Jerky playback

[Chris Jensen]

Hi,
I've tryed to use mplayer with xvideo to test my xvideo and I get this error

Sorry, Xv not supported by this X11 version/driver

This is strange because XFree says

(II) Loading extension XVideo

when it's loading (and theres no error messages after it).
I'm using kernel 2.4.6 with devfs, glibc 2.2.3, XFree 4.1.0 which I
installed from source. I'm using the NVIDIA drivers (1.0-1251) for my Riva
TNT M64 which should have xvideo support as far as i can tell.
I haven't installed anything else of note (I compiled everything on my
system so unless it was required for the above to install it probably isn't
on my system), is there anything I haven't mentioned that I should have?
Please tell me even if it seems obvious, because I think it must be because
I can't find anyone else who's had this problem.

Thanks for any help
Chris Jensen