History.com videos will not play when using the Sophos Web Appliance in transparent or bridged mode.
History.com uses RMTP protocol to play videos. The site attempts to use the non-HTTP version of RMTP over port 80 and 443 and because the SWA can only relay HTTP(S) traffic, and not the binary traffic being sent to the history.com site, the videos will not play.
Sophos Web Appliance Virtual
Sophos Web Appliance
What To Do
Due to history.com using Akamai for the delivery of their video content, a bypass based on IPs is not satisfactory workaround as these IPs can change. Currently the only workaround is to set the clients to use the appliance as an explicit proxy, which forces the site to switch to the RMTPT (RMTP encapsulated in HTTP) protocol.