Original link: http://www.cnblogs.com/zmlohw/p/5155662.html
In MSDN described, for performance reasons, media resources need to be set to the content (Content), as follows:
For media processing on a Windows Phone is optimized to work with files and network flow, instead of using the stream in memory. Any media files (such as sound effects) This means that the application should be included in the "Build Action" is set to "content" rather than a "resource" . When the media file as a compile-time content, it will be as loose files and application files (.XAP) stored together, rather than stored in the application file. When the media file as a resource compiler, usually accessed through the stream to retrieve the file, which may reduce performance. In addition, when playing compiled for the content of media files directly play. When the media file as a resource compiler, you need to copy the contents to a file before playing on the Windows Phone, which can degrade performance.