If you are trying to connect to a webinar from work, a school or religious organization, there maybe a network Firewall enabled. If there is a network Firewall enabled, you may see a black video screen or a Connection Can't Be Established warning:
http://www.netscan.co/demo/ Click "start network scan."
You'll need to save, or copy and paste the URL of your test results and forward them to BigMarker at email@example.com. However, if you see that you have a red "X" in your results for WebRTC connectivity, you most likely have a network firewall.
If possible, please contact your IT department and have them open the necessary Ports (see below).
Minimum Requirement: Assumed by default is that TCP ports 80 and 443 are open. Some firewall rules only allow for TCP traffic over port 443, make sure that all traffic can pass over this port.
Best Experience: In addition to the minimum requirements being met, we recommend that UDP ports 1025 - 65535 be open.
If this does not work, have your IT department email firstname.lastname@example.org.