Deploy IGP LFA FRR.
Deploy ISIS LFA FRR or OSPF LFA FRR to the protection nodes, such as DeviceA, so that the nodes can generate main and backup unicast routes.
Configure PIM FRR.
PIM FRR is configured on protection nodes, such as DeviceA. When a user joins in, a main multicast forwarding entry and a backup multicast forwarding entry are generated. If the network operates normally, the protection nodes only receive the multicast traffic from main link and drop the traffic from backup link. If the main link fails, the protection node rapidly switches to the backup link to protect the multicast traffic.