device are hooked up to the same Wi-Fi connection.
On your mobile device, open Spotify.
The device now appears on your computer below Devices in the Spotify window’s left sidebar.
On an iPhone, browse to the playlist that you want to sync and swipe the switch that appears at the top-right of the screen to Offline.
On Android devices, tap Edit Offline Playlists, select the check boxes next to the playlists you want to sync, and tap Done.