Convert · runs on your device

Convert WMV to MP4 in your browser

WMV to MP4 is always a full re-encode: the WMV 9 video inside a .wmv file cannot be copied into MP4, so Video Mender decodes it and encodes H.264 instead — entirely on your own machine.

Nothing is uploaded

Drop video files here

WMV

Choose video files to convert

Output format

Plays on effectively every browser, phone, TV and editor when it holds H.264 and AAC.

Video codec

The universal baseline. Hardware decoding exists on essentially every device sold since 2010.

How to size the output

A constant quality target. File sizes vary with how demanding the footage is.

Quality — 8 of 10

Resolution limit

Files smaller than the limit are left alone. Capping usually looks better than lowering the bitrate.

Frame rate

Audio

Fast rewrapCopy streams without re-encoding when the codecs already fit

Lossless and near-instant when it applies. It cannot reduce file size, so turn it off if you need a smaller file.

A .wmv file is an ASF container holding WMV 9 or VC-1 video and Windows Media Audio. None of those can legally live inside an MP4, and nothing outside the Microsoft stack decodes them reliably, so there is no fast path here. Every frame gets decoded and compressed again as H.264 with AAC audio.

That is worth doing anyway, because WMV has quietly become one of the least playable formats around. No browser plays it, no phone gallery opens it, and Apple devices refuse it outright. Converting to MP4 is usually the difference between a file you can still watch and a file you cannot.

Since a re-encode is unavoidable, this page defaults to the High quality preset. WMV sources are typically low-bitrate to begin with, and spending bits generously on the H.264 encode keeps the second generation of compression from becoming visible.

What this actually does to your file

Rewrap or re-encode

There is no rewrap path. WMV 9, WMV 8, VC-1 and Windows Media Audio are all decode-only in this build, and MP4 cannot carry them regardless, so the fast-copy badge never appears on this page.

Quality

Re-encoding is mandatory for this format, so some loss is guaranteed. High quality keeps it below the threshold most people notice on footage of this vintage.

DRM-protected WMV files cannot be converted by anything, including this tool. They will fail at the decode step.
Some WMV files from screen-recording software have unusual variable frame rates; set an explicit frame rate if the result stutters.
WMV Image (the slideshow variant) is not supported and will be reported as unsupported rather than converted badly.

How to use this page

Add your WMV files. The queue will label each one "Re-encode" — that is expected for this format.
Keep MP4 as the output and the High quality preset.
Start the queue and watch real per-file progress.
Download each MP4, or take a ZIP of the batch.

Where the result plays

Checked against the containers and codecs this page produces, stated conservatively.

Target	Works	Detail
Safari and iOS	Yes	MP4 plays natively. WMV does not play on any Apple device.
Browsers	Yes	No browser has played WMV since Silverlight was retired; MP4 plays everywhere.
Android	Yes	MP4 opens in the gallery; WMV support depends on a third-party player.
Video editors	Yes	MP4 imports on both platforms. WMV import is Windows-only at best.

The formats involved

Format	Read	Write	What it is
WMV	Yes	No	Windows Media Video inside an ASF container. The video is normally WMV3/VC-1, which nothing outside the Microsoft stack decodes reliably.
MP4	Yes	Yes	The MPEG-4 Part 14 container. It is a wrapper, not a codec — an MP4 usually holds H.264 or HEVC video with AAC audio.
MKV	Yes	Yes	Matroska. The most permissive common container: it will carry almost any codec, plus multiple audio tracks, chapters and subtitles.
WebM	Yes	Yes	A deliberately restricted Matroska profile for the web: VP8/VP9/AV1 video with Opus or Vorbis audio, and nothing else.

Tested limits

Real ceilings measured on real devices, not a marketing claim of unlimited.

Limit	Desktop	iPhone / iPad	Why
File size — rewrap	1.3 GiB	384 MiB	Rewrapping never decodes a frame, so it tolerates far larger files.
File size — re-encode	1.0 GiB	256 MiB	Decoding holds uncompressed frames in memory, which is the real constraint.
Clip length — re-encode	4:00:00	30:00	Beyond this, progress reporting and memory behaviour stop being dependable.
Resolution — re-encode	4096 × 2160	1920 × 1080	A 4K frame is about 12 MB decoded, before the encoder allocates anything.

If something goes wrong

The file failed immediately with a decode error.

The most likely cause is DRM. Windows Media DRM cannot be removed by a converter; if the file was bought from a store that used it, no tool will convert it.

Conversion is slower than I expected.

WMV decode plus H.264 encode is two full codec passes with no shortcut available. Capping the resolution to 720p is the most effective way to speed it up.

The output has no audio.

Windows Media Audio has to be re-encoded to AAC. If the audio setting was left on copy, switch it to AAC and run the file again.

Your video never leaves this device

This is a structural property of the application, not a policy we ask you to take on trust. There is no upload endpoint, no API route and no server action anywhere in the codebase, so there is nowhere for a video to be sent even by mistake.

Conversion runs in WebAssembly inside this browser tab. The engine is served from this domain and loaded only when you start a job.
The Content-Security-Policy restricts network connections to this origin, so the page is not permitted to contact a third party at all.
Nothing is stored. Close the tab and every queued file and finished output is gone — which is also why you should download results before you leave.
There are no accounts and no AI. Anonymous page views are counted — which page, roughly what country, what kind of device — and nothing whatsoever about your files.

The repository contains a test that fails the build if any media byte is passed to fetch, XMLHttpRequest, sendBeacon or a WebSocket. See the privacy page for how that is verified.

Questions

Why can WMV not be converted without re-encoding?

Two reasons at once: MP4 has no standard way to carry WMV 9 or VC-1 video, and this build can only decode those codecs, not write them. A rewrap is therefore impossible in either direction.

Will I lose quality converting WMV to MP4?

Some, unavoidably. The practical answer is that H.264 at the High preset is efficient enough to hold on to nearly all of what a typical WMV file contained.

Can you convert a DRM-protected WMV?

No. Digital rights management is enforced at the decode stage and this tool has no way around it, which is the correct outcome rather than a limitation to work around.

Is my WMV uploaded to a server to be converted?

No. The decoder and encoder are WebAssembly running in this tab. Nothing about the file leaves your device, which is why this works on confidential recordings.

Why is WMV so badly supported now?

It was designed for the Windows Media ecosystem and never adopted elsewhere. As browsers dropped plugins and phones standardised on H.264, WMV was left without a platform.