twineconvert

free · in-browser · no upload

MP4 to WebM
Converter

Drop your MP4 file. We'll convert it to WebM right here in your browser, your file never leaves your device.

or drop your file

Select your file here to get started

or drop your file here.

Accepts .mp4

nothing uploaded no file size cap no signup

How it works

Three steps. No upload, no signup.

  1. 1

    Drop your file

    Click the dropzone above or drag a MP4 from your desktop. Files of any size, there's no upload, so there's no upload limit.

  2. 2

    Convert in your browser

    The conversion runs entirely in this tab using JavaScript and WebAssembly. Your file never touches our servers, we don't have any.

  3. 3

    Download

    Get your WebM the moment the conversion finishes. Convert another, or close the tab.

Files stay on your device

Your file is never uploaded. The entire conversion runs in your browser using WebAssembly. We can't see what you convert because we have no server to see it.

No file size limit

Server converters cap free users at 1-2 GB and gate larger files behind a paid plan. Since nothing uploads, our limit is whatever your browser can handle.

Free, no signup, no ads on conversions

No account required. No watermark on the output. No queue. Drop a file, get a converted file.

Why convert MP4 → WebM

What this conversion is actually for

WebM (VP9 + Opus) is the open codec target the modern web prefers. Smaller files than equivalent H.264 MP4 for background autoplay videos, no patent worries, native Chrome / Firefox playback. The right format if you are publishing web video.

A real example

You want a hero background video on your landing page. MP4 is 8 MB; the WebM equivalent at the same perceived quality lands around 3 MB. Convert here, ship the WebM.

Troubleshooting

Safari does not play the result on older iOS.

Safari only added VP9 / Opus in WebM support in iOS 14.5 (April 2021) and macOS Big Sur. For older Safari, serve MP4 as a fallback inside the same <video> tag.

Formats involved

About MP4 and WebM

MP4, MPEG-4 Part 14

MP4 is the dominant video container on the web, H.264 video plus AAC audio, in a structure designed for streaming. Every browser, mobile device, smart TV, and editing tool reads MP4. The format is technically a container (not a codec), so two MP4 files can have very different internal codecs, but the H.264+AAC default is what enables universal playback.

How to open

Every video player on the planet, VLC, QuickTime, Windows Media Player, browsers (HTML5 video), iOS, Android, smart TVs, game consoles. Universal.

Full MP4 format guide →
WebM, WebM

WebM is Google's open-source video container, designed for web streaming. Uses VP8/VP9 video and Vorbis/Opus audio. About 25-35% smaller than equivalent H.264 MP4 at the same quality. Universal browser support; less common on standalone media players and older hardware.

How to open

All modern web browsers, VLC, MPV. Some smart TVs and older players don't recognize WebM, converting to MP4 is the standard fix.

Full WebM format guide →

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FAQ

Common questions

Is this MP4 → WebM converter really free?

Yes. No signup, no watermark, no daily file count limit. Every conversion runs in your browser, your file never touches our servers because there are no servers.

Where does my file go when I convert it?

Nowhere. The conversion runs entirely in your browser using JavaScript and WebAssembly. Your file is never uploaded to our servers. We don't have any servers handling files, there's nothing for us to log, store, or accidentally leak.

What's the maximum file size?

Whatever your browser can hold in memory. Practically, this means a few hundred MB on most computers, significantly larger than the 1-2 GB caps that server-upload converters charge for. Very large files (multi-GB) may require closing other browser tabs first.

Why convert MP4 to WebM?

Web video, mobile video recording, video sharing. Web video where smaller file size matters more than universal playback. The most common reason to convert is compatibility, WebM works in places where MP4 doesn't, or vice versa.

How do I open a MP4 file in the first place?

Every video player on the planet, VLC, QuickTime, Windows Media Player, browsers (HTML5 video), iOS, Android, smart TVs, game consoles. Universal.

Does this work offline?

Once the page is loaded, the conversion itself runs entirely offline. The first time you use a tool, your browser downloads the conversion library (a one-time cache). If you reload while offline, the page won't load, but you can install the site as a Progressive Web App for full offline use.

Can I convert multiple files at once?

Single file at a time for now. Batch conversion is on the roadmap, for now, drop one file, download the result, then convert the next.