We show a methodology for a user-driven, top down approach to research in quality of service issues in multimedia systems. As a case study, we show the development of metrics, validation by means of a user study, and a performance evaluation of a prototyping environment. The Berkeley Continuous Media Toolkit (CMT) is a popular environment that satisfies this need. From a user's perspective, in order for multimedia demonstrations to be comprehensible, the number of audio or video frames dropped and the timing delays in the ones that are displayed, need to be kept to a minimum. Therefore, it is important to know the frame dropping characteristics of CMT. In a series of experiments we monitored the variation of these parameters with respect to processor and network loads. It was observed that loads affect aggregate frame drops at lower rates and consecutive frame drops at higher rates. Because at a higher rate a large number of consecutive frames are dropped, the ones that are played appear in a more timely manner. As a solution to the observed problems, we present some QoS based approaches to control drop and delay parameters.