Guide
WebM to MP4: make browser recordings play everywhere
Drop a WebM file above and get an MP4 with H.264 video and AAC sound. It opens in editors, on phones and in social apps.
In short
- This converter turns a WebM file into an MP4 with H.264 video and AAC sound.
- Editors, phones and upload forms usually expect MP4, and often refuse WebM.
- WebM video is always re-encoded, because it cannot be copied into a playable MP4.
- Nothing is uploaded. Everything runs inside this browser tab.
WebM to MP4
Runs in your browser · files never leave this page
Drop a WebM file here
or
The engine reads the file first. An H.264 picture with AAC sound is copied into the MP4 with no re-encode. Anything else is written as H.264 + AAC.
Your file never leaves this page. The engine downloads once, the work happens in this tab, and there is no upload, no account and no storage. Close the tab and the file is gone unless you downloaded it.
More free tools: Video compressor · Video resizer · Video to MP4 · Video to MP3 · Video clipper · all tools
What is a WebM file?
WebM is an open video format from Google, made for playing video in the browser.
- WebM files come from browser screen recorders, meeting tools and web downloads.
- Inside a WebM you usually find VP8 or VP9 video, with Opus or Vorbis sound.
- Many editors, phones and apps expect H.264 video in an MP4 instead.
What the converter does
It copies what an MP4 can hold as it is, and re-encodes only what it cannot.
- Copied: H.264 video and AAC sound go into the MP4 untouched. No quality loss.
- Re-encoded: any other video becomes H.264 at a high quality setting (CRF 23).
- Sound: any other sound becomes AAC at 160 kbps.
- Web ready: the MP4 is set up to start playing before it fully loads.
What happens to each part of your WebM file
The first video track and the first sound track are used. The rest is left out.
| Inside the file | What you get in the MP4 | How long |
|---|---|---|
| VP8 or VP9 video | Re-encoded once to H.264 | Minutes for a long file |
| Opus or Vorbis sound | Converted to AAC at 160 kbps | Seconds |
| No sound (silent screen recording) | An MP4 without sound | - |
| Picture size and length | Kept the same | - |
Inside the file: VP8 or VP9 video
- What you get in the MP4
- Re-encoded once to H.264
- How long
- Minutes for a long file
Inside the file: Opus or Vorbis sound
- What you get in the MP4
- Converted to AAC at 160 kbps
- How long
- Seconds
Inside the file: No sound (silent screen recording)
- What you get in the MP4
- An MP4 without sound
- How long
- -
Inside the file: Picture size and length
- What you get in the MP4
- Kept the same
- How long
- -
This is the whole editor
Highlight a phrase and a clip lands on those exact words. No timeline, no keyframes, no layers.
How to convert WebM to MP4
Four steps, all in this tab.
WebM to MP4 in four steps
Drop your WebM file
In the box at the top
The engine reads it
Which video and sound it holds
Copy or re-encode
Only what MP4 cannot hold is redone
Download the MP4
Saved to your device
Limits of a browser tool
Everything runs on your own device, so your device sets the limits.
- File size: up to 500 MB runs comfortably. Bigger files may run out of memory.
- Speed: the engine uses one processor core, so a long re-encode takes minutes.
- First run: the engine downloads once, about 32 MB. After that it starts fast.
- Phones: it works, but a laptop is faster and has more memory.
Questions people ask
- Why convert WebM to MP4 at all?
- Because many editors, phones and upload forms expect MP4 with H.264. WebM holds VP8 or VP9 video, which they often refuse. The MP4 opens in far more places.
- Why does WebM take longer than other formats?
- WebM video always has to be encoded again, frame by frame. That runs on one core of your device. A short clip is quick; an hour-long recording takes a long time.
- Will the MP4 be bigger than the WebM?
- It can be. VP9 packs video tightly, and H.264 needs more data for the same picture. If size matters, run the MP4 through the free video compressor afterwards.
- Does the sound come along?
- Yes. Opus or Vorbis sound is converted to AAC at 160 kbps, which every MP4 player understands. A recording without sound stays silent.
- Is my WebM file uploaded anywhere?
- No. The tool runs inside this browser tab, so your WebM file never leaves your device. Only the engine itself is downloaded, about 32 MB, once per visit.
Want a finished video with captions, not just a converted file? Cutroom edits your clip for you. Your first video is free.