Several caching schemes for realtime multimedia systems have been proposed, but they focus only on increasing the hit ratio without providing any means to utilize the saved disk bandwidth due to cache hits. One of the most important metrics in multimedia systems is the number of clients that the systems can service simultaneously guaranteeing Quality of Service(QoS). Preemptive but Safe Interval Caching(PSIC) was proposed as a caching scheme which makes it possible to provide deterministic QoS.. However, it has no ability to adapt to the change of system environments since it has no mechanism to change the cache size. In this paper, we present a new caching scheme, Dynamic Interval Caching(DIC), which maximizes the performance, regardless of the change of system environments, providing hiccup-free service, by managing memory buffers dynamically. And it is demonstrated that DIC allocates buffer cache optimally, by comparing with PSIC through trace-driven simulations.