Since a little while now, I used to have the problem of the music skipping in mplayer. I guessed bad audio or crappy I/O, but I never noticed any errors anywhere.

What was happening was that when I moved my laptop, bumped against the laptop or table it was standing on it would skip or rewind the music. Sometimes a little, sometimes a lot.

Now I have a Thinkpad X40 and it only happened with mplayer, no other audio/video player.

Since yesterday I finally realised the problem after confirming it was related to me bumping against the table/laptop.

The thinkpad X40 is one of earlier models with HDAPS, or tilt/shock detection. This is implemented by de hdaps module as an event device and a joystick device.

MPlayer looks for alternative control interfaces people might like to use, which are by default, enabled. One of those interfaces is the joystick.

So in short, every time I bumped my laptop, my shock/tilt detection would create a joystick movement interpreted by mplayer as a skip forward or backward event.

Talk about obscure problems :)
The simple solution is ofcourse to force disable the joystick controls in mplayer with the -nojoy option. Or disable the hdaps module.