IGMP configuration for Crestron NVX setup

I'm setting up a Crestron NVX proof of concept - it's basically a video switcher over IP / Multicast.

It sends 1gpbs per stream, so good IGMP configuration is required to not flood uplinks but I'm hitting an issue.

I have an L2 switch (Catalyst 9300) setup with a single 1G copper uplink to our access switch, that switch port is set to a specific AV Vlan which then goes back to our core that deals with L3.

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All my decoder and encoder boxes are connected to the C9300, so I'm expecting multicast traffic to stay within that switch

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IGMP snooping is enabled on the C9300, querier enabled on the Vlan, but somehow even though the core doesnt have anything subscribing to those multicast streams, I'm flooding my 1Gbps uplink to the access switch, then using 1Gbps of the 10Gbps from the core to the access (basically all the multicast streams from my encoder boxes are trying to get back to the core).

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I'm the AV guy here, I'm trying to help out our network guys, my understanding of multicast networking is limited.