IRiver MPlayer User Manual page 23

Chapter3
Music
Selecting additional functions (Moving to next / previous directory)
1. While playing music, turn the [ ] button shortly
to left, then turn and hold it again to the same
direction within 2 seconds to play the first track
in the previous directory. You will hear a beep.
22
Using the Mplayer
[Previous track]
2. While playing music, turn the [ ] button shortly
to right, then turn and hold it again to the same
direction within 2 seconds to play the first track
in the next directory. You will hear a beep.
[Next track]