To rapidly evolve new designs of peer-to-peer (P2P) multimedia streaming systems, it is highly desirable to test and troubleshoot them in a controlled and repeatable experimental environment in a local cluster of servers, as it is risky to integrate untested protocols in live production and mission-critical peer-to-peer sessions, such as live P2P streaming. Though it is possible to construct such controlled experiments with virtual machine monitors, there are a number of challenges and roadblocks: (1) The deployment of such resource-hungry virtual machine environments are complicated and time-consuming for researchers without prior systems expertise; (2) The system designer needs to implement many basic streaming elements, such as playback buffers and message switches. In this paper, we seek to address these challenges by introducing Crystal, an emulation framework for practical P2P multimedia streaming systems, which provides support for developing, testing, and troubleshooting new s...