Convert MP4 to WebM
Your files are processed on your device. We never upload them.
Video is read and written with Mediabunny, under the Mozilla Public License.
How to convert MP4 to WebM
- 01A ▸Choose your MP4 videos, or drop them on the page.
- 02A ▸Check what the page says under each video. Re-encoding takes a while.
- 03A ▸Select Convert to WebM, wait for the progress bar, then download each video.
About MP4 to WebM
Where MP4 files come from
MP4 with H.264 is what phones and cameras record and what most apps share. Websites often want WebM as well, for smaller files and for browsers and platforms that prefer open formats.
What changes
- The picture is re-encoded to VP9 (VP8 where the browser has no VP9 encoder) and the sound to Opus, at a high quality setting.
- Size and frame rate stay the same. The rotation of a phone video is applied to the pixels, because WebM has no rotation setting.
- The file size depends on the video and the browser's encoder. At the high quality setting used here, our sample's WebM came out about a tenth larger than the MP4.
Measured
Our one-minute 1080p sample at 30 frames a second with H.264 video and AAC sound (a synthetic test pattern, which is easier to encode than real footage), converted in Chrome on a laptop. Phone timings are still to be measured.
| MP4 file | 61.1 MB |
|---|---|
| WebM file (VP9 and Opus) | 68.6 MB |
| Time (Chrome, laptop) | 4.8 seconds; real footage takes longer |
| Time on phones | still to be measured |
In your browser
Needs the browser's own encoders (WebCodecs). Chrome, Edge, and Firefox encode VP9 and Opus; Safari encodes VP9 video from 16.4 and Opus sound from 26. Few browsers encode VP9 with the graphics chip, so it is slower than encoding H.264.
Limits
- VP9 encoding is done in software in most browsers, so long or high-resolution videos take a while, and much longer on phones.
- HEVC (H.265) MP4s from recent iPhones can be converted only where the browser decodes HEVC, such as Safari.
Other options
- WebM to MP4: the reverse, for phones, TVs, and editors.
- Mute video: background videos usually play muted; drop the sound first.
Questions
Why convert MP4 to WebM?
WebM is the web's own, royalty-free video format. Websites use it for background and HTML5 videos, and some web platforms and tools ask for it.
Are my videos uploaded?
No. Your files are processed on your device. We never upload them.
How long does it take?
The picture is re-encoded frame by frame, so expect a good fraction of the video's length on a computer, and longer on a phone. On a computer, the page shows an estimate under each video before you start.
Will WebM play on an iPhone?
Recent versions of Safari play WebM on Mac and iPhone, but older iPhones and many apps can't, so keep the MP4 for them.