QoS Based Evaluation of the Berkeley Continuous Media Toolkit

摘要

This paper presents a performance analysis of the Continuous Media service provided by the Berkeley, Continous Media Tool kit (CMT). We show a development of metrics, validation by means of a user study, and a performance evaluation of a prototyping environment. From a human 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, and the degree of asynchrony between two streams such as audio and video, need to be kept within limits. Therefore, it is important to know the frame dropping, timing delay, and synchronization drift characteristics of CMT. In a series of experiments we monitored the variation of these parameters with respect to processor, network and event loop loads. It was observed that loads affect aggregate frame drops at lower rates, and consecutive frame drops at higher rates. Because at a higher rates, a large number of consecutive frames are dropped, the ones that are played appear in a more timely manner. It is shown that according to metrics provided by other studies, CMT provides imperceptible audio-video mis-synchronization for about 10 seconds, and tolerable synchronization for about 13 seconds, from the start of the clips for local clients under low processor loads. It is also shown that under high loads, synchronization is achieved at the cost of losing media frames.