Why convert WebM to MP4
WebM is the open video format Google created for the web. Chrome, Firefox and Edge play it, and browser-based tools such as screen recorders, meeting recorders and many download sites save in WebM. Outside the browser it’s a different story: iPhones and iPads, QuickTime on Mac, PowerPoint, Instagram, many TVs and editors like iMovie or older Premiere versions won’t open it.
MP4 with H.264 video and AAC audio is the format they all accept, so that’s exactly what this converter makes.
How to use it
- Choose your
.webmfiles or drop them on the box above. - Watch the percentage while the video is re-encoded. Longer videos take longer.
- Download the MP4.
What changes in the conversion
| In the WebM | In the MP4 |
|---|---|
| VP9, VP8 or AV1 video | Re-encoded to H.264 at high quality |
| Opus or Vorbis audio | Re-encoded to AAC |
| Resolution and frame rate | Kept |
| Transparency (alpha) | Not kept |
Because the video is decoded and encoded again, the conversion isn’t lossless. It’s set to a high quality level so the difference isn’t visible in normal viewing.
Audio-only WebM files
Some .webm files contain only sound, for example audio saved from a web player or a voice recording made in the browser. Those have no picture to put in an MP4, so the converter tells you the file has no video track rather than producing an empty video.
Speed and your computer
Encoding video is demanding. The converter uses your browser’s built-in video encoder, which takes advantage of your graphics chip where the browser allows. Chrome and Edge on a computer are the fastest. On a phone, short clips work, but long recordings are better converted on a computer.
Privacy
Screen and meeting recordings often show emails, documents and faces. The conversion runs inside your browser using Mediabunny, an open-source media library, so your recording is never uploaded or stored anywhere.
Questions
Why is the MP4 bigger than the WebM?
WebM usually holds VP9 video, which squeezes the same picture into a smaller file than H.264 can. To keep the quality the same, the H.264 version needs more data, so the MP4 is often noticeably larger, sometimes two or three times the size for detailed footage. The trade-off is that the MP4 plays everywhere.
How long does it take?
WebM video always has to be re-encoded, because MP4 players expect H.264. That runs at roughly the speed of playback on a typical computer, and faster on machines with a recent graphics chip. A 10-minute recording takes a few minutes. Keep the tab open until it finishes.
Does it work with screen recordings from Chrome, OBS or Loom?
Yes. Browser-based recorders save WebM with VP8 or VP9 video and Opus audio, all of which convert. Recordings with a changing frame rate are fine too.
Is transparency kept?
No. Some WebM animations have a transparent background, but H.264 MP4s can't store transparency, so it's dropped and the background becomes solid. Keep the WebM if you need the transparent version.
Last reviewed 4 November 2026