Released on Jan 8, 2008.
We have ffmpeg and mencoder built in the 2008Q2 package set. They do not have any dependencies that are not available in 2007Q4 though, so can be added even there, be temporarily pointing the PKG_PATH environment variable to the new repository:
export PKG_PATH=http://pkgsrc.joyent.com/2008Q2/All pkg_add ffmpeg pkg_add mencoder