The N800s standard media player will play 400x240 video which is something that could not be achieved using the standard player on the 770 (mplayer could do it though). The N800 media player obviously has updated codecs and is an improvement over that in the 770.

mplayer on the N800 isn't so good at the moment - it needs more optimisation which I'm sure Serge will work on in future, assuming he gets a developer device (he deserves one!)