Scheduling for real-time interactive multimedia systems (IMS) raises specific challenges that require particular attention. Examples are triggering and coordination of heterogeneous tasks, especially for IMS that use a physical time, but also a musical time that depends on a particular performance, and how tasks that deal with audio processing interact with control tasks. Moreover , IMS have to ensure a timed scenario, for instance specified in an augmented musical score, and current IMS do not deal with their reliability and predictability. We present how to formally interleave audio processing with control by using buffer types that represent audio buffers and the way of interrupting computations that occur on them, and how to check the property of time-safety of IMS timed scenarios, in particular augmented scores for the IMS Antescofo for automatic accompaniment developed at Ircam. Our approach is based on the extension of an intermediate representation similar to the E code of the real-time embedded programming language Giotto, and on static analysis procedures run on the graph of the intermediate representation.