Convert WEBM to MP4
WEBM is made for browsers, and almost nothing else takes it: not Premiere, not Resolve, not PowerPoint, not an iPhone. Convert it to H.264 in an MP4 and it drops straight into any of them.
- Never stored
- No queue, no waiting
- No signup, no watermark
How it works
Add your WEBM
Drop the file. VP8, VP9 or AV1 video and Opus or Vorbis sound are all supported.
Let it convert
The picture is re-encoded as H.264 at the original size and frame rate, and the sound as AAC.
Download the MP4
Ready for an editor, a phone, a slide deck or a client.
Always a re-encode, and why
WebM was made for the open web and holds VP8, VP9 or AV1 video with Vorbis or Opus sound. None of those belongs in an MP4 in any way that things will actually play, so unlike an MKV or a MOV this conversion can never be a simple relabel — every frame is decoded and encoded again as H.264, and the sound as AAC. It takes real time, proportional to the length of the video, and it costs one generation of quality.
It also usually makes the file larger, which surprises people. VP9 and AV1 are newer and more efficient than H.264 — AV1 substantially so — and giving that up costs what it saved. Converting to MP4 buys compatibility and nothing else: an MP4 plays on essentially every device, television, editor and messaging app ever made, and a WebM does not.
If the WebM has transparency, this will quietly flatten it. VP8 and VP9 can carry an alpha channel, which is why WebM is used for animated overlays, stickers and logos meant to sit over other content. H.264 in an MP4 has no alpha channel at all, so the transparent areas come out as solid colour. The file will play perfectly and be wrong, with nothing to warn you but your own eyes.
AV1 is the other thing to check before converting. It is efficient enough that more and more WebM files use it, and decoding it here depends on the device being able to decode AV1 at all — recent Chrome, Edge and Firefox can, older machines and some phones cannot, and on those the file simply will not open. Sound converts to AAC in every case; Opus in particular is a better codec than AAC at low bitrates, so speech recordings lose a little more than music does.
When you want something else
Check first whether anything needs the MP4. Every current browser plays WebM, and so do VLC, MPV and most recent televisions — converting a file that already plays costs time, size and quality for nothing. The real reasons are older Apple devices, video editors that refuse the format, and messaging apps.
When you do convert, ffmpeg gives you the control that matters: ffmpeg -i in.webm -c:v libx264 -crf 18 -preset slow -c:a aac -b:a 192k out.mp4 keeps the second generation effectively invisible, which is worth the extra minutes on something you will keep. To preserve transparency rather than losing it, there is no MP4 answer — keep the WebM, or export an image sequence with alpha and take that into an editor.
Frequently asked questions
Why must WEBM be re-encoded?
Because its video is VP8, VP9 or AV1, and an MP4 that programs actually accept holds H.264. The picture is decoded and re-encoded at high quality — a screen recording or animation comes through looking the same.
Is my file stored anywhere?
No. Nothing is stored, so the file stays yours.
The file got bigger. Why?
VP9 is more efficient than H.264 at the same quality, so matching the quality costs more bits. That is the price of a format everything can open. Use Compress Video afterwards if the size matters.
What about the transparency in my WEBM?
MP4 with H.264 has no alpha channel, so transparent areas become black. For transparency, keep the WEBM, or export a GIF with Video to GIF.
Does it work for long screen recordings?
Yes. The output is written out as it goes rather than held all at once, so an hour-long recording is no problem.
Will the sound stay in sync?
Yes. Both tracks are rebuilt on one clock, which also repairs WEBM recordings that start with a gap — a common quirk of browser-recorded video.
Good to know: Alpha transparency is lost, because H.264 in MP4 cannot carry it. AV1 video is decoded only where the browser can decode AV1 — recent Chrome, Edge and Firefox can.
Put this tool on your website
Free for any blog, class page or help article. Paste one snippet and your visitors can use it right on your page.