pmedia_aud... and pmedia_vid... errors in compiling

[ncherry@xxxxxxxxxxxx (Neil Cherry)]

I am trying to compile a program based on the Simple UA sample program 
at http://www.pjsip.org/pjsip/docs/html/page_pjsip_sample_simple_ua_c.htm

But When I attempt to compile I get 34 errors like below:
undefined reference to `pjmedia_vid_port_param_default'

All off the errors refer to either "pjmedia_vid_..." or "pjmedia_aud_...".

I have `pkg-config --libs libpjproject` in my LIBS line of my Makefile 
and I have include the pjmedia.h in my source, but obviously there is 
something else I need to do.

Can anyone tell me what I am missing ?

Thanks,
     Neil Cherry