ConvertWhat happens when you convert MP4 to WebM
- WebM uses VP9 (or VP8) video and Opus audio. Videos that already use these codecs are copied without re-encoding.
- Otherwise the video is re-encoded with your device's built-in hardware encoder, so even long videos convert quickly.
- The sound is kept: copied when WebM supports it, otherwise converted to AAC (Opus for WebM).
- Phone videos keep their orientation: portrait stays portrait. You can also shrink videos to 1080p, 720p or 480p.
- Everything runs on your device. Very long or 4K videos need a lot of memory; on phones, keep videos under about 1 GB.
MP4 vs WebM
| Feature | MP4 | WebM |
|---|---|---|
| Video codecs | H.264, HEVC, AV1 | VP9, VP8, AV1 |
| Sound | Yes | Yes |
| Plays on | Almost everything | Browsers, Android, VLC |
| Best for | Video | Websites |
How to convert MP4 to WebM
- Drop your MP4 files on the box above, or click it to choose files. You can add many at once.
- Adjust the options if you want. The defaults work well for most files.
- Click Download for each WebM file, or "Download all" to get a ZIP.
Frequently asked questions
Is it safe to convert my files here?
Yes. Conversion happens entirely in your browser. Your files are never uploaded to a server, so nobody else can see them.
Is it free? Are there limits?
It's completely free, with no sign-up, watermarks or daily limits. The only limit is your device's memory for very large files.
Can I convert many MP4 files at once?
Yes. Drop as many files as you like; they're converted one after another and you can download them all as a ZIP.
Will converting MP4 to WebM reduce quality?
When the video stream is copied, quality is identical. When it's re-encoded, “Same as original” and “High” look the same as the source for most videos; pick Medium or Small for smaller files.
Is there a file size limit?
Nothing is uploaded, so there's no upload limit. The limit is your device's memory: a few GB is fine on most computers; on phones, stay under about 1 GB.
How long does it take?
Copying a stream takes seconds. Re-encoding uses your device's hardware encoder and is usually faster than real time on a computer.
Is the sound kept?
Yes. The audio is copied when the new format supports it, otherwise converted (AAC for MP4/MOV, Opus for WebM).