This indicates an attempt to access VLC media player.
VLC is an open-source media player that supports most multimedia files as well as DVD, CD, VCD, and streaming protocols. It is available for both desktop and mobile platforms which include iOS and Android. It is also able to stream media over networks and transcode multimedia file.
To completely block/monitor VLC, "RTP", "MMS" and "RTSP" has to be set together with "VLC" to the desired Fortigate action.