Windows Media Metafile

From Just Solve the File Format Problem
(Redirected from ASX)
Jump to: navigation, search
File Format
Name Windows Media Metafile
Extension(s) .asx, .wax, .wxv
MIME Type(s) video/x-ms-asf, audio/x-ms-wax, video/x-ms-asx
Wikidata ID Q298178
Released 1998[2]
Not to be confused with Windows Metafile.

The Windows Media Metafile format, very often referred to as ASX, is a playlist format associated with Windows Media Player. Its name is sometimes given as "Advanced Stream Redirector"[3], and also as ASF Redirector[4]. The Windows Media Metafile format is very strongly associated with ASF, and in practice almost always points to variants of the ASF format. Windows Media Metafile is based on XML, although one source notes that it "doesn't requires [sic] to be a strict XML document", as it apparently specifies that tag and attribute names are case-insensitive and does not properly escape some strings[5]. It additionally resembles the SMIL format, suggesting that one was based on the other. The two are nonetheless incompatible. Its most common use is to serve as an index of media files which are on remote servers instead of users' their own computers (Windows Media Playlist seems to have been more widely used when making playlists of local content); compare M3U.

Windows Media Metafile files may be converted from Windows Media Playlist files and to ISX[6]. ISX files will be in turn converted back to Windows Media Metafile in the process of streaming media from a server to clients.[7]


Names and Identifiers

Although "Windows Media Metafile" is this format's official name, it is hardly ever used outside of official sources, with the most prominent third-party users of that name being technical sources[8] and several "file information" sites that have (presumably copying from one another) confused it with WMA[9][10] (WMA files are often pointed to by Windows Media Metafile files, but are not part of them). ".asx" is one of three extensions, the other two being ".wax" and ".wxv"; the three of these point to .asf, .wma, and .wmv files, respectively, which are all ASF files, but with different extensions depending on their content (see the ASF page for more details). Probably because there seems to have been little indication of the real name in the user-facing information, when the format is discussed, it almost always seems to have taken on its most common extension as a name.

Windows Media Metafile files share the mimetype video/x-ms-asf with ASF. They also use the mimetype audio/x-ms-wax, presumably when pointing to .wma files.[11] Some sources[1][12][13] gives their mimetype as being video/x-ms-asx; however, it seems to be in very rare use, and it would not be surprising if it was only an erroneous "correction" of video/x-ms-asf.


Parsed as XML, Windows Media Metafile files have a root element with a (case-insensitive) name "asx" and an attribute "version".


  • The text in the image at the beginning of [1]




  1. 1.0 1.1
  2. One source ( says that Windows Media Metafiles were first introduced in version 7 of Windows Media player, putting its date of release in 1998 (
  5. VLC source → modules/demux/playlist/asx.c → comment above function ASXToXML
  7. asdf
  11. VLC source → modules/demux/playlist/asx.c → function Import_ASX
Personal tools