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 CouterPath's free 'X-Lite' application to make video calls to other Asterisk extensions.