MP4 to ASF Converter

Convert MP4 to ASF Online

ASF (Advanced Systems Format) is Microsoft's streaming container — the format that underpins Windows Media Video (WMV) and Windows Media Audio (WMA). Converting MP4 to ASF is the move when you need a file for Windows Media Player, legacy Windows Media Services, or a corporate intranet that expects .asf. This converter re-encodes your MP4 into ASF; it defaults to H.264 video, but for playback in stock Windows Media Player you'll usually want to switch the Video Codec to WMV 2 in Advanced Options.

How to Convert MP4 to ASF

1. Upload Your MP4 File: Drag and drop your .mp4 (or .m4v) onto the page, or click "Add Files" to browse. Add several at once to batch-convert with the same settings.
2. Pick a Video Codec: Open Advanced Options and set the Video Codec. The default is H.264 (smallest files), but for the broadest Windows Media Player compatibility switch it to WMV 2 (Windows Media Video); WMV 1, MS MPEG-4, H.265, and MPEG-4 are also available if a player supports them inside ASF.
3. Set Quality Preset or Target Size: Choose a Quality Preset (Very High is the default), or switch to Specific file size, Constant Bitrate, or Constant Quality to cap the output. Optionally trim with Time Range or rescale under Video resolution.
4. Convert and Download: Click Convert and download your ASF file. No sign-up, no watermark.

MP4 vs ASF at a Glance

Frequently Asked Questions

Is ASF the same as WMV?

No, though they are closely related. ASF is the container; WMV is a video codec that is usually stored inside an ASF container. A .wmv file is an ASF file whose payload is Windows Media Video, and a .wma file is an ASF file holding Windows Media Audio. Because ASF is the underlying wrapper, it can also carry other codecs, which is why this tool lets you pick WMV, MS MPEG-4, or even H.264 inside the .asf output.

Which codec should I choose for maximum Windows compatibility?

Switch the Video Codec to WMV 2. Microsoft calls ASF "the preferred Windows Media file format," and Windows Media Player plays WMV-in-ASF natively without extra codecs. WMV 1 is older and even more broadly supported but lower quality; the default H.264 (and MS MPEG-4 or H.265) inside ASF play in VLC and PotPlayer but may need codecs Windows Media Player does not ship with.

What opens an ASF file after I convert it?

Windows Media Player opens .asf natively on Windows. On macOS, Linux, or for guaranteed playback anywhere, VLC and PotPlayer both handle ASF without plugins. If a player refuses the file, it is almost always a missing codec for the stream inside, not the ASF container itself — choosing WMV 2 here avoids that.

Will the audio from my MP4 be kept?

Yes. Both the video and audio streams from your MP4 are re-encoded and packaged into the ASF container. The audio is transcoded to a Windows Media-compatible track so it plays alongside the video in Windows Media Player.

How large can the output ASF be, and how good is the quality?

In our testing, a 60-second 1080p MP4 converted at the Very High preset with the WMV 2 codec produced an ASF of roughly 9-11 MB. (The default H.264 codec encodes smaller still at comparable quality, but WMV 2 is the more compatible choice for Windows Media Player.) There is no file-count limit; the practical limit on a single file is upload size and time over your connection, not your device.

Is ASF still worth using in 2026, or should I pick MP4 or WMV instead?

ASF is a legacy, Windows-centric format — its last specification revision was 2004 — so for general sharing, web, and mobile, MP4 remains the better choice. Convert to ASF only when something specifically requires it: older Windows Media Services, a DRM-enabled Windows workflow, or software that ingests .asf. If you need a Windows Media file but want the more familiar extension, use our MP4 to WMV converter instead; to undo a conversion, the ASF to MP4 converter reverses it.

Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion — no sign-up, no watermark, never shared or made public.