Looking at console.

PinAssignment
1Audio Left
2Ground
3Video
4+5v
5Audio Right

This port applies to the Japanese and US Duo systems, as well as the CoreGrafx and PC-Engine consoles, the Super CD-ROM system, SuperGrafx console and the LT. Sorry boys and girls - there is no S-video or RGB output from the Duo's port. You can tap RGB internally, and using a commercial adaptor convert the RGB to S-video, but it gets expensive at this point. Thanks to Shou-Sama for finding the pinout which I lost.