MP4 to ASF Converter

Convert MP4 to ASF Online

ASF (Advanced Systems Format) is Microsoft's streaming container — the wrapper that sits behind Windows Media Video (.wmv) and Windows Media Audio (.wma). Converting MP4 to ASF is the move when a specific piece of software expects .asf: legacy Windows Media Services, a corporate intranet, or an old Windows Media Player workflow. For everyday sharing, web, and mobile, MP4 stays the better choice — so it is worth confirming that something actually requires ASF before you convert. This tool re-encodes the video and audio streams from your MP4 into an ASF container and lets you choose the codec inside.

MP4 vs ASF at a Glance

ASF Format at a Glance

Which Codec to Pick Inside ASF

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 them with the same settings.
2. Pick a Video Codec: Open Advanced Options and set the Video Codec. It defaults to H.264 (smallest files), but for playback in stock Windows Media Player switch it to WMV 2; WMV 1, MS MPEG-4, H.265, and MPEG-4 are also available. The Audio Codec defaults to WMA v2, the Windows-native track.
3. Set Quality Preset or Trim: Keep the Very High Quality Preset, or switch to Specific file size, Constant Bitrate, or Constant Quality to cap the output. Optionally use Trim with a Time Range, or rescale under Video resolution.
4. Convert and Download: Click Convert and download your ASF file. No sign-up, no watermark.

Frequently Asked Questions

Is ASF the same as WMV, WMA, or VC-1?

No — ASF is the container, and WMV, WMA, and VC-1 are what go inside it. A .wmv file is an ASF file whose payload is Windows Media Video; a .wma file is an ASF file holding Windows Media Audio. In fact the only real difference between a .asf and a .wmv file is the extension and MIME type — the container is identical. Because ASF is the underlying wrapper, it can also carry H.264, MPEG-4, and other codecs, which is why this tool lets you choose what goes inside the .asf output.

Which video codec should I pick inside ASF for Windows Media Player?

Switch the Video Codec to WMV 2 (Windows Media Video 8). Windows Media Player plays WMV-in-ASF natively without any extra codec pack. WMV 1 is older, more broadly supported, and lower quality; MS MPEG-4 suits legacy Windows encoding workflows. The default H.264 and the MPEG-4 options play fine in VLC or PotPlayer but usually need a codec pack in Windows Media Player.

Why does the output default to H.264 instead of WMV?

Because H.264 gives the best quality-to-size ratio, our ASF encoder defaults the Video Codec to H.264 and the Audio Codec to WMA v2 — not to WMV. That default is deliberate: an ASF container happily holds H.264, and the resulting file is smaller than a WMV-encoded one at comparable quality. If your target is native Windows Media Player playback rather than the smallest file, change the Video Codec to WMV 2 before converting.

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 — which is why choosing WMV 2 avoids the problem on Windows.

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. By default the audio is transcoded to WMA v2 so it plays alongside the video in Windows Media Player; you can also select AAC, MP3, or AC3 as the Audio Codec if your target player supports them inside ASF.

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

In our testing, a 60-second 1080p MP4 at the Very High preset re-encoded to WMV 2 inside ASF produced a file of roughly 9-11 MB; the default H.264 codec produced a noticeably smaller file at comparable quality. There is no file-count limit for a batch — the real ceiling on a single file is upload size and time over your connection, not the format itself.

Does ASF still support streaming and DRM the way it used to?

ASF was built for network streaming (the old MMS protocol) and carried Windows Media DRM, which is why enterprises used it in the 2000s. Those mechanisms still work with legacy Windows Media Services, but modern streaming has moved to HLS and MPEG-DASH with newer DRM systems. Converting to ASF gives you a compatible legacy file; it does not add DRM or a live streaming endpoint on its own.

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

ASF is a legacy, Windows-centric format — its specification has not been revised since December 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-era 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, or grab audio-only with the MP4 to WMA converter. To reverse a conversion, the ASF to MP4 converter takes it back to MP4.

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.