What is MIME type "application/x-ms-asx"?

A MIME type is a string that tells browsers and other tools how to handle a particular kind of file.

The MIME type application/x-ms-asx handles files that act as an Advanced Stream Redirector. It is a plain text file, usually written in XML, that tells media players where to find and load streaming content.

When a media player opens a file with this MIME type, it reads the XML instructions to redirect playback to one or more online media URLs. It does not contain the media itself but serves as a roadmap to where the media is hosted.

This format is widely used in Microsoft environments and is favored by applications like Windows Media Player. Files using this format typically have the extension ASX.

Media redirection: Instructs media players to locate and stream content from remote servers.
Playlist management: Organizes multiple media references for seamless playback.
XML-based structure: Uses simple, editable text that defines stream locations and metadata.
Microsoft integration: Key for Windows Media Player and similar applications.

For more detailed information, see the Advanced Stream Redirector article.

Associated file extensions

.asx

Usage Examples

HTTP Header

When serving content with this MIME type, set the Content-Type header:


    Content-Type: application/x-ms-asx

HTML

In HTML, you can specify the MIME type in various elements:


    <a href="file.dat" type="application/x-ms-asx">Download file</a>

Server-side (Node.js)

Setting the Content-Type header in Node.js:


    const http = require('http');    
    
    http.createServer((req, res) => {    
      res.setHeader('Content-Type', 'application/x-ms-asx');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.asx

FAQs

How do I open a file with the MIME type application/x-ms-asx?

Since these files are playlists or redirectors, you need a media player that supports the Advanced Stream Redirector format. The most common application is Windows Media Player, but third-party players like VLC Media Player also handle them well. If you open the file in a text editor like Notepad, you will see the raw XML code rather than the video or audio content.

Why does my browser download the ASX file instead of playing it?

Modern web browsers (Chrome, Firefox, Edge) do not natively support the application/x-ms-asx MIME type or the legacy plugins required to play them inside the webpage. Because the browser cannot render the content directly, it defaults to downloading the file. To fix this, users usually need to open the downloaded file manually in a desktop media player.

How do I configure Apache or Nginx to serve ASX files correctly?

You must ensure your web server sends the correct Content-Type header so the client recognizes the file as a playlist. For Apache, add AddType application/x-ms-asx .asx to your .htaccess or config file. For Nginx, add application/x-ms-asx asx; inside your mime.types file or types block.

What is the difference between an ASX file and a WMV file?

A WMV file contains the actual video and audio data, whereas an ASX file is a small text file that points to the location of that WMV file. Think of the application/x-ms-asx file as a shortcut or a playlist; it contains URLs and metadata, but it does not store the media itself. You can learn more about the media format at WMV.

Can I use application/x-ms-asx in an HTML5 video tag?

No, the HTML5 <video> element does not support the ASX format or the application/x-ms-asx MIME type. HTML5 standardizes on formats like MP4, WebM, and Ogg. If you are developing a modern website, you should convert your media to H.264/MP4 and link directly to the video file, rather than using an ASX redirector.

How can I create or edit an application/x-ms-asx file?

Because these files are essentially XML text files, you can create or edit them using any basic text editor, such as Notepad on Windows or TextEdit on macOS. You define the media source using the <REF HREF="url"/> tag structure. Ensure you save the file with the .asx extension and plain text encoding.

General FAQ

What is a MIME type?

A MIME (Multipurpose Internet Mail Extensions) type is a standard that indicates the nature and format of a document, file, or assortment of bytes. MIME types are defined and standardized in IETF's RFC 6838.

MIME types are important because they help browsers and servers understand how to process a file. When a browser receives a file from a server, it uses the MIME type to determine how to display or handle the content, whether it's an image to display, a PDF to open in a viewer, or a video to play.

MIME types consist of a type and a subtype, separated by a slash (e.g., text/html, image/jpeg, application/pdf). Some MIME types also include optional parameters.

How do I find the MIME type for a file?

You can check the file extension or use a file identification tool such as file --mime-type on the command line. Many programming languages also provide libraries to detect MIME types.

Why are multiple MIME types listed for one extension?

Different applications and historical conventions may use alternative MIME identifiers for the same kind of file. Showing them all helps ensure compatibility across systems.