What is MIME type "video/x-ms-asf"?

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

video/x-ms-asf is a MIME type used by Windows Media files.
It defines a container format that holds audio, video, and metadata. This format supports smooth streaming over networks and often works with digital rights management.
It is tied to several file types such as the main ASF file, which serves as the core container. The ASX file works as a playlist, while WAX and WXV are variants that support similar media functionalities.

Associated file extensions

.asf, .asx, .wax, .wxv

Usage Examples

HTTP Header

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


    Content-Type: video/x-ms-asf

HTML

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


    <a href="file.dat" type="video/x-ms-asf">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', 'video/x-ms-asf');    
      res.end('Content here');    
    }).listen(3000);

Associated file extensions

.asf, .asx, .wax, .wxv

FAQs

Which file extensions use the video/x-ms-asf MIME type?

The video/x-ms-asf MIME type is primarily associated with .asf (Advanced Systems Format) files. It is also commonly used for Windows Media metafiles and playlists such as asx, wax, and wxv, which redirect players to the actual media stream.

How do I configure Apache to serve ASF files correctly?

To ensure your Apache server sends the correct headers, add the following line to your .htaccess file or main configuration: AddType video/x-ms-asf .asf .asx .wax .wxv. This ensures browsers and media players recognize the content as Windows Media video.

Can I play video/x-ms-asf files directly in modern web browsers?

Generally, no. Modern browsers like Chrome, Firefox, and Edge do not support ASF or Windows Media formats natively via the HTML5 <video> tag. Users typically need to download the file and open it in a desktop application like Windows Media Player or VLC, or use a browser extension that launches an external player.

What is the difference between ASF and ASX files with this MIME type?

While both may use video/x-ms-asf, an ASF file contains the actual audio and video data. An ASX file is a text-based XML playlist that contains the URL of the stream; when a user clicks an ASX link, it instructs the media player to connect to the stream source rather than downloading the whole video file.

How do I add support for video/x-ms-asf in Nginx?

In Nginx, you should verify or add the entry within your mime.types file or the types block in nginx.conf. The configuration should look like this: video/x-ms-asf asf asx wax wxv;. Restart Nginx after saving the changes to apply them.

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

This usually happens because the browser does not have a plugin to handle the MIME type or the operating system isn't configured to automatically open video/x-ms-asf content in a media player. Ensuring the server sends the correct Content-Type header helps, but users often need to associate the file extension with a player like VLC manually.

Is video/x-ms-asf still recommended for web streaming?

No, this is considered a legacy format. For modern web streaming that works across mobile devices and all major browsers without plugins, you should use video/mp4 (H.264) or video/webm combined with HTML5 standards.

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.