Transmission of digital audio and video streams is one of the major applications in future wireless networks. Increasing bandwidths and processing power make it possible to receive video streams almost everywhere. But the classes of mobile devices vary from multimedia enabled mobile phones to high-end notebooks. The varying capabilities of these devices such as display resolution, processing power, memory size or network connection result in a great heterogeneity of client devices. To support as many different devices as possible, some kind of video adaptation is needed. In this book we propose a multimedia gateway system that provides a video adaptation service to its clients. The main focus, however, is the adaptation process itself. Therefore, we investigated different compressed domain transcoding techniques and identified three adaptation dimensions that need to be considered to support a great heterogeneity of devices. Based on these observations a novel transcoding architecture is presented that smartly combines existing transcoding mechanisms to build a multidimensional compressed domain transcoder.