.wmv

Advanced Systems Format

This image illustrates the computer icons that Windows 8.1 displays for Advanced Systems Format, depending on the file name extension. From left to right, the icons correspond to .asf, .wma and .wmv files.
Filename extension	.asf .wma .wmv
Internet media type	video/x-ms-asf, application/vnd.ms-asf
Type code	'ASF_'
Uniform Type Identifier (UTI)	com.microsoft.advanced-systems-format
Magic number	30 26 B2 75 8E 66 CF 11 A6 D9 00 AA 00 62 CE 6C
Developed by	Microsoft
Type of format	Digital container format
Container for	Windows Media Audio, Windows Media Video, VC-1

30 26 B2 75 8E 66 CF 11

Advanced Systems Format (formerly Advanced Streaming Format, Active Streaming Format) is Microsoft's proprietary digital audio/digital video container format, especially meant for streaming media. ASF is part of the Media Foundation framework.

ASF is based on serialized objects which are essentially byte sequences identified by a GUID marker.

The format does not specify how (i.e. with which codec) the video or audio should be encoded; it just specifies the structure of the video/audio stream. This is similar to the function performed by the QuickTime, AVI, or Ogg container formats. One of the objectives of ASF was to support playback from digital media servers, HTTP servers, and local storage devices such as hard disk drives.

The most common media contained within an ASF file are Windows Media Audio (WMA) and Windows Media Video (WMV). The most common file extensions for ASF files are extension .WMA (audio-only files using Windows Media Audio, with MIME-type audio/x-ms-wma) and .WMV (files containing video, using the Windows Media Audio and Video codecs, with MIME-type video/x-ms-asf). These files are identical to the old .ASF files but for their extension and MIME-type. The different extensions are used to make it easier to identify the content of a media file.