What is a .asf file?
Advanced Systems Format File · Video · Microsoft · 1996
An .asf file is Microsoft's Advanced Systems Format, the streaming container that underlies WMV and WMA. The extension usually appears on Windows Media streams and older recordings.
What is a .asf file used for?
ASF is a container, not a codec: it was built for streaming over unreliable networks, with objects identified by GUIDs. A .wmv or .wma file is literally an ASF file whose contents are Windows Media video or audio, which is why all three share one signature.
The .asf extension itself mostly survives on legacy streams, screen recordings and camera output from the Windows Media era. Modern players handle it, and conversion to MP4 is straightforward.
How to open a .asf file
The .asf format opens in the following apps, grouped by operating system. If one app does not work, try another from the same list. For a step-by-step walkthrough, see how to open a .asf file.
Windows
- Windows Media Player (legacy)
- VLC
- MPC-HC
macOS
- VLC
- Elmedia Player
Linux
- VLC
- ffmpeg
How to convert a .asf file
You can convert a .asf file to mp4, mkv, mp3 (audio) using a conversion tool or the export menu of an app that opens it.
.asf file signature (magic bytes)
Programs recognise a .asf file by the bytes at the start of the file, not by its name. These are the signatures for ASF. For a full breakdown, see the ASF file signature page.
| Hex signature | Offset | Note |
|---|---|---|
| 30 26 B2 75 8E 66 CF 11 A6 D9 00 AA 00 62 CE 6C | 0 | ASF header GUID |
See the full magic-numbers reference for every format.
Frequently asked questions
What is a .asf file?
An .asf file is Microsoft's Advanced Systems Format, the streaming container that underlies WMV and WMA. The extension usually appears on Windows Media streams and older recordings.
What is the difference between .asf, .wmv and .wma?
One container, three names. ASF is the container format; Microsoft used .wmv for video content and .wma for audio, and generic or streamed content kept the .asf extension.
How do I play an .asf file?
VLC plays ASF on all platforms. On older Windows, Windows Media Player opens it natively.
How do I convert .asf to MP4?
Run ffmpeg -i input.asf output.mp4, or use HandBrake. Expect re-encoding, since the old WMV codecs cannot be copied into an MP4 container.
Related formats
Sources
Details on this page were checked against authoritative references: