USB sync
step 1:
open iTunes, select your device in the left panel, the newest iTunes, you need to select your device in the top right.
step 2:
select Apps section, and scroll down to the File Sharing.
step 3:
select OPlayer in the Apps section, then OPlayer Documents show the files under OPlayer,
step 4:
you can do Add... and Save to... operations now.
Please see attachment for detail.