I do have ffmpeg installed, but I always install it.
I had your trouble with Etch, (dropped
frames) and found I had the refresh
rate on monitor set wrongly.
Have you tried any other media
players, Mplayer, Xine ?
I have used
most types of Linux distros and found
some players work better than others
on all distros, depending on distro.
In case you ask
( have answered this
question "many" times
), to configure
Mplayer, right click on screen, preferences,
video x11, audio alsa,
You might have to do the same again,
if you attempt to watch streaming video
Worth trying to change video settings
to other than x11 if you are having