http://www.md3v.com/enable-video-support-for-asterisk-in-freepbx
FreePBX → Settings → Asterisk SIP Settings → Video Codecs
Select Enabled.
Select h264, h263p, h263 and h261.
Click Apply to save the settings.
You can now use soft phone applications such as CounterPath's free 'X-Lite' application to make video calls to other Asterisk extensions.