We present an event-driven video adaptation system in this paper. Events are detected by audio/video analysis and annotated by the description schemes (DSs) provided by MPEG-7 Multimedia Description Schemes (MDSs). And then, adaptation take account of users' preference of events and network characteristic to adapt video by event selection and frame dropping as following three steps: 1) the event information is parsed from MPEG-7 annotation XML file together with bitstream to generate generic Bitstream Syntax Description (gBSD). 2) Users' preference, Network Characteristic and Adaptation QoS (AQoS) are considered for making adaptation decision. 3) adaptation engine automatically parses adaptation decisions and gBSD to achieve adaptation. Different from most existing adaptation work, the system adapts video by interesting events according to users' preference. To achieve a generic adaptation solution, the system is developed following MPEG-7 and MPEG-21 standards. gBSD based adaptation avoids complex video computation. 30 students from various departments test the system with satisfaction. Although, the system is tested on basketball video adaptation so far, it is easy to extend to other video domains.