Multimedia applications are often executed on standard Personal Computers. The absence of established standards has hindered the adoption of real-time scheduling solutions in this class of applications. Developers have adopted a wide range of heuristic approaches to achieve an acceptable timing behaviour but the result is often unreliable. We propose a mechanism to extend the benefits of real-time scheduling to legacy applications based on the combination of two techniques: 1) a real-time monitor that observes and infers the activation period of the application, and 2) a feedback mechanism that adapts the scheduling parameters to improve its real-time performance