Convert WebM to MP4 Online

Pick a WebM file and convert it to universally compatible MP4. No software to install; the conversion runs directly in your browser.

How it works

  1. Upload your WebM video. Drag your WebM file into DomeScribe. Files using VP8 or VP9 video and Opus or Vorbis audio are accepted.
  2. Choose MP4. Select MP4 as the output. Because WebM and MP4 use different codecs, the video is re-encoded as H.264 with AAC audio — the combination every phone, TV, and browser plays.
  3. Pick a resolution if you like. Keep "Original" to match the source, or downscale to 1080p or 720p to make the output smaller. Frame rate can also be set to 60, 30, or 24 fps.
  4. Convert and save the MP4 file. Click Convert. Encoding runs in your browser, so a short clip takes under a minute and longer videos proportionally more. Save the result with a free account.

Converter at a glance

Video formats
MP4, MOV, AVI, WebM, MKV, FLV — optional resolution (4K to 360p) and frame rate (60/30/24 fps)
Audio formats
MP3, WAV, FLAC, AAC, OGG, M4A
Privacy
Runs 100% in your browser (WebAssembly) — your file is never uploaded to a server
Speed
No upload wait — processing starts as soon as the in-browser engine loads (~31 MB, cached after the first run)
File size
Limited by your device's memory — up to about 500 MB works reliably
Watermark
None
Limits
Free — no monthly limit; runs on your device (a free account is needed to save the file)

Frequently asked questions

Why won't my WebM file play on my phone or TV?

WebM uses VP8 or VP9 codecs that many hardware devices do not decode natively. iPhones, most smart TVs, and older Android devices lack built-in WebM support. Converting to MP4 with H.264 encoding in DomeScribe solves this compatibility issue.

Is WebM to MP4 conversion lossy?

Yes — WebM and MP4 use different video codecs, so a full re-encode to H.264 is required. DomeScribe uses a quality-based setting (CRF 23) that makes the visual difference negligible in nearly all practical cases.

I downloaded a WebM from a website — can I convert it?

Yes. WebM is the default format many websites and browsers use for embedded video. Upload the downloaded WebM file and DomeScribe transcodes it to a universally playable MP4 on your device.

Will the file size change when going from WebM to MP4?

It depends on the source. VP9 WebM files are already quite efficient, so the H.264 MP4 may be similar in size or somewhat larger at the same resolution. Downscaling to 720p is the easiest way to make it smaller.

Does the conversion preserve the original resolution and frame rate?

By default, yes — DomeScribe matches the source resolution and frame rate. You can optionally downscale (for example from 4K to 1080p) or set 60, 30, or 24 fps.

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