first step :
configure igmp static group
second step :
SAP
"The trick to making a Juniper router initiate a PIM join, while also creating a process that listens to the associated group in contrast to a static IGMP join, is to enable the SAP process on the group in question. SAP always operates on the well-known group address 224.2.127.254, using port 9875, but you can configure SAP to operate on other groups (and ports) as well(in your case the group configured with igmp static)."