Since MWG 7.1.6. there is Streaming Detector filter that allows to detect streaming media and skip AV filtering, based on this detection. You can import new "Webgateway Antimalware" ruleset from Rules Library - it already includes this check. Please, also look to this discussion: https://community.mcafee.com/thread/42864?tstart=0
P.S. in 18.104.22.168, there are changes that improves streaming detection for some stream types, like Flash Video over RTMP, etc.