How to convert WebM to MP4 online for free
- Pick your WebM file. Drop it on the box above or click to choose it. The file is read by your browser and never uploaded.
- Press Convert to MP4. The page decodes the VP8, VP9 or AV1 video and re-encodes it as H.264, with the Opus or Vorbis sound turned into AAC.
- Download the MP4. It downloads automatically when the bar fills; the Download button gives you another copy.
Why WebM files often need converting
WebM is what browsers produce when they record: Chrome’s screen and tab recorders, the MediaRecorder API, many web-based meeting and screen recording tools, and OBS when it’s set to WebM. It plays fine in a browser, but plenty of other places want MP4:
- Older versions of iMovie, Final Cut Pro and QuickTime Player don’t open WebM.
- Some social and learning platforms reject WebM uploads or handle them badly.
- Phones and TVs play H.264 MP4 almost everywhere, while VP9 support varies.
- Browser recordings often have no duration in the file, so editors show the length as zero and seeking is slow. Re-encoding to MP4 writes a proper index.
What you get
| Typical WebM recording | MP4 from this page | |
|---|---|---|
| Video codec | VP8, VP9 or AV1 | H.264 (AVC) |
| Audio codec | Opus or Vorbis | AAC |
| Resolution and frame rate | As recorded | Kept the same (odd sizes are trimmed by one pixel, which H.264 needs) |
| Plays in | Browsers, VLC | Almost everything |
The MP4 can be larger or smaller than the WebM. H.264 is less efficient than VP9 or AV1, so a high-quality MP4 of the same video is often a bit bigger.
Which browsers work
Converting uses WebCodecs, the browser’s built-in video encoder. Recent Chrome and Edge on Mac and Windows handle H.264 and AAC well. Recent Safari can encode H.264 but may not decode every WebM. If your browser can’t, the page tells you instead of failing quietly.
The free command-line alternative
If you’d rather use ffmpeg, this does the same thing:
ffmpeg -i input.webm -c:v libx264 -crf 20 -preset medium -pix_fmt yuv420p -c:a aac -b:a 160k -movflags +faststart output.mp4
Lower -crf means higher quality and a bigger file; 18 to 23 is a sensible range.
FAQ
How do I convert WebM to MP4 for free?
Open this page, drop your WebM file on the box and press Convert to MP4. It runs in your browser with no sign-up, no watermark and no length limit, then downloads the MP4.
Is my video uploaded when I convert it?
No. The file is decoded and re-encoded on your own computer with your browser’s WebCodecs encoder. Nothing is sent to a server.
Why won’t my browser convert the file?
Converting needs WebCodecs video encoding, which recent Chrome and Edge have. Some browsers lack it or can’t decode VP9 or AV1 WebM. Try Chrome, or use the ffmpeg command in the guide.
Does converting WebM to MP4 lose quality?
Any re-encode loses a little, but at the high-quality setting used here the difference is hard to see. Resolution and frame rate stay the same as the original.