Services to provide live streaming video from mobile sources are becoming widespread, including Ustream. It is expected that this type of services will be deployed particularly in local community networks using wireless mesh networks, in addition to the current services provided in the Internet. For providing live video streaming services in wireless mesh networks from mobile sources, adaptive multicast tree construction is the key issue to be addressed. In this paper, we propose a two-layer multicast routing architecture where only pre-determined APs have multicast router functions and the rest of APs have layer 2 switch function for AP-to-AP communication. Here, a shortest path tree is constructed rooted at a router closest a mobile source terminal connecting the rest of routers and APs closest to each of the receiver terminals. In terms of bandwidth utilization efficiency, APs to which routers are connected should be selected so that average end-to-end hop length along the multicast tree is as small as possible. This paper presents two types of router assignment methods, and shows the performance evaluation results by simulation.