MP4 to WebM — free online tool
WebM is the open video format designed for the web. If you publish a video on your site, in an HTML page or in an app, this tool converts your MP4 file to WebM. Unlike a simple container change, this conversion re-encodes the video, because WebM does not use the same codecs as MP4.
Drop a MP4 file here, or click to choose one
Processed temporarily, deleted afterDrop a MP4 file here, or click to choose one
MP4
How it works
Why re-encoding is necessary
WebM is a Matroska-based container limited to open codecs: VP8 or VP9 (sometimes AV1) for the picture, Vorbis or Opus for the sound. An MP4 usually contains H.264 and AAC, which are not allowed in WebM. So you cannot simply change the packaging: every frame is decoded and then recompressed, which takes longer than a remux.
Usage
Upload your .mp4 file, start the conversion and collect the WebM when processing finishes. Expect a time proportional to the video's length and resolution: VP9 is more demanding to compute than H.264. If your video is long or in very high resolution, consider trimming or resizing it first, to speed up processing and lighten the result.
When to choose WebM over MP4
WebM suits videos embedded in a page with the video tag, animated backgrounds, short product demos and sites that favor open formats. At comparable visual quality, VP9 often gives a lighter file than H.264, a useful advantage for cutting load times. For sharing in a messaging app or on iPhone, however, MP4 remains the safer choice.
Browser compatibility
Chrome, Firefox, Edge and Opera have played WebM for a long time. Safari supports it in recent versions, but older support was partial, notably on iPhone. The best practice for a public site is to offer both sources in the video tag: WebM first, with MP4 as the fallback. That way each visitor gets the file their browser can play.
Quality and size
Re-encoding causes a slight loss, because the source file was already compressed. Avoid converting several times in a row. If the result seems bigger than expected, it is often because the video is high definition or very dynamic: reduce the resolution with the video resizer before converting. A short duration gives the best size-to-quality ratio.
Common pitfalls
A WebM is not always playable in mainstream editing software or messaging apps: it is made for the web, not for universal exchange. If your video does not open on a device, convert it back to MP4 with the reverse tool. Finally, check that your original file is a valid MP4, as a truncated file will fail during encoding.
Limitations
Only .mp4 files are accepted. The conversion is a re-encode with a slight loss, slower than a remux. WebM is less universal than MP4 outside browsers, and you cannot set the codec yourself.
Frequently asked questions
Why does the conversion take longer than with other formats?
Because MP4 and WebM do not use the same codecs: every frame has to be decoded and then recompressed. A simple container change would be almost instant, but it is not possible here.
Is WebM smaller than MP4?
Often at equal quality thanks to VP9, but not always. The result depends on the video and the encoding settings. Compare the size before and after on your own file.
Will my WebM file play on iPhone?
Recent versions of Safari play it, but support was limited for a long time. For sharing on mobile, favor MP4. For a website, provide both formats.
Is the sound kept?
Yes. The MP4's audio is re-encoded to a WebM-compatible codec (Opus or Vorbis). If your video has no sound, the resulting WebM will have none either.
Can I turn a WebM into an MP4?
Yes, with Vidlora's WebM to MP4 tool, built for the reverse case and for recordings made in a browser.
What should I do if the video is too large after conversion?
Reduce the resolution with the video resizer, shorten the duration with the trimmer, then run the conversion again. The size depends above all on the resolution and the amount of motion in the picture.