What is the ASX file format?
The .asx file format - Advanced Stream Redirector - is a type of XML-based metafile developed by Microsoft. The main purpose of the .asx format is to store a playlist of Windows Media stream references for a multimedia presentation, directing the player to remote audio or video rather than containing any media data itself.
These files contain information related to the specific media streams to which they point. An .asx document uses an <ASX> root element (normally declaring VERSION="3.0") with one or more <ENTRY> children; each entry holds a <REF HREF="..."> URL - typically an mms://, rtsp://, or http:// address - plus optional title, author, and copyright metadata.
.asx files provide Windows Media Player with a shortcut to the specified media stream, launching playback without the user needing to know the raw URL. Because the format is plain text, any .asx file can also be inspected or edited in any text editor such as Notepad. Sibling formats .wax (audio-only) and .wvx (video) share the identical XML schema.
To open such files you need a media player such as Windows Media Player or VLC. For local library playlists, Microsoft later introduced .wpl as a more capable replacement, while open formats like .m3u8 now handle most internet radio and streaming scenarios.
Security & safety
RISK: MEDIUMThe ASX file itself is harmless text, but because it auto-launches a player and fetches a remote URL it has historically been abused: crafted ASX/ASF metafiles triggered Windows Media Player buffer-overflow exploits in the 2000s, and malicious .asx files can redirect to scripted or scam stream pages. Open unknown .asx files in a text editor first to inspect the URLs. Many "ASX player" downloads from ad-heavy portals are adware (GOM/KMP/jetAudio bundlers) - use VLC instead.
Format details
in a nutshell- Cheyenne/ARCserve session log - Some legacy backup tools wrote .asx index/session files unrelated to streaming.
Programs that open ASX files
Windows3 apps
Windows Media Player
Built-in Double-click the .asx; WMP follows the redirector to the stream (if the URL is still live). 
VLC media player
Open-source Media > Open File, pick the .asx; VLC resolves the REF URLs and plays the stream. 
Any text editor (Notepad, Notepad++)
Free Right-click > Open with > Notepad to read the stream URLs inside the file. 
macOS1 app
VLC media player
Open-source File > Open File, select the .asx; VLC follows the embedded stream URLs. 
Linux1 app
Android1 app
Technical details
deep spec| Format type | XML-based plain-text metafile (redirector); contains no audio or video data |
| Developer | Microsoft |
| Primary MIME type | video/x-ms-asf |
| Alternate MIME types | application/x-ms-asf, video/x-ms-asx, application/x-mplayer2 |
| Root XML element | <ASX> with a VERSION attribute; standard value is "3.0" |
| Entry structure | Each <ENTRY> element contains a <REF HREF="..."> pointing to the stream URL, plus optional <TITLE>, <AUTHOR>, <COPYRIGHT> |
| Supported stream protocols | mms://, mmst://, mmsu://, rtsp://, http:// |
| File signature | None (plain text); file begins with <ASX or <asx - element names are parsed case-insensitively |
| Text encoding | ASCII or UTF-8 (most common); UTF-16 also accepted; <?xml?> prolog is optional |
| Typical file size | 200 bytes - 10 KB |
| DRM relationship | The .asx file itself is unencrypted; streams it references may be WMDRM-protected |
| Sibling metafile formats | .wax (audio redirector) and .wvx (video redirector) use the identical XML schema |
| Modern alternatives | .wpl replaced ASX for local WMP playlists; .m3u8 and XSPF cover current streaming use cases |
| Released | 1999 (Windows Media Player 6.x / Windows Media Technologies 4) |
| Latest version | ASX 3.0 (Windows Media format; version declared in the <ASX VERSION="3.0"> root attribute) |
| Specification | learn.microsoft.com |
ASX conversions
Community Q&A
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