If you just transferred some media files to your device and they are not showing in the database(galleries, music players...) Media Scanner could help you. Media Scanner forces Android to do a full media scan based at the path you chose and then it updates Android Media Store database with the new items. So basically this application will search for all media files on your device and update your Android media store. Updating media store will fix some of your applications which can't see your media files. This problem is most seen on Android KitKat.