What is an ASF file?
ASF stands for Advanced Systems Format. It was created by Microsoft and first released in 1996. ASF is the container behind WMV and WMA. Many CCTV systems and DVRs still export ASF files, which few programs outside Windows will open.
| Type | video |
|---|---|
| Compression | Lossy |
| Usually contains | Windows Media Video and Audio |
| In a browser | does not play in browsers; plays in Windows Media Player |
| Common uses | security cameras, DVRs and old Windows streams |
| MIME type | video/x-ms-asf |
Which format should you convert ASF to?
- ASF to MP4 to play on any phone, computer or TV, or to upload to YouTube and social media.
- ASF to MP3 to keep only the soundtrack, for music or a podcast.
ASF is already lossy, so converting it to a lossless format makes the file bigger without improving it; pick a lossless target only if a program requires one.
How to open an ASF file
Whether an ASF file opens with a double click depends on the device. Here is what works on each, without buying software:
| Windows | Films and TV and Media Player open the common formats; VLC opens almost any video file, ASF included. |
|---|---|
| Mac | QuickTime Player opens formats Apple supports; VLC or IINA open the rest. |
| iPhone and iPad | The Files app plays formats Apple supports. For others, a player such as VLC for iOS, or converting the file here, is the easiest route. |
| Android | Most gallery and music apps play the common formats; VLC for Android plays almost everything. |
| Web browser | ASF does not play in browsers; plays in Windows Media Player. |
Want the technical details? See what a .asf file is, with its MIME type, file signature and a viewer.
ASF compared with other video formats
How ASF stacks up against the formats people most often convert it to or from:
| Format | Compression | Usually contains | Released | Best for |
|---|---|---|---|---|
| ASF | Lossy | Windows Media Video and Audio | 1996 | security cameras, DVRs and old Windows streams |
| MP4 | Lossy | H.264 or H.265 video with AAC audio | 2001 | phone videos, YouTube uploads, social media and streaming |
| MOV | Lossy | H.264, HEVC or ProRes video with AAC audio | 1991 | iPhone recordings, Final Cut Pro and screen recordings on Mac |
| MKV | Lossy | almost any codec, often H.264 or H.265 with several audio and subtitle tracks | 2002 | films and TV rips, OBS recordings and anime releases |
| WebM | Lossy | VP8, VP9 or AV1 video with Vorbis or Opus audio | 2010 | web video, screen recorders and browser-based recordings |
How to use the ASF converter
- Choose the format you want in the Convert to menu.
- Drop your ASF files on the box, or press Choose ASF files. Several files can go in at once.
- Adjust the settings if you need to; the defaults suit most people.
- Press Convert and save each file with its Download button. Nothing is uploaded at any point.
Tips for converting ASF files without losing quality
ASF is lossy, so some detail was already discarded when the file was made. Converting it cannot bring that back. Converting to a lossless format preserves what is left exactly but makes the file larger; converting to another lossy format adds a small extra loss, which is invisible at sensible settings.
- Keep the original recording. Every re-encode costs a little detail, so convert from the best copy you have, not from a file that was already converted.
- Know whether you need a new container or a new codec. MOV, MKV and MP4 can all hold H.264 video, and switching between them is fast and lossless; changing the codec means re-encoding, which is slower.
- For sharing, MP4 with H.264 at 1080p or 720p is the safe choice: every phone, browser and social network plays it.
- Phones record at very high bitrates. If a file is too big to send, lowering the resolution to 720p usually shrinks it far more than any quality setting.
Convert ASF files from the command line
Everything this page does can also be done in a terminal. The most common ASF conversion, to MP4, looks like this with ffmpeg:
ffmpeg -i input.asf -c:v libx264 -crf 23 -preset veryfast -c:a aac -b:a 128k -movflags +faststart output.mp4Change the output extension to pick another format. The converter above runs the same ffmpeg engine inside your browser, so you get the result without installing anything.
ASF converter FAQ
What is an ASF file?
ASF stands for Advanced Systems Format, a video format created by Microsoft in 1996. ASF is the container behind WMV and WMA. Many CCTV systems and DVRs still export ASF files, which few programs outside Windows will open.
How do I open an ASF file?
ASF does not play in browsers; plays in Windows Media Player. If the program you need will not open it, convert it to a more widely supported format above.
What is the most common ASF conversion?
ASF to MP4 is the conversion people search for most. The video is re-encoded to H.264 video with AAC audio.
Does converting ASF files here upload them?
No. Every conversion on this page runs inside your browser, so your ASF files never leave your device.
Is the ASF converter free?
Yes. There is no sign-up and no watermark, and no limit on how many ASF files you convert. The site is supported by advertising.
Can I convert ASF files on iPhone or Android?
Yes. Open this page in Safari on iPhone and iPad, or in Chrome on Android, choose your ASF files and download the results to your Downloads folder.
Can I convert several ASF files at once?
Yes. Drop as many as you like; they are converted one after another, each with its own download button.