Free browser tool
Turn a WebM into something everything plays
Drop a WebM in and get an H.264 MP4 back. It converts in this tab, so the file stays on your machine.
- No sign up
- Nothing uploaded
- No queue
- Up to 300 MB a file
Drop a WebM in
Drag a file onto this panel or open one. It is converted to MP4 in this tab, on your own machine, and never uploaded.
WebM is a browser format
It holds VP8 or VP9 video and Opus audio, all of which browsers decode and most other things do not. Premiere and Final Cut will not import a WebM. Older iPhones, smart TVs and set-top boxes will not play one. That is the whole reason this page exists.
An MP4 holds H.264 and AAC, which has been decoded in hardware on every device made this century.
It is a real re-encode
Nothing inside a WebM can be lifted into an MP4 untouched, so every frame is decoded and encoded again as H.264 at CRF 23, with the audio re-encoded to AAC at 160 kbps. That takes about the length of the clip on a current laptop, because the encoder is WebAssembly on a single thread.
The MP4 is written with its index at the front, so a file you post or send starts playing before it has finished downloading.
Where your WebM came from
Almost always a browser. Chrome and Firefox record to WebM, so anything captured by a web-based recorder, a meeting tool or a screen recorder extension arrives in this format, and then will not import into the editor you wanted to use.
Nothing leaves the tab
The conversion runs in the same browser that made the file. ffmpeg compiled to WebAssembly reads it, converts it and writes the MP4 back, with no upload and no queue.
If you are on a Mac and tired of the round trip, Prequel records the screen straight to MP4 at up to 4K, with the zooms already placed when the editor opens.
How it works
Converting in 3 steps
- Drop the WebM inA browser recording, a download from a web app, an export from an online editor. Up to 300 MB.
- ConvertVP8 or VP9 video is re-encoded to H.264 and Opus or Vorbis audio to AAC, because MP4 holds neither of the originals.
- DownloadThe MP4 imports into Premiere, Final Cut and Resolve, and plays on a phone, which a WebM often will not.
What it does
Free, and still worth using
Get a file your editor will import
Premiere and Final Cut do not take WebM. H.264 in an MP4 is the format every editor on every platform opens without a plugin.
Play it on hardware that will not
WebM depends on VP8 or VP9, which older iPhones, smart TVs and set-top boxes do not decode. H.264 has been in silicon everywhere for fifteen years.
Keep it off a server
A WebM is usually something you just recorded in a browser. It is converted here in the same browser, by ffmpeg compiled to WebAssembly, and uploaded nowhere.
Start playing before it finishes downloading
The MP4 is written with its index at the front, so a file posted to a site or sent in a chat starts playing immediately rather than after the whole download.
On a Mac, the editing is already done
Prequel records your screen at its full resolution, then opens an editor with the zooms already placed, your camera framed and a background applied. Export one MP4 at up to 4K.
No credit card required
- Zooms placed on every click
- Camera shaped, sized and framed
- Background, padding and shadow
- Microphone and system on separate gains
- Cursor smoothed and resized
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A QuickTime recording in, its audio out as an MP3.
FAQ
Codecs, speed and quality
Why does WebM need converting at all?
Because of what is inside it. WebM holds VP8 or VP9 video and Opus audio, which browsers decode and most editors, phones and televisions do not. MP4 holds H.264 and AAC, which everything decodes.
Does the conversion lose quality?
A little, as any second encode does. It re-encodes at CRF 23, a delivery-quality setting, so the result is visually very close to the WebM at a similar or smaller size.
Why is it slower than converting a MOV?
A MOV usually holds H.264 already and is simply rewrapped. Nothing in a WebM can go into an MP4 untouched, so every frame is decoded and encoded again, on one thread in WebAssembly.
Is the file uploaded?
No. It is converted in this tab on your own processor, which is why there is no queue and no link to wait for.
Can it convert a browser screen recording?
Yes, and that is the common case. Browser recorders write WebM in Chrome and Firefox, which is exactly what will not import into an editor afterwards.
How large a file can it take?
About 300 MB. The input, the output and the encoder share the tab's memory, so the ceiling is set where a long transcode stops being reliable.
What happens to the audio?
Opus or Vorbis is decoded and re-encoded as AAC at 160 kbps, which is what an MP4 can carry and what every player expects.
How do I avoid the conversion next time?
Record somewhere that writes MP4 to begin with. Prequel records your Mac's screen straight to H.264 or HEVC in an MP4, at up to 4K, with no conversion step afterwards.