It’s a port called an eXport. It was part of the Panasonic IFE system
OK I think I found it! About 10 years ago Panasonic’s IFE system (which appears to have been used on the B773ER and A333) contained a new port called eXport. It was a 9-pin mini-DIN port for iPods. You could purchase an adapter cable made by Griffin that was essentially an adapter between the 9 pin mini-DIN and 30-pin ipod dock connector. It would allow you to charge your ipod, control it via the IFE and stream media from it into the IFE system.
Edit, I’ve looked about for some actual port specifications but it’s searching for “Panasonic Export” just seems to return information about panasonic’s exports.
I did find this from a guy who took a multimeter to the port to find out which port is which. Port information
Credit:stackoverflow.com‘