No XVideo support for Radeon HD 4200?

[george+freebsd at m5p.com]

HP Compaq Presario CQ61-420US (dual core amd64)
ATI Mobility Radeon HD 4200

Xorg starts and loads the extmod module with the the XVideo extension,
and then a little later the radeon module, according to Xorg.0.log,
but xvinfo says

X-Video Extension version 2.2
screen #0
 no adaptors present

Needless to say, this gives poor performance for mplayer and such
programs.  What's going on?                      -- George Mitchell