Media streaming has found applications in many domains such as education, entertainment, communication and video surveillance. Many of these applications require non-trivial manipulations of media streams, beyond the usual capture/playback operations supported by typical multimedia software and tools. To support rapid development of such applications, we have designed and implemented a scripting language called Plasma. Plasma treats media streams as first-class objects, and caters to the characteristic differences between stored media files and live media streams. In this paper, we illustrate the design and features of Plasma through several small examples. We also describe two example applications that we developed on top of Plasma. These two applications demonstrated that using Plasma, complex applications that compose, mix, and filter multimedia streams can be written with relatively little effort.