In this demonstration paper we present a stream query processor capable of handling media (audio, video, motion ...) and feature streams. We show that due to their inherent semantics, a number of constraints can be specified on the streams and the dependencies among streams. These are expressed using a Media Stream Definition Language (MSDL). We also show how MSDL constructs are utilized by the query planner and executor, for example, to reduce redundant stream elements. The system is demonstrated using an immersive environment application called IMMERSI-MEET that enables a user to launch continuous queries against a live meeting.