The MediaElement is a high-level wrapper for audio or video playback. It provides plenty of worthwhile features and is reasonably flexible. You can use it to play background music or to create your own customized video player.
However, the MediaElement isn't a natural fit for applications that need to combine or manipulate real-time audio. For example, if you want to use sound in an arcade game or build a music synthesizer, the MediaElement is awkward at best. Here are some of the challenges you'll face: