MP4 to ASF Converter

What happens when you convert MP4 to ASF

• The video is re-encoded to Windows Media Video 8 with WMA audio.
• Re-encoding in a browser is slow: expect several times the video's length for HD footage on a laptop, and longer on a phone. Short and low-resolution clips finish much sooner.
• A WMV file is itself an ASF, so Windows Media Player, the Films and TV app and CCTV software that ask for ASF all read it.

How to convert MP4 to ASF online

1. Press "Choose MP4 files" and select one or more files, or drag them onto the box. You can add files of any size your device can hold in memory.
2. Adjust the settings if you need to: resolution and quality control the size of the result. The defaults suit most people.
3. Press "Convert to ASF". The first audio or video conversion downloads the converter engine, about 32 MB, which your browser then keeps for next time.
4. Save each ASF with its download button. Close the tab and every trace of the files is gone from memory.

Why convert MP4 to ASF?

MP4 files usually come from phone videos, YouTube uploads, social media and streaming. People convert them to ASF because ASF is what Windows Media tools, some CCTV and DVR software and older Windows programs ask for.

In short, MP4 is good at what it was made for, and ASF is the more practical choice when the file has to play, upload or edit somewhere else. MP4 plays in every browser, phone and smart TV, while ASF does not play in browsers; plays in Windows Media Player.

How to convert MP4 to ASF on Windows, Mac, iPhone and Android

On Windows

Open this page in Chrome, Edge or Firefox, drag your MP4 files in from File Explorer, and press Convert. Each ASF is saved to your Downloads folder. If you prefer a desktop program, VLC can also convert MP4 to ASF: choose Media, then Convert / Save.

On a Mac

Safari, Chrome and Firefox all work. Drag the MP4 files from Finder onto the drop zone and the ASF files land in Downloads.

On iPhone and iPad

Open the page in Safari and tap Choose MP4 files. You can pick from Photos or from the Files app. The converted ASF appears in Files, in the Downloads folder; to put it in your photo library, open it there, tap Share and choose Save Video.

On Android

Open the page in Chrome, tap Choose MP4 files and pick them from Files or your gallery. The ASF is saved to the Download folder, where any file manager can find it. Keep the screen on while a long video converts, because Android may pause a tab in the background.

Best settings for MP4 to ASF

ASF is written as Windows Media Video 8 with WMA audio. The Resolution setting is the one to reach for: 1080p keeps full HD detail, 720p is plenty for phones and laptops and roughly halves the size, and 480p suits email and old devices.

The quality levels map to the H.264 CRF scale where the target uses H.264, and to fixed high-quality settings for older codecs such as MPEG-2, MPEG-4 Part 2, WMV and Theora. Re-encoding always costs a little detail, so convert from the best copy of the MP4 you have.

MP4 vs ASF: the differences

About MP4 and ASF files

What is an MP4 file?

MP4 is the most widely supported video format, and H.264 video with AAC audio inside it plays on essentially every device made in the last fifteen years.

What is an ASF file?

ASF is the container behind WMV and WMA. Many CCTV systems and DVRs still export ASF files, which few programs outside Windows will open.

MP4 to ASF not working? Common problems

• The conversion is slow. Audio and container changes take seconds, but re-encoding video runs on your own processor. Lower the resolution to 720p, close other tabs, and keep the device plugged in.
• The tab stops or reloads on a very large file. Browsers limit how much memory one tab can use, around 2 GB and less on phones. Split long recordings or convert them on a computer.
• The ASF will not play on an old device. Try the other formats offered for MP4, or choose 720p, which older players handle more reliably.

Convert MP4 to ASF with ffmpeg

This converter runs ffmpeg inside your browser. If you would rather use the ffmpeg command line on your own computer, this command produces an equivalent ASF with the same kind of settings:

ffmpeg -i input.mp4 -c:v wmv2 -b:v 2500k -c:a wmav2 -b:a 192k -f asf output.asf

Replace input.mp4 with the name of your file. For a whole folder of MP4 files, run the command in a loop, or drop them all on the converter above, which processes them one after another.