How to convert MP4 to WebM
- Add your files. Drop MP4 files anywhere on the page, or use Choose files. Folders and ZIP archives work too; every MP4 inside is picked up.
- Check that WebM is selected. WebM is already chosen on this page. Other formats in the same row are one tap away if you change your mind.
- Adjust options if you need to. Leave quality on Original to copy streams when possible, or pick High, Medium or Small file and an optional resolution.
- Convert and download. Press Convert. Each file shows its progress, then a Download button. With several files, “Download all” gives you a single ZIP.
What happens to your MP4
A video file is a container holding a video stream and an audio stream. With the quality option on Original, Myriadfile checks what is inside your MP4: if the video already uses VP9, it is copied into the new WebM untouched. That is a remux: no quality is lost and it finishes quickly, even for long files. If the codec does not fit WebM, the video is re-encoded to VP9 with your browser’s built-in encoder, which can use your graphics hardware. Audio is copied when it is already Opus and re-encoded to Opus otherwise.
Choose High, Medium or Small file to always re-encode, for example to shrink the file or to get VP9. The resolution option scales the picture down to 1080p, 720p or 480p.
About MP4 and WebM
MP4: MP4 is the most compatible video format. With H.264 video and AAC audio it plays on phones, TVs, browsers and every editing app.
WebM: WebM is an open web video format using VP8, VP9 or AV1 video with Opus or Vorbis audio. Browsers play it natively; Apple devices and editors are less reliable.
Questions
Is my MP4 file uploaded anywhere?
No. The conversion runs inside this browser tab using code served by this site, and the WebM is created on your device. You can even disconnect from the internet once the page and its converter have loaded.
Will the WebM lose quality?
Not when the streams can be copied: with the quality option on Original, a compatible MP4 is remuxed into WebM without re-encoding, so the picture is identical. When the video must be re-encoded, High keeps it visually very close to the original.
Can I convert several MP4 files at once?
Yes. Drop as many MP4 files as you like, a whole folder or a ZIP. They convert one after another, and “Download all” saves every WebM in one ZIP that keeps your folder structure.
Is there a file size limit?
There is no fixed limit, because nothing is uploaded. The practical limit is your device’s memory: a phone may struggle with very large videos that a laptop converts easily.