Free tool

WebM to MP4 Converter

WebM videos from browsers and screen recorders use VP8 or VP9 pictures, which iPhones, many editors and some upload forms don't accept. This tool re-encodes them to H.264 MP4 on your own device. It is the slowest conversion on this site, and this page tells you exactly what to expect.

01 — Your file

Choose a file

02 — Result

Your converted file

Choose a file and press Convert to MP4. The conversion runs in this tab, so even large files never leave your computer or phone.

Converting WebM to MP4

  1. Choose the WebM above. The file card shows the picture codec, usually VP8 or VP9, and the length.
  2. Press "Convert to MP4" and leave the tab open. A progress bar and elapsed time show how far it has got.
  3. Download the MP4 when it's done.

Why this one takes longer

Unlike MOV or MKV, a WebM's picture can't simply be copied into an MP4 that plays everywhere, because most MP4 players expect H.264. Every frame has to be decoded and compressed again. The converter uses the x264 encoder at a fast preset and a standard quality setting, and converts Opus or Vorbis sound to AAC.

Doing that in a browser tab is slower than in a desktop app. In our tests on a recent laptop, 720p WebM converted at about half of real time, so a 10-minute 720p recording takes around 20 minutes. 1080p takes considerably longer, and phones are slower than laptops. Low-resolution clips and short recordings finish quickly.

AV1 WebM files

Some newer WebM files use the AV1 codec. The in-browser converter can't decode AV1 pictures, so it tells you when a file uses it instead of failing silently. The sound of an AV1 WebM still converts, with the WebM to MP3 converter.

Faster options

  • If you only need the sound, WebM to MP3 takes seconds, because the picture isn't touched.
  • If you need just part of a long recording, cut it in your screen recorder or editor first, then convert the shorter file.
  • For hours of WebM footage, a desktop tool such as HandBrake or ffmpeg uses your full processor and is much faster.
  • If the goal is a transcript or translation, mydubly accepts WebM directly on the WebM to text and video translator pages.

Where WebM comes from

Browsers record camera, microphone and screen as WebM, so browser-based screen recorders, online webcam recorders and some meeting tools produce it. The video codec explainer covers how VP9, H.264 and AV1 differ and why support varies.

How the free converter works

The converter is ffmpeg, the open-source media toolkit, compiled to WebAssembly so it runs inside your browser tab. Your file is read straight from your disk by that engine; it is never uploaded to mydubly or anywhere else, and no account is needed.

  • The engine is about 30 MB and downloads the first time you convert something. After that your browser normally keeps it.
  • Large inputs are fine because the file is read in place, but the result is built in memory, so outputs are capped at about 1.5 GB.
  • Speed depends on your device. Copying streams takes seconds; re-encoding video is the slow case.
  • Keep the tab open until the download button appears. Closing it stops the conversion.

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Frequently asked questions

Why does WebM to MP4 take so long?

The VP8 or VP9 picture has to be re-encoded to H.264, frame by frame, inside your browser. In our tests 720p converted at about half of real time on a laptop.

Will an MP4 converted from WebM play on iPhone?

Yes. The output is H.264 video with AAC sound, which iPhones, Windows, Macs and editors all play.

Can I convert an AV1 WebM?

Not to MP4 in the browser; the converter tells you when a file uses AV1. Its sound can still be converted to MP3.

Does the quality drop?

Re-encoding always changes the picture slightly. At the default quality setting the difference is hard to see at normal viewing size.