What Is an ASF File?

Advanced Systems Format (ASF) is a container format designed for media streaming

What to Know

  • ASF is a container format for Windows Media Audio/Video-based content (WMA and WMV).
  • Play one with VLC, Windows Media Player, and other multimedia players.
  • Convert from ASF to MP4, MP3, AVI, etc., with Zamzar.

This article explains what an ASF file is and how to open or convert one on your computer.

What Is an ASF File?

A file with the ASF file extension is an Advanced Systems Format file developed by Microsoft that's commonly used for streaming audio and video data. An ASF file can contain metadata like a title, author data, rating, and description.

The structure of the audio or video data is understood by an ASF file, but it doesn't specify the encoding method. WMA (audio) and WMV (video) are the two most common kinds of data that's stored in the ASF container, so ASF files are most often seen with one of those file extensions.

The ASF file format supports chapters and subtitles, and also stream prioritization and compression, which is what makes them ideal for streaming.

ASF files in Windows 10

ASF is also short for Atmel Software Framework and a texting abbreviation that means "and so forth," but neither have anything to do with the file format.

Opening and Converting ASF Files

Play an ASF file with Windows Media Player, VLC, PotPlayer, GOM Player, MediaPlayerLite, and probably several other free multimedia players.

There are numerous applications that can convert an ASF file, including free video converter programs and free audio converters. Just open the file in one of those applications and choose to convert the file to a new format.

For example, if you need your ASF file to be an MP4, WMV, MOV, or AVI file, consider using Any Video Converter or Avidemux.

Zamzar is one way to convert ASF to MP4 on a Mac or any other operating system. Just upload your file to that website and choose to convert it to MP4 or any other supported format, like 3G2, 3GP, AAC, AC3, AVI, FLAC, FLV, MOV, MP3, MPG, OGG, WAV, WMV, etc.

Still Can't Open It?

The file extension is the first thing to check for if you can't open it with the programs mentioned above. Make sure it actually reads .ASF and not something similar.

For example, AFS is a file extension for STAAD foundation projects that are created by CAD software. Even though the same file extensions letters are used, they have nothing to do with Microsoft's ASF file format.

The same is true for others like Street Atlas USA maps, secure audio, SafeText, and McAfee Fortress. All of those formats use the SAF file extension and belong to (mostly) discontinued software.

Ability spreadsheet templates (AST) use two of the three extension letters ASF files do, but they're also unrelated.

One exception is ASX files, which are playlists used to listen to ASF files (or some other media file). You can most likely open one like you would an ASF file since some multimedia players support the playlist format, but you can't treat the ASX file as an ASF file; it's just a shortcut to the audio data.

More Information on ASF Files

ASF was formerly known as Active Streaming Format and Advanced Streaming Format.

Multiple independent or dependent audio/video streams can be included in an ASF file, including multiple bit rate streams, which is useful for networks with varying bandwidths. The file format can also store web page, scripts, and text streams.

There are three sections, or objects, that are contained within an ASF file:

  • Header: File size information, the number of streams that it has, error correction details, codecs, metadata, and other objects and general information are stored in the file's header.
  • Data: The section holds the actual content that's to be streamed.
  • Simple Index: A time stamp, frame number, or presentation time is stored in the Simple Index object so that the ASF playback program can seek through the file.

When an ASF file is streamed over the internet, it doesn't need to be fully downloaded before it can be viewed. Once a particular number of bytes have been downloaded (at least the header and one data object), the file can be streamed as the rest is downloaded in the background.

For example, if an AVI file is converted into ASF, the file can begin playing shortly after instead of having to wait for the whole file to download, like what's necessary for the AVI format.

  • What is the best ASF file player for Windows 10?

    ASF is the preferred format for Windows Media Player, which is included in clean installs of Windows 10 and upgrades from Windows 8.1 and Windows 7. In some editions of Windows 10, you must enable Windows Media Player in Settings > Apps > Apps & features > Manage optional features > Add a feature > Windows Media Player.

  • How do I open an ASF file on a Mac?

    To open an ASF file on a Mac, download a free video converter for Mac to convert the ASF file to one of the formats that's accepted by QuickTime Player, which comes on all Macs. 

Was this page helpful?