Nice tutorial, Smurf - although it's maybe worth noting that the GP2X movie player will crop the bottom of a 320x[whatever] video if it's dimensions are not exact multiples of 16... so only the top 320x128 pixels of your 320x136 example are displayed.
Maybe this will be fixed with future...
update: I tried some differerent earphones and it's working perfectly... the plugs on the all the other ones I had tried wouldn't fit all the way in due to the socket being slightly recessed from the hole in the casing
This happens for me - the headphones work perfectly but the sound keeps coming from the built-in speakers... so is it correct that with the music and video player the speakers should automatically mute when headphones are plugged in?