What are you using to render the videos (Xv, GL)? Did you also
change
your desktop environment? Note that if you are using a compositing
manager (compiz, gnome shell, kwm, etc.), the compositing manager is
responsible for preventing tearing by syncing screen updates to
vsync.
If you are using Xv, the driver's anti-tearing Xv features only work
when rendering directly to the display buffer. If you are using a
composting manager, the driver renders to an offscreen buffer and the
compositor is responsible for updating the display buffer with the
new
Xv data.