Per their website, it appears they fly the older seat style on both routes. According to FlightAware, it's a 777-200. The pitch is 34" for all econ seats (rarely you get a 32 or 33" in certain weird sections of the cabin), which is most likely the most generous of any airline flying TPAC. It is certainly more than DL's E+, for instance. You can go to the website like I mentioned and plug in your dates to find out exactly what they will offer as far as the seat (On Board -- Flight Schedule with New Aircraft) and movies (On Board -- Entertainment). With regards to movies, they offer way more than they list, obviously.
http://www.koreanair.com/local/kr/gd...if_cs_ec.jsp#2
Presuming you have the "old" seat, you will have AVOD I. It just means the OS is a little older, the screen is negligibly smaller and you don't have a camera on the tail/nose. It is not that big of a deal between this and a "new" seat.
The only downside is that you will NOT have a USB port at your seat to charge anything. Otherwise, the pitch and comfort of the seat are the exact same between old and new.
With regards to service, for IAD-ICN (just like ATL/JFK-ICN), they will do a drink and peanuts after takeoff in the first hour or so. In the next hour or so, they will do a lunch, presumably offering bibimbap. Go for it, it's good. Don't skimp on the sesame oil or red pepper paste. After lunch, they will close all the shades and turn off all the lights for the next six hours or so. In that time, they'll offer you a snack (hot curry bun? seaweed and rice triangle?). Then, after those six hours, they will feed you a dinner. Then back into darkness for the last of the flight. Perfect for sleep. If at any time you are hungry, they have snacks in the galley. They also walk the aisles with juices and water.
I do the ATL-ICN RT run once a year to visit the States and it is the same for those flights.