Instructions
Turn off the portable DVD player. Attach the AV cables from the GameCube to the corresponding AV inputs on the portable DVD player. For example, the red cable goes into the red port, blue into blue and so on.
Connect the GameCube&'s AC adapter into any available power outlet.
Turn on the portable DVD player. Turn on the GameCube. Set the portable DVD player to its "Video" display mode (it might also be referred to as "Input 1" or something similar). The image from the GameCube will now be displayed on the portable DVD player.