Windows Media file with Audio and/or Video (WMV): You can use a .wmv file either to download and play files or to stream content. The .wmv file format is similar to the .asf file format. MS Sample File
WMV is a MS Windows Media file with audio and/or video and is used to download and play files or to stream content. The WMV format is similar to the ASF format. Please see the ASF file documentation for more information about the capabilities of these files.
Microsoft's proprietary compression format for motion video, Windows Media Video is used for both streaming and downloading content via the Internet. Microsoft's Windows Media Player, an application bundled with Windows XP operating systems, lets you playback and manage a range of audio and video file types, including, of course, WMA and WMV.