We have a location with approximately 28 CW9164I wireless ap's. Location is a school and we do a fair amount of airplay casting. We seem to be having issues with either slow casting or people not being able to cast all. This school has a number of samsung tv's that have native airplay. Our client devices are either ipads or macbooks. Are there any recommended best practices as far as wifi settings that need to be adjusted. My suspicion is that we have a lot of multicast traffic on our lan.
mDNS which is the discovery process generally used is not meant to scale well in high client count environments. The clients will send a discovery and all devices that are capable will respond. If you are having issues with discovering devices limiting where they are observed would help. For casting it would be unicast to the TV where it would send a single stream and make sure reachability and bandwidth between the devices are there to support the cast.
Back of the napkin math of ~30 clients per AP and 28 APs is 840 devices. 28 classrooms assuming 1 AP a classroom and 1 TV per classroom isn't untenable, in terms of multicast but all TVs would respond any time someone looks for devices to cast to. This puts it more in the High-density category and less about the multicast traffic to me.