Hi, tell us:
1. are you using media converter?
2. what settings on media converter? I use Optimize, 400x... and then watch it using mplayer.
I am pretty new myself to converting FOR 770. I always run the video through media converter before I try to watch. So I decrypt the video (which I own) and then use AutoGK. Then media converter. I get pretty good quality, but can't watch using the preinstalled video player because the video is 400x (240? I think).
Media converter can do a good job without having to figure out the best settings or fps, etc.

Search under media converter or convert video. there are a lot of good posts already which can help you.